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SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1131 AM CDT Mon Jul 15 2024 Valid 151630Z - 161200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS THIS MORNING OVER PARTS OF EASTERN IOWA...NORTHERN ILLINOIS...NORTHERN INDIANA...SOUTHERN WISCONSIN...AND SOUTHERN LOWER MICHIGAN... ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PARTS OF THE HIGH PLAINS...AND PORTIONS OF NEW YORK AND PENNSYLVANIA... ...SUMMARY... Severe thunderstorms are possible this afternoon and evening across portions of the Midwest, central High Plains, lower Great Lakes, and Arizona. The greatest potential for severe gusts is over eastern Iowa into Illinois and Indiana. ...Midwest... A broad upper trough is digging southeastward across northwest Ontario and MN today, with strengthening mid level flow across much of the Midwest. Rapid thunderstorm development is expected to occur by mid afternoon across portions of WI/northeast IA, with storms tracking rapidly east-southeastward into northern IL and eventually parts of IN/Lower MI. 12z CAM guidance remains in general agreement that a large bowing complex is likely, although details of the corridor of greatest risk vary between solutions. Regardless, an active severe event is expected for this region, with the potential for isolated instances of significant damaging winds. ...NY/PA... Thunderstorms have begun to intensify over eastern Lake Erie, ahead of a strong upper trough and remnant MCVs. These storms are expected to increase in coverage and spread eastward through the day, possibly as far east as southeast NY and northern NJ by evening. Damaging winds and hail are the main concerns with these storms. ...Central High Plains... Scattered high-based thunderstorm development is expected this afternoon from western NE southward into parts of northeast CO and western KS. The combination of a deeply mixed boundary layer, sufficient CAPE, and 30+ knots of westerly mid level flow will pose a risk of locally damaging wind gusts in the stronger cells. ..Hart/Halbert/Squitieri.. 07/15/2024 Read more

SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1131 AM CDT Mon Jul 15 2024 Valid 151630Z - 161200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS THIS MORNING OVER PARTS OF EASTERN IOWA...NORTHERN ILLINOIS...NORTHERN INDIANA...SOUTHERN WISCONSIN...AND SOUTHERN LOWER MICHIGAN... ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PARTS OF THE HIGH PLAINS...AND PORTIONS OF NEW YORK AND PENNSYLVANIA... ...SUMMARY... Severe thunderstorms are possible this afternoon and evening across portions of the Midwest, central High Plains, lower Great Lakes, and Arizona. The greatest potential for severe gusts is over eastern Iowa into Illinois and Indiana. ...Midwest... A broad upper trough is digging southeastward across northwest Ontario and MN today, with strengthening mid level flow across much of the Midwest. Rapid thunderstorm development is expected to occur by mid afternoon across portions of WI/northeast IA, with storms tracking rapidly east-southeastward into northern IL and eventually parts of IN/Lower MI. 12z CAM guidance remains in general agreement that a large bowing complex is likely, although details of the corridor of greatest risk vary between solutions. Regardless, an active severe event is expected for this region, with the potential for isolated instances of significant damaging winds. ...NY/PA... Thunderstorms have begun to intensify over eastern Lake Erie, ahead of a strong upper trough and remnant MCVs. These storms are expected to increase in coverage and spread eastward through the day, possibly as far east as southeast NY and northern NJ by evening. Damaging winds and hail are the main concerns with these storms. ...Central High Plains... Scattered high-based thunderstorm development is expected this afternoon from western NE southward into parts of northeast CO and western KS. The combination of a deeply mixed boundary layer, sufficient CAPE, and 30+ knots of westerly mid level flow will pose a risk of locally damaging wind gusts in the stronger cells. ..Hart/Halbert/Squitieri.. 07/15/2024 Read more

No watches are valid as of Mon Jul 15 15:55:02 UTC 2024.

A Knoxville lawn care business was providing different services, such as pulling out bushes, trimming bushes, and pulling out weeds while the grass was not growing, and lawns did not need to be mowed. Lawn mowing brings in about 60% of their revenue. WVLT (Knoxville, Tenn.), July 12, 2024

Dry conditions and heat in eastern Tennessee have cut production at a farm, leaving less to share with food pantries. WVLT (Knoxville, Tenn.), July 12, 2024

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0752 AM CDT Mon Jul 15 2024 Valid 151300Z - 161200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM PARTS OF IOWA TO SOUTHWESTERN LOWER MICHIGAN AND NORTHERN INDIANA... ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS SURROUNDING THE ENHANCED RISK...ALSO SEPARATELY OVER PARTS OF NEW YORK/PENNSYLVANIA AND THE CENTRAL HIGH PLAINS... ...SUMMARY... Severe thunderstorms are possible this afternoon and evening across portions of the Midwest, central High Plains, lower Great Lakes, and Arizona. The greatest potential for severe gusts is over eastern Iowa into Illinois and Indiana. ...Synopsis... Mid/upper-level pattern amplification in the northern stream will contribute to weakening (but not dissipation) of the persistent anticyclone over the Four Corners region. A 500-mb low over northern MB will dig south-southeastward to northwesternmost parts of ON through the period, combining with a series of small shortwave perturbations in the cyclone's southern semicircle to increase both cyclonic flow speeds and height curvature over upper parts of the Midwest, Mississippi Valley and Great Lakes. As this occurs, a shortwave trough -- evident in moisture-channel imagery over the Black Hills and vicinity -- will accelerate eastward to southern MN and northern/western IA by 00Z, then reach Lake Huron, northwestern OH and northern IN by the end of the period. That feature should be preceded by a smaller shortwave trough and MCV -- now apparent over western MN -- and forecast to move across northern WI and Upper MI through this evening. To its southeast and well downstream from the Black Hills perturbation, another MCV was quite evident in composite radar imagery over southern Lower MI, with shortwave trough southwestward to parts of central/eastern IL. This perturbation should move westward to western parts of NY/PA by 00Z, then near-coastal areas of central/ southern New England and the northern Mid-Atlantic by 12Z tomorrow. At the surface, 11Z analysis showed a low over northeastern SD with cold front southwestward across western NE and northern CO. By 00Z, the low should move/redevelop to a position near DBQ, with cold front southwestward across northeastern to northwestern KS and east-central/southeastern CO. By 12Z, the front should reach Lower MI, northern/western IL (perhaps obscured by convective effects), southern KS, and northeastern NM. Relevant prefrontal boundaries are discussed below. ...IA to southern Lower Great Lakes... The decaying remnants of the prior/overnight MCS responsible for the southern Lower MI MCV also have left an outflow boundary over southern portions of IN/IL, arching northwestward and becoming quasistationary over western IL into southeastern/central IA. Clouds/precip from the prior MCS, and shortwave subsidence/DNVA immediately following its associated shortwave trough, should be long gone by mid/late afternoon, when the airmass along the outflow boundary will have had several hours to modify favorably from west to east. The boundary itself also may drift northward amidst weak but steady ambient warm advection, with the boundary layer favorably destabilizing on both sides. A combination of lift near the boundary, increasing large-scale ascent ahead of the upstream mid/upper-level shortwave trough, steepening low-level lapse rates from diurnal heating, and rich moisture (surface dewpoints commonly upper 60s to low 70s F) are expected to prepare the corridor in and near the "enhanced risk" area for severe potential through the afternoon. Isolated to scattered thunderstorms should develop near and north of the western limb of the outflow boundary (mainly IA, but also possibly western IL) from mid/late afternoon into early evening. Some of this activity may be supercellular in the first few hours, with large hail possible. However, given the presence of a convergent, moisture-rich, broad gradient of instability north of the boundary aligned strongly parallel to favorably strong mid/upper winds, large low/middle-level lapse rates, and a related reservoir of high buoyancy (MLCAPE of 3000-5000 J/kg) this activity should evolve quickly upscale to an MCS with severe gusts (some over 75 mph) becoming the greatest hazard. With a vorticity-laden boundary, and potential for backed surface winds and vertical-shear/hodograph enhancement to its north, a corridor of relatively maximized tornado potential (from supercells and/or QLCS-embedded circulations) also exists -- likely narrower than depicted here due to current boundary-position uncertainty. Uncertainty exists also on how far the MCS will travel (and whether far enough to qualify as a derecho) before weakening tonight. This will be related to depth/breadth of the cold pool and mesobeta-scale rear-inflow jet dynamics, and their ability to exert forced ascent on a moist but gradually stabilizing inflow layer with eastward extent. ...Northeast... Scattered thunderstorms are expected to move eastward across this area this afternoon into early evening -- some of which may initiate late morning into midday back in ON closer to the MCV. Activity should aggregate into clusters and/or a short QLCS, yielding damaging to severe gusts. Isolated discrete or line-embedded supercells also are possible, with some attendant severe-hail potential. As the MCV crosses southernmost parts of ON and also Lake Erie today, the foregoing boundary layer over parts of NY/PA will destabilize diurnally, while remaining favorably moist (with lower- elevation surface dewpoints commonly in the mid 60s to near 70 F). This will support a buildup of preconvective MLCAPE into the 1500- 2000 J/kg range (locally higher). Note that models with RAP physics (RAP, HRRR) may be over-mixing higher elevations and underforecasting buoyancy as a result (a common bias). Increase and slight veering of winds with height will contribute to around 30-40 kt effective-shear magnitudes, which may be locally greater in any channels of gradient-flow enhancement from the MCV that extend to or past the zone of convective forcing. Meanwhile, a well-mixed subcloud layer will supports damaging-downdraft potential. ...Central High Plains... Isolate to scattered, high-based thunderstorms are expected to form this afternoon over a broad area from central WY to the Front Range and foothills of CO, with the most concentrated convection still progged for portions of southeastern WY, western NE and northeastern CO. Steep low/middle-level lapse rates (8.5-9 deg C/km) are expected by midafternoon over this region, with enough easterly component of flow behind the front (and relate moist advection) to offset mixing and maintain mid 40s to low 50s surface dewpoints in the "slight risk" area. These should contribute to a field of peak/preconvective MLCAPE ranging from around 300 J/kg just east of the mountains to around 1500 J/kg over parts of west-central/ southwestern NE. The post-frontal boundary-layer flow also will enhance both storm-relative low-level winds and deep shear (effective-shear magnitudes in the 35-45-kt range). This, along with potential for cold-pool clustering, favors some organization and maintenance of convection across the outlook this evening before diminishing in a more strongly capped, nocturnal boundary layer over lower Plains elevations. ...AZ... Widely scattered thunderstorms are expected to form again this afternoon over portions of the Mogollon Rim and smaller terrain maxima to its south, offering locally strong-severe downbursts. Although the synoptic anticyclone will be weakening through the period, associated flow still will support motion toward the west or southwest, atop deep/well-mixed boundary layers of the desert floor. Airmass recovery from the prior day's convection by afternoon will be aided by warm/moist advection and strong diurnal heating. Large dewpoint depressions and deep subcloud layers in lower elevations -- beneath about 1000-1500 J/kg MLCAPE -- will support the gust potential, especially wherever activity can become clustered and maximize regenerative potential through cold-pool-aided lift. ..Edwards/Broyles.. 07/15/2024 Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0752 AM CDT Mon Jul 15 2024 Valid 151300Z - 161200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM PARTS OF IOWA TO SOUTHWESTERN LOWER MICHIGAN AND NORTHERN INDIANA... ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS SURROUNDING THE ENHANCED RISK...ALSO SEPARATELY OVER PARTS OF NEW YORK/PENNSYLVANIA AND THE CENTRAL HIGH PLAINS... ...SUMMARY... Severe thunderstorms are possible this afternoon and evening across portions of the Midwest, central High Plains, lower Great Lakes, and Arizona. The greatest potential for severe gusts is over eastern Iowa into Illinois and Indiana. ...Synopsis... Mid/upper-level pattern amplification in the northern stream will contribute to weakening (but not dissipation) of the persistent anticyclone over the Four Corners region. A 500-mb low over northern MB will dig south-southeastward to northwesternmost parts of ON through the period, combining with a series of small shortwave perturbations in the cyclone's southern semicircle to increase both cyclonic flow speeds and height curvature over upper parts of the Midwest, Mississippi Valley and Great Lakes. As this occurs, a shortwave trough -- evident in moisture-channel imagery over the Black Hills and vicinity -- will accelerate eastward to southern MN and northern/western IA by 00Z, then reach Lake Huron, northwestern OH and northern IN by the end of the period. That feature should be preceded by a smaller shortwave trough and MCV -- now apparent over western MN -- and forecast to move across northern WI and Upper MI through this evening. To its southeast and well downstream from the Black Hills perturbation, another MCV was quite evident in composite radar imagery over southern Lower MI, with shortwave trough southwestward to parts of central/eastern IL. This perturbation should move westward to western parts of NY/PA by 00Z, then near-coastal areas of central/ southern New England and the northern Mid-Atlantic by 12Z tomorrow. At the surface, 11Z analysis showed a low over northeastern SD with cold front southwestward across western NE and northern CO. By 00Z, the low should move/redevelop to a position near DBQ, with cold front southwestward across northeastern to northwestern KS and east-central/southeastern CO. By 12Z, the front should reach Lower MI, northern/western IL (perhaps obscured by convective effects), southern KS, and northeastern NM. Relevant prefrontal boundaries are discussed below. ...IA to southern Lower Great Lakes... The decaying remnants of the prior/overnight MCS responsible for the southern Lower MI MCV also have left an outflow boundary over southern portions of IN/IL, arching northwestward and becoming quasistationary over western IL into southeastern/central IA. Clouds/precip from the prior MCS, and shortwave subsidence/DNVA immediately following its associated shortwave trough, should be long gone by mid/late afternoon, when the airmass along the outflow boundary will have had several hours to modify favorably from west to east. The boundary itself also may drift northward amidst weak but steady ambient warm advection, with the boundary layer favorably destabilizing on both sides. A combination of lift near the boundary, increasing large-scale ascent ahead of the upstream mid/upper-level shortwave trough, steepening low-level lapse rates from diurnal heating, and rich moisture (surface dewpoints commonly upper 60s to low 70s F) are expected to prepare the corridor in and near the "enhanced risk" area for severe potential through the afternoon. Isolated to scattered thunderstorms should develop near and north of the western limb of the outflow boundary (mainly IA, but also possibly western IL) from mid/late afternoon into early evening. Some of this activity may be supercellular in the first few hours, with large hail possible. However, given the presence of a convergent, moisture-rich, broad gradient of instability north of the boundary aligned strongly parallel to favorably strong mid/upper winds, large low/middle-level lapse rates, and a related reservoir of high buoyancy (MLCAPE of 3000-5000 J/kg) this activity should evolve quickly upscale to an MCS with severe gusts (some over 75 mph) becoming the greatest hazard. With a vorticity-laden boundary, and potential for backed surface winds and vertical-shear/hodograph enhancement to its north, a corridor of relatively maximized tornado potential (from supercells and/or QLCS-embedded circulations) also exists -- likely narrower than depicted here due to current boundary-position uncertainty. Uncertainty exists also on how far the MCS will travel (and whether far enough to qualify as a derecho) before weakening tonight. This will be related to depth/breadth of the cold pool and mesobeta-scale rear-inflow jet dynamics, and their ability to exert forced ascent on a moist but gradually stabilizing inflow layer with eastward extent. ...Northeast... Scattered thunderstorms are expected to move eastward across this area this afternoon into early evening -- some of which may initiate late morning into midday back in ON closer to the MCV. Activity should aggregate into clusters and/or a short QLCS, yielding damaging to severe gusts. Isolated discrete or line-embedded supercells also are possible, with some attendant severe-hail potential. As the MCV crosses southernmost parts of ON and also Lake Erie today, the foregoing boundary layer over parts of NY/PA will destabilize diurnally, while remaining favorably moist (with lower- elevation surface dewpoints commonly in the mid 60s to near 70 F). This will support a buildup of preconvective MLCAPE into the 1500- 2000 J/kg range (locally higher). Note that models with RAP physics (RAP, HRRR) may be over-mixing higher elevations and underforecasting buoyancy as a result (a common bias). Increase and slight veering of winds with height will contribute to around 30-40 kt effective-shear magnitudes, which may be locally greater in any channels of gradient-flow enhancement from the MCV that extend to or past the zone of convective forcing. Meanwhile, a well-mixed subcloud layer will supports damaging-downdraft potential. ...Central High Plains... Isolate to scattered, high-based thunderstorms are expected to form this afternoon over a broad area from central WY to the Front Range and foothills of CO, with the most concentrated convection still progged for portions of southeastern WY, western NE and northeastern CO. Steep low/middle-level lapse rates (8.5-9 deg C/km) are expected by midafternoon over this region, with enough easterly component of flow behind the front (and relate moist advection) to offset mixing and maintain mid 40s to low 50s surface dewpoints in the "slight risk" area. These should contribute to a field of peak/preconvective MLCAPE ranging from around 300 J/kg just east of the mountains to around 1500 J/kg over parts of west-central/ southwestern NE. The post-frontal boundary-layer flow also will enhance both storm-relative low-level winds and deep shear (effective-shear magnitudes in the 35-45-kt range). This, along with potential for cold-pool clustering, favors some organization and maintenance of convection across the outlook this evening before diminishing in a more strongly capped, nocturnal boundary layer over lower Plains elevations. ...AZ... Widely scattered thunderstorms are expected to form again this afternoon over portions of the Mogollon Rim and smaller terrain maxima to its south, offering locally strong-severe downbursts. Although the synoptic anticyclone will be weakening through the period, associated flow still will support motion toward the west or southwest, atop deep/well-mixed boundary layers of the desert floor. Airmass recovery from the prior day's convection by afternoon will be aided by warm/moist advection and strong diurnal heating. Large dewpoint depressions and deep subcloud layers in lower elevations -- beneath about 1000-1500 J/kg MLCAPE -- will support the gust potential, especially wherever activity can become clustered and maximize regenerative potential through cold-pool-aided lift. ..Edwards/Broyles.. 07/15/2024 Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0752 AM CDT Mon Jul 15 2024 Valid 151300Z - 161200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM PARTS OF IOWA TO SOUTHWESTERN LOWER MICHIGAN AND NORTHERN INDIANA... ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS SURROUNDING THE ENHANCED RISK...ALSO SEPARATELY OVER PARTS OF NEW YORK/PENNSYLVANIA AND THE CENTRAL HIGH PLAINS... ...SUMMARY... Severe thunderstorms are possible this afternoon and evening across portions of the Midwest, central High Plains, lower Great Lakes, and Arizona. The greatest potential for severe gusts is over eastern Iowa into Illinois and Indiana. ...Synopsis... Mid/upper-level pattern amplification in the northern stream will contribute to weakening (but not dissipation) of the persistent anticyclone over the Four Corners region. A 500-mb low over northern MB will dig south-southeastward to northwesternmost parts of ON through the period, combining with a series of small shortwave perturbations in the cyclone's southern semicircle to increase both cyclonic flow speeds and height curvature over upper parts of the Midwest, Mississippi Valley and Great Lakes. As this occurs, a shortwave trough -- evident in moisture-channel imagery over the Black Hills and vicinity -- will accelerate eastward to southern MN and northern/western IA by 00Z, then reach Lake Huron, northwestern OH and northern IN by the end of the period. That feature should be preceded by a smaller shortwave trough and MCV -- now apparent over western MN -- and forecast to move across northern WI and Upper MI through this evening. To its southeast and well downstream from the Black Hills perturbation, another MCV was quite evident in composite radar imagery over southern Lower MI, with shortwave trough southwestward to parts of central/eastern IL. This perturbation should move westward to western parts of NY/PA by 00Z, then near-coastal areas of central/ southern New England and the northern Mid-Atlantic by 12Z tomorrow. At the surface, 11Z analysis showed a low over northeastern SD with cold front southwestward across western NE and northern CO. By 00Z, the low should move/redevelop to a position near DBQ, with cold front southwestward across northeastern to northwestern KS and east-central/southeastern CO. By 12Z, the front should reach Lower MI, northern/western IL (perhaps obscured by convective effects), southern KS, and northeastern NM. Relevant prefrontal boundaries are discussed below. ...IA to southern Lower Great Lakes... The decaying remnants of the prior/overnight MCS responsible for the southern Lower MI MCV also have left an outflow boundary over southern portions of IN/IL, arching northwestward and becoming quasistationary over western IL into southeastern/central IA. Clouds/precip from the prior MCS, and shortwave subsidence/DNVA immediately following its associated shortwave trough, should be long gone by mid/late afternoon, when the airmass along the outflow boundary will have had several hours to modify favorably from west to east. The boundary itself also may drift northward amidst weak but steady ambient warm advection, with the boundary layer favorably destabilizing on both sides. A combination of lift near the boundary, increasing large-scale ascent ahead of the upstream mid/upper-level shortwave trough, steepening low-level lapse rates from diurnal heating, and rich moisture (surface dewpoints commonly upper 60s to low 70s F) are expected to prepare the corridor in and near the "enhanced risk" area for severe potential through the afternoon. Isolated to scattered thunderstorms should develop near and north of the western limb of the outflow boundary (mainly IA, but also possibly western IL) from mid/late afternoon into early evening. Some of this activity may be supercellular in the first few hours, with large hail possible. However, given the presence of a convergent, moisture-rich, broad gradient of instability north of the boundary aligned strongly parallel to favorably strong mid/upper winds, large low/middle-level lapse rates, and a related reservoir of high buoyancy (MLCAPE of 3000-5000 J/kg) this activity should evolve quickly upscale to an MCS with severe gusts (some over 75 mph) becoming the greatest hazard. With a vorticity-laden boundary, and potential for backed surface winds and vertical-shear/hodograph enhancement to its north, a corridor of relatively maximized tornado potential (from supercells and/or QLCS-embedded circulations) also exists -- likely narrower than depicted here due to current boundary-position uncertainty. Uncertainty exists also on how far the MCS will travel (and whether far enough to qualify as a derecho) before weakening tonight. This will be related to depth/breadth of the cold pool and mesobeta-scale rear-inflow jet dynamics, and their ability to exert forced ascent on a moist but gradually stabilizing inflow layer with eastward extent. ...Northeast... Scattered thunderstorms are expected to move eastward across this area this afternoon into early evening -- some of which may initiate late morning into midday back in ON closer to the MCV. Activity should aggregate into clusters and/or a short QLCS, yielding damaging to severe gusts. Isolated discrete or line-embedded supercells also are possible, with some attendant severe-hail potential. As the MCV crosses southernmost parts of ON and also Lake Erie today, the foregoing boundary layer over parts of NY/PA will destabilize diurnally, while remaining favorably moist (with lower- elevation surface dewpoints commonly in the mid 60s to near 70 F). This will support a buildup of preconvective MLCAPE into the 1500- 2000 J/kg range (locally higher). Note that models with RAP physics (RAP, HRRR) may be over-mixing higher elevations and underforecasting buoyancy as a result (a common bias). Increase and slight veering of winds with height will contribute to around 30-40 kt effective-shear magnitudes, which may be locally greater in any channels of gradient-flow enhancement from the MCV that extend to or past the zone of convective forcing. Meanwhile, a well-mixed subcloud layer will supports damaging-downdraft potential. ...Central High Plains... Isolate to scattered, high-based thunderstorms are expected to form this afternoon over a broad area from central WY to the Front Range and foothills of CO, with the most concentrated convection still progged for portions of southeastern WY, western NE and northeastern CO. Steep low/middle-level lapse rates (8.5-9 deg C/km) are expected by midafternoon over this region, with enough easterly component of flow behind the front (and relate moist advection) to offset mixing and maintain mid 40s to low 50s surface dewpoints in the "slight risk" area. These should contribute to a field of peak/preconvective MLCAPE ranging from around 300 J/kg just east of the mountains to around 1500 J/kg over parts of west-central/ southwestern NE. The post-frontal boundary-layer flow also will enhance both storm-relative low-level winds and deep shear (effective-shear magnitudes in the 35-45-kt range). This, along with potential for cold-pool clustering, favors some organization and maintenance of convection across the outlook this evening before diminishing in a more strongly capped, nocturnal boundary layer over lower Plains elevations. ...AZ... Widely scattered thunderstorms are expected to form again this afternoon over portions of the Mogollon Rim and smaller terrain maxima to its south, offering locally strong-severe downbursts. Although the synoptic anticyclone will be weakening through the period, associated flow still will support motion toward the west or southwest, atop deep/well-mixed boundary layers of the desert floor. Airmass recovery from the prior day's convection by afternoon will be aided by warm/moist advection and strong diurnal heating. Large dewpoint depressions and deep subcloud layers in lower elevations -- beneath about 1000-1500 J/kg MLCAPE -- will support the gust potential, especially wherever activity can become clustered and maximize regenerative potential through cold-pool-aided lift. ..Edwards/Broyles.. 07/15/2024 Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0752 AM CDT Mon Jul 15 2024 Valid 151300Z - 161200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM PARTS OF IOWA TO SOUTHWESTERN LOWER MICHIGAN AND NORTHERN INDIANA... ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS SURROUNDING THE ENHANCED RISK...ALSO SEPARATELY OVER PARTS OF NEW YORK/PENNSYLVANIA AND THE CENTRAL HIGH PLAINS... ...SUMMARY... Severe thunderstorms are possible this afternoon and evening across portions of the Midwest, central High Plains, lower Great Lakes, and Arizona. The greatest potential for severe gusts is over eastern Iowa into Illinois and Indiana. ...Synopsis... Mid/upper-level pattern amplification in the northern stream will contribute to weakening (but not dissipation) of the persistent anticyclone over the Four Corners region. A 500-mb low over northern MB will dig south-southeastward to northwesternmost parts of ON through the period, combining with a series of small shortwave perturbations in the cyclone's southern semicircle to increase both cyclonic flow speeds and height curvature over upper parts of the Midwest, Mississippi Valley and Great Lakes. As this occurs, a shortwave trough -- evident in moisture-channel imagery over the Black Hills and vicinity -- will accelerate eastward to southern MN and northern/western IA by 00Z, then reach Lake Huron, northwestern OH and northern IN by the end of the period. That feature should be preceded by a smaller shortwave trough and MCV -- now apparent over western MN -- and forecast to move across northern WI and Upper MI through this evening. To its southeast and well downstream from the Black Hills perturbation, another MCV was quite evident in composite radar imagery over southern Lower MI, with shortwave trough southwestward to parts of central/eastern IL. This perturbation should move westward to western parts of NY/PA by 00Z, then near-coastal areas of central/ southern New England and the northern Mid-Atlantic by 12Z tomorrow. At the surface, 11Z analysis showed a low over northeastern SD with cold front southwestward across western NE and northern CO. By 00Z, the low should move/redevelop to a position near DBQ, with cold front southwestward across northeastern to northwestern KS and east-central/southeastern CO. By 12Z, the front should reach Lower MI, northern/western IL (perhaps obscured by convective effects), southern KS, and northeastern NM. Relevant prefrontal boundaries are discussed below. ...IA to southern Lower Great Lakes... The decaying remnants of the prior/overnight MCS responsible for the southern Lower MI MCV also have left an outflow boundary over southern portions of IN/IL, arching northwestward and becoming quasistationary over western IL into southeastern/central IA. Clouds/precip from the prior MCS, and shortwave subsidence/DNVA immediately following its associated shortwave trough, should be long gone by mid/late afternoon, when the airmass along the outflow boundary will have had several hours to modify favorably from west to east. The boundary itself also may drift northward amidst weak but steady ambient warm advection, with the boundary layer favorably destabilizing on both sides. A combination of lift near the boundary, increasing large-scale ascent ahead of the upstream mid/upper-level shortwave trough, steepening low-level lapse rates from diurnal heating, and rich moisture (surface dewpoints commonly upper 60s to low 70s F) are expected to prepare the corridor in and near the "enhanced risk" area for severe potential through the afternoon. Isolated to scattered thunderstorms should develop near and north of the western limb of the outflow boundary (mainly IA, but also possibly western IL) from mid/late afternoon into early evening. Some of this activity may be supercellular in the first few hours, with large hail possible. However, given the presence of a convergent, moisture-rich, broad gradient of instability north of the boundary aligned strongly parallel to favorably strong mid/upper winds, large low/middle-level lapse rates, and a related reservoir of high buoyancy (MLCAPE of 3000-5000 J/kg) this activity should evolve quickly upscale to an MCS with severe gusts (some over 75 mph) becoming the greatest hazard. With a vorticity-laden boundary, and potential for backed surface winds and vertical-shear/hodograph enhancement to its north, a corridor of relatively maximized tornado potential (from supercells and/or QLCS-embedded circulations) also exists -- likely narrower than depicted here due to current boundary-position uncertainty. Uncertainty exists also on how far the MCS will travel (and whether far enough to qualify as a derecho) before weakening tonight. This will be related to depth/breadth of the cold pool and mesobeta-scale rear-inflow jet dynamics, and their ability to exert forced ascent on a moist but gradually stabilizing inflow layer with eastward extent. ...Northeast... Scattered thunderstorms are expected to move eastward across this area this afternoon into early evening -- some of which may initiate late morning into midday back in ON closer to the MCV. Activity should aggregate into clusters and/or a short QLCS, yielding damaging to severe gusts. Isolated discrete or line-embedded supercells also are possible, with some attendant severe-hail potential. As the MCV crosses southernmost parts of ON and also Lake Erie today, the foregoing boundary layer over parts of NY/PA will destabilize diurnally, while remaining favorably moist (with lower- elevation surface dewpoints commonly in the mid 60s to near 70 F). This will support a buildup of preconvective MLCAPE into the 1500- 2000 J/kg range (locally higher). Note that models with RAP physics (RAP, HRRR) may be over-mixing higher elevations and underforecasting buoyancy as a result (a common bias). Increase and slight veering of winds with height will contribute to around 30-40 kt effective-shear magnitudes, which may be locally greater in any channels of gradient-flow enhancement from the MCV that extend to or past the zone of convective forcing. Meanwhile, a well-mixed subcloud layer will supports damaging-downdraft potential. ...Central High Plains... Isolate to scattered, high-based thunderstorms are expected to form this afternoon over a broad area from central WY to the Front Range and foothills of CO, with the most concentrated convection still progged for portions of southeastern WY, western NE and northeastern CO. Steep low/middle-level lapse rates (8.5-9 deg C/km) are expected by midafternoon over this region, with enough easterly component of flow behind the front (and relate moist advection) to offset mixing and maintain mid 40s to low 50s surface dewpoints in the "slight risk" area. These should contribute to a field of peak/preconvective MLCAPE ranging from around 300 J/kg just east of the mountains to around 1500 J/kg over parts of west-central/ southwestern NE. The post-frontal boundary-layer flow also will enhance both storm-relative low-level winds and deep shear (effective-shear magnitudes in the 35-45-kt range). This, along with potential for cold-pool clustering, favors some organization and maintenance of convection across the outlook this evening before diminishing in a more strongly capped, nocturnal boundary layer over lower Plains elevations. ...AZ... Widely scattered thunderstorms are expected to form again this afternoon over portions of the Mogollon Rim and smaller terrain maxima to its south, offering locally strong-severe downbursts. Although the synoptic anticyclone will be weakening through the period, associated flow still will support motion toward the west or southwest, atop deep/well-mixed boundary layers of the desert floor. Airmass recovery from the prior day's convection by afternoon will be aided by warm/moist advection and strong diurnal heating. Large dewpoint depressions and deep subcloud layers in lower elevations -- beneath about 1000-1500 J/kg MLCAPE -- will support the gust potential, especially wherever activity can become clustered and maximize regenerative potential through cold-pool-aided lift. ..Edwards/Broyles.. 07/15/2024 Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0752 AM CDT Mon Jul 15 2024 Valid 151300Z - 161200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM PARTS OF IOWA TO SOUTHWESTERN LOWER MICHIGAN AND NORTHERN INDIANA... ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS SURROUNDING THE ENHANCED RISK...ALSO SEPARATELY OVER PARTS OF NEW YORK/PENNSYLVANIA AND THE CENTRAL HIGH PLAINS... ...SUMMARY... Severe thunderstorms are possible this afternoon and evening across portions of the Midwest, central High Plains, lower Great Lakes, and Arizona. The greatest potential for severe gusts is over eastern Iowa into Illinois and Indiana. ...Synopsis... Mid/upper-level pattern amplification in the northern stream will contribute to weakening (but not dissipation) of the persistent anticyclone over the Four Corners region. A 500-mb low over northern MB will dig south-southeastward to northwesternmost parts of ON through the period, combining with a series of small shortwave perturbations in the cyclone's southern semicircle to increase both cyclonic flow speeds and height curvature over upper parts of the Midwest, Mississippi Valley and Great Lakes. As this occurs, a shortwave trough -- evident in moisture-channel imagery over the Black Hills and vicinity -- will accelerate eastward to southern MN and northern/western IA by 00Z, then reach Lake Huron, northwestern OH and northern IN by the end of the period. That feature should be preceded by a smaller shortwave trough and MCV -- now apparent over western MN -- and forecast to move across northern WI and Upper MI through this evening. To its southeast and well downstream from the Black Hills perturbation, another MCV was quite evident in composite radar imagery over southern Lower MI, with shortwave trough southwestward to parts of central/eastern IL. This perturbation should move westward to western parts of NY/PA by 00Z, then near-coastal areas of central/ southern New England and the northern Mid-Atlantic by 12Z tomorrow. At the surface, 11Z analysis showed a low over northeastern SD with cold front southwestward across western NE and northern CO. By 00Z, the low should move/redevelop to a position near DBQ, with cold front southwestward across northeastern to northwestern KS and east-central/southeastern CO. By 12Z, the front should reach Lower MI, northern/western IL (perhaps obscured by convective effects), southern KS, and northeastern NM. Relevant prefrontal boundaries are discussed below. ...IA to southern Lower Great Lakes... The decaying remnants of the prior/overnight MCS responsible for the southern Lower MI MCV also have left an outflow boundary over southern portions of IN/IL, arching northwestward and becoming quasistationary over western IL into southeastern/central IA. Clouds/precip from the prior MCS, and shortwave subsidence/DNVA immediately following its associated shortwave trough, should be long gone by mid/late afternoon, when the airmass along the outflow boundary will have had several hours to modify favorably from west to east. The boundary itself also may drift northward amidst weak but steady ambient warm advection, with the boundary layer favorably destabilizing on both sides. A combination of lift near the boundary, increasing large-scale ascent ahead of the upstream mid/upper-level shortwave trough, steepening low-level lapse rates from diurnal heating, and rich moisture (surface dewpoints commonly upper 60s to low 70s F) are expected to prepare the corridor in and near the "enhanced risk" area for severe potential through the afternoon. Isolated to scattered thunderstorms should develop near and north of the western limb of the outflow boundary (mainly IA, but also possibly western IL) from mid/late afternoon into early evening. Some of this activity may be supercellular in the first few hours, with large hail possible. However, given the presence of a convergent, moisture-rich, broad gradient of instability north of the boundary aligned strongly parallel to favorably strong mid/upper winds, large low/middle-level lapse rates, and a related reservoir of high buoyancy (MLCAPE of 3000-5000 J/kg) this activity should evolve quickly upscale to an MCS with severe gusts (some over 75 mph) becoming the greatest hazard. With a vorticity-laden boundary, and potential for backed surface winds and vertical-shear/hodograph enhancement to its north, a corridor of relatively maximized tornado potential (from supercells and/or QLCS-embedded circulations) also exists -- likely narrower than depicted here due to current boundary-position uncertainty. Uncertainty exists also on how far the MCS will travel (and whether far enough to qualify as a derecho) before weakening tonight. This will be related to depth/breadth of the cold pool and mesobeta-scale rear-inflow jet dynamics, and their ability to exert forced ascent on a moist but gradually stabilizing inflow layer with eastward extent. ...Northeast... Scattered thunderstorms are expected to move eastward across this area this afternoon into early evening -- some of which may initiate late morning into midday back in ON closer to the MCV. Activity should aggregate into clusters and/or a short QLCS, yielding damaging to severe gusts. Isolated discrete or line-embedded supercells also are possible, with some attendant severe-hail potential. As the MCV crosses southernmost parts of ON and also Lake Erie today, the foregoing boundary layer over parts of NY/PA will destabilize diurnally, while remaining favorably moist (with lower- elevation surface dewpoints commonly in the mid 60s to near 70 F). This will support a buildup of preconvective MLCAPE into the 1500- 2000 J/kg range (locally higher). Note that models with RAP physics (RAP, HRRR) may be over-mixing higher elevations and underforecasting buoyancy as a result (a common bias). Increase and slight veering of winds with height will contribute to around 30-40 kt effective-shear magnitudes, which may be locally greater in any channels of gradient-flow enhancement from the MCV that extend to or past the zone of convective forcing. Meanwhile, a well-mixed subcloud layer will supports damaging-downdraft potential. ...Central High Plains... Isolate to scattered, high-based thunderstorms are expected to form this afternoon over a broad area from central WY to the Front Range and foothills of CO, with the most concentrated convection still progged for portions of southeastern WY, western NE and northeastern CO. Steep low/middle-level lapse rates (8.5-9 deg C/km) are expected by midafternoon over this region, with enough easterly component of flow behind the front (and relate moist advection) to offset mixing and maintain mid 40s to low 50s surface dewpoints in the "slight risk" area. These should contribute to a field of peak/preconvective MLCAPE ranging from around 300 J/kg just east of the mountains to around 1500 J/kg over parts of west-central/ southwestern NE. The post-frontal boundary-layer flow also will enhance both storm-relative low-level winds and deep shear (effective-shear magnitudes in the 35-45-kt range). This, along with potential for cold-pool clustering, favors some organization and maintenance of convection across the outlook this evening before diminishing in a more strongly capped, nocturnal boundary layer over lower Plains elevations. ...AZ... Widely scattered thunderstorms are expected to form again this afternoon over portions of the Mogollon Rim and smaller terrain maxima to its south, offering locally strong-severe downbursts. Although the synoptic anticyclone will be weakening through the period, associated flow still will support motion toward the west or southwest, atop deep/well-mixed boundary layers of the desert floor. Airmass recovery from the prior day's convection by afternoon will be aided by warm/moist advection and strong diurnal heating. Large dewpoint depressions and deep subcloud layers in lower elevations -- beneath about 1000-1500 J/kg MLCAPE -- will support the gust potential, especially wherever activity can become clustered and maximize regenerative potential through cold-pool-aided lift. ..Edwards/Broyles.. 07/15/2024 Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0752 AM CDT Mon Jul 15 2024 Valid 151300Z - 161200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM PARTS OF IOWA TO SOUTHWESTERN LOWER MICHIGAN AND NORTHERN INDIANA... ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS SURROUNDING THE ENHANCED RISK...ALSO SEPARATELY OVER PARTS OF NEW YORK/PENNSYLVANIA AND THE CENTRAL HIGH PLAINS... ...SUMMARY... Severe thunderstorms are possible this afternoon and evening across portions of the Midwest, central High Plains, lower Great Lakes, and Arizona. The greatest potential for severe gusts is over eastern Iowa into Illinois and Indiana. ...Synopsis... Mid/upper-level pattern amplification in the northern stream will contribute to weakening (but not dissipation) of the persistent anticyclone over the Four Corners region. A 500-mb low over northern MB will dig south-southeastward to northwesternmost parts of ON through the period, combining with a series of small shortwave perturbations in the cyclone's southern semicircle to increase both cyclonic flow speeds and height curvature over upper parts of the Midwest, Mississippi Valley and Great Lakes. As this occurs, a shortwave trough -- evident in moisture-channel imagery over the Black Hills and vicinity -- will accelerate eastward to southern MN and northern/western IA by 00Z, then reach Lake Huron, northwestern OH and northern IN by the end of the period. That feature should be preceded by a smaller shortwave trough and MCV -- now apparent over western MN -- and forecast to move across northern WI and Upper MI through this evening. To its southeast and well downstream from the Black Hills perturbation, another MCV was quite evident in composite radar imagery over southern Lower MI, with shortwave trough southwestward to parts of central/eastern IL. This perturbation should move westward to western parts of NY/PA by 00Z, then near-coastal areas of central/ southern New England and the northern Mid-Atlantic by 12Z tomorrow. At the surface, 11Z analysis showed a low over northeastern SD with cold front southwestward across western NE and northern CO. By 00Z, the low should move/redevelop to a position near DBQ, with cold front southwestward across northeastern to northwestern KS and east-central/southeastern CO. By 12Z, the front should reach Lower MI, northern/western IL (perhaps obscured by convective effects), southern KS, and northeastern NM. Relevant prefrontal boundaries are discussed below. ...IA to southern Lower Great Lakes... The decaying remnants of the prior/overnight MCS responsible for the southern Lower MI MCV also have left an outflow boundary over southern portions of IN/IL, arching northwestward and becoming quasistationary over western IL into southeastern/central IA. Clouds/precip from the prior MCS, and shortwave subsidence/DNVA immediately following its associated shortwave trough, should be long gone by mid/late afternoon, when the airmass along the outflow boundary will have had several hours to modify favorably from west to east. The boundary itself also may drift northward amidst weak but steady ambient warm advection, with the boundary layer favorably destabilizing on both sides. A combination of lift near the boundary, increasing large-scale ascent ahead of the upstream mid/upper-level shortwave trough, steepening low-level lapse rates from diurnal heating, and rich moisture (surface dewpoints commonly upper 60s to low 70s F) are expected to prepare the corridor in and near the "enhanced risk" area for severe potential through the afternoon. Isolated to scattered thunderstorms should develop near and north of the western limb of the outflow boundary (mainly IA, but also possibly western IL) from mid/late afternoon into early evening. Some of this activity may be supercellular in the first few hours, with large hail possible. However, given the presence of a convergent, moisture-rich, broad gradient of instability north of the boundary aligned strongly parallel to favorably strong mid/upper winds, large low/middle-level lapse rates, and a related reservoir of high buoyancy (MLCAPE of 3000-5000 J/kg) this activity should evolve quickly upscale to an MCS with severe gusts (some over 75 mph) becoming the greatest hazard. With a vorticity-laden boundary, and potential for backed surface winds and vertical-shear/hodograph enhancement to its north, a corridor of relatively maximized tornado potential (from supercells and/or QLCS-embedded circulations) also exists -- likely narrower than depicted here due to current boundary-position uncertainty. Uncertainty exists also on how far the MCS will travel (and whether far enough to qualify as a derecho) before weakening tonight. This will be related to depth/breadth of the cold pool and mesobeta-scale rear-inflow jet dynamics, and their ability to exert forced ascent on a moist but gradually stabilizing inflow layer with eastward extent. ...Northeast... Scattered thunderstorms are expected to move eastward across this area this afternoon into early evening -- some of which may initiate late morning into midday back in ON closer to the MCV. Activity should aggregate into clusters and/or a short QLCS, yielding damaging to severe gusts. Isolated discrete or line-embedded supercells also are possible, with some attendant severe-hail potential. As the MCV crosses southernmost parts of ON and also Lake Erie today, the foregoing boundary layer over parts of NY/PA will destabilize diurnally, while remaining favorably moist (with lower- elevation surface dewpoints commonly in the mid 60s to near 70 F). This will support a buildup of preconvective MLCAPE into the 1500- 2000 J/kg range (locally higher). Note that models with RAP physics (RAP, HRRR) may be over-mixing higher elevations and underforecasting buoyancy as a result (a common bias). Increase and slight veering of winds with height will contribute to around 30-40 kt effective-shear magnitudes, which may be locally greater in any channels of gradient-flow enhancement from the MCV that extend to or past the zone of convective forcing. Meanwhile, a well-mixed subcloud layer will supports damaging-downdraft potential. ...Central High Plains... Isolate to scattered, high-based thunderstorms are expected to form this afternoon over a broad area from central WY to the Front Range and foothills of CO, with the most concentrated convection still progged for portions of southeastern WY, western NE and northeastern CO. Steep low/middle-level lapse rates (8.5-9 deg C/km) are expected by midafternoon over this region, with enough easterly component of flow behind the front (and relate moist advection) to offset mixing and maintain mid 40s to low 50s surface dewpoints in the "slight risk" area. These should contribute to a field of peak/preconvective MLCAPE ranging from around 300 J/kg just east of the mountains to around 1500 J/kg over parts of west-central/ southwestern NE. The post-frontal boundary-layer flow also will enhance both storm-relative low-level winds and deep shear (effective-shear magnitudes in the 35-45-kt range). This, along with potential for cold-pool clustering, favors some organization and maintenance of convection across the outlook this evening before diminishing in a more strongly capped, nocturnal boundary layer over lower Plains elevations. ...AZ... Widely scattered thunderstorms are expected to form again this afternoon over portions of the Mogollon Rim and smaller terrain maxima to its south, offering locally strong-severe downbursts. Although the synoptic anticyclone will be weakening through the period, associated flow still will support motion toward the west or southwest, atop deep/well-mixed boundary layers of the desert floor. Airmass recovery from the prior day's convection by afternoon will be aided by warm/moist advection and strong diurnal heating. Large dewpoint depressions and deep subcloud layers in lower elevations -- beneath about 1000-1500 J/kg MLCAPE -- will support the gust potential, especially wherever activity can become clustered and maximize regenerative potential through cold-pool-aided lift. ..Edwards/Broyles.. 07/15/2024 Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0752 AM CDT Mon Jul 15 2024 Valid 151300Z - 161200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM PARTS OF IOWA TO SOUTHWESTERN LOWER MICHIGAN AND NORTHERN INDIANA... ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS SURROUNDING THE ENHANCED RISK...ALSO SEPARATELY OVER PARTS OF NEW YORK/PENNSYLVANIA AND THE CENTRAL HIGH PLAINS... ...SUMMARY... Severe thunderstorms are possible this afternoon and evening across portions of the Midwest, central High Plains, lower Great Lakes, and Arizona. The greatest potential for severe gusts is over eastern Iowa into Illinois and Indiana. ...Synopsis... Mid/upper-level pattern amplification in the northern stream will contribute to weakening (but not dissipation) of the persistent anticyclone over the Four Corners region. A 500-mb low over northern MB will dig south-southeastward to northwesternmost parts of ON through the period, combining with a series of small shortwave perturbations in the cyclone's southern semicircle to increase both cyclonic flow speeds and height curvature over upper parts of the Midwest, Mississippi Valley and Great Lakes. As this occurs, a shortwave trough -- evident in moisture-channel imagery over the Black Hills and vicinity -- will accelerate eastward to southern MN and northern/western IA by 00Z, then reach Lake Huron, northwestern OH and northern IN by the end of the period. That feature should be preceded by a smaller shortwave trough and MCV -- now apparent over western MN -- and forecast to move across northern WI and Upper MI through this evening. To its southeast and well downstream from the Black Hills perturbation, another MCV was quite evident in composite radar imagery over southern Lower MI, with shortwave trough southwestward to parts of central/eastern IL. This perturbation should move westward to western parts of NY/PA by 00Z, then near-coastal areas of central/ southern New England and the northern Mid-Atlantic by 12Z tomorrow. At the surface, 11Z analysis showed a low over northeastern SD with cold front southwestward across western NE and northern CO. By 00Z, the low should move/redevelop to a position near DBQ, with cold front southwestward across northeastern to northwestern KS and east-central/southeastern CO. By 12Z, the front should reach Lower MI, northern/western IL (perhaps obscured by convective effects), southern KS, and northeastern NM. Relevant prefrontal boundaries are discussed below. ...IA to southern Lower Great Lakes... The decaying remnants of the prior/overnight MCS responsible for the southern Lower MI MCV also have left an outflow boundary over southern portions of IN/IL, arching northwestward and becoming quasistationary over western IL into southeastern/central IA. Clouds/precip from the prior MCS, and shortwave subsidence/DNVA immediately following its associated shortwave trough, should be long gone by mid/late afternoon, when the airmass along the outflow boundary will have had several hours to modify favorably from west to east. The boundary itself also may drift northward amidst weak but steady ambient warm advection, with the boundary layer favorably destabilizing on both sides. A combination of lift near the boundary, increasing large-scale ascent ahead of the upstream mid/upper-level shortwave trough, steepening low-level lapse rates from diurnal heating, and rich moisture (surface dewpoints commonly upper 60s to low 70s F) are expected to prepare the corridor in and near the "enhanced risk" area for severe potential through the afternoon. Isolated to scattered thunderstorms should develop near and north of the western limb of the outflow boundary (mainly IA, but also possibly western IL) from mid/late afternoon into early evening. Some of this activity may be supercellular in the first few hours, with large hail possible. However, given the presence of a convergent, moisture-rich, broad gradient of instability north of the boundary aligned strongly parallel to favorably strong mid/upper winds, large low/middle-level lapse rates, and a related reservoir of high buoyancy (MLCAPE of 3000-5000 J/kg) this activity should evolve quickly upscale to an MCS with severe gusts (some over 75 mph) becoming the greatest hazard. With a vorticity-laden boundary, and potential for backed surface winds and vertical-shear/hodograph enhancement to its north, a corridor of relatively maximized tornado potential (from supercells and/or QLCS-embedded circulations) also exists -- likely narrower than depicted here due to current boundary-position uncertainty. Uncertainty exists also on how far the MCS will travel (and whether far enough to qualify as a derecho) before weakening tonight. This will be related to depth/breadth of the cold pool and mesobeta-scale rear-inflow jet dynamics, and their ability to exert forced ascent on a moist but gradually stabilizing inflow layer with eastward extent. ...Northeast... Scattered thunderstorms are expected to move eastward across this area this afternoon into early evening -- some of which may initiate late morning into midday back in ON closer to the MCV. Activity should aggregate into clusters and/or a short QLCS, yielding damaging to severe gusts. Isolated discrete or line-embedded supercells also are possible, with some attendant severe-hail potential. As the MCV crosses southernmost parts of ON and also Lake Erie today, the foregoing boundary layer over parts of NY/PA will destabilize diurnally, while remaining favorably moist (with lower- elevation surface dewpoints commonly in the mid 60s to near 70 F). This will support a buildup of preconvective MLCAPE into the 1500- 2000 J/kg range (locally higher). Note that models with RAP physics (RAP, HRRR) may be over-mixing higher elevations and underforecasting buoyancy as a result (a common bias). Increase and slight veering of winds with height will contribute to around 30-40 kt effective-shear magnitudes, which may be locally greater in any channels of gradient-flow enhancement from the MCV that extend to or past the zone of convective forcing. Meanwhile, a well-mixed subcloud layer will supports damaging-downdraft potential. ...Central High Plains... Isolate to scattered, high-based thunderstorms are expected to form this afternoon over a broad area from central WY to the Front Range and foothills of CO, with the most concentrated convection still progged for portions of southeastern WY, western NE and northeastern CO. Steep low/middle-level lapse rates (8.5-9 deg C/km) are expected by midafternoon over this region, with enough easterly component of flow behind the front (and relate moist advection) to offset mixing and maintain mid 40s to low 50s surface dewpoints in the "slight risk" area. These should contribute to a field of peak/preconvective MLCAPE ranging from around 300 J/kg just east of the mountains to around 1500 J/kg over parts of west-central/ southwestern NE. The post-frontal boundary-layer flow also will enhance both storm-relative low-level winds and deep shear (effective-shear magnitudes in the 35-45-kt range). This, along with potential for cold-pool clustering, favors some organization and maintenance of convection across the outlook this evening before diminishing in a more strongly capped, nocturnal boundary layer over lower Plains elevations. ...AZ... Widely scattered thunderstorms are expected to form again this afternoon over portions of the Mogollon Rim and smaller terrain maxima to its south, offering locally strong-severe downbursts. Although the synoptic anticyclone will be weakening through the period, associated flow still will support motion toward the west or southwest, atop deep/well-mixed boundary layers of the desert floor. Airmass recovery from the prior day's convection by afternoon will be aided by warm/moist advection and strong diurnal heating. Large dewpoint depressions and deep subcloud layers in lower elevations -- beneath about 1000-1500 J/kg MLCAPE -- will support the gust potential, especially wherever activity can become clustered and maximize regenerative potential through cold-pool-aided lift. ..Edwards/Broyles.. 07/15/2024 Read more

000
ABPZ20 KNHC 151130
TWOEP

Tropical Weather Outlook
NWS National Hurricane Center Miami FL
500 AM PDT Mon Jul 15 2024

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

Central and Western East Pacific:
A tropical wave located several hundred miles southwest of the
southern tip of the Baja California peninsula continues to produce a
large area of showers and thunderstorms. Environmental conditions
appear conducive for development in the next couple of days and a
tropical depression could form mid- to late-week as the system moves
west-northwestward at 10 to 15 mph across the central and western
portion of the basin.
* Formation chance through 48 hours...low...30 percent.
* Formation chance through 7 days...medium...40 percent.

$$
Forecaster Kelly

MD 1627 CONCERNING SEVERE THUNDERSTORM WATCH 536... FOR FAR SOUTHEAST NORTH DAKOTA...FAR NORTHEAST SOUTH DAKOTA...WESTERN AND SOUTHWESTERN MINNESOTA
Mesoscale Discussion 1627 NWS Storm Prediction Center Norman OK 0437 AM CDT Mon Jul 15 2024 Areas affected...Far Southeast North Dakota...Far Northeast South Dakota...Western and Southwestern Minnesota Concerning...Severe Thunderstorm Watch 536... Valid 150937Z - 151130Z The severe weather threat for Severe Thunderstorm Watch 536 continues. SUMMARY...An isolated severe threat may continue for a couple more hours. Isolated severe gusts and hail will be the primary threats. Watch issuance is not expected to the southeast of WW 536. DISCUSSION...The latest mosaic radar imagery shows a cluster of strong thunderstorms from far southeast North Dakota into southwest Minnesota, which is located along the eastern edge of a moderately unstable airmass. The activity is being supported by a subtle shortwave trough over the northern Plains, and by a 30 to 40 knot low-level jet over central and northeast South Dakota. As the storms move southeastward across western Minnesota over the next few hours, an isolated severe threat should continue. However, instability is considerably weaker over southwestern Minnesota, suggesting that the overall intensity of the cluster should gradually decrease as daybreak approaches. ..Broyles.. 07/15/2024 ...Please see www.spc.noaa.gov for graphic product... ATTN...WFO...MPX...FGF...FSD...ABR... LAT...LON 46689625 46799681 46689725 46389756 46059761 45469718 44119562 43679481 43989418 44979470 45719524 46689625 Read more

MD 1626 CONCERNING SEVERE THUNDERSTORM WATCH 536... FOR CENTRAL AND SOUTHEAST NORTH DAKOTA
Mesoscale Discussion 1626 NWS Storm Prediction Center Norman OK 0236 AM CDT Mon Jul 15 2024 Areas affected...Central and Southeast North Dakota Concerning...Severe Thunderstorm Watch 536... Valid 150736Z - 150930Z The severe weather threat for Severe Thunderstorm Watch 536 continues. SUMMARY...A threat for large hail and severe gusts will continue to be possible for at least a couple more hours across parts of central and southeastern North Dakota. DISCUSSION...The latest mosaic radar imagery shows an MCS across central and southeastern South Dakota, where a cluster of strong to severe storms is ongoing. The cluster is located along a northwest-to-southeast gradient of moderate instability extending across central and southeastern North Dakota. The storms are being supported by large-scale ascent associated with a subtle shortwave trough, evident on water vapor imagery. The latest WSR-88D VWP at Bismarck has 0-6 km shear near 70 knots, owing mostly to strong speed shear in the lowest 6 km. This is expected to support continued cell organization within the MCS over the next couple of hours. Large hail and isolated severe gusts will be the primary threats. ..Broyles.. 07/15/2024 ...Please see www.spc.noaa.gov for graphic product... ATTN...WFO...FGF...ABR...BIS... LAT...LON 47129729 47579825 47669871 47689917 47509961 47279995 46929994 46609949 46249894 45969834 45939780 45949727 46009684 46179654 46499652 47129729 Read more

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0352 AM CDT Mon Jul 15 2024 Valid 181200Z - 231200Z ...DISCUSSION... Medium-range guidance continues to show that the upper ridging expected to be in place across the western CONUS early D4/Thursday will persist through the weekend and into early next week while also building into western Canada. Upper troughing is expected to persist across the central and eastern CONUS through the weekend as well. Flow aloft within these features will be modest, but some moderate northwesterly flow aloft is anticipated between these two features across the High Plains. A cold front will likely stretch from the Mid-Atlantic through north Texas. This front is expected to become increasingly diffuse on D4/Thursday and D5/Friday as it moves only slightly southward. Thunderstorms are possible along this boundary on each day, but weak vertical shear should keep the severe potential low. Aforementioned northwesterly flow aloft will help support some severe potential across the High Plains, where modest low-level moisture beneath vertically veering wind profiles could support a few strong to severe storms each afternoon on D4/Thursday through D6/Saturday. After D6/Saturday, the upper ridge may shift westward, placing the northwesterly flow over the higher terrain and likely limited the severe potential. Read more

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0352 AM CDT Mon Jul 15 2024 Valid 181200Z - 231200Z ...DISCUSSION... Medium-range guidance continues to show that the upper ridging expected to be in place across the western CONUS early D4/Thursday will persist through the weekend and into early next week while also building into western Canada. Upper troughing is expected to persist across the central and eastern CONUS through the weekend as well. Flow aloft within these features will be modest, but some moderate northwesterly flow aloft is anticipated between these two features across the High Plains. A cold front will likely stretch from the Mid-Atlantic through north Texas. This front is expected to become increasingly diffuse on D4/Thursday and D5/Friday as it moves only slightly southward. Thunderstorms are possible along this boundary on each day, but weak vertical shear should keep the severe potential low. Aforementioned northwesterly flow aloft will help support some severe potential across the High Plains, where modest low-level moisture beneath vertically veering wind profiles could support a few strong to severe storms each afternoon on D4/Thursday through D6/Saturday. After D6/Saturday, the upper ridge may shift westward, placing the northwesterly flow over the higher terrain and likely limited the severe potential. Read more

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0352 AM CDT Mon Jul 15 2024 Valid 181200Z - 231200Z ...DISCUSSION... Medium-range guidance continues to show that the upper ridging expected to be in place across the western CONUS early D4/Thursday will persist through the weekend and into early next week while also building into western Canada. Upper troughing is expected to persist across the central and eastern CONUS through the weekend as well. Flow aloft within these features will be modest, but some moderate northwesterly flow aloft is anticipated between these two features across the High Plains. A cold front will likely stretch from the Mid-Atlantic through north Texas. This front is expected to become increasingly diffuse on D4/Thursday and D5/Friday as it moves only slightly southward. Thunderstorms are possible along this boundary on each day, but weak vertical shear should keep the severe potential low. Aforementioned northwesterly flow aloft will help support some severe potential across the High Plains, where modest low-level moisture beneath vertically veering wind profiles could support a few strong to severe storms each afternoon on D4/Thursday through D6/Saturday. After D6/Saturday, the upper ridge may shift westward, placing the northwesterly flow over the higher terrain and likely limited the severe potential. Read more

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0352 AM CDT Mon Jul 15 2024 Valid 181200Z - 231200Z ...DISCUSSION... Medium-range guidance continues to show that the upper ridging expected to be in place across the western CONUS early D4/Thursday will persist through the weekend and into early next week while also building into western Canada. Upper troughing is expected to persist across the central and eastern CONUS through the weekend as well. Flow aloft within these features will be modest, but some moderate northwesterly flow aloft is anticipated between these two features across the High Plains. A cold front will likely stretch from the Mid-Atlantic through north Texas. This front is expected to become increasingly diffuse on D4/Thursday and D5/Friday as it moves only slightly southward. Thunderstorms are possible along this boundary on each day, but weak vertical shear should keep the severe potential low. Aforementioned northwesterly flow aloft will help support some severe potential across the High Plains, where modest low-level moisture beneath vertically veering wind profiles could support a few strong to severe storms each afternoon on D4/Thursday through D6/Saturday. After D6/Saturday, the upper ridge may shift westward, placing the northwesterly flow over the higher terrain and likely limited the severe potential. Read more

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0352 AM CDT Mon Jul 15 2024 Valid 181200Z - 231200Z ...DISCUSSION... Medium-range guidance continues to show that the upper ridging expected to be in place across the western CONUS early D4/Thursday will persist through the weekend and into early next week while also building into western Canada. Upper troughing is expected to persist across the central and eastern CONUS through the weekend as well. Flow aloft within these features will be modest, but some moderate northwesterly flow aloft is anticipated between these two features across the High Plains. A cold front will likely stretch from the Mid-Atlantic through north Texas. This front is expected to become increasingly diffuse on D4/Thursday and D5/Friday as it moves only slightly southward. Thunderstorms are possible along this boundary on each day, but weak vertical shear should keep the severe potential low. Aforementioned northwesterly flow aloft will help support some severe potential across the High Plains, where modest low-level moisture beneath vertically veering wind profiles could support a few strong to severe storms each afternoon on D4/Thursday through D6/Saturday. After D6/Saturday, the upper ridge may shift westward, placing the northwesterly flow over the higher terrain and likely limited the severe potential. Read more