Severe Storms

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0757 AM CDT Tue Sep 10 2019 Valid 101300Z - 111200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ASTRIDE MUCH OF THE NEBRASKA/SOUTH DAKOTA STATE LINE AND INTO ADJOINING PARTS OF EACH STATE... ...SUMMARY... An enhanced threat for severe hail and wind should develop this afternoon and evening across parts of the north-central Plains, mostly near the Nebraska/South Dakota line. A tornado threat exists in that area as well. ...Synopsis... A strong shortwave trough located about 1000 nm west of Vancouver Island is forecast to deepen into an expansive, progressive 500-mb cyclone today. As this occurs, downstream ridging across eastern Canada and a closed cyclone over the Pacific Northwest each will begin to break down somewhat, thereby eroding the Rex configuration now in place over northwestern North America. A substantial synoptic-scale trough extends from the Pacific Northwest cyclone south-southeastward across coastal southern CA. As the cyclone weakens/opens slightly, the trough will move eastward, reaching to near an axis from MSO-TWF-LAS-YUM by 12Z. Associated height falls will spread across the central Rockies and High Plains during the latter half of the period, supporting a broad, hybrid frontal-wave/ lee cyclone at the surface over the central High Plains. A weak mid/upper-level shortwave trough -- now evident in moisture- channel imagery from the southern MB/ON border across northwestern MN -- will move eastward across the width of northern ON, reaching western QC by 12Z. As this occurs, the associated surface frontal- wave cyclone -- analyzed at 11Z over northern MN -- should ripple eastward across the length of Lake Superior and much of adjoining northeastern ON toward QC this evening. The trailing cold front was drawn initially from the MN low to north-central NE, becoming nearly stationary from north-central NE west-southwestward across northern CO. A trough was drawn from a weak low over east- central CO north-northeastward to the front in western NE. By 00Z, the cold front should reach eastern Upper MI and south-central WI, becoming quasistationary from there across extreme northern IA, then a warm front across northern NE near the SD line and into east-central/ southeastern WY. By 12Z, the front should extend across central Lower MI, south-central WI, north-central/northwestern IA and northern NE near SD, with much of the NE part likely having been altered by convective outflow. ...North-central Plains... Thunderstorms are expected to develop this afternoon in two principal regimes: convergence along/near the surface front over northwestern NE and perhaps nearby southwestern SD, and upslope postfrontal lift across parts of eastern WY into the Black Hills region. During the first few hours of both regimes, supercells will be possible with all severe hazards (tornado, wind, hail), with some significant/damaging hail supported by forecast soundings. The most unstable air mass will exist along and south of the warm front, where surface dew points in the 60s F and steep low/middle- level lapse rates will contribute to peak preconvective MLCAPE commonly reaching the 3000-3500 J/kg range, transitioning to 1500- 2500 J/kg westward across eastern WY in the upslope regime. Northwest and south of the front, long low-level hodographs and favorable deep shear will prevail, while backed flow along and just north of the front will enlarge low-level shear and storm-relative boundary-layer winds. Deep shear should increase area-wide from late afternoon through evening, with forecast soundings reasonably depicting 45-55-kt effective-shear vectors. Between the latter factor and focused convergence, the frontal zone should serve as the focus for upscale convective growth through evening. One or two clusters of convection should evolve from the supercellular activity and shift eastward across the outlook area, offering a growing threat for severe gusts -- some of which also may reach significant levels (hurricane force) on a localized basis. A roughly eastward forward-propagational MCS appears possible astride the NE/SD line through the evening and into parts of the overnight hours, with a continuing wind-damage threat toward the Siouxland area of northwestern IA and southeastern SD before the activity wanes tonight. ...Southern Lower MI... Scattered thunderstorms are ongoing over eastern WI and portions of Lake Michigan, in a regime of strong low-level warm advection and moisture transport. While expected to remain below severe limits, the downshear spread of clouds and precip across Lower MI should foster a prefrontal outflow/differential-heating boundary with relatively maximized low-level lift, over portions of southern Lower MI. While the specific location of the boundary remains somewhat uncertain, confidence in its development and in some related afternoon genesis of at least isolated strong/severe convection has increased enough to warrant introducing marginal unconditional probabilities. The main concerns with any sustained convection near the boundary will be damaging gusts and marginally severe hail. Forecast soundings in the nearby warm sector suggest that strong surface heating and dew points generally in the 60s F will support peak mid/late-afternoon MLCAPE near 2000 J/kg. A well-mixed/ inverted-v thermodynamic profile should develop in the boundary layer, amidst minimal MLCINH. Very little directional shear is expected, limiting hodograph sizes, though deep/cloud-layer shear may be sufficient to support organized multicells. Convective potential also exists farther north nearer to the cold front, but this is very conditional on destabilization within/behind the morning clouds/convection, and too conditional for any probabilities at this time. ...Portions of Intermountain/northern Great Basin... Widely scattered to scattered thunderstorms should form through much of the afternoon and into the early evening over an irregularly shaped swath from northeastern NV to extreme southern MT, northern UT, western WY and northwestern CO. Isolated severe gusts/hail will be possible. Cooling aloft related to the approaching mid/upper- level trough, overlying diurnal surface heating, will result in minimal MLCINH and steep deep-layer lapse rates (e.g, near 8 deg c/km from surface-300 mb in some forecast soundings), amidst sufficient low-level moisture to support sustained/deep convection. Cooling aloft will offset diabatic low-level cooling enough to maintain an isolated strong-severe threat a few more hours into the evening/nighttime hours than less synoptically forced scenarios. ..Edwards/Dial.. 09/10/2019 Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0757 AM CDT Tue Sep 10 2019 Valid 101300Z - 111200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ASTRIDE MUCH OF THE NEBRASKA/SOUTH DAKOTA STATE LINE AND INTO ADJOINING PARTS OF EACH STATE... ...SUMMARY... An enhanced threat for severe hail and wind should develop this afternoon and evening across parts of the north-central Plains, mostly near the Nebraska/South Dakota line. A tornado threat exists in that area as well. ...Synopsis... A strong shortwave trough located about 1000 nm west of Vancouver Island is forecast to deepen into an expansive, progressive 500-mb cyclone today. As this occurs, downstream ridging across eastern Canada and a closed cyclone over the Pacific Northwest each will begin to break down somewhat, thereby eroding the Rex configuration now in place over northwestern North America. A substantial synoptic-scale trough extends from the Pacific Northwest cyclone south-southeastward across coastal southern CA. As the cyclone weakens/opens slightly, the trough will move eastward, reaching to near an axis from MSO-TWF-LAS-YUM by 12Z. Associated height falls will spread across the central Rockies and High Plains during the latter half of the period, supporting a broad, hybrid frontal-wave/ lee cyclone at the surface over the central High Plains. A weak mid/upper-level shortwave trough -- now evident in moisture- channel imagery from the southern MB/ON border across northwestern MN -- will move eastward across the width of northern ON, reaching western QC by 12Z. As this occurs, the associated surface frontal- wave cyclone -- analyzed at 11Z over northern MN -- should ripple eastward across the length of Lake Superior and much of adjoining northeastern ON toward QC this evening. The trailing cold front was drawn initially from the MN low to north-central NE, becoming nearly stationary from north-central NE west-southwestward across northern CO. A trough was drawn from a weak low over east- central CO north-northeastward to the front in western NE. By 00Z, the cold front should reach eastern Upper MI and south-central WI, becoming quasistationary from there across extreme northern IA, then a warm front across northern NE near the SD line and into east-central/ southeastern WY. By 12Z, the front should extend across central Lower MI, south-central WI, north-central/northwestern IA and northern NE near SD, with much of the NE part likely having been altered by convective outflow. ...North-central Plains... Thunderstorms are expected to develop this afternoon in two principal regimes: convergence along/near the surface front over northwestern NE and perhaps nearby southwestern SD, and upslope postfrontal lift across parts of eastern WY into the Black Hills region. During the first few hours of both regimes, supercells will be possible with all severe hazards (tornado, wind, hail), with some significant/damaging hail supported by forecast soundings. The most unstable air mass will exist along and south of the warm front, where surface dew points in the 60s F and steep low/middle- level lapse rates will contribute to peak preconvective MLCAPE commonly reaching the 3000-3500 J/kg range, transitioning to 1500- 2500 J/kg westward across eastern WY in the upslope regime. Northwest and south of the front, long low-level hodographs and favorable deep shear will prevail, while backed flow along and just north of the front will enlarge low-level shear and storm-relative boundary-layer winds. Deep shear should increase area-wide from late afternoon through evening, with forecast soundings reasonably depicting 45-55-kt effective-shear vectors. Between the latter factor and focused convergence, the frontal zone should serve as the focus for upscale convective growth through evening. One or two clusters of convection should evolve from the supercellular activity and shift eastward across the outlook area, offering a growing threat for severe gusts -- some of which also may reach significant levels (hurricane force) on a localized basis. A roughly eastward forward-propagational MCS appears possible astride the NE/SD line through the evening and into parts of the overnight hours, with a continuing wind-damage threat toward the Siouxland area of northwestern IA and southeastern SD before the activity wanes tonight. ...Southern Lower MI... Scattered thunderstorms are ongoing over eastern WI and portions of Lake Michigan, in a regime of strong low-level warm advection and moisture transport. While expected to remain below severe limits, the downshear spread of clouds and precip across Lower MI should foster a prefrontal outflow/differential-heating boundary with relatively maximized low-level lift, over portions of southern Lower MI. While the specific location of the boundary remains somewhat uncertain, confidence in its development and in some related afternoon genesis of at least isolated strong/severe convection has increased enough to warrant introducing marginal unconditional probabilities. The main concerns with any sustained convection near the boundary will be damaging gusts and marginally severe hail. Forecast soundings in the nearby warm sector suggest that strong surface heating and dew points generally in the 60s F will support peak mid/late-afternoon MLCAPE near 2000 J/kg. A well-mixed/ inverted-v thermodynamic profile should develop in the boundary layer, amidst minimal MLCINH. Very little directional shear is expected, limiting hodograph sizes, though deep/cloud-layer shear may be sufficient to support organized multicells. Convective potential also exists farther north nearer to the cold front, but this is very conditional on destabilization within/behind the morning clouds/convection, and too conditional for any probabilities at this time. ...Portions of Intermountain/northern Great Basin... Widely scattered to scattered thunderstorms should form through much of the afternoon and into the early evening over an irregularly shaped swath from northeastern NV to extreme southern MT, northern UT, western WY and northwestern CO. Isolated severe gusts/hail will be possible. Cooling aloft related to the approaching mid/upper- level trough, overlying diurnal surface heating, will result in minimal MLCINH and steep deep-layer lapse rates (e.g, near 8 deg c/km from surface-300 mb in some forecast soundings), amidst sufficient low-level moisture to support sustained/deep convection. Cooling aloft will offset diabatic low-level cooling enough to maintain an isolated strong-severe threat a few more hours into the evening/nighttime hours than less synoptically forced scenarios. ..Edwards/Dial.. 09/10/2019 Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0757 AM CDT Tue Sep 10 2019 Valid 101300Z - 111200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ASTRIDE MUCH OF THE NEBRASKA/SOUTH DAKOTA STATE LINE AND INTO ADJOINING PARTS OF EACH STATE... ...SUMMARY... An enhanced threat for severe hail and wind should develop this afternoon and evening across parts of the north-central Plains, mostly near the Nebraska/South Dakota line. A tornado threat exists in that area as well. ...Synopsis... A strong shortwave trough located about 1000 nm west of Vancouver Island is forecast to deepen into an expansive, progressive 500-mb cyclone today. As this occurs, downstream ridging across eastern Canada and a closed cyclone over the Pacific Northwest each will begin to break down somewhat, thereby eroding the Rex configuration now in place over northwestern North America. A substantial synoptic-scale trough extends from the Pacific Northwest cyclone south-southeastward across coastal southern CA. As the cyclone weakens/opens slightly, the trough will move eastward, reaching to near an axis from MSO-TWF-LAS-YUM by 12Z. Associated height falls will spread across the central Rockies and High Plains during the latter half of the period, supporting a broad, hybrid frontal-wave/ lee cyclone at the surface over the central High Plains. A weak mid/upper-level shortwave trough -- now evident in moisture- channel imagery from the southern MB/ON border across northwestern MN -- will move eastward across the width of northern ON, reaching western QC by 12Z. As this occurs, the associated surface frontal- wave cyclone -- analyzed at 11Z over northern MN -- should ripple eastward across the length of Lake Superior and much of adjoining northeastern ON toward QC this evening. The trailing cold front was drawn initially from the MN low to north-central NE, becoming nearly stationary from north-central NE west-southwestward across northern CO. A trough was drawn from a weak low over east- central CO north-northeastward to the front in western NE. By 00Z, the cold front should reach eastern Upper MI and south-central WI, becoming quasistationary from there across extreme northern IA, then a warm front across northern NE near the SD line and into east-central/ southeastern WY. By 12Z, the front should extend across central Lower MI, south-central WI, north-central/northwestern IA and northern NE near SD, with much of the NE part likely having been altered by convective outflow. ...North-central Plains... Thunderstorms are expected to develop this afternoon in two principal regimes: convergence along/near the surface front over northwestern NE and perhaps nearby southwestern SD, and upslope postfrontal lift across parts of eastern WY into the Black Hills region. During the first few hours of both regimes, supercells will be possible with all severe hazards (tornado, wind, hail), with some significant/damaging hail supported by forecast soundings. The most unstable air mass will exist along and south of the warm front, where surface dew points in the 60s F and steep low/middle- level lapse rates will contribute to peak preconvective MLCAPE commonly reaching the 3000-3500 J/kg range, transitioning to 1500- 2500 J/kg westward across eastern WY in the upslope regime. Northwest and south of the front, long low-level hodographs and favorable deep shear will prevail, while backed flow along and just north of the front will enlarge low-level shear and storm-relative boundary-layer winds. Deep shear should increase area-wide from late afternoon through evening, with forecast soundings reasonably depicting 45-55-kt effective-shear vectors. Between the latter factor and focused convergence, the frontal zone should serve as the focus for upscale convective growth through evening. One or two clusters of convection should evolve from the supercellular activity and shift eastward across the outlook area, offering a growing threat for severe gusts -- some of which also may reach significant levels (hurricane force) on a localized basis. A roughly eastward forward-propagational MCS appears possible astride the NE/SD line through the evening and into parts of the overnight hours, with a continuing wind-damage threat toward the Siouxland area of northwestern IA and southeastern SD before the activity wanes tonight. ...Southern Lower MI... Scattered thunderstorms are ongoing over eastern WI and portions of Lake Michigan, in a regime of strong low-level warm advection and moisture transport. While expected to remain below severe limits, the downshear spread of clouds and precip across Lower MI should foster a prefrontal outflow/differential-heating boundary with relatively maximized low-level lift, over portions of southern Lower MI. While the specific location of the boundary remains somewhat uncertain, confidence in its development and in some related afternoon genesis of at least isolated strong/severe convection has increased enough to warrant introducing marginal unconditional probabilities. The main concerns with any sustained convection near the boundary will be damaging gusts and marginally severe hail. Forecast soundings in the nearby warm sector suggest that strong surface heating and dew points generally in the 60s F will support peak mid/late-afternoon MLCAPE near 2000 J/kg. A well-mixed/ inverted-v thermodynamic profile should develop in the boundary layer, amidst minimal MLCINH. Very little directional shear is expected, limiting hodograph sizes, though deep/cloud-layer shear may be sufficient to support organized multicells. Convective potential also exists farther north nearer to the cold front, but this is very conditional on destabilization within/behind the morning clouds/convection, and too conditional for any probabilities at this time. ...Portions of Intermountain/northern Great Basin... Widely scattered to scattered thunderstorms should form through much of the afternoon and into the early evening over an irregularly shaped swath from northeastern NV to extreme southern MT, northern UT, western WY and northwestern CO. Isolated severe gusts/hail will be possible. Cooling aloft related to the approaching mid/upper- level trough, overlying diurnal surface heating, will result in minimal MLCINH and steep deep-layer lapse rates (e.g, near 8 deg c/km from surface-300 mb in some forecast soundings), amidst sufficient low-level moisture to support sustained/deep convection. Cooling aloft will offset diabatic low-level cooling enough to maintain an isolated strong-severe threat a few more hours into the evening/nighttime hours than less synoptically forced scenarios. ..Edwards/Dial.. 09/10/2019 Read more

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0247 AM CDT Tue Sep 10 2019 Valid 131200Z - 181200Z ...DISCUSSION... ...Friday/Day 4 to Saturday/Day 5... On Friday, the medium-range models are in good agreement. The models have an upper-level trough in the Upper Mississippi Valley with a cold front from the Great Lakes to the mid Mississippi Valley. Thunderstorm development will be possible along parts of the front Friday afternoon and evening. On Saturday, the models move a shortwave trough and associated cold front across the north-central U.S. Thunderstorm development, with some possibly severe, will be possible along the front during the afternoon and evening. The models vary somewhat on the quick eastward progression of the shortwave trough. This introduces considerable uncertainty. Where the instability axis ends up near peak heating will help determine the corridor with the greatest severe threat. ...Sunday/Day 6 to Tuesday/Day 8... From Sunday through Tuesday, the models develop an upper-level ridge from the northern Plains into the Great Lakes but show significant differences in its character. Although moderate instability will be possible beneath the ridge each afternoon, convective coverage would remain very isolated. Even so, an isolated severe threat can not be ruled out across parts of the north-central states each afternoon. Spatial uncertainty is substantial during this time in the forecast. Read more

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0247 AM CDT Tue Sep 10 2019 Valid 131200Z - 181200Z ...DISCUSSION... ...Friday/Day 4 to Saturday/Day 5... On Friday, the medium-range models are in good agreement. The models have an upper-level trough in the Upper Mississippi Valley with a cold front from the Great Lakes to the mid Mississippi Valley. Thunderstorm development will be possible along parts of the front Friday afternoon and evening. On Saturday, the models move a shortwave trough and associated cold front across the north-central U.S. Thunderstorm development, with some possibly severe, will be possible along the front during the afternoon and evening. The models vary somewhat on the quick eastward progression of the shortwave trough. This introduces considerable uncertainty. Where the instability axis ends up near peak heating will help determine the corridor with the greatest severe threat. ...Sunday/Day 6 to Tuesday/Day 8... From Sunday through Tuesday, the models develop an upper-level ridge from the northern Plains into the Great Lakes but show significant differences in its character. Although moderate instability will be possible beneath the ridge each afternoon, convective coverage would remain very isolated. Even so, an isolated severe threat can not be ruled out across parts of the north-central states each afternoon. Spatial uncertainty is substantial during this time in the forecast. Read more

SPC 0730Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0215 AM CDT Tue Sep 10 2019 Valid 121200Z - 131200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE SOUTHERN AND CENTRAL PLAINS...LOWER TO MID MISSOURI VALLEY AND UPPER MIDWEST... ...SUMMARY... Thunderstorms associated with wind damage and isolated large hail will be possible on Thursday from eastern Kansas into northwest Missouri and Iowa. ...Southern and Central Plains/Lower to Mid Missouri Valley/Upper Midwest... An upper-level low is forecast to move northeastward across the northern Plains on Thursday. At the surface, a low is forecast to move into the Upper Mississippi Valley as a cold front advances eastward across Iowa, northwest Missouri and central Kansas. Ahead of the front, surface dewpoints should be in the upper 60s to near 70 F, helping moderate instability to develop around midday. Model consensus suggests that convective coverage should gradually increase along the front from Thursday morning into afternoon until a line is established. This convective line is forecast to move eastward across Iowa, northern Missouri and eastern Kansas from late afternoon to mid evening. Veered winds to the south-southwest ahead of the front along with 0-6 km shear values in the 30 to 40 kt range would be favorable for organized multicell bowing segments. The bowing segments would be capable of damaging wind gusts and hail. If cell rotation can develop along the stronger portions of the convective line, then isolated large hail would also be possible. The severe threat should taper off with south-southwestward extent into southern Kansas and northwestern Oklahoma, where deep-layer shear is forecast to be much weaker. ..Broyles.. 09/10/2019 Read more

SPC 0730Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0215 AM CDT Tue Sep 10 2019 Valid 121200Z - 131200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE SOUTHERN AND CENTRAL PLAINS...LOWER TO MID MISSOURI VALLEY AND UPPER MIDWEST... ...SUMMARY... Thunderstorms associated with wind damage and isolated large hail will be possible on Thursday from eastern Kansas into northwest Missouri and Iowa. ...Southern and Central Plains/Lower to Mid Missouri Valley/Upper Midwest... An upper-level low is forecast to move northeastward across the northern Plains on Thursday. At the surface, a low is forecast to move into the Upper Mississippi Valley as a cold front advances eastward across Iowa, northwest Missouri and central Kansas. Ahead of the front, surface dewpoints should be in the upper 60s to near 70 F, helping moderate instability to develop around midday. Model consensus suggests that convective coverage should gradually increase along the front from Thursday morning into afternoon until a line is established. This convective line is forecast to move eastward across Iowa, northern Missouri and eastern Kansas from late afternoon to mid evening. Veered winds to the south-southwest ahead of the front along with 0-6 km shear values in the 30 to 40 kt range would be favorable for organized multicell bowing segments. The bowing segments would be capable of damaging wind gusts and hail. If cell rotation can develop along the stronger portions of the convective line, then isolated large hail would also be possible. The severe threat should taper off with south-southwestward extent into southern Kansas and northwestern Oklahoma, where deep-layer shear is forecast to be much weaker. ..Broyles.. 09/10/2019 Read more

SPC Day 2 Fire Weather Outlook
Day 2 Fire Weather Outlook NWS Storm Prediction Center Norman OK 0204 AM CDT Tue Sep 10 2019 Valid 111200Z - 121200Z ...Synopsis... A pronounced mid-level shortwave trough will move across the western CONUS during the Day 2/Wednesday period. Stronger flow aloft will accompany the through, with a belt of 50+ knot 500 mb flow expected to traverse the Four Corners region by late afternoon. At the same time, deep boundary layer mixing may occur across parts of the Four Corners, promoting modest potential for wildfire spread. ...Parts of the Four Corners area... By afternoon peak heating, 15-25 mph sustained westerly winds and 15-20% RH will become commonplace across portions of the northern Colorado Plateau, to the windward side of the central Rockies. Given modestly dry fuels in place, an elevated area was delineated to account for marginal wildfire-spread potential in this area. ..Squitieri.. 09/10/2019 ...Please see www.spc.noaa.gov/fire for graphic product... Read more

SPC Day 2 Fire Weather Outlook
Day 2 Fire Weather Outlook NWS Storm Prediction Center Norman OK 0204 AM CDT Tue Sep 10 2019 Valid 111200Z - 121200Z ...Synopsis... A pronounced mid-level shortwave trough will move across the western CONUS during the Day 2/Wednesday period. Stronger flow aloft will accompany the through, with a belt of 50+ knot 500 mb flow expected to traverse the Four Corners region by late afternoon. At the same time, deep boundary layer mixing may occur across parts of the Four Corners, promoting modest potential for wildfire spread. ...Parts of the Four Corners area... By afternoon peak heating, 15-25 mph sustained westerly winds and 15-20% RH will become commonplace across portions of the northern Colorado Plateau, to the windward side of the central Rockies. Given modestly dry fuels in place, an elevated area was delineated to account for marginal wildfire-spread potential in this area. ..Squitieri.. 09/10/2019 ...Please see www.spc.noaa.gov/fire for graphic product... Read more

SPC Day 1 Fire Weather Outlook
Day 1 Fire Weather Outlook NWS Storm Prediction Center Norman OK 0134 AM CDT Tue Sep 10 2019 Valid 101200Z - 111200Z ...Synopsis... Broad cyclonic flow, associated with a deepening mid-level shortwave trough, will prevail across the western CONUS during the period. Breezy conditions, with patchy areas of drier air, will result from a low-level mass response to the impinging mid-level trough, promoting very modest wildfire-spread potential across parts of the Great Basin. In addition, widespread deep-layer ascent ahead of the trough will promote isolated to scattered thunderstorms across eastern portions of the Great Basin, into the Four Corners, central/northern Rockies, northwestward into parts of the Pacific Northwest. On the backside of the trough, surface to mid-level flow will be predominantly northerly/offshore, encouraging a modest Sundowner event across parts of Coastal Southern California towards the end of the period. ...Parts of the Great Basin... While elevated conditions will be mostly localized in nature in advance of the mid-level trough, some widespread 15-20 mph sustained south-southwesterly surface winds coinciding with 15-20% RH may occur across parts of central, eastern, and southern Nevada. The most likely timing of these conditions would be after peak heating of the afternoon. Farther east into Utah, surface southwesterly winds may easily exceed 20 mph, particularly in terrain-favoring locations, but surface RH above 20% depicted by the latest model guidance suggests that elevated fire concerns will be mainly localized in nature, with an elevated delineation withheld for this outlook. ...Eastern Great Basin into the central/northern Rockies... At least isolated to scattered thunderstorms will develop during the afternoon hours, aided by afternoon peak heating/boundary-layer mixing, and by deep-layer ascent provided by the mid-level shortwave trough. These storms are expected to be relatively fast-moving in nature, with precipitable water values under 0.75 inches and dry sub-cloud layers extending well above 700 mb in most locales. Still, fuels across these area are expected to be marginally to modestly receptive to new ignitions and subsequent fire spread on the large scale. As such, the localized threat for new dry-lightning induced fire starts precludes an isolated dry thunderstorm delineation. ...Parts of Coastal Southern California... Towards the end of the period, northerly sustained surface winds within the 15-25 mph range are expected along with 20-25% RH. Given dry fuels receptive to fire spread, elevated fire weather conditions are expected across portions of Ventura and Santa Barbara Counties, particularly in the higher terrain of the Santa Ynez Mountains, where winds will be strongest, with the poorest RH recovery. ..Squitieri.. 09/10/2019 ...Please see www.spc.noaa.gov/fire for graphic product... Read more

SPC Day 1 Fire Weather Outlook
Day 1 Fire Weather Outlook NWS Storm Prediction Center Norman OK 0134 AM CDT Tue Sep 10 2019 Valid 101200Z - 111200Z ...Synopsis... Broad cyclonic flow, associated with a deepening mid-level shortwave trough, will prevail across the western CONUS during the period. Breezy conditions, with patchy areas of drier air, will result from a low-level mass response to the impinging mid-level trough, promoting very modest wildfire-spread potential across parts of the Great Basin. In addition, widespread deep-layer ascent ahead of the trough will promote isolated to scattered thunderstorms across eastern portions of the Great Basin, into the Four Corners, central/northern Rockies, northwestward into parts of the Pacific Northwest. On the backside of the trough, surface to mid-level flow will be predominantly northerly/offshore, encouraging a modest Sundowner event across parts of Coastal Southern California towards the end of the period. ...Parts of the Great Basin... While elevated conditions will be mostly localized in nature in advance of the mid-level trough, some widespread 15-20 mph sustained south-southwesterly surface winds coinciding with 15-20% RH may occur across parts of central, eastern, and southern Nevada. The most likely timing of these conditions would be after peak heating of the afternoon. Farther east into Utah, surface southwesterly winds may easily exceed 20 mph, particularly in terrain-favoring locations, but surface RH above 20% depicted by the latest model guidance suggests that elevated fire concerns will be mainly localized in nature, with an elevated delineation withheld for this outlook. ...Eastern Great Basin into the central/northern Rockies... At least isolated to scattered thunderstorms will develop during the afternoon hours, aided by afternoon peak heating/boundary-layer mixing, and by deep-layer ascent provided by the mid-level shortwave trough. These storms are expected to be relatively fast-moving in nature, with precipitable water values under 0.75 inches and dry sub-cloud layers extending well above 700 mb in most locales. Still, fuels across these area are expected to be marginally to modestly receptive to new ignitions and subsequent fire spread on the large scale. As such, the localized threat for new dry-lightning induced fire starts precludes an isolated dry thunderstorm delineation. ...Parts of Coastal Southern California... Towards the end of the period, northerly sustained surface winds within the 15-25 mph range are expected along with 20-25% RH. Given dry fuels receptive to fire spread, elevated fire weather conditions are expected across portions of Ventura and Santa Barbara Counties, particularly in the higher terrain of the Santa Ynez Mountains, where winds will be strongest, with the poorest RH recovery. ..Squitieri.. 09/10/2019 ...Please see www.spc.noaa.gov/fire for graphic product... Read more

SPC 0600Z Day 2 Outlook
Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1254 AM CDT Tue Sep 10 2019 Valid 111200Z - 121200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF NEBRASKA AND SOUTH DAKOTA... ...SUMMARY... Thunderstorms associated with large hail, damaging wind gusts and a tornado threat are expected to develop on Wednesday from parts of the central and northern Plains eastward into the Upper Mississippi Valley. ...Central and Northern Plains/Upper Mississippi Valley... An upper-level ridge will move eastward across eastern sections of the northern Plains on Wednesday as an upper-level trough moves through the Intermountain West. At the surface, a low is forecast to deepen across the central High Plains along a slow-moving warm front extending eastward from northern Nebraska into northern Iowa. Surface dewpoints south of the front should be in the mid to upper 60s F, contributing to moderate to strong instability by afternoon. Model consensus places the strongest instability across west-central Nebraska by late afternoon where convective initiation appears likely by early evening. NAM and GFS forecast sounding late Wednesday afternoon across west-central Nebraska show conditions favorable for supercells with MLCAPE values in the 2000 to 3000 J/kg range, 0-6 km shear of 40 to 50 kt and steep mid-level lapse rates. Supercells may be capable of producing hailstones greater than 2 inches in diameter. Wind damage will also be possible as an MCS grows upscale. A tornado threat is also expected as the low-level jet ramps up during the early to mid evening. The severe threat should develop northeastward across eastern South Dakota and southwestern Minnesota during the evening. Further to the east, some models suggest a secondary maximum of strong instability will develop across the Upper Mississippi Valley. This combined with enhanced low-level convergence along the warm front should result in scattered thunderstorm development Wednesday afternoon. Although an isolated severe threat will be possible, the upper-level ridge to the west will help to marginalize cell organization. ...Northeast... Westerly mid-level flow will be in place in the Northeast on Wednesday. At the surface, a cold front is forecast to move southward into New York. South of the front, surface dewpoints in the upper 60s to near 70 F should contribute to moderate instability by afternoon. Model forecasts suggest that scattered thunderstorms will initiate near peak heating along and south of the front where low-level lapse rates will be steep. This may be enough for marginally severe wind gusts. Some uncertainty exists concerning the magnitude of the severe threat mainly due to a large spread among model solutions regarding instability and deep-layer shear. ...MAXIMUM RISK BY HAZARD... Tornado: 5% - Slight Wind: 30% - Enhanced Hail: 30% SIG - Enhanced ..Broyles.. 09/10/2019 Read more

SPC 0600Z Day 2 Outlook
Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1254 AM CDT Tue Sep 10 2019 Valid 111200Z - 121200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF NEBRASKA AND SOUTH DAKOTA... ...SUMMARY... Thunderstorms associated with large hail, damaging wind gusts and a tornado threat are expected to develop on Wednesday from parts of the central and northern Plains eastward into the Upper Mississippi Valley. ...Central and Northern Plains/Upper Mississippi Valley... An upper-level ridge will move eastward across eastern sections of the northern Plains on Wednesday as an upper-level trough moves through the Intermountain West. At the surface, a low is forecast to deepen across the central High Plains along a slow-moving warm front extending eastward from northern Nebraska into northern Iowa. Surface dewpoints south of the front should be in the mid to upper 60s F, contributing to moderate to strong instability by afternoon. Model consensus places the strongest instability across west-central Nebraska by late afternoon where convective initiation appears likely by early evening. NAM and GFS forecast sounding late Wednesday afternoon across west-central Nebraska show conditions favorable for supercells with MLCAPE values in the 2000 to 3000 J/kg range, 0-6 km shear of 40 to 50 kt and steep mid-level lapse rates. Supercells may be capable of producing hailstones greater than 2 inches in diameter. Wind damage will also be possible as an MCS grows upscale. A tornado threat is also expected as the low-level jet ramps up during the early to mid evening. The severe threat should develop northeastward across eastern South Dakota and southwestern Minnesota during the evening. Further to the east, some models suggest a secondary maximum of strong instability will develop across the Upper Mississippi Valley. This combined with enhanced low-level convergence along the warm front should result in scattered thunderstorm development Wednesday afternoon. Although an isolated severe threat will be possible, the upper-level ridge to the west will help to marginalize cell organization. ...Northeast... Westerly mid-level flow will be in place in the Northeast on Wednesday. At the surface, a cold front is forecast to move southward into New York. South of the front, surface dewpoints in the upper 60s to near 70 F should contribute to moderate instability by afternoon. Model forecasts suggest that scattered thunderstorms will initiate near peak heating along and south of the front where low-level lapse rates will be steep. This may be enough for marginally severe wind gusts. Some uncertainty exists concerning the magnitude of the severe threat mainly due to a large spread among model solutions regarding instability and deep-layer shear. ...MAXIMUM RISK BY HAZARD... Tornado: 5% - Slight Wind: 30% - Enhanced Hail: 30% SIG - Enhanced ..Broyles.. 09/10/2019 Read more

SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1259 AM CDT Tue Sep 10 2019 Valid 101200Z - 111200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS OVER NORTHERN NEBRASKA AND SOUTHERN SOUTH DAKOTA... ...SUMMARY... Thunderstorms with severe wind gusts, large hail and a tornado or two are possible across parts of Nebraska, South Dakota and east-central Wyoming from late afternoon through evening. Some of the hail could be very large, with a few significant damaging wind gusts. ...Synopsis... An upper trough will amplify over the western states with significant cooling aloft and increasing shear developing over the Great Basin into the central Rockies. A cyclonically curved upper jet with midlevel speeds of 50-60 kt will nose into NV and UT late in the day, while shortwave ridging occurs over the Plains. At the surface, low pressure will deepen over northeast CO, where strong heating will occur. A warm front will develop northward toward the NE/SD border through evening, with eastward extension of this boundary becoming nearly stationary along the MN/IA border. South of this front, warm southerly winds will bring upper 60s F dewpoints northward, resulting in substantial instability from the northern High Plains eastward to southern WI. ...Northern Plains... Southerly low-level winds and heating within the large-scale warm advection regime will aid the northward transport of mid to upper 60s F dewpoints across NE and into southern SD. Weakening easterlies north of the warm front will also maintain 50s F dewpoints into southwest MT and eastern WY, where heating will lead to an uncapped air mass. Increasing convergence and upslope flow will lead to storm initiation over eastern WY by around 21Z, with long hodographs supporting large hail into western SD and NE. Additional storms are expected to develop late in the day and into the evening near the warm front, where substantial low-level shear and SRH will develop. A few supercells are possible over northern NE and southern SD, with very large hail and a couple tornadoes possible before storms grow upscale into an MCS with the primary risk damaging wind gusts. The damaging-wind threat may persist eastward into MN and IA where warm advection with the low-level jet will aid lift. ...Northeast NV...northern UT...southeast ID...western WY into southern MT... Strong heating near the surface trough will result in scattered thunderstorms during the late afternoon from northern NV into southern ID and western WY. Forecast soundings show steep lapse rates and lengthening hodographs which will support cells or small bows capable of marginally severe hail or wind. Storms are also expected to increase in coverage from eastern NV into UT during the evening as large-scale lift with the upper trough is maximized. Despite the time of day, marginal hail and a few severe wind gusts will remain possible as instability remains sufficient, given cold temperatures aloft. ..Jewell.. 09/10/2019 Read more

SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1259 AM CDT Tue Sep 10 2019 Valid 101200Z - 111200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS OVER NORTHERN NEBRASKA AND SOUTHERN SOUTH DAKOTA... ...SUMMARY... Thunderstorms with severe wind gusts, large hail and a tornado or two are possible across parts of Nebraska, South Dakota and east-central Wyoming from late afternoon through evening. Some of the hail could be very large, with a few significant damaging wind gusts. ...Synopsis... An upper trough will amplify over the western states with significant cooling aloft and increasing shear developing over the Great Basin into the central Rockies. A cyclonically curved upper jet with midlevel speeds of 50-60 kt will nose into NV and UT late in the day, while shortwave ridging occurs over the Plains. At the surface, low pressure will deepen over northeast CO, where strong heating will occur. A warm front will develop northward toward the NE/SD border through evening, with eastward extension of this boundary becoming nearly stationary along the MN/IA border. South of this front, warm southerly winds will bring upper 60s F dewpoints northward, resulting in substantial instability from the northern High Plains eastward to southern WI. ...Northern Plains... Southerly low-level winds and heating within the large-scale warm advection regime will aid the northward transport of mid to upper 60s F dewpoints across NE and into southern SD. Weakening easterlies north of the warm front will also maintain 50s F dewpoints into southwest MT and eastern WY, where heating will lead to an uncapped air mass. Increasing convergence and upslope flow will lead to storm initiation over eastern WY by around 21Z, with long hodographs supporting large hail into western SD and NE. Additional storms are expected to develop late in the day and into the evening near the warm front, where substantial low-level shear and SRH will develop. A few supercells are possible over northern NE and southern SD, with very large hail and a couple tornadoes possible before storms grow upscale into an MCS with the primary risk damaging wind gusts. The damaging-wind threat may persist eastward into MN and IA where warm advection with the low-level jet will aid lift. ...Northeast NV...northern UT...southeast ID...western WY into southern MT... Strong heating near the surface trough will result in scattered thunderstorms during the late afternoon from northern NV into southern ID and western WY. Forecast soundings show steep lapse rates and lengthening hodographs which will support cells or small bows capable of marginally severe hail or wind. Storms are also expected to increase in coverage from eastern NV into UT during the evening as large-scale lift with the upper trough is maximized. Despite the time of day, marginal hail and a few severe wind gusts will remain possible as instability remains sufficient, given cold temperatures aloft. ..Jewell.. 09/10/2019 Read more

WW 0639 Status Updates
STATUS REPORT ON WW 639 SEVERE WEATHER THREAT CONTINUES RIGHT OF A LINE FROM 30 WSW DBQ TO 40 SSW ALO TO 30 NW ALO TO 15 S LSE. ..KERR..09/10/19 ATTN...WFO...DMX...ARX...DVN...MPX... STATUS REPORT FOR WT 639 SEVERE WEATHER THREAT CONTINUES FOR THE FOLLOWING AREAS IAC005-011-013-017-019-023-037-043-055-065-075-171-191-100240- IA . IOWA COUNTIES INCLUDED ARE ALLAMAKEE BENTON BLACK HAWK BREMER BUCHANAN BUTLER CHICKASAW CLAYTON DELAWARE FAYETTE GRUNDY TAMA WINNESHIEK MNC055-100240- MN . MINNESOTA COUNTIES INCLUDED ARE HOUSTON THE WATCH STATUS MESSAGE IS FOR GUIDANCE PURPOSES ONLY. PLEASE REFER TO WATCH COUNTY NOTIFICATION STATEMENTS FOR OFFICIAL INFORMATION ON COUNTIES...INDEPENDENT CITIES AND MARINE ZONES CLEARED FROM SEVERE THUNDERSTORM AND TORNADO WATCHES. Read more

WW 639 TORNADO IA MN 092030Z - 100300Z
URGENT - IMMEDIATE BROADCAST REQUESTED Tornado Watch Number 639 NWS Storm Prediction Center Norman OK 330 PM CDT Mon Sep 9 2019 The NWS Storm Prediction Center has issued a * Tornado Watch for portions of Central and Northern Iowa Southeast Minnesota * Effective this Monday afternoon and evening from 330 PM until 1000 PM CDT. * Primary threats include... A few tornadoes possible Scattered damaging wind gusts to 70 mph possible Scattered large hail events to 1.5 inches in diameter possible SUMMARY...Thunderstorms are expected to intensify this afternoon over central Iowa and track northeastward across the watch area. Initial storms may pose a risk of a few tornadoes and large hail, with an increasing risk of damaging wind gusts this evening. The tornado watch area is approximately along and 75 statute miles north and south of a line from 55 miles west southwest of Fort Dodge IA to 60 miles east northeast of Waterloo IA. For a complete depiction of the watch see the associated watch outline update (WOUS64 KWNS WOU9). PRECAUTIONARY/PREPAREDNESS ACTIONS... REMEMBER...A Tornado Watch means conditions are favorable for tornadoes and severe thunderstorms in and close to the watch area. Persons in these areas should be on the lookout for threatening weather conditions and listen for later statements and possible warnings. && AVIATION...Tornadoes and a few severe thunderstorms with hail surface and aloft to 1.5 inches. Extreme turbulence and surface wind gusts to 60 knots. A few cumulonimbi with maximum tops to 500. Mean storm motion vector 25030. ...Hart Read more

SPC 0100Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0746 PM CDT Mon Sep 09 2019 Valid 100100Z - 101200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS NORTHEAST IOWA INTO SOUTHWEST WISCONSIN AND SOUTHEAST MINNESOTA... ...SUMMARY... A few severe thunderstorms remain possible from Iowa into southwest Wisconsin, and over northeast South Dakota this evening. ...IA into southwest WI... Storms persist this evening over northeast IA near a warm front which will continue advancing northeastward tonight. Strong low-level shear near this boundary may support a localized tornado threat with any of the strong cells. Otherwise, damaging winds appear possible. For more information see mesoscale discussion 1943. ...Northeast SD into western MN... Cells are beginning to develop over northeast SD near the surface low. The 00Z ABR sounding shows sufficient instability to support severe storms, but cooler surface temperatures exist just north and east of the area. Therefore, it appears the severe threat will remain confined to a small area, perhaps extending into west-central MN later this evening. A supercell or two is possible, with hail, or even a brief tornado should cells become severe before becoming elevated. For more information see mesoscale discussion 1944. ..Jewell.. 09/10/2019 Read more

SPC 0100Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0746 PM CDT Mon Sep 09 2019 Valid 100100Z - 101200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS NORTHEAST IOWA INTO SOUTHWEST WISCONSIN AND SOUTHEAST MINNESOTA... ...SUMMARY... A few severe thunderstorms remain possible from Iowa into southwest Wisconsin, and over northeast South Dakota this evening. ...IA into southwest WI... Storms persist this evening over northeast IA near a warm front which will continue advancing northeastward tonight. Strong low-level shear near this boundary may support a localized tornado threat with any of the strong cells. Otherwise, damaging winds appear possible. For more information see mesoscale discussion 1943. ...Northeast SD into western MN... Cells are beginning to develop over northeast SD near the surface low. The 00Z ABR sounding shows sufficient instability to support severe storms, but cooler surface temperatures exist just north and east of the area. Therefore, it appears the severe threat will remain confined to a small area, perhaps extending into west-central MN later this evening. A supercell or two is possible, with hail, or even a brief tornado should cells become severe before becoming elevated. For more information see mesoscale discussion 1944. ..Jewell.. 09/10/2019 Read more

SPC 0100Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0746 PM CDT Mon Sep 09 2019 Valid 100100Z - 101200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS NORTHEAST IOWA INTO SOUTHWEST WISCONSIN AND SOUTHEAST MINNESOTA... ...SUMMARY... A few severe thunderstorms remain possible from Iowa into southwest Wisconsin, and over northeast South Dakota this evening. ...IA into southwest WI... Storms persist this evening over northeast IA near a warm front which will continue advancing northeastward tonight. Strong low-level shear near this boundary may support a localized tornado threat with any of the strong cells. Otherwise, damaging winds appear possible. For more information see mesoscale discussion 1943. ...Northeast SD into western MN... Cells are beginning to develop over northeast SD near the surface low. The 00Z ABR sounding shows sufficient instability to support severe storms, but cooler surface temperatures exist just north and east of the area. Therefore, it appears the severe threat will remain confined to a small area, perhaps extending into west-central MN later this evening. A supercell or two is possible, with hail, or even a brief tornado should cells become severe before becoming elevated. For more information see mesoscale discussion 1944. ..Jewell.. 09/10/2019 Read more