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SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0754 AM CDT Sun Aug 04 2024 Valid 041300Z - 051200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FOR TROPICAL-CYCLONE TORNADOES...OVER PARTS OF FLORIDA AND EXTREME SOUTHERN GEORGIA... ...SUMMARY... Tropical Storm Debby may produce a few tornadoes over parts of Florida and extreme southern Georgia through early tomorrow morning as it intensifies. ...Synopsis... A persistent, mid/upper-level anticyclone will remain centered over the Four Corners region through the period, but with deamplification of the ridge to its north. This will occur as a long-lived shortwave trough -- that emanated from the subtropical easterlies a few days ago and is located over the interior Northwest -- pivots eastward through the mean-ridge position across the northern Rockies. By 12Z tomorrow, this perturbation should reach north- central/northeastern MT. Downstream, a belt of relatively enhanced, slightly difluent northwesterly flow will persist over the northern Plains and Upper Midwest, maintained by a large cyclone centered over northeastern Canada. Farther downstream, a persistent, positively tilted, mid/upper-level trough was apparent in moisture-channel imagery from western/central NY southwestward over the central/southern Appalachians to portions of AL. This feature is expected to deamplify through the period, with the middle-northern part ejecting off the Mid-Atlantic and New England Coasts by about 06Z. Though weakening, the southern part of this trough will contribute to the continuing recurvature of what now is Tropical Storm Debbie, per NHC discussions. At the surface, 11Z analysis showed a low over the northern shore of Lake Ontario, with a weak, slow-moving cold front across central NY, eastern PA, to northern/central VA. This boundary should move slowly eastward while continuing to weaken through the period. Another, wavy, quasistationary frontal zone was analyzed from the same low across northwestern OH, southern Lake Michigan, southern MN, to another low near YKN, then across southwestern SD to southeastern MT. This boundary will oscillate on the mesoscale through the period in response to weak perturbations aloft, and proximal convective processes. ...FL, southern GA... Tropical Storm Debby continues to intensify in accordance with NHC forecasts, and is expected to strengthen further to a hurricane near the end of the period and just prior to landfall. [Refer to latest NHC advisories for track and intensity forecasts for Debby, as well as tropical-cyclone watches and warnings. See SPC mesoscale discussion 1812 for coverage of marginal/near-term tornado potential very near the west-central FL Coast.] As Debby strengthens today into this evening: 1. Expansion of the peripheral wind fields will provide supercell-favorable low-level shear and hodograph size, and 2. The diurnal-heating cycle should destabilize moisture-rich inland areas of peninsular FL and remove MLCINH, while 3. Low-level convergence/lift will strengthen in step with system intensification. Those factors should enlarge the outer convective pattern eastward over more of the landmass. Such development may backbuild into parts of south FL, but the greater probability for mature supercells will be in the "slight-risk (5% tornado) area over western/central FL today, spreading north toward the area near the FL/GA line overnight. Late in the period into early day 2, as the system approaches landfall and precip increases across interior northern FL and southern GA, an overland, low-level baroclinic zone should develop and strengthen. This feature -- with relatively stable, rain-cooled air to its poleward side -- should act as a fairly sharp, buoyancy-limiting boundary for the northern edge of the tornado threat. However, a looser tornado-probability gradient remains for now in the outlook lines, since the boundary's specific location will depend strongly on mesobeta-scale convective/precip geometry and density yet to be determined, within and just off the northern rim of Debby's circulation. ...Southeastern/south-central MT and vicinity... Widely scattered to scattered thunderstorms are expected to develop over the higher terrain of southwestern/south-central MT this afternoon, offering a few strong-severe gusts and isolated/marginal hail. Steepening of low/middle-level lapse rates and concordant erosion of MLCINH should occur as: 1. DCVA and accompanying large-scale ascent /destabilization aloft spread into the area ahead of the shortwave trough, and 2. Diurnal heating acts on higher elevations amidst marginal but sufficient low-level moisture, with lower-elevation surface dewpoints remaining in the mid 40s to lower 50s through the mixing cycle. Though low-level windspeeds will be modest, strong veering with height north of the front will underlie strengthening mid/upper winds to contribute to areas of 35-45-kt effective-shear magnitudes in support of storm organization (and at least brief supercell characteristics for any discrete activity). In general, an upscale aggregation of high-based convection should move eastward over the outlook area, and over a deep/well-mixed subcloud layer, to support gust potential. Activity should weaken considerably during the evening as the foregoing boundary layer stabilizes. ...Upper Midwest/upper Mississippi Valley... A corridor of favorable moisture (dewpoints commonly in the 60s, locally topping 70 F) and diurnal heating may support late-afternoon development near the front, with isolated severe hail/gusts conditionally possible. However, strong capping, on the northeastern rim of a well-developed EML, may preclude this scenario. More confidence exists in later development (evening) in a regime of increasingly focused low-level warm advection and lift over eastern SD and southwestern MN, shifting east-southeastward across the outlook area into tonight. Steep midlevel lapse rates will support 1500-2500 J/kg MUCAPE, with around 35-45-kt effective-shear magnitudes. Clustering of cells may promote wind potential, with isolated severe gusts potentially penetrating the near-surface stable layer, and occasional hail near severe limits also possible. ...Northeast CONUS... Widely scattered to scattered thunderstorms are forecast to develop along/ahead of the weak/leading front and ejecting shortwave trough through the afternoon, with isolated damaging to marginally severe gusts being the primary concern. Marginally severe hail may occur in the most intense cores, especially over northern parts of the outlook area under somewhat colder temperatures aloft. This activity should occur in a regime of diurnally minimized MLCINH and rich low-level moisture, with surface dewpoints commonly in the upper 60s to low 70s F. This will offset modest mid/upper-level lapse rates enough to yield peak/preconvective MLCAPE in the 1000-1500 J/kg range (locally/briefly higher). Low-middle-level flow should be modest, keeping hodographs small, but with strong upper/anvil-level winds to aid in multicellular storm organization. ..Edwards/Grams.. 08/04/2024 Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0754 AM CDT Sun Aug 04 2024 Valid 041300Z - 051200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FOR TROPICAL-CYCLONE TORNADOES...OVER PARTS OF FLORIDA AND EXTREME SOUTHERN GEORGIA... ...SUMMARY... Tropical Storm Debby may produce a few tornadoes over parts of Florida and extreme southern Georgia through early tomorrow morning as it intensifies. ...Synopsis... A persistent, mid/upper-level anticyclone will remain centered over the Four Corners region through the period, but with deamplification of the ridge to its north. This will occur as a long-lived shortwave trough -- that emanated from the subtropical easterlies a few days ago and is located over the interior Northwest -- pivots eastward through the mean-ridge position across the northern Rockies. By 12Z tomorrow, this perturbation should reach north- central/northeastern MT. Downstream, a belt of relatively enhanced, slightly difluent northwesterly flow will persist over the northern Plains and Upper Midwest, maintained by a large cyclone centered over northeastern Canada. Farther downstream, a persistent, positively tilted, mid/upper-level trough was apparent in moisture-channel imagery from western/central NY southwestward over the central/southern Appalachians to portions of AL. This feature is expected to deamplify through the period, with the middle-northern part ejecting off the Mid-Atlantic and New England Coasts by about 06Z. Though weakening, the southern part of this trough will contribute to the continuing recurvature of what now is Tropical Storm Debbie, per NHC discussions. At the surface, 11Z analysis showed a low over the northern shore of Lake Ontario, with a weak, slow-moving cold front across central NY, eastern PA, to northern/central VA. This boundary should move slowly eastward while continuing to weaken through the period. Another, wavy, quasistationary frontal zone was analyzed from the same low across northwestern OH, southern Lake Michigan, southern MN, to another low near YKN, then across southwestern SD to southeastern MT. This boundary will oscillate on the mesoscale through the period in response to weak perturbations aloft, and proximal convective processes. ...FL, southern GA... Tropical Storm Debby continues to intensify in accordance with NHC forecasts, and is expected to strengthen further to a hurricane near the end of the period and just prior to landfall. [Refer to latest NHC advisories for track and intensity forecasts for Debby, as well as tropical-cyclone watches and warnings. See SPC mesoscale discussion 1812 for coverage of marginal/near-term tornado potential very near the west-central FL Coast.] As Debby strengthens today into this evening: 1. Expansion of the peripheral wind fields will provide supercell-favorable low-level shear and hodograph size, and 2. The diurnal-heating cycle should destabilize moisture-rich inland areas of peninsular FL and remove MLCINH, while 3. Low-level convergence/lift will strengthen in step with system intensification. Those factors should enlarge the outer convective pattern eastward over more of the landmass. Such development may backbuild into parts of south FL, but the greater probability for mature supercells will be in the "slight-risk (5% tornado) area over western/central FL today, spreading north toward the area near the FL/GA line overnight. Late in the period into early day 2, as the system approaches landfall and precip increases across interior northern FL and southern GA, an overland, low-level baroclinic zone should develop and strengthen. This feature -- with relatively stable, rain-cooled air to its poleward side -- should act as a fairly sharp, buoyancy-limiting boundary for the northern edge of the tornado threat. However, a looser tornado-probability gradient remains for now in the outlook lines, since the boundary's specific location will depend strongly on mesobeta-scale convective/precip geometry and density yet to be determined, within and just off the northern rim of Debby's circulation. ...Southeastern/south-central MT and vicinity... Widely scattered to scattered thunderstorms are expected to develop over the higher terrain of southwestern/south-central MT this afternoon, offering a few strong-severe gusts and isolated/marginal hail. Steepening of low/middle-level lapse rates and concordant erosion of MLCINH should occur as: 1. DCVA and accompanying large-scale ascent /destabilization aloft spread into the area ahead of the shortwave trough, and 2. Diurnal heating acts on higher elevations amidst marginal but sufficient low-level moisture, with lower-elevation surface dewpoints remaining in the mid 40s to lower 50s through the mixing cycle. Though low-level windspeeds will be modest, strong veering with height north of the front will underlie strengthening mid/upper winds to contribute to areas of 35-45-kt effective-shear magnitudes in support of storm organization (and at least brief supercell characteristics for any discrete activity). In general, an upscale aggregation of high-based convection should move eastward over the outlook area, and over a deep/well-mixed subcloud layer, to support gust potential. Activity should weaken considerably during the evening as the foregoing boundary layer stabilizes. ...Upper Midwest/upper Mississippi Valley... A corridor of favorable moisture (dewpoints commonly in the 60s, locally topping 70 F) and diurnal heating may support late-afternoon development near the front, with isolated severe hail/gusts conditionally possible. However, strong capping, on the northeastern rim of a well-developed EML, may preclude this scenario. More confidence exists in later development (evening) in a regime of increasingly focused low-level warm advection and lift over eastern SD and southwestern MN, shifting east-southeastward across the outlook area into tonight. Steep midlevel lapse rates will support 1500-2500 J/kg MUCAPE, with around 35-45-kt effective-shear magnitudes. Clustering of cells may promote wind potential, with isolated severe gusts potentially penetrating the near-surface stable layer, and occasional hail near severe limits also possible. ...Northeast CONUS... Widely scattered to scattered thunderstorms are forecast to develop along/ahead of the weak/leading front and ejecting shortwave trough through the afternoon, with isolated damaging to marginally severe gusts being the primary concern. Marginally severe hail may occur in the most intense cores, especially over northern parts of the outlook area under somewhat colder temperatures aloft. This activity should occur in a regime of diurnally minimized MLCINH and rich low-level moisture, with surface dewpoints commonly in the upper 60s to low 70s F. This will offset modest mid/upper-level lapse rates enough to yield peak/preconvective MLCAPE in the 1000-1500 J/kg range (locally/briefly higher). Low-middle-level flow should be modest, keeping hodographs small, but with strong upper/anvil-level winds to aid in multicellular storm organization. ..Edwards/Grams.. 08/04/2024 Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0754 AM CDT Sun Aug 04 2024 Valid 041300Z - 051200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FOR TROPICAL-CYCLONE TORNADOES...OVER PARTS OF FLORIDA AND EXTREME SOUTHERN GEORGIA... ...SUMMARY... Tropical Storm Debby may produce a few tornadoes over parts of Florida and extreme southern Georgia through early tomorrow morning as it intensifies. ...Synopsis... A persistent, mid/upper-level anticyclone will remain centered over the Four Corners region through the period, but with deamplification of the ridge to its north. This will occur as a long-lived shortwave trough -- that emanated from the subtropical easterlies a few days ago and is located over the interior Northwest -- pivots eastward through the mean-ridge position across the northern Rockies. By 12Z tomorrow, this perturbation should reach north- central/northeastern MT. Downstream, a belt of relatively enhanced, slightly difluent northwesterly flow will persist over the northern Plains and Upper Midwest, maintained by a large cyclone centered over northeastern Canada. Farther downstream, a persistent, positively tilted, mid/upper-level trough was apparent in moisture-channel imagery from western/central NY southwestward over the central/southern Appalachians to portions of AL. This feature is expected to deamplify through the period, with the middle-northern part ejecting off the Mid-Atlantic and New England Coasts by about 06Z. Though weakening, the southern part of this trough will contribute to the continuing recurvature of what now is Tropical Storm Debbie, per NHC discussions. At the surface, 11Z analysis showed a low over the northern shore of Lake Ontario, with a weak, slow-moving cold front across central NY, eastern PA, to northern/central VA. This boundary should move slowly eastward while continuing to weaken through the period. Another, wavy, quasistationary frontal zone was analyzed from the same low across northwestern OH, southern Lake Michigan, southern MN, to another low near YKN, then across southwestern SD to southeastern MT. This boundary will oscillate on the mesoscale through the period in response to weak perturbations aloft, and proximal convective processes. ...FL, southern GA... Tropical Storm Debby continues to intensify in accordance with NHC forecasts, and is expected to strengthen further to a hurricane near the end of the period and just prior to landfall. [Refer to latest NHC advisories for track and intensity forecasts for Debby, as well as tropical-cyclone watches and warnings. See SPC mesoscale discussion 1812 for coverage of marginal/near-term tornado potential very near the west-central FL Coast.] As Debby strengthens today into this evening: 1. Expansion of the peripheral wind fields will provide supercell-favorable low-level shear and hodograph size, and 2. The diurnal-heating cycle should destabilize moisture-rich inland areas of peninsular FL and remove MLCINH, while 3. Low-level convergence/lift will strengthen in step with system intensification. Those factors should enlarge the outer convective pattern eastward over more of the landmass. Such development may backbuild into parts of south FL, but the greater probability for mature supercells will be in the "slight-risk (5% tornado) area over western/central FL today, spreading north toward the area near the FL/GA line overnight. Late in the period into early day 2, as the system approaches landfall and precip increases across interior northern FL and southern GA, an overland, low-level baroclinic zone should develop and strengthen. This feature -- with relatively stable, rain-cooled air to its poleward side -- should act as a fairly sharp, buoyancy-limiting boundary for the northern edge of the tornado threat. However, a looser tornado-probability gradient remains for now in the outlook lines, since the boundary's specific location will depend strongly on mesobeta-scale convective/precip geometry and density yet to be determined, within and just off the northern rim of Debby's circulation. ...Southeastern/south-central MT and vicinity... Widely scattered to scattered thunderstorms are expected to develop over the higher terrain of southwestern/south-central MT this afternoon, offering a few strong-severe gusts and isolated/marginal hail. Steepening of low/middle-level lapse rates and concordant erosion of MLCINH should occur as: 1. DCVA and accompanying large-scale ascent /destabilization aloft spread into the area ahead of the shortwave trough, and 2. Diurnal heating acts on higher elevations amidst marginal but sufficient low-level moisture, with lower-elevation surface dewpoints remaining in the mid 40s to lower 50s through the mixing cycle. Though low-level windspeeds will be modest, strong veering with height north of the front will underlie strengthening mid/upper winds to contribute to areas of 35-45-kt effective-shear magnitudes in support of storm organization (and at least brief supercell characteristics for any discrete activity). In general, an upscale aggregation of high-based convection should move eastward over the outlook area, and over a deep/well-mixed subcloud layer, to support gust potential. Activity should weaken considerably during the evening as the foregoing boundary layer stabilizes. ...Upper Midwest/upper Mississippi Valley... A corridor of favorable moisture (dewpoints commonly in the 60s, locally topping 70 F) and diurnal heating may support late-afternoon development near the front, with isolated severe hail/gusts conditionally possible. However, strong capping, on the northeastern rim of a well-developed EML, may preclude this scenario. More confidence exists in later development (evening) in a regime of increasingly focused low-level warm advection and lift over eastern SD and southwestern MN, shifting east-southeastward across the outlook area into tonight. Steep midlevel lapse rates will support 1500-2500 J/kg MUCAPE, with around 35-45-kt effective-shear magnitudes. Clustering of cells may promote wind potential, with isolated severe gusts potentially penetrating the near-surface stable layer, and occasional hail near severe limits also possible. ...Northeast CONUS... Widely scattered to scattered thunderstorms are forecast to develop along/ahead of the weak/leading front and ejecting shortwave trough through the afternoon, with isolated damaging to marginally severe gusts being the primary concern. Marginally severe hail may occur in the most intense cores, especially over northern parts of the outlook area under somewhat colder temperatures aloft. This activity should occur in a regime of diurnally minimized MLCINH and rich low-level moisture, with surface dewpoints commonly in the upper 60s to low 70s F. This will offset modest mid/upper-level lapse rates enough to yield peak/preconvective MLCAPE in the 1000-1500 J/kg range (locally/briefly higher). Low-middle-level flow should be modest, keeping hodographs small, but with strong upper/anvil-level winds to aid in multicellular storm organization. ..Edwards/Grams.. 08/04/2024 Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0754 AM CDT Sun Aug 04 2024 Valid 041300Z - 051200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FOR TROPICAL-CYCLONE TORNADOES...OVER PARTS OF FLORIDA AND EXTREME SOUTHERN GEORGIA... ...SUMMARY... Tropical Storm Debby may produce a few tornadoes over parts of Florida and extreme southern Georgia through early tomorrow morning as it intensifies. ...Synopsis... A persistent, mid/upper-level anticyclone will remain centered over the Four Corners region through the period, but with deamplification of the ridge to its north. This will occur as a long-lived shortwave trough -- that emanated from the subtropical easterlies a few days ago and is located over the interior Northwest -- pivots eastward through the mean-ridge position across the northern Rockies. By 12Z tomorrow, this perturbation should reach north- central/northeastern MT. Downstream, a belt of relatively enhanced, slightly difluent northwesterly flow will persist over the northern Plains and Upper Midwest, maintained by a large cyclone centered over northeastern Canada. Farther downstream, a persistent, positively tilted, mid/upper-level trough was apparent in moisture-channel imagery from western/central NY southwestward over the central/southern Appalachians to portions of AL. This feature is expected to deamplify through the period, with the middle-northern part ejecting off the Mid-Atlantic and New England Coasts by about 06Z. Though weakening, the southern part of this trough will contribute to the continuing recurvature of what now is Tropical Storm Debbie, per NHC discussions. At the surface, 11Z analysis showed a low over the northern shore of Lake Ontario, with a weak, slow-moving cold front across central NY, eastern PA, to northern/central VA. This boundary should move slowly eastward while continuing to weaken through the period. Another, wavy, quasistationary frontal zone was analyzed from the same low across northwestern OH, southern Lake Michigan, southern MN, to another low near YKN, then across southwestern SD to southeastern MT. This boundary will oscillate on the mesoscale through the period in response to weak perturbations aloft, and proximal convective processes. ...FL, southern GA... Tropical Storm Debby continues to intensify in accordance with NHC forecasts, and is expected to strengthen further to a hurricane near the end of the period and just prior to landfall. [Refer to latest NHC advisories for track and intensity forecasts for Debby, as well as tropical-cyclone watches and warnings. See SPC mesoscale discussion 1812 for coverage of marginal/near-term tornado potential very near the west-central FL Coast.] As Debby strengthens today into this evening: 1. Expansion of the peripheral wind fields will provide supercell-favorable low-level shear and hodograph size, and 2. The diurnal-heating cycle should destabilize moisture-rich inland areas of peninsular FL and remove MLCINH, while 3. Low-level convergence/lift will strengthen in step with system intensification. Those factors should enlarge the outer convective pattern eastward over more of the landmass. Such development may backbuild into parts of south FL, but the greater probability for mature supercells will be in the "slight-risk (5% tornado) area over western/central FL today, spreading north toward the area near the FL/GA line overnight. Late in the period into early day 2, as the system approaches landfall and precip increases across interior northern FL and southern GA, an overland, low-level baroclinic zone should develop and strengthen. This feature -- with relatively stable, rain-cooled air to its poleward side -- should act as a fairly sharp, buoyancy-limiting boundary for the northern edge of the tornado threat. However, a looser tornado-probability gradient remains for now in the outlook lines, since the boundary's specific location will depend strongly on mesobeta-scale convective/precip geometry and density yet to be determined, within and just off the northern rim of Debby's circulation. ...Southeastern/south-central MT and vicinity... Widely scattered to scattered thunderstorms are expected to develop over the higher terrain of southwestern/south-central MT this afternoon, offering a few strong-severe gusts and isolated/marginal hail. Steepening of low/middle-level lapse rates and concordant erosion of MLCINH should occur as: 1. DCVA and accompanying large-scale ascent /destabilization aloft spread into the area ahead of the shortwave trough, and 2. Diurnal heating acts on higher elevations amidst marginal but sufficient low-level moisture, with lower-elevation surface dewpoints remaining in the mid 40s to lower 50s through the mixing cycle. Though low-level windspeeds will be modest, strong veering with height north of the front will underlie strengthening mid/upper winds to contribute to areas of 35-45-kt effective-shear magnitudes in support of storm organization (and at least brief supercell characteristics for any discrete activity). In general, an upscale aggregation of high-based convection should move eastward over the outlook area, and over a deep/well-mixed subcloud layer, to support gust potential. Activity should weaken considerably during the evening as the foregoing boundary layer stabilizes. ...Upper Midwest/upper Mississippi Valley... A corridor of favorable moisture (dewpoints commonly in the 60s, locally topping 70 F) and diurnal heating may support late-afternoon development near the front, with isolated severe hail/gusts conditionally possible. However, strong capping, on the northeastern rim of a well-developed EML, may preclude this scenario. More confidence exists in later development (evening) in a regime of increasingly focused low-level warm advection and lift over eastern SD and southwestern MN, shifting east-southeastward across the outlook area into tonight. Steep midlevel lapse rates will support 1500-2500 J/kg MUCAPE, with around 35-45-kt effective-shear magnitudes. Clustering of cells may promote wind potential, with isolated severe gusts potentially penetrating the near-surface stable layer, and occasional hail near severe limits also possible. ...Northeast CONUS... Widely scattered to scattered thunderstorms are forecast to develop along/ahead of the weak/leading front and ejecting shortwave trough through the afternoon, with isolated damaging to marginally severe gusts being the primary concern. Marginally severe hail may occur in the most intense cores, especially over northern parts of the outlook area under somewhat colder temperatures aloft. This activity should occur in a regime of diurnally minimized MLCINH and rich low-level moisture, with surface dewpoints commonly in the upper 60s to low 70s F. This will offset modest mid/upper-level lapse rates enough to yield peak/preconvective MLCAPE in the 1000-1500 J/kg range (locally/briefly higher). Low-middle-level flow should be modest, keeping hodographs small, but with strong upper/anvil-level winds to aid in multicellular storm organization. ..Edwards/Grams.. 08/04/2024 Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0754 AM CDT Sun Aug 04 2024 Valid 041300Z - 051200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FOR TROPICAL-CYCLONE TORNADOES...OVER PARTS OF FLORIDA AND EXTREME SOUTHERN GEORGIA... ...SUMMARY... Tropical Storm Debby may produce a few tornadoes over parts of Florida and extreme southern Georgia through early tomorrow morning as it intensifies. ...Synopsis... A persistent, mid/upper-level anticyclone will remain centered over the Four Corners region through the period, but with deamplification of the ridge to its north. This will occur as a long-lived shortwave trough -- that emanated from the subtropical easterlies a few days ago and is located over the interior Northwest -- pivots eastward through the mean-ridge position across the northern Rockies. By 12Z tomorrow, this perturbation should reach north- central/northeastern MT. Downstream, a belt of relatively enhanced, slightly difluent northwesterly flow will persist over the northern Plains and Upper Midwest, maintained by a large cyclone centered over northeastern Canada. Farther downstream, a persistent, positively tilted, mid/upper-level trough was apparent in moisture-channel imagery from western/central NY southwestward over the central/southern Appalachians to portions of AL. This feature is expected to deamplify through the period, with the middle-northern part ejecting off the Mid-Atlantic and New England Coasts by about 06Z. Though weakening, the southern part of this trough will contribute to the continuing recurvature of what now is Tropical Storm Debbie, per NHC discussions. At the surface, 11Z analysis showed a low over the northern shore of Lake Ontario, with a weak, slow-moving cold front across central NY, eastern PA, to northern/central VA. This boundary should move slowly eastward while continuing to weaken through the period. Another, wavy, quasistationary frontal zone was analyzed from the same low across northwestern OH, southern Lake Michigan, southern MN, to another low near YKN, then across southwestern SD to southeastern MT. This boundary will oscillate on the mesoscale through the period in response to weak perturbations aloft, and proximal convective processes. ...FL, southern GA... Tropical Storm Debby continues to intensify in accordance with NHC forecasts, and is expected to strengthen further to a hurricane near the end of the period and just prior to landfall. [Refer to latest NHC advisories for track and intensity forecasts for Debby, as well as tropical-cyclone watches and warnings. See SPC mesoscale discussion 1812 for coverage of marginal/near-term tornado potential very near the west-central FL Coast.] As Debby strengthens today into this evening: 1. Expansion of the peripheral wind fields will provide supercell-favorable low-level shear and hodograph size, and 2. The diurnal-heating cycle should destabilize moisture-rich inland areas of peninsular FL and remove MLCINH, while 3. Low-level convergence/lift will strengthen in step with system intensification. Those factors should enlarge the outer convective pattern eastward over more of the landmass. Such development may backbuild into parts of south FL, but the greater probability for mature supercells will be in the "slight-risk (5% tornado) area over western/central FL today, spreading north toward the area near the FL/GA line overnight. Late in the period into early day 2, as the system approaches landfall and precip increases across interior northern FL and southern GA, an overland, low-level baroclinic zone should develop and strengthen. This feature -- with relatively stable, rain-cooled air to its poleward side -- should act as a fairly sharp, buoyancy-limiting boundary for the northern edge of the tornado threat. However, a looser tornado-probability gradient remains for now in the outlook lines, since the boundary's specific location will depend strongly on mesobeta-scale convective/precip geometry and density yet to be determined, within and just off the northern rim of Debby's circulation. ...Southeastern/south-central MT and vicinity... Widely scattered to scattered thunderstorms are expected to develop over the higher terrain of southwestern/south-central MT this afternoon, offering a few strong-severe gusts and isolated/marginal hail. Steepening of low/middle-level lapse rates and concordant erosion of MLCINH should occur as: 1. DCVA and accompanying large-scale ascent /destabilization aloft spread into the area ahead of the shortwave trough, and 2. Diurnal heating acts on higher elevations amidst marginal but sufficient low-level moisture, with lower-elevation surface dewpoints remaining in the mid 40s to lower 50s through the mixing cycle. Though low-level windspeeds will be modest, strong veering with height north of the front will underlie strengthening mid/upper winds to contribute to areas of 35-45-kt effective-shear magnitudes in support of storm organization (and at least brief supercell characteristics for any discrete activity). In general, an upscale aggregation of high-based convection should move eastward over the outlook area, and over a deep/well-mixed subcloud layer, to support gust potential. Activity should weaken considerably during the evening as the foregoing boundary layer stabilizes. ...Upper Midwest/upper Mississippi Valley... A corridor of favorable moisture (dewpoints commonly in the 60s, locally topping 70 F) and diurnal heating may support late-afternoon development near the front, with isolated severe hail/gusts conditionally possible. However, strong capping, on the northeastern rim of a well-developed EML, may preclude this scenario. More confidence exists in later development (evening) in a regime of increasingly focused low-level warm advection and lift over eastern SD and southwestern MN, shifting east-southeastward across the outlook area into tonight. Steep midlevel lapse rates will support 1500-2500 J/kg MUCAPE, with around 35-45-kt effective-shear magnitudes. Clustering of cells may promote wind potential, with isolated severe gusts potentially penetrating the near-surface stable layer, and occasional hail near severe limits also possible. ...Northeast CONUS... Widely scattered to scattered thunderstorms are forecast to develop along/ahead of the weak/leading front and ejecting shortwave trough through the afternoon, with isolated damaging to marginally severe gusts being the primary concern. Marginally severe hail may occur in the most intense cores, especially over northern parts of the outlook area under somewhat colder temperatures aloft. This activity should occur in a regime of diurnally minimized MLCINH and rich low-level moisture, with surface dewpoints commonly in the upper 60s to low 70s F. This will offset modest mid/upper-level lapse rates enough to yield peak/preconvective MLCAPE in the 1000-1500 J/kg range (locally/briefly higher). Low-middle-level flow should be modest, keeping hodographs small, but with strong upper/anvil-level winds to aid in multicellular storm organization. ..Edwards/Grams.. 08/04/2024 Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0754 AM CDT Sun Aug 04 2024 Valid 041300Z - 051200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FOR TROPICAL-CYCLONE TORNADOES...OVER PARTS OF FLORIDA AND EXTREME SOUTHERN GEORGIA... ...SUMMARY... Tropical Storm Debby may produce a few tornadoes over parts of Florida and extreme southern Georgia through early tomorrow morning as it intensifies. ...Synopsis... A persistent, mid/upper-level anticyclone will remain centered over the Four Corners region through the period, but with deamplification of the ridge to its north. This will occur as a long-lived shortwave trough -- that emanated from the subtropical easterlies a few days ago and is located over the interior Northwest -- pivots eastward through the mean-ridge position across the northern Rockies. By 12Z tomorrow, this perturbation should reach north- central/northeastern MT. Downstream, a belt of relatively enhanced, slightly difluent northwesterly flow will persist over the northern Plains and Upper Midwest, maintained by a large cyclone centered over northeastern Canada. Farther downstream, a persistent, positively tilted, mid/upper-level trough was apparent in moisture-channel imagery from western/central NY southwestward over the central/southern Appalachians to portions of AL. This feature is expected to deamplify through the period, with the middle-northern part ejecting off the Mid-Atlantic and New England Coasts by about 06Z. Though weakening, the southern part of this trough will contribute to the continuing recurvature of what now is Tropical Storm Debbie, per NHC discussions. At the surface, 11Z analysis showed a low over the northern shore of Lake Ontario, with a weak, slow-moving cold front across central NY, eastern PA, to northern/central VA. This boundary should move slowly eastward while continuing to weaken through the period. Another, wavy, quasistationary frontal zone was analyzed from the same low across northwestern OH, southern Lake Michigan, southern MN, to another low near YKN, then across southwestern SD to southeastern MT. This boundary will oscillate on the mesoscale through the period in response to weak perturbations aloft, and proximal convective processes. ...FL, southern GA... Tropical Storm Debby continues to intensify in accordance with NHC forecasts, and is expected to strengthen further to a hurricane near the end of the period and just prior to landfall. [Refer to latest NHC advisories for track and intensity forecasts for Debby, as well as tropical-cyclone watches and warnings. See SPC mesoscale discussion 1812 for coverage of marginal/near-term tornado potential very near the west-central FL Coast.] As Debby strengthens today into this evening: 1. Expansion of the peripheral wind fields will provide supercell-favorable low-level shear and hodograph size, and 2. The diurnal-heating cycle should destabilize moisture-rich inland areas of peninsular FL and remove MLCINH, while 3. Low-level convergence/lift will strengthen in step with system intensification. Those factors should enlarge the outer convective pattern eastward over more of the landmass. Such development may backbuild into parts of south FL, but the greater probability for mature supercells will be in the "slight-risk (5% tornado) area over western/central FL today, spreading north toward the area near the FL/GA line overnight. Late in the period into early day 2, as the system approaches landfall and precip increases across interior northern FL and southern GA, an overland, low-level baroclinic zone should develop and strengthen. This feature -- with relatively stable, rain-cooled air to its poleward side -- should act as a fairly sharp, buoyancy-limiting boundary for the northern edge of the tornado threat. However, a looser tornado-probability gradient remains for now in the outlook lines, since the boundary's specific location will depend strongly on mesobeta-scale convective/precip geometry and density yet to be determined, within and just off the northern rim of Debby's circulation. ...Southeastern/south-central MT and vicinity... Widely scattered to scattered thunderstorms are expected to develop over the higher terrain of southwestern/south-central MT this afternoon, offering a few strong-severe gusts and isolated/marginal hail. Steepening of low/middle-level lapse rates and concordant erosion of MLCINH should occur as: 1. DCVA and accompanying large-scale ascent /destabilization aloft spread into the area ahead of the shortwave trough, and 2. Diurnal heating acts on higher elevations amidst marginal but sufficient low-level moisture, with lower-elevation surface dewpoints remaining in the mid 40s to lower 50s through the mixing cycle. Though low-level windspeeds will be modest, strong veering with height north of the front will underlie strengthening mid/upper winds to contribute to areas of 35-45-kt effective-shear magnitudes in support of storm organization (and at least brief supercell characteristics for any discrete activity). In general, an upscale aggregation of high-based convection should move eastward over the outlook area, and over a deep/well-mixed subcloud layer, to support gust potential. Activity should weaken considerably during the evening as the foregoing boundary layer stabilizes. ...Upper Midwest/upper Mississippi Valley... A corridor of favorable moisture (dewpoints commonly in the 60s, locally topping 70 F) and diurnal heating may support late-afternoon development near the front, with isolated severe hail/gusts conditionally possible. However, strong capping, on the northeastern rim of a well-developed EML, may preclude this scenario. More confidence exists in later development (evening) in a regime of increasingly focused low-level warm advection and lift over eastern SD and southwestern MN, shifting east-southeastward across the outlook area into tonight. Steep midlevel lapse rates will support 1500-2500 J/kg MUCAPE, with around 35-45-kt effective-shear magnitudes. Clustering of cells may promote wind potential, with isolated severe gusts potentially penetrating the near-surface stable layer, and occasional hail near severe limits also possible. ...Northeast CONUS... Widely scattered to scattered thunderstorms are forecast to develop along/ahead of the weak/leading front and ejecting shortwave trough through the afternoon, with isolated damaging to marginally severe gusts being the primary concern. Marginally severe hail may occur in the most intense cores, especially over northern parts of the outlook area under somewhat colder temperatures aloft. This activity should occur in a regime of diurnally minimized MLCINH and rich low-level moisture, with surface dewpoints commonly in the upper 60s to low 70s F. This will offset modest mid/upper-level lapse rates enough to yield peak/preconvective MLCAPE in the 1000-1500 J/kg range (locally/briefly higher). Low-middle-level flow should be modest, keeping hodographs small, but with strong upper/anvil-level winds to aid in multicellular storm organization. ..Edwards/Grams.. 08/04/2024 Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0754 AM CDT Sun Aug 04 2024 Valid 041300Z - 051200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FOR TROPICAL-CYCLONE TORNADOES...OVER PARTS OF FLORIDA AND EXTREME SOUTHERN GEORGIA... ...SUMMARY... Tropical Storm Debby may produce a few tornadoes over parts of Florida and extreme southern Georgia through early tomorrow morning as it intensifies. ...Synopsis... A persistent, mid/upper-level anticyclone will remain centered over the Four Corners region through the period, but with deamplification of the ridge to its north. This will occur as a long-lived shortwave trough -- that emanated from the subtropical easterlies a few days ago and is located over the interior Northwest -- pivots eastward through the mean-ridge position across the northern Rockies. By 12Z tomorrow, this perturbation should reach north- central/northeastern MT. Downstream, a belt of relatively enhanced, slightly difluent northwesterly flow will persist over the northern Plains and Upper Midwest, maintained by a large cyclone centered over northeastern Canada. Farther downstream, a persistent, positively tilted, mid/upper-level trough was apparent in moisture-channel imagery from western/central NY southwestward over the central/southern Appalachians to portions of AL. This feature is expected to deamplify through the period, with the middle-northern part ejecting off the Mid-Atlantic and New England Coasts by about 06Z. Though weakening, the southern part of this trough will contribute to the continuing recurvature of what now is Tropical Storm Debbie, per NHC discussions. At the surface, 11Z analysis showed a low over the northern shore of Lake Ontario, with a weak, slow-moving cold front across central NY, eastern PA, to northern/central VA. This boundary should move slowly eastward while continuing to weaken through the period. Another, wavy, quasistationary frontal zone was analyzed from the same low across northwestern OH, southern Lake Michigan, southern MN, to another low near YKN, then across southwestern SD to southeastern MT. This boundary will oscillate on the mesoscale through the period in response to weak perturbations aloft, and proximal convective processes. ...FL, southern GA... Tropical Storm Debby continues to intensify in accordance with NHC forecasts, and is expected to strengthen further to a hurricane near the end of the period and just prior to landfall. [Refer to latest NHC advisories for track and intensity forecasts for Debby, as well as tropical-cyclone watches and warnings. See SPC mesoscale discussion 1812 for coverage of marginal/near-term tornado potential very near the west-central FL Coast.] As Debby strengthens today into this evening: 1. Expansion of the peripheral wind fields will provide supercell-favorable low-level shear and hodograph size, and 2. The diurnal-heating cycle should destabilize moisture-rich inland areas of peninsular FL and remove MLCINH, while 3. Low-level convergence/lift will strengthen in step with system intensification. Those factors should enlarge the outer convective pattern eastward over more of the landmass. Such development may backbuild into parts of south FL, but the greater probability for mature supercells will be in the "slight-risk (5% tornado) area over western/central FL today, spreading north toward the area near the FL/GA line overnight. Late in the period into early day 2, as the system approaches landfall and precip increases across interior northern FL and southern GA, an overland, low-level baroclinic zone should develop and strengthen. This feature -- with relatively stable, rain-cooled air to its poleward side -- should act as a fairly sharp, buoyancy-limiting boundary for the northern edge of the tornado threat. However, a looser tornado-probability gradient remains for now in the outlook lines, since the boundary's specific location will depend strongly on mesobeta-scale convective/precip geometry and density yet to be determined, within and just off the northern rim of Debby's circulation. ...Southeastern/south-central MT and vicinity... Widely scattered to scattered thunderstorms are expected to develop over the higher terrain of southwestern/south-central MT this afternoon, offering a few strong-severe gusts and isolated/marginal hail. Steepening of low/middle-level lapse rates and concordant erosion of MLCINH should occur as: 1. DCVA and accompanying large-scale ascent /destabilization aloft spread into the area ahead of the shortwave trough, and 2. Diurnal heating acts on higher elevations amidst marginal but sufficient low-level moisture, with lower-elevation surface dewpoints remaining in the mid 40s to lower 50s through the mixing cycle. Though low-level windspeeds will be modest, strong veering with height north of the front will underlie strengthening mid/upper winds to contribute to areas of 35-45-kt effective-shear magnitudes in support of storm organization (and at least brief supercell characteristics for any discrete activity). In general, an upscale aggregation of high-based convection should move eastward over the outlook area, and over a deep/well-mixed subcloud layer, to support gust potential. Activity should weaken considerably during the evening as the foregoing boundary layer stabilizes. ...Upper Midwest/upper Mississippi Valley... A corridor of favorable moisture (dewpoints commonly in the 60s, locally topping 70 F) and diurnal heating may support late-afternoon development near the front, with isolated severe hail/gusts conditionally possible. However, strong capping, on the northeastern rim of a well-developed EML, may preclude this scenario. More confidence exists in later development (evening) in a regime of increasingly focused low-level warm advection and lift over eastern SD and southwestern MN, shifting east-southeastward across the outlook area into tonight. Steep midlevel lapse rates will support 1500-2500 J/kg MUCAPE, with around 35-45-kt effective-shear magnitudes. Clustering of cells may promote wind potential, with isolated severe gusts potentially penetrating the near-surface stable layer, and occasional hail near severe limits also possible. ...Northeast CONUS... Widely scattered to scattered thunderstorms are forecast to develop along/ahead of the weak/leading front and ejecting shortwave trough through the afternoon, with isolated damaging to marginally severe gusts being the primary concern. Marginally severe hail may occur in the most intense cores, especially over northern parts of the outlook area under somewhat colder temperatures aloft. This activity should occur in a regime of diurnally minimized MLCINH and rich low-level moisture, with surface dewpoints commonly in the upper 60s to low 70s F. This will offset modest mid/upper-level lapse rates enough to yield peak/preconvective MLCAPE in the 1000-1500 J/kg range (locally/briefly higher). Low-middle-level flow should be modest, keeping hodographs small, but with strong upper/anvil-level winds to aid in multicellular storm organization. ..Edwards/Grams.. 08/04/2024 Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0754 AM CDT Sun Aug 04 2024 Valid 041300Z - 051200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FOR TROPICAL-CYCLONE TORNADOES...OVER PARTS OF FLORIDA AND EXTREME SOUTHERN GEORGIA... ...SUMMARY... Tropical Storm Debby may produce a few tornadoes over parts of Florida and extreme southern Georgia through early tomorrow morning as it intensifies. ...Synopsis... A persistent, mid/upper-level anticyclone will remain centered over the Four Corners region through the period, but with deamplification of the ridge to its north. This will occur as a long-lived shortwave trough -- that emanated from the subtropical easterlies a few days ago and is located over the interior Northwest -- pivots eastward through the mean-ridge position across the northern Rockies. By 12Z tomorrow, this perturbation should reach north- central/northeastern MT. Downstream, a belt of relatively enhanced, slightly difluent northwesterly flow will persist over the northern Plains and Upper Midwest, maintained by a large cyclone centered over northeastern Canada. Farther downstream, a persistent, positively tilted, mid/upper-level trough was apparent in moisture-channel imagery from western/central NY southwestward over the central/southern Appalachians to portions of AL. This feature is expected to deamplify through the period, with the middle-northern part ejecting off the Mid-Atlantic and New England Coasts by about 06Z. Though weakening, the southern part of this trough will contribute to the continuing recurvature of what now is Tropical Storm Debbie, per NHC discussions. At the surface, 11Z analysis showed a low over the northern shore of Lake Ontario, with a weak, slow-moving cold front across central NY, eastern PA, to northern/central VA. This boundary should move slowly eastward while continuing to weaken through the period. Another, wavy, quasistationary frontal zone was analyzed from the same low across northwestern OH, southern Lake Michigan, southern MN, to another low near YKN, then across southwestern SD to southeastern MT. This boundary will oscillate on the mesoscale through the period in response to weak perturbations aloft, and proximal convective processes. ...FL, southern GA... Tropical Storm Debby continues to intensify in accordance with NHC forecasts, and is expected to strengthen further to a hurricane near the end of the period and just prior to landfall. [Refer to latest NHC advisories for track and intensity forecasts for Debby, as well as tropical-cyclone watches and warnings. See SPC mesoscale discussion 1812 for coverage of marginal/near-term tornado potential very near the west-central FL Coast.] As Debby strengthens today into this evening: 1. Expansion of the peripheral wind fields will provide supercell-favorable low-level shear and hodograph size, and 2. The diurnal-heating cycle should destabilize moisture-rich inland areas of peninsular FL and remove MLCINH, while 3. Low-level convergence/lift will strengthen in step with system intensification. Those factors should enlarge the outer convective pattern eastward over more of the landmass. Such development may backbuild into parts of south FL, but the greater probability for mature supercells will be in the "slight-risk (5% tornado) area over western/central FL today, spreading north toward the area near the FL/GA line overnight. Late in the period into early day 2, as the system approaches landfall and precip increases across interior northern FL and southern GA, an overland, low-level baroclinic zone should develop and strengthen. This feature -- with relatively stable, rain-cooled air to its poleward side -- should act as a fairly sharp, buoyancy-limiting boundary for the northern edge of the tornado threat. However, a looser tornado-probability gradient remains for now in the outlook lines, since the boundary's specific location will depend strongly on mesobeta-scale convective/precip geometry and density yet to be determined, within and just off the northern rim of Debby's circulation. ...Southeastern/south-central MT and vicinity... Widely scattered to scattered thunderstorms are expected to develop over the higher terrain of southwestern/south-central MT this afternoon, offering a few strong-severe gusts and isolated/marginal hail. Steepening of low/middle-level lapse rates and concordant erosion of MLCINH should occur as: 1. DCVA and accompanying large-scale ascent /destabilization aloft spread into the area ahead of the shortwave trough, and 2. Diurnal heating acts on higher elevations amidst marginal but sufficient low-level moisture, with lower-elevation surface dewpoints remaining in the mid 40s to lower 50s through the mixing cycle. Though low-level windspeeds will be modest, strong veering with height north of the front will underlie strengthening mid/upper winds to contribute to areas of 35-45-kt effective-shear magnitudes in support of storm organization (and at least brief supercell characteristics for any discrete activity). In general, an upscale aggregation of high-based convection should move eastward over the outlook area, and over a deep/well-mixed subcloud layer, to support gust potential. Activity should weaken considerably during the evening as the foregoing boundary layer stabilizes. ...Upper Midwest/upper Mississippi Valley... A corridor of favorable moisture (dewpoints commonly in the 60s, locally topping 70 F) and diurnal heating may support late-afternoon development near the front, with isolated severe hail/gusts conditionally possible. However, strong capping, on the northeastern rim of a well-developed EML, may preclude this scenario. More confidence exists in later development (evening) in a regime of increasingly focused low-level warm advection and lift over eastern SD and southwestern MN, shifting east-southeastward across the outlook area into tonight. Steep midlevel lapse rates will support 1500-2500 J/kg MUCAPE, with around 35-45-kt effective-shear magnitudes. Clustering of cells may promote wind potential, with isolated severe gusts potentially penetrating the near-surface stable layer, and occasional hail near severe limits also possible. ...Northeast CONUS... Widely scattered to scattered thunderstorms are forecast to develop along/ahead of the weak/leading front and ejecting shortwave trough through the afternoon, with isolated damaging to marginally severe gusts being the primary concern. Marginally severe hail may occur in the most intense cores, especially over northern parts of the outlook area under somewhat colder temperatures aloft. This activity should occur in a regime of diurnally minimized MLCINH and rich low-level moisture, with surface dewpoints commonly in the upper 60s to low 70s F. This will offset modest mid/upper-level lapse rates enough to yield peak/preconvective MLCAPE in the 1000-1500 J/kg range (locally/briefly higher). Low-middle-level flow should be modest, keeping hodographs small, but with strong upper/anvil-level winds to aid in multicellular storm organization. ..Edwards/Grams.. 08/04/2024 Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0754 AM CDT Sun Aug 04 2024 Valid 041300Z - 051200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FOR TROPICAL-CYCLONE TORNADOES...OVER PARTS OF FLORIDA AND EXTREME SOUTHERN GEORGIA... ...SUMMARY... Tropical Storm Debby may produce a few tornadoes over parts of Florida and extreme southern Georgia through early tomorrow morning as it intensifies. ...Synopsis... A persistent, mid/upper-level anticyclone will remain centered over the Four Corners region through the period, but with deamplification of the ridge to its north. This will occur as a long-lived shortwave trough -- that emanated from the subtropical easterlies a few days ago and is located over the interior Northwest -- pivots eastward through the mean-ridge position across the northern Rockies. By 12Z tomorrow, this perturbation should reach north- central/northeastern MT. Downstream, a belt of relatively enhanced, slightly difluent northwesterly flow will persist over the northern Plains and Upper Midwest, maintained by a large cyclone centered over northeastern Canada. Farther downstream, a persistent, positively tilted, mid/upper-level trough was apparent in moisture-channel imagery from western/central NY southwestward over the central/southern Appalachians to portions of AL. This feature is expected to deamplify through the period, with the middle-northern part ejecting off the Mid-Atlantic and New England Coasts by about 06Z. Though weakening, the southern part of this trough will contribute to the continuing recurvature of what now is Tropical Storm Debbie, per NHC discussions. At the surface, 11Z analysis showed a low over the northern shore of Lake Ontario, with a weak, slow-moving cold front across central NY, eastern PA, to northern/central VA. This boundary should move slowly eastward while continuing to weaken through the period. Another, wavy, quasistationary frontal zone was analyzed from the same low across northwestern OH, southern Lake Michigan, southern MN, to another low near YKN, then across southwestern SD to southeastern MT. This boundary will oscillate on the mesoscale through the period in response to weak perturbations aloft, and proximal convective processes. ...FL, southern GA... Tropical Storm Debby continues to intensify in accordance with NHC forecasts, and is expected to strengthen further to a hurricane near the end of the period and just prior to landfall. [Refer to latest NHC advisories for track and intensity forecasts for Debby, as well as tropical-cyclone watches and warnings. See SPC mesoscale discussion 1812 for coverage of marginal/near-term tornado potential very near the west-central FL Coast.] As Debby strengthens today into this evening: 1. Expansion of the peripheral wind fields will provide supercell-favorable low-level shear and hodograph size, and 2. The diurnal-heating cycle should destabilize moisture-rich inland areas of peninsular FL and remove MLCINH, while 3. Low-level convergence/lift will strengthen in step with system intensification. Those factors should enlarge the outer convective pattern eastward over more of the landmass. Such development may backbuild into parts of south FL, but the greater probability for mature supercells will be in the "slight-risk (5% tornado) area over western/central FL today, spreading north toward the area near the FL/GA line overnight. Late in the period into early day 2, as the system approaches landfall and precip increases across interior northern FL and southern GA, an overland, low-level baroclinic zone should develop and strengthen. This feature -- with relatively stable, rain-cooled air to its poleward side -- should act as a fairly sharp, buoyancy-limiting boundary for the northern edge of the tornado threat. However, a looser tornado-probability gradient remains for now in the outlook lines, since the boundary's specific location will depend strongly on mesobeta-scale convective/precip geometry and density yet to be determined, within and just off the northern rim of Debby's circulation. ...Southeastern/south-central MT and vicinity... Widely scattered to scattered thunderstorms are expected to develop over the higher terrain of southwestern/south-central MT this afternoon, offering a few strong-severe gusts and isolated/marginal hail. Steepening of low/middle-level lapse rates and concordant erosion of MLCINH should occur as: 1. DCVA and accompanying large-scale ascent /destabilization aloft spread into the area ahead of the shortwave trough, and 2. Diurnal heating acts on higher elevations amidst marginal but sufficient low-level moisture, with lower-elevation surface dewpoints remaining in the mid 40s to lower 50s through the mixing cycle. Though low-level windspeeds will be modest, strong veering with height north of the front will underlie strengthening mid/upper winds to contribute to areas of 35-45-kt effective-shear magnitudes in support of storm organization (and at least brief supercell characteristics for any discrete activity). In general, an upscale aggregation of high-based convection should move eastward over the outlook area, and over a deep/well-mixed subcloud layer, to support gust potential. Activity should weaken considerably during the evening as the foregoing boundary layer stabilizes. ...Upper Midwest/upper Mississippi Valley... A corridor of favorable moisture (dewpoints commonly in the 60s, locally topping 70 F) and diurnal heating may support late-afternoon development near the front, with isolated severe hail/gusts conditionally possible. However, strong capping, on the northeastern rim of a well-developed EML, may preclude this scenario. More confidence exists in later development (evening) in a regime of increasingly focused low-level warm advection and lift over eastern SD and southwestern MN, shifting east-southeastward across the outlook area into tonight. Steep midlevel lapse rates will support 1500-2500 J/kg MUCAPE, with around 35-45-kt effective-shear magnitudes. Clustering of cells may promote wind potential, with isolated severe gusts potentially penetrating the near-surface stable layer, and occasional hail near severe limits also possible. ...Northeast CONUS... Widely scattered to scattered thunderstorms are forecast to develop along/ahead of the weak/leading front and ejecting shortwave trough through the afternoon, with isolated damaging to marginally severe gusts being the primary concern. Marginally severe hail may occur in the most intense cores, especially over northern parts of the outlook area under somewhat colder temperatures aloft. This activity should occur in a regime of diurnally minimized MLCINH and rich low-level moisture, with surface dewpoints commonly in the upper 60s to low 70s F. This will offset modest mid/upper-level lapse rates enough to yield peak/preconvective MLCAPE in the 1000-1500 J/kg range (locally/briefly higher). Low-middle-level flow should be modest, keeping hodographs small, but with strong upper/anvil-level winds to aid in multicellular storm organization. ..Edwards/Grams.. 08/04/2024 Read more

MD 1812 CONCERNING SEVERE POTENTIAL...WATCH UNLIKELY FOR COASTAL WEST-CENTRAL/SOUTHWEST FL PENINSULA
Mesoscale Discussion 1812 NWS Storm Prediction Center Norman OK 0647 AM CDT Sun Aug 04 2024 Areas affected...Coastal west-central/southwest FL Peninsula Concerning...Severe potential...Watch unlikely Valid 041147Z - 041315Z Probability of Watch Issuance...20 percent SUMMARY...A brief tornado or two is possible into late morning with an outer band of showers gradually advancing north from the southwest to west-central Florida Gulf Coast, in association with TS Debby. DISCUSSION...A persistent arc of moderate-topped showers from western Collier to Sarasota counties has had transient but largely weak attempts at low-level rotation. This arc is within a corridor for enhanced low-level SRH, around 200-250 m2/s2, per time-series of TBW VWP data. Diminishing hodograph curvature exists to its south per BYX VWP data, where low-level and surface winds are nearly unidirectional from the south. The overall threat will likely remain spatially confined and limited in potential intensity beyond a weak, brief tornado or two. Greater potential for rotating cells across a broader area of the central peninsula may become evident towards midday. ..Grams/Edwards.. 08/04/2024 ...Please see www.spc.noaa.gov for graphic product... ATTN...WFO...MFL...TBW... LAT...LON 28038284 28018246 27308166 26808148 26448156 26278172 26348178 26408194 26978220 27248268 27498283 27848298 28038284 Read more

000
ABPZ20 KNHC 041210 CCA
TWOEP

Tropical Weather Outlook...Corrected
NWS National Hurricane Center Miami FL
500 AM PDT Sun Aug 4 2024

For the eastern North Pacific...east of 140 degrees west longitude:

Corrected to update active systems and include statement for gale
warnings for EP96.

Active Systems:
The National Hurricane Center is issuing advisories on recently
downgraded Tropical Storm Carlotta, located several hundred miles to
the west-southwest of the southern tip of the Baja California
peninsula, and on Tropical Storm Daniel, located more than one
thousand miles to the west-southwest of the southern tip of the Baja
California peninsula.

South of Southwestern Mexico (EP96):
Shower and thunderstorm activity has increased with a broad area of
low pressure located a few hundred miles south of southwestern
Mexico. Environmental conditions remain conducive for gradual
development, and a tropical depression is likely to form during the
next day or two while the system moves generally west-northwestward
at 10 to 15 mph, remaining well offshore of the coast of Mexico. For
more information of this system, including Gale Warnings, see High
Seas Forecasts issued by the National Weather Service.
* Formation chance through 48 hours...high...70 percent.
* Formation chance through 7 days...high...90 percent.

South-Southwest of the Baja California Peninsula (EP97):
Shower and thunderstorm activity is showing signs of organization
with an area of low pressure located several hundred miles to the
south-southwest of the southern tip of the Baja California
peninsula. Environmental conditions appear conducive for development
over the next day or two, and a tropical depression is likely to
form during that time while the system meanders within weak steering
currents. Thereafter, the system is forecast to interact with the
disturbance (EP96) to its southeast, which should limit the chances
of further development afterwards.
* Formation chance through 48 hours...high...70 percent.
* Formation chance through 7 days...high...70 percent.

&&
Public Advisories on Tropical Storm Daniel are issued under
WMO header WTPZ34 KNHC and under AWIPS header MIATCPEP4.
Forecast/Advisories on Tropical Storm Daniel are issued under
WMO header WTPZ24 KNHC and under AWIPS header MIATCMEP4.

High Seas Forecasts issued by the National Weather Service
can be found under AWIPS header NFDHSFEPI, WMO header FZPN02
KWBC, and on the web at ocean.weather.gov/shtml/NFDHSFEPI.php

$$
Forecaster Papin/D. Zelinsky

000
ABPZ20 KNHC 041139
TWOEP

Tropical Weather Outlook
NWS National Hurricane Center Miami FL
500 AM PDT Sun Aug 4 2024

For the eastern North Pacific...east of 140 degrees west longitude:

Active Systems:
The National Hurricane Center is issuing advisories on Hurricane
Carlotta, located several hundred miles to the west-southwest of the
southern tip of the Baja California peninsula, and on Tropical Storm
Daniel, located more than one thousand miles to the west-southwest
of the southern tip of the Baja California peninsula.

South of Southwestern Mexico (EP96):
Shower and thunderstorm activity has increased with a broad area of
low pressure located a few hundred miles south of southwestern
Mexico. Environmental conditions remain conducive for gradual
development, and a tropical depression is likely to form during the
next day or two while the system moves generally west-northwestward
at 10 to 15 mph, remaining well offshore of the coast of Mexico.
* Formation chance through 48 hours...high...70 percent.
* Formation chance through 7 days...high...90 percent.

South-Southwest of the Baja California Peninsula (EP97):
Shower and thunderstorm activity is showing signs of organization
with an area of low pressure located several hundred miles to the
south-southwest of the southern tip of the Baja California
peninsula. Environmental conditions appear conducive for development
over the next day or two, and a tropical depression is likely to
form during that time while the system meanders within weak steering
currents. Thereafter, the system is forecast to interact with the
disturbance (EP96) to its southeast, which should limit the chances
of further development afterwards.
* Formation chance through 48 hours...high...70 percent.
* Formation chance through 7 days...high...70 percent.

&&
Public Advisories on Tropical Storm Daniel are issued under
WMO header WTPZ34 KNHC and under AWIPS header MIATCPEP4.
Forecast/Advisories on Tropical Storm Daniel are issued under
WMO header WTPZ24 KNHC and under AWIPS header MIATCMEP4.

$$
Forecaster Papin/D. Zelinsky

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0359 AM CDT Sun Aug 04 2024 Valid 071200Z - 121200Z ...DISCUSSION... Medium-range guidance suggests that fairly prominent mid-level ridging will be maintained through this period across much of the Southwest and southern Rockies through the southern Great Plains. Upstream, it appears that mid-level troughing may become established near the U.S. Pacific coast by next weekend. Otherwise, the evolution of troughing downstream of a prominent mid-level high initially shifting across the Canadian Northwest Territories is more unclear. Some amplification may eventually contribute to the northeastward acceleration of the remnants of Debby, near/ahead of a southeastward advancing cold front, after the lingering low-level circulation center likely shifts back inland across coastal areas into the southern South Carolina vicinity by Thursday. If this were to occur, it probably would be accompanied by at least some risk for convection capable of producing tornadoes into the Mid Atlantic coast vicinity. However, it is not clear that this potential will support more than low severe probabilities, and severe weather elsewhere across the U.S. still appears likely to remain limited through this period. Read more

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0359 AM CDT Sun Aug 04 2024 Valid 071200Z - 121200Z ...DISCUSSION... Medium-range guidance suggests that fairly prominent mid-level ridging will be maintained through this period across much of the Southwest and southern Rockies through the southern Great Plains. Upstream, it appears that mid-level troughing may become established near the U.S. Pacific coast by next weekend. Otherwise, the evolution of troughing downstream of a prominent mid-level high initially shifting across the Canadian Northwest Territories is more unclear. Some amplification may eventually contribute to the northeastward acceleration of the remnants of Debby, near/ahead of a southeastward advancing cold front, after the lingering low-level circulation center likely shifts back inland across coastal areas into the southern South Carolina vicinity by Thursday. If this were to occur, it probably would be accompanied by at least some risk for convection capable of producing tornadoes into the Mid Atlantic coast vicinity. However, it is not clear that this potential will support more than low severe probabilities, and severe weather elsewhere across the U.S. still appears likely to remain limited through this period. Read more

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0359 AM CDT Sun Aug 04 2024 Valid 071200Z - 121200Z ...DISCUSSION... Medium-range guidance suggests that fairly prominent mid-level ridging will be maintained through this period across much of the Southwest and southern Rockies through the southern Great Plains. Upstream, it appears that mid-level troughing may become established near the U.S. Pacific coast by next weekend. Otherwise, the evolution of troughing downstream of a prominent mid-level high initially shifting across the Canadian Northwest Territories is more unclear. Some amplification may eventually contribute to the northeastward acceleration of the remnants of Debby, near/ahead of a southeastward advancing cold front, after the lingering low-level circulation center likely shifts back inland across coastal areas into the southern South Carolina vicinity by Thursday. If this were to occur, it probably would be accompanied by at least some risk for convection capable of producing tornadoes into the Mid Atlantic coast vicinity. However, it is not clear that this potential will support more than low severe probabilities, and severe weather elsewhere across the U.S. still appears likely to remain limited through this period. Read more

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0359 AM CDT Sun Aug 04 2024 Valid 071200Z - 121200Z ...DISCUSSION... Medium-range guidance suggests that fairly prominent mid-level ridging will be maintained through this period across much of the Southwest and southern Rockies through the southern Great Plains. Upstream, it appears that mid-level troughing may become established near the U.S. Pacific coast by next weekend. Otherwise, the evolution of troughing downstream of a prominent mid-level high initially shifting across the Canadian Northwest Territories is more unclear. Some amplification may eventually contribute to the northeastward acceleration of the remnants of Debby, near/ahead of a southeastward advancing cold front, after the lingering low-level circulation center likely shifts back inland across coastal areas into the southern South Carolina vicinity by Thursday. If this were to occur, it probably would be accompanied by at least some risk for convection capable of producing tornadoes into the Mid Atlantic coast vicinity. However, it is not clear that this potential will support more than low severe probabilities, and severe weather elsewhere across the U.S. still appears likely to remain limited through this period. Read more

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0359 AM CDT Sun Aug 04 2024 Valid 071200Z - 121200Z ...DISCUSSION... Medium-range guidance suggests that fairly prominent mid-level ridging will be maintained through this period across much of the Southwest and southern Rockies through the southern Great Plains. Upstream, it appears that mid-level troughing may become established near the U.S. Pacific coast by next weekend. Otherwise, the evolution of troughing downstream of a prominent mid-level high initially shifting across the Canadian Northwest Territories is more unclear. Some amplification may eventually contribute to the northeastward acceleration of the remnants of Debby, near/ahead of a southeastward advancing cold front, after the lingering low-level circulation center likely shifts back inland across coastal areas into the southern South Carolina vicinity by Thursday. If this were to occur, it probably would be accompanied by at least some risk for convection capable of producing tornadoes into the Mid Atlantic coast vicinity. However, it is not clear that this potential will support more than low severe probabilities, and severe weather elsewhere across the U.S. still appears likely to remain limited through this period. Read more

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0359 AM CDT Sun Aug 04 2024 Valid 071200Z - 121200Z ...DISCUSSION... Medium-range guidance suggests that fairly prominent mid-level ridging will be maintained through this period across much of the Southwest and southern Rockies through the southern Great Plains. Upstream, it appears that mid-level troughing may become established near the U.S. Pacific coast by next weekend. Otherwise, the evolution of troughing downstream of a prominent mid-level high initially shifting across the Canadian Northwest Territories is more unclear. Some amplification may eventually contribute to the northeastward acceleration of the remnants of Debby, near/ahead of a southeastward advancing cold front, after the lingering low-level circulation center likely shifts back inland across coastal areas into the southern South Carolina vicinity by Thursday. If this were to occur, it probably would be accompanied by at least some risk for convection capable of producing tornadoes into the Mid Atlantic coast vicinity. However, it is not clear that this potential will support more than low severe probabilities, and severe weather elsewhere across the U.S. still appears likely to remain limited through this period. Read more

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0359 AM CDT Sun Aug 04 2024 Valid 071200Z - 121200Z ...DISCUSSION... Medium-range guidance suggests that fairly prominent mid-level ridging will be maintained through this period across much of the Southwest and southern Rockies through the southern Great Plains. Upstream, it appears that mid-level troughing may become established near the U.S. Pacific coast by next weekend. Otherwise, the evolution of troughing downstream of a prominent mid-level high initially shifting across the Canadian Northwest Territories is more unclear. Some amplification may eventually contribute to the northeastward acceleration of the remnants of Debby, near/ahead of a southeastward advancing cold front, after the lingering low-level circulation center likely shifts back inland across coastal areas into the southern South Carolina vicinity by Thursday. If this were to occur, it probably would be accompanied by at least some risk for convection capable of producing tornadoes into the Mid Atlantic coast vicinity. However, it is not clear that this potential will support more than low severe probabilities, and severe weather elsewhere across the U.S. still appears likely to remain limited through this period. Read more

5-Day Uncertainty Track last updated Sun, 04 Aug 2024 08:50:35 GMT


Wind Speed Probabilities last updated Sun, 04 Aug 2024 09:34:55 GMT