Severe Storms

MD 1941 CONCERNING SEVERE POTENTIAL...TORNADO WATCH LIKELY FOR PORTIONS OF IA INTO SOUTHERN MN AND EXTREME SOUTHWEST WI
Mesoscale Discussion 1941 NWS Storm Prediction Center Norman OK 0249 PM CDT Mon Sep 09 2019 Areas affected...portions of IA into southern MN and extreme southwest WI Concerning...Severe potential...Tornado Watch likely Valid 091949Z - 092145Z Probability of Watch Issuance...80 percent SUMMARY...Storms will continue to develop and intensify this afternoon. Isolated supercells capable of all severe hazards are expected, and a watch will likely be need by 21z. DISCUSSION...A surface warm front was noted in 19z surface analysis near MBG to south of ABR in South Dakota and then extending east/southeast across northern/central IA. To the south of the front, southerly low level flow is maintaining upper 60s to low 70s dewpoints across southeast SD into eastern NE, and much of IA. Strong heating in broken cloudiness has resulted in temperatures in the mid 70s to mid 80s south of the front, supporting MLCAPE around 1000-2000 J/kg and weakening inhibition. Subtle forcing ejecting northeast across the central Plains is evident in water vapor imagery as well as via deepening CU both across the central Plains and into parts of southern/central IA. This is aiding in the development of isolated storms in low level confluence ahead of the surface low over western SD. Latest VWP data from KDMX indicates a shear profile supportive of supercells with backed low level winds increasing/veering with height. In fact, a 50 kt speed max was noted at around 1.5 kft. This is leading to enlarged, curved low level hodographs. Given deep boundary layer moisture, a tornado threat will accompany strongest cells, especially those nearer the warm front where low level SRH will be maximized. Midlevel lapse rates are modest, but given instability and strength of shear, hail is also possible, in addition to strong wind gusts. With time and increased forcing and the development of a southwesterly low level jet, convection may eventually grow upscale into a bowing line segment as activity spreads north and east into southeast MN and portions of southwest/south-central WI later this evening. ..Leitman/Hart.. 09/09/2019 ...Please see www.spc.noaa.gov for graphic product... ATTN...WFO...DVN...ARX...MPX...DMX...FSD...OAX... LAT...LON 41789576 42939520 43579496 44009443 44259356 44249278 44099197 43749118 42829060 42109097 41539155 41149235 41019317 40999440 41029543 41119575 41789576 Read more

No watches are valid as of Mon Sep 9 18:30:06 UTC 2019.

SPC Day 2 Fire Weather Outlook
Day 2 Fire Weather Outlook NWS Storm Prediction Center Norman OK 0127 PM CDT Mon Sep 09 2019 Valid 101200Z - 111200Z Models remain somewhat inconsistent with depiction of minimum RH values during the afternoon on Tuesday. Nevertheless, with strong (20-25 mph) southwesterly surface winds and areas of 15-25% RH, localized areas of elevated fire weather appear likely. The greatest confidence of these conditions being observed is across south-central Utah and north-central Arizona, and a small elevated area has been introduced to address this. Locally elevated fire weather may be observed as far west as east-central Nevada and also into northwestern Colorado. Model trends will be monitored for potential reconfigurations of the new risk area in later outlook updates. In southern California, a persistent surface pattern favoring Sundowner winds will continue through late Tuesday. Gusty winds (perhaps exceeding 40 mph) and 20-30% RH values support elevated fire weather conditions and the ongoing risk area is maintained for this outlook. See the previous discussion below for more details. ..Cook.. 09/09/2019 .PREV DISCUSSION... /ISSUED 0134 AM CDT Mon Sep 09 2019/ ...Synopsis... Broad mid/upper-level cyclonic flow is forecast to remain over the western CONUS Day 2/Tuesday. As this occurs, an area of enhanced mid-level flow -- located near the base of the trough -- is forecast to strengthen while overspreading portions of Southern California, the Southwest, and the southern Great Basin. ...Southern California: Santa Barbara and Ventura Counties... Gusty Sundowner winds are forecast to continue through Day 2/Tuesday across eastern Santa Barbara and western Ventura Counties. While minimum RH values are forecast to be a bit higher than previous days (e.g., 20-25%), elevated fire weather conditions will likely persist given the gusty winds and receptive fuels. As with previous nights, locally elevated conditions may remain overnight at higher elevations (e.g., > 1 kft) due to relatively poor RH recoveries and lingering gusty winds. ...Nevada/Utah/Arizona... While strong/gusty winds are forecast across portions of southern Nevada/Utah and northern Arizona, increasing low-level moisture should temper fire weather conditions relative to recent days. Nevertheless, locally elevated conditions are possible. ...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 0127 PM CDT Mon Sep 09 2019 Valid 101200Z - 111200Z Models remain somewhat inconsistent with depiction of minimum RH values during the afternoon on Tuesday. Nevertheless, with strong (20-25 mph) southwesterly surface winds and areas of 15-25% RH, localized areas of elevated fire weather appear likely. The greatest confidence of these conditions being observed is across south-central Utah and north-central Arizona, and a small elevated area has been introduced to address this. Locally elevated fire weather may be observed as far west as east-central Nevada and also into northwestern Colorado. Model trends will be monitored for potential reconfigurations of the new risk area in later outlook updates. In southern California, a persistent surface pattern favoring Sundowner winds will continue through late Tuesday. Gusty winds (perhaps exceeding 40 mph) and 20-30% RH values support elevated fire weather conditions and the ongoing risk area is maintained for this outlook. See the previous discussion below for more details. ..Cook.. 09/09/2019 .PREV DISCUSSION... /ISSUED 0134 AM CDT Mon Sep 09 2019/ ...Synopsis... Broad mid/upper-level cyclonic flow is forecast to remain over the western CONUS Day 2/Tuesday. As this occurs, an area of enhanced mid-level flow -- located near the base of the trough -- is forecast to strengthen while overspreading portions of Southern California, the Southwest, and the southern Great Basin. ...Southern California: Santa Barbara and Ventura Counties... Gusty Sundowner winds are forecast to continue through Day 2/Tuesday across eastern Santa Barbara and western Ventura Counties. While minimum RH values are forecast to be a bit higher than previous days (e.g., 20-25%), elevated fire weather conditions will likely persist given the gusty winds and receptive fuels. As with previous nights, locally elevated conditions may remain overnight at higher elevations (e.g., > 1 kft) due to relatively poor RH recoveries and lingering gusty winds. ...Nevada/Utah/Arizona... While strong/gusty winds are forecast across portions of southern Nevada/Utah and northern Arizona, increasing low-level moisture should temper fire weather conditions relative to recent days. Nevertheless, locally elevated conditions are possible. ...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 0127 PM CDT Mon Sep 09 2019 Valid 101200Z - 111200Z Models remain somewhat inconsistent with depiction of minimum RH values during the afternoon on Tuesday. Nevertheless, with strong (20-25 mph) southwesterly surface winds and areas of 15-25% RH, localized areas of elevated fire weather appear likely. The greatest confidence of these conditions being observed is across south-central Utah and north-central Arizona, and a small elevated area has been introduced to address this. Locally elevated fire weather may be observed as far west as east-central Nevada and also into northwestern Colorado. Model trends will be monitored for potential reconfigurations of the new risk area in later outlook updates. In southern California, a persistent surface pattern favoring Sundowner winds will continue through late Tuesday. Gusty winds (perhaps exceeding 40 mph) and 20-30% RH values support elevated fire weather conditions and the ongoing risk area is maintained for this outlook. See the previous discussion below for more details. ..Cook.. 09/09/2019 .PREV DISCUSSION... /ISSUED 0134 AM CDT Mon Sep 09 2019/ ...Synopsis... Broad mid/upper-level cyclonic flow is forecast to remain over the western CONUS Day 2/Tuesday. As this occurs, an area of enhanced mid-level flow -- located near the base of the trough -- is forecast to strengthen while overspreading portions of Southern California, the Southwest, and the southern Great Basin. ...Southern California: Santa Barbara and Ventura Counties... Gusty Sundowner winds are forecast to continue through Day 2/Tuesday across eastern Santa Barbara and western Ventura Counties. While minimum RH values are forecast to be a bit higher than previous days (e.g., 20-25%), elevated fire weather conditions will likely persist given the gusty winds and receptive fuels. As with previous nights, locally elevated conditions may remain overnight at higher elevations (e.g., > 1 kft) due to relatively poor RH recoveries and lingering gusty winds. ...Nevada/Utah/Arizona... While strong/gusty winds are forecast across portions of southern Nevada/Utah and northern Arizona, increasing low-level moisture should temper fire weather conditions relative to recent days. Nevertheless, locally elevated conditions are possible. ...Please see www.spc.noaa.gov/fire for graphic product... Read more

SPC 1730Z Day 2 Outlook
Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1230 PM CDT Mon Sep 09 2019 Valid 101200Z - 111200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE NORTHERN AND CENTRAL PLAINS... ...SUMMARY... Thunderstorms with severe wind gusts, large hail and isolated tornadoes will be possible across parts of the northern and central Plains on Tuesday. Some of the hail could be very large, and significant damaging winds may occur. ...Northern/Central Plains into the Upper Midwest... An upper trough over the western CONUS is forecast to amplify through the period, while downstream upper ridging builds over parts of the northern Plains and Upper Midwest. At the surface, a broad area of low pressure should gradually deepen across eastern WY/CO by Tuesday afternoon, with a pronounced baroclinic zone becoming established along the NE/SD border. Persistent easterly low-level upslope flow along with modest ascent preceding the upper trough will likely encourage convective initiation across parts of eastern WY by early Tuesday afternoon, with storms then spreading eastward across northern NE and southern SD through the evening and overnight. Steep mid-level lapse rates emanating from the central Rockies will likely overspread this region, and strong surface heating is expected to the south of the front along the NE/SD border. Moderate to strong instability, with MLCAPE around 2000-4000+ J/kg, will likely develop in response and as surface dewpoints increase into the mid 60s to lower 70s. Mid-level winds should gradually increase through the day as the upper trough amplifies over the western CONUS, and some guidance hints at a shortwave trough embedded within the southwesterly mid-level flow over the northern/central High Plains overspreading western NE/SD by midday. Related effective bulk shear values will likely increase into the 40-50 kt range along/near the surface front, which will easily support supercells with initial development. Large hail will be a threat with these storms across eastern WY into southwestern SD and the NE Panhandle, and some of the hail could be very large (2+ inches in diameter) given the forecast values of both instability and shear. Isolated tornadoes may also occur, especially with any storms that form along the surface front where low-level flow will be locally backed to east-southeasterly. A 35-45 kt southerly low-level jet will strengthen across the central Plains Tuesday evening, and upscale growth into a MCS appears likely as storms move into south-central SD and north-central NE. Severe, damaging winds should become an increasing concern with eastward extent across NE/SD Tuesday evening, and some of these winds could be significant. At least an isolated damaging wind threat may persist into parts of eastern NE/SD and the Upper Midwest through the early overnight hours, although instability will decrease farther east. There is still some uncertainty in the placement of the surface front along/near the NE/SD border, and the potential track of the MCS. Greater severe probabilities may be needed in a future outlook update if confidence increases in a more focused corridor of scattered damaging winds. ...Great Basin/Northern Rockies... Mid-level southwesterly winds are forecast to strengthen across parts of the northern Great Basin into the northern Rockies on Tuesday. Although instability will remain limited, enough MLCAPE may develop in combination with sufficient shear by late afternoon to support some organized storms across northern UT into southeastern ID and western WY. Isolated strong to damaging winds would be the main threat with this activity. ...MAXIMUM RISK BY HAZARD... Tornado: 5% - Slight Wind: 15% SIG - Slight Hail: 15% SIG - Slight ..Gleason.. 09/09/2019 Read more

SPC 1730Z Day 2 Outlook
Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1230 PM CDT Mon Sep 09 2019 Valid 101200Z - 111200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE NORTHERN AND CENTRAL PLAINS... ...SUMMARY... Thunderstorms with severe wind gusts, large hail and isolated tornadoes will be possible across parts of the northern and central Plains on Tuesday. Some of the hail could be very large, and significant damaging winds may occur. ...Northern/Central Plains into the Upper Midwest... An upper trough over the western CONUS is forecast to amplify through the period, while downstream upper ridging builds over parts of the northern Plains and Upper Midwest. At the surface, a broad area of low pressure should gradually deepen across eastern WY/CO by Tuesday afternoon, with a pronounced baroclinic zone becoming established along the NE/SD border. Persistent easterly low-level upslope flow along with modest ascent preceding the upper trough will likely encourage convective initiation across parts of eastern WY by early Tuesday afternoon, with storms then spreading eastward across northern NE and southern SD through the evening and overnight. Steep mid-level lapse rates emanating from the central Rockies will likely overspread this region, and strong surface heating is expected to the south of the front along the NE/SD border. Moderate to strong instability, with MLCAPE around 2000-4000+ J/kg, will likely develop in response and as surface dewpoints increase into the mid 60s to lower 70s. Mid-level winds should gradually increase through the day as the upper trough amplifies over the western CONUS, and some guidance hints at a shortwave trough embedded within the southwesterly mid-level flow over the northern/central High Plains overspreading western NE/SD by midday. Related effective bulk shear values will likely increase into the 40-50 kt range along/near the surface front, which will easily support supercells with initial development. Large hail will be a threat with these storms across eastern WY into southwestern SD and the NE Panhandle, and some of the hail could be very large (2+ inches in diameter) given the forecast values of both instability and shear. Isolated tornadoes may also occur, especially with any storms that form along the surface front where low-level flow will be locally backed to east-southeasterly. A 35-45 kt southerly low-level jet will strengthen across the central Plains Tuesday evening, and upscale growth into a MCS appears likely as storms move into south-central SD and north-central NE. Severe, damaging winds should become an increasing concern with eastward extent across NE/SD Tuesday evening, and some of these winds could be significant. At least an isolated damaging wind threat may persist into parts of eastern NE/SD and the Upper Midwest through the early overnight hours, although instability will decrease farther east. There is still some uncertainty in the placement of the surface front along/near the NE/SD border, and the potential track of the MCS. Greater severe probabilities may be needed in a future outlook update if confidence increases in a more focused corridor of scattered damaging winds. ...Great Basin/Northern Rockies... Mid-level southwesterly winds are forecast to strengthen across parts of the northern Great Basin into the northern Rockies on Tuesday. Although instability will remain limited, enough MLCAPE may develop in combination with sufficient shear by late afternoon to support some organized storms across northern UT into southeastern ID and western WY. Isolated strong to damaging winds would be the main threat with this activity. ...MAXIMUM RISK BY HAZARD... Tornado: 5% - Slight Wind: 15% SIG - Slight Hail: 15% SIG - Slight ..Gleason.. 09/09/2019 Read more

SPC 1730Z Day 2 Outlook
Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1230 PM CDT Mon Sep 09 2019 Valid 101200Z - 111200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE NORTHERN AND CENTRAL PLAINS... ...SUMMARY... Thunderstorms with severe wind gusts, large hail and isolated tornadoes will be possible across parts of the northern and central Plains on Tuesday. Some of the hail could be very large, and significant damaging winds may occur. ...Northern/Central Plains into the Upper Midwest... An upper trough over the western CONUS is forecast to amplify through the period, while downstream upper ridging builds over parts of the northern Plains and Upper Midwest. At the surface, a broad area of low pressure should gradually deepen across eastern WY/CO by Tuesday afternoon, with a pronounced baroclinic zone becoming established along the NE/SD border. Persistent easterly low-level upslope flow along with modest ascent preceding the upper trough will likely encourage convective initiation across parts of eastern WY by early Tuesday afternoon, with storms then spreading eastward across northern NE and southern SD through the evening and overnight. Steep mid-level lapse rates emanating from the central Rockies will likely overspread this region, and strong surface heating is expected to the south of the front along the NE/SD border. Moderate to strong instability, with MLCAPE around 2000-4000+ J/kg, will likely develop in response and as surface dewpoints increase into the mid 60s to lower 70s. Mid-level winds should gradually increase through the day as the upper trough amplifies over the western CONUS, and some guidance hints at a shortwave trough embedded within the southwesterly mid-level flow over the northern/central High Plains overspreading western NE/SD by midday. Related effective bulk shear values will likely increase into the 40-50 kt range along/near the surface front, which will easily support supercells with initial development. Large hail will be a threat with these storms across eastern WY into southwestern SD and the NE Panhandle, and some of the hail could be very large (2+ inches in diameter) given the forecast values of both instability and shear. Isolated tornadoes may also occur, especially with any storms that form along the surface front where low-level flow will be locally backed to east-southeasterly. A 35-45 kt southerly low-level jet will strengthen across the central Plains Tuesday evening, and upscale growth into a MCS appears likely as storms move into south-central SD and north-central NE. Severe, damaging winds should become an increasing concern with eastward extent across NE/SD Tuesday evening, and some of these winds could be significant. At least an isolated damaging wind threat may persist into parts of eastern NE/SD and the Upper Midwest through the early overnight hours, although instability will decrease farther east. There is still some uncertainty in the placement of the surface front along/near the NE/SD border, and the potential track of the MCS. Greater severe probabilities may be needed in a future outlook update if confidence increases in a more focused corridor of scattered damaging winds. ...Great Basin/Northern Rockies... Mid-level southwesterly winds are forecast to strengthen across parts of the northern Great Basin into the northern Rockies on Tuesday. Although instability will remain limited, enough MLCAPE may develop in combination with sufficient shear by late afternoon to support some organized storms across northern UT into southeastern ID and western WY. Isolated strong to damaging winds would be the main threat with this activity. ...MAXIMUM RISK BY HAZARD... Tornado: 5% - Slight Wind: 15% SIG - Slight Hail: 15% SIG - Slight ..Gleason.. 09/09/2019 Read more

SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1113 AM CDT Mon Sep 09 2019 Valid 091630Z - 101200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PORTIONS OF NORTHERN IOWA...SOUTHERN MINNESOTA...AND WESTERN WISCONSIN... ...SUMMARY... Severe thunderstorms are possible this afternoon and evening over parts of the Upper Midwest and upper Mississippi Valley regions. ...IA/MN/WI... A series of shortwave troughs are rotating across the central/northern Plains today. Forcing for ascent is evident in water vapor imagery ahead of these features, moving into eastern SD/NE and much of MN/IA. Meanwhile at the surface, a warm front extends from southeast SD across central IA. This boundary will lift slowly northward through the afternoon. Forecast soundings suggest that continued slow heating along/south of the warm front will sufficiently weaken the capping inversion, leading to scattered thunderstorms by late afternoon over western IA. These storms will track into the frontal zone, where backed low-level winds and enhanced vorticity may aid in the development of low-level mesocyclones and isolated tornadoes. Forecast hodographs show effective helicity values of 300-400 m2/s2 and sufficient deep layer shear to maintain supercell characteristics. Otherwise, hail and gusty winds will be possible in the strongest cells. This activity should persist into the early evening - moving across parts of southern MN and into western WI. ...Eastern SD... Widespread cloud cover is present this morning over eastern SD. This should limit the risk of strong convection through much of the day. However, the combination of a midlevel dry slot and the approach of the surface low may result in a few thunderstorms developing late this afternoon over northeast SD. The strongest of these cells could produce gusty winds. ..Hart/Wendt.. 09/09/2019 Read more

SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1113 AM CDT Mon Sep 09 2019 Valid 091630Z - 101200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PORTIONS OF NORTHERN IOWA...SOUTHERN MINNESOTA...AND WESTERN WISCONSIN... ...SUMMARY... Severe thunderstorms are possible this afternoon and evening over parts of the Upper Midwest and upper Mississippi Valley regions. ...IA/MN/WI... A series of shortwave troughs are rotating across the central/northern Plains today. Forcing for ascent is evident in water vapor imagery ahead of these features, moving into eastern SD/NE and much of MN/IA. Meanwhile at the surface, a warm front extends from southeast SD across central IA. This boundary will lift slowly northward through the afternoon. Forecast soundings suggest that continued slow heating along/south of the warm front will sufficiently weaken the capping inversion, leading to scattered thunderstorms by late afternoon over western IA. These storms will track into the frontal zone, where backed low-level winds and enhanced vorticity may aid in the development of low-level mesocyclones and isolated tornadoes. Forecast hodographs show effective helicity values of 300-400 m2/s2 and sufficient deep layer shear to maintain supercell characteristics. Otherwise, hail and gusty winds will be possible in the strongest cells. This activity should persist into the early evening - moving across parts of southern MN and into western WI. ...Eastern SD... Widespread cloud cover is present this morning over eastern SD. This should limit the risk of strong convection through much of the day. However, the combination of a midlevel dry slot and the approach of the surface low may result in a few thunderstorms developing late this afternoon over northeast SD. The strongest of these cells could produce gusty winds. ..Hart/Wendt.. 09/09/2019 Read more

SPC Day 1 Fire Weather Outlook
Day 1 Fire Weather Outlook NWS Storm Prediction Center Norman OK 1107 AM CDT Mon Sep 09 2019 Valid 091700Z - 101200Z ...CRITICAL FIRE WEATHER AREA FOR PORTIONS OF SOUTHERN NEVADA... Added a small critical area in southeastern Nevada for this update, where latest guidance is more in agreement with sub-15% RH values for a few hours this afternoon amidst surface winds of around 20 mph. Fuels are also dry in this region, further supporting the ongoing fire weather risk areas. Sundowner winds are also expected to continue across portions of southern California tonight, with gusts potentially exceeding 40 mph in a few areas. See the previous outlook below for additional information. ..Cook.. 09/09/2019 .PREV DISCUSSION... /ISSUED 0132 AM CDT Mon Sep 09 2019/ ...Synopsis... A broad area of cyclonic flow -- attendant to a deepening mid/upper-level longwave trough -- is forecast to remain over the western CONUS through today. As this occurs, an area of enhanced mid-level flow near the base of the trough is forecast to strengthen while overspreading portions of southern California, the Southwest, and the southern Great Basin. ...Nevada/Utah/Arizona... Efficient vertical mixing of the aforementioned enhanced mid-level flow should allow for several hours of sustained surface winds of 15-20 mph (locally greater) this afternoon. Elevated to locally critical fire weather conditions are likely as these winds overlap near-critical RH values (e.g., around 15%) and receptive fuels. Currently, the expected brief/spotty nature of critical fire weather conditions precludes upgrading to a critical fire weather area. Locally elevated fire weather conditions are also possible in the lee of the Sierra Mountains over portions of western Inyo County in California, where several fires -- including the Taboose fire -- are ongoing. However, the limited coverage of elevated fire weather conditions precludes expanding the current area farther west. ...Southern California: Santa Barbara and Ventura Counties... Locally elevated fire weather conditions may be ongoing at higher elevations (e.g., > 1 kft) of eastern Santa Barbara and western Ventura Counties this morning due to poor overnight RH recoveries and lingering gusty Sundowner winds. While surface winds are forecast to become less gusty during the late morning, elevated fire weather conditions are expected to redevelop by afternoon as surface winds increase. Elevated fire weather conditions may persist through tonight due to poor overnight RH recoveries and gusty winds. ...Please see www.spc.noaa.gov/fire for graphic product... Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0800 AM CDT Mon Sep 09 2019 Valid 091300Z - 101200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PARTS OF THE UPPER MIDWEST AND UPPER MISSISSIPPI VALLEY REGIONS... ...SUMMARY... Severe thunderstorms appear most probable this afternoon and evening over parts of the Upper Midwest and upper Mississippi Valley regions. ...Synopsis... In mid/upper levels, the CONUS subset of the longwave pattern will amplify as mean troughing becomes more prominent in the West, anchored by a slow-moving synoptic cyclone over the Pacific Northwest. That feature, in turn, will remain part of a Rex block, with the anticyclonic member located over northwestern Canada. Meanwhile, a separate regime of ridging will amplify across the mid/upper Mississippi Valley and upper Great Lakes regions. In between, a leading shortwave trough -- with several embedded or closely associated vorticity maxima -- is evident in moisture- channel imagery from north-central MT across eastern WY to central CO. This perturbation should pivot northeastward, with the basal vorticity lobe(s) ejecting across the central Dakotas around 00Z and reaching that part of ON near the MN border by 12Z. A low-amplitude shortwave trough -- initially located over portions of Lake Erie and OH -- will move southeastward across portions of PA, WV and MD, reaching NJ and the Delmarva Peninsula around 00Z, before moving offshore. At the surface, 11Z analysis showed a wavy/quasistationary frontal zone from southeastern VA across central NC, central GA, and northeastern MS, becoming a diffuse, weakening warm-frontal segment across northwestern AR and central KS. A warm front was drawn from northern NE across portions of IA to western IL. As a broad/weak area of low pressure shifts eastward across SD today, ahead of the shortwave trough aloft, the warm front will move northeastward across the upper Mississippi Valley region, modulated on the mesoscale by areas of baroclinicity related to clouds and precip. Meanwhile, the frontal segment across VA and NC may buckle northward across northern NC and southern VA some more, but on broader scales will exhibit little net movement. ...Upper Midwest and upper Mississippi Valley regions... Isolated to scattered thunderstorms, in episodic fashion, are possible across a broad area from eastern SD and eastern NE across the upper Mississippi Valley this afternoon through tonight. The more sustained/organized among this convection will pose a risk of large hail and severe gusts, and a few tornadoes cannot be ruled out. Considerable uncertainties linger from the prior outlook cycle regarding both strength of destabilization south of the warm front (with considerable antecedent cloud cover), and timing and density of convection in the region near the warm front. Still, potential does appear lower across central SD and greater over parts of IA/MN. Low-level shear will be favorable near the surface warm front, where backed near-surface winds enlarge low-level hodographs beneath a southwesterly LLJ that will strengthen and shift eastward through the evening. Conditionally, the kinematic profile within and proximally south of the warm-frontal zone (over portions of IA and southern MN) will become favorable for supercells and at least a slight tornado risk, in addition to associated wind and hail. Forecast soundings suggest effective SRH 240-400 J/kg and MLCAPE 1500-2500 J/kg available to any relatively sustained convection moving into this region, as forecast by a few CAMS and in a more smudged/generic sense by a couple synoptic models. ...Central Plains... Isolated to scattered thunderstorms should develop late this afternoon and early evening in a swath extending southwestward from the main outlook area across eastern NE and northern/western KS, near a moisture/buoyancy axis. Well-mixed subcloud layers will support gust potential, and isolated severe hail also may occur. Forecast soundings suggest that strong surface heating will occur this afternoon behind the ongoing areas of clouds/precip this morning, combining with favorable boundary-layer moisture to boost MLCAPE into the 1500-2000 J/kg range (locally higher) across much of this corridor, with minimal MLCINH. Mid/upper flow and deep shear each will be weaker than in areas farther north and northeast, with effective-shear magnitudes generally remaining below 35 kt. The dominant mode should be multicellular, with discrete storms and clustering each possible. The overall severe threat should diminish late evening into the overnight hours, in the absence of mid/upper- level support and beneath confluent flow aloft, as the boundary layer nocturnally stabilizes. ...NC/VA... Widely scattered thunderstorms should develop this afternoon from the higher terrain near the Blue Ridge of western VA, southeastward across northeastern NC. This activity will form amidst a combination of diurnal surface heating and related steepening of low-level lapse rates and weakening of MLCINH, with some aid from frontal lift. Conterminous increasing of large-scale ascent/cooling aloft, ahead of the shortwave trough, also will nurture a favorable convective environment. Thunderstorms should move southeastward to east-southeastward, offering damaging gusts and isolated severe hail. Areas of ongoing convection from southern VA across extreme northeastern NC, and adjoining Atlantic waters southeast of the Hampton Roads, appear to be reinforcing the baroclinic zone across the region. The associated instability gradient will help to focus and confine the northeastern extent of substantial convective potential this afternoon, while warm-sector development also may occur amidst weak capping. Favorably rich low-level moisture (e.g., surface dewpoints upper 60s to mid 70s F and PW 1.5-2 inches) should contribute to MLCAPE ranging from around 1000-1500 J/kg near the front, where lift will be best-organized, to around 2000-3000 J/kg over eastern NC's lower elevations in the warm sector. Low-level winds will be weak. Still, over the VA part of the outlook area, backed near-surface flow and somewhat greater mid/upper winds will foster enough vertical shear to support well-organized multicells and/or transient/marginal supercell characteristics. Farther south where CAPE is larger, water-loaded downdrafts may approach severe levels. ..Edwards/Dial.. 09/09/2019 Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0800 AM CDT Mon Sep 09 2019 Valid 091300Z - 101200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PARTS OF THE UPPER MIDWEST AND UPPER MISSISSIPPI VALLEY REGIONS... ...SUMMARY... Severe thunderstorms appear most probable this afternoon and evening over parts of the Upper Midwest and upper Mississippi Valley regions. ...Synopsis... In mid/upper levels, the CONUS subset of the longwave pattern will amplify as mean troughing becomes more prominent in the West, anchored by a slow-moving synoptic cyclone over the Pacific Northwest. That feature, in turn, will remain part of a Rex block, with the anticyclonic member located over northwestern Canada. Meanwhile, a separate regime of ridging will amplify across the mid/upper Mississippi Valley and upper Great Lakes regions. In between, a leading shortwave trough -- with several embedded or closely associated vorticity maxima -- is evident in moisture- channel imagery from north-central MT across eastern WY to central CO. This perturbation should pivot northeastward, with the basal vorticity lobe(s) ejecting across the central Dakotas around 00Z and reaching that part of ON near the MN border by 12Z. A low-amplitude shortwave trough -- initially located over portions of Lake Erie and OH -- will move southeastward across portions of PA, WV and MD, reaching NJ and the Delmarva Peninsula around 00Z, before moving offshore. At the surface, 11Z analysis showed a wavy/quasistationary frontal zone from southeastern VA across central NC, central GA, and northeastern MS, becoming a diffuse, weakening warm-frontal segment across northwestern AR and central KS. A warm front was drawn from northern NE across portions of IA to western IL. As a broad/weak area of low pressure shifts eastward across SD today, ahead of the shortwave trough aloft, the warm front will move northeastward across the upper Mississippi Valley region, modulated on the mesoscale by areas of baroclinicity related to clouds and precip. Meanwhile, the frontal segment across VA and NC may buckle northward across northern NC and southern VA some more, but on broader scales will exhibit little net movement. ...Upper Midwest and upper Mississippi Valley regions... Isolated to scattered thunderstorms, in episodic fashion, are possible across a broad area from eastern SD and eastern NE across the upper Mississippi Valley this afternoon through tonight. The more sustained/organized among this convection will pose a risk of large hail and severe gusts, and a few tornadoes cannot be ruled out. Considerable uncertainties linger from the prior outlook cycle regarding both strength of destabilization south of the warm front (with considerable antecedent cloud cover), and timing and density of convection in the region near the warm front. Still, potential does appear lower across central SD and greater over parts of IA/MN. Low-level shear will be favorable near the surface warm front, where backed near-surface winds enlarge low-level hodographs beneath a southwesterly LLJ that will strengthen and shift eastward through the evening. Conditionally, the kinematic profile within and proximally south of the warm-frontal zone (over portions of IA and southern MN) will become favorable for supercells and at least a slight tornado risk, in addition to associated wind and hail. Forecast soundings suggest effective SRH 240-400 J/kg and MLCAPE 1500-2500 J/kg available to any relatively sustained convection moving into this region, as forecast by a few CAMS and in a more smudged/generic sense by a couple synoptic models. ...Central Plains... Isolated to scattered thunderstorms should develop late this afternoon and early evening in a swath extending southwestward from the main outlook area across eastern NE and northern/western KS, near a moisture/buoyancy axis. Well-mixed subcloud layers will support gust potential, and isolated severe hail also may occur. Forecast soundings suggest that strong surface heating will occur this afternoon behind the ongoing areas of clouds/precip this morning, combining with favorable boundary-layer moisture to boost MLCAPE into the 1500-2000 J/kg range (locally higher) across much of this corridor, with minimal MLCINH. Mid/upper flow and deep shear each will be weaker than in areas farther north and northeast, with effective-shear magnitudes generally remaining below 35 kt. The dominant mode should be multicellular, with discrete storms and clustering each possible. The overall severe threat should diminish late evening into the overnight hours, in the absence of mid/upper- level support and beneath confluent flow aloft, as the boundary layer nocturnally stabilizes. ...NC/VA... Widely scattered thunderstorms should develop this afternoon from the higher terrain near the Blue Ridge of western VA, southeastward across northeastern NC. This activity will form amidst a combination of diurnal surface heating and related steepening of low-level lapse rates and weakening of MLCINH, with some aid from frontal lift. Conterminous increasing of large-scale ascent/cooling aloft, ahead of the shortwave trough, also will nurture a favorable convective environment. Thunderstorms should move southeastward to east-southeastward, offering damaging gusts and isolated severe hail. Areas of ongoing convection from southern VA across extreme northeastern NC, and adjoining Atlantic waters southeast of the Hampton Roads, appear to be reinforcing the baroclinic zone across the region. The associated instability gradient will help to focus and confine the northeastern extent of substantial convective potential this afternoon, while warm-sector development also may occur amidst weak capping. Favorably rich low-level moisture (e.g., surface dewpoints upper 60s to mid 70s F and PW 1.5-2 inches) should contribute to MLCAPE ranging from around 1000-1500 J/kg near the front, where lift will be best-organized, to around 2000-3000 J/kg over eastern NC's lower elevations in the warm sector. Low-level winds will be weak. Still, over the VA part of the outlook area, backed near-surface flow and somewhat greater mid/upper winds will foster enough vertical shear to support well-organized multicells and/or transient/marginal supercell characteristics. Farther south where CAPE is larger, water-loaded downdrafts may approach severe levels. ..Edwards/Dial.. 09/09/2019 Read more

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0354 AM CDT Mon Sep 09 2019 Valid 121200Z - 171200Z ...DISCUSSION... ...Thursday/Day 4 and Friday/Day 5... The medium-range models move an upper-level trough across the Great Plains on Thursday as a cold front advances quickly eastward through the north-central states. Model consensus places the cold front on Thursday afternoon from western Minnesota southward into western Iowa and far northwest Missouri. A moist and unstable airmass is forecast ahead of the front in the mid to upper Mississippi Valley where deep-layer shear is forecast to be strong enough for organized severe thunderstorms. Although the models are in good agreement concerning the timing of the front, will wait for run-to-run consistency before adding a threat area. For Friday, the models move the upper-level trough eastward into the Great Lakes as a cold front advances into the lower Great Lakes and Ohio Valley. Thunderstorms are expected to develop along the front during the day on Friday. Although an isolated severe threat will be possible, uncertainty is substantial concerning the amount of instability that will develop ahead of the front. ...Saturday/Day 6 to Monday/Day 8... From Saturday into Sunday, model solutions diverge sharply. The GFS develops an upper-level trough across the north-central U.S. while the ECMWF and Canadian have an upper-level ridge in the same area. Large differences also exist for the surface pattern. For this reason, uncertainty is substantial on Saturday and Sunday concerning where thunderstorm development will occur. This uncertainty continues into Monday as large spreads continue among the model solutions. Read more

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0354 AM CDT Mon Sep 09 2019 Valid 121200Z - 171200Z ...DISCUSSION... ...Thursday/Day 4 and Friday/Day 5... The medium-range models move an upper-level trough across the Great Plains on Thursday as a cold front advances quickly eastward through the north-central states. Model consensus places the cold front on Thursday afternoon from western Minnesota southward into western Iowa and far northwest Missouri. A moist and unstable airmass is forecast ahead of the front in the mid to upper Mississippi Valley where deep-layer shear is forecast to be strong enough for organized severe thunderstorms. Although the models are in good agreement concerning the timing of the front, will wait for run-to-run consistency before adding a threat area. For Friday, the models move the upper-level trough eastward into the Great Lakes as a cold front advances into the lower Great Lakes and Ohio Valley. Thunderstorms are expected to develop along the front during the day on Friday. Although an isolated severe threat will be possible, uncertainty is substantial concerning the amount of instability that will develop ahead of the front. ...Saturday/Day 6 to Monday/Day 8... From Saturday into Sunday, model solutions diverge sharply. The GFS develops an upper-level trough across the north-central U.S. while the ECMWF and Canadian have an upper-level ridge in the same area. Large differences also exist for the surface pattern. For this reason, uncertainty is substantial on Saturday and Sunday concerning where thunderstorm development will occur. This uncertainty continues into Monday as large spreads continue among the model solutions. Read more

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0354 AM CDT Mon Sep 09 2019 Valid 121200Z - 171200Z ...DISCUSSION... ...Thursday/Day 4 and Friday/Day 5... The medium-range models move an upper-level trough across the Great Plains on Thursday as a cold front advances quickly eastward through the north-central states. Model consensus places the cold front on Thursday afternoon from western Minnesota southward into western Iowa and far northwest Missouri. A moist and unstable airmass is forecast ahead of the front in the mid to upper Mississippi Valley where deep-layer shear is forecast to be strong enough for organized severe thunderstorms. Although the models are in good agreement concerning the timing of the front, will wait for run-to-run consistency before adding a threat area. For Friday, the models move the upper-level trough eastward into the Great Lakes as a cold front advances into the lower Great Lakes and Ohio Valley. Thunderstorms are expected to develop along the front during the day on Friday. Although an isolated severe threat will be possible, uncertainty is substantial concerning the amount of instability that will develop ahead of the front. ...Saturday/Day 6 to Monday/Day 8... From Saturday into Sunday, model solutions diverge sharply. The GFS develops an upper-level trough across the north-central U.S. while the ECMWF and Canadian have an upper-level ridge in the same area. Large differences also exist for the surface pattern. For this reason, uncertainty is substantial on Saturday and Sunday concerning where thunderstorm development will occur. This uncertainty continues into Monday as large spreads continue among the model solutions. Read more

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0354 AM CDT Mon Sep 09 2019 Valid 121200Z - 171200Z ...DISCUSSION... ...Thursday/Day 4 and Friday/Day 5... The medium-range models move an upper-level trough across the Great Plains on Thursday as a cold front advances quickly eastward through the north-central states. Model consensus places the cold front on Thursday afternoon from western Minnesota southward into western Iowa and far northwest Missouri. A moist and unstable airmass is forecast ahead of the front in the mid to upper Mississippi Valley where deep-layer shear is forecast to be strong enough for organized severe thunderstorms. Although the models are in good agreement concerning the timing of the front, will wait for run-to-run consistency before adding a threat area. For Friday, the models move the upper-level trough eastward into the Great Lakes as a cold front advances into the lower Great Lakes and Ohio Valley. Thunderstorms are expected to develop along the front during the day on Friday. Although an isolated severe threat will be possible, uncertainty is substantial concerning the amount of instability that will develop ahead of the front. ...Saturday/Day 6 to Monday/Day 8... From Saturday into Sunday, model solutions diverge sharply. The GFS develops an upper-level trough across the north-central U.S. while the ECMWF and Canadian have an upper-level ridge in the same area. Large differences also exist for the surface pattern. For this reason, uncertainty is substantial on Saturday and Sunday concerning where thunderstorm development will occur. This uncertainty continues into Monday as large spreads continue among the model solutions. Read more

SPC 0730Z Day 3 Outlook
Day 3 Convective Outlook RESENT 1 NWS Storm Prediction Center Norman OK 0302 AM CDT Mon Sep 09 2019 Valid 111200Z - 121200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE CENTRAL AND NORTHERN PLAINS INTO THE UPPER MISSISSIPPI VALLEY... ...SUMMARY... Thunderstorms associated with large hail and damaging wind gusts 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... A shortwave ridge is forecast to move northeastward into the Upper Mississippi Valley on Wednesday as an upper-level trough moves across the Intermountain West. Southwest mid-level flow will be in place across the central and northern Plains as a surface low moves eastward into the central High Plains. A well-defined warm front is forecast to extend eastward from the surface low from southern South Dakota into far northern Iowa. Surface dewpoints south of the front should be in the upper 60s to near 70 F, aiding the development of an east to west axis of moderate instability by afternoon. The latest model runs continue to develop elevated convection during the day to the north of the warm front and have the strongest instability further to the west in southeastern South Dakota. The current thinking is that surface-based thunderstorms will develop in the late afternoon on the western edge of this pocket of strong instability from south-central South Dakota into north-central Nebraska. This convection should spread east-northeastward across southeastern South Dakota from late afternoon to mid evening. NAM and GFS forecast soundings to the west of Sioux Falls for early Wednesday evening continue to show a favorable environment for severe storms with strong instability, moderate deep-layer shear and steep mid-level lapse rates. This environment should support supercells with large hail. Wind damage may also occur especially if an MCS can develop during the evening as the GFS and ECMWF suggest. Although a capping inversion will limit convective development across the mid Missouri Valley, confidence is higher that a cluster of strong to severe thunderstorms will develop in southeastern South Dakota. For this reason, a 15 percent contour has been continued in that area for this outlook. ..Broyles.. 09/09/2019 Read more

SPC 0730Z Day 3 Outlook
Day 3 Convective Outlook RESENT 1 NWS Storm Prediction Center Norman OK 0302 AM CDT Mon Sep 09 2019 Valid 111200Z - 121200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE CENTRAL AND NORTHERN PLAINS INTO THE UPPER MISSISSIPPI VALLEY... ...SUMMARY... Thunderstorms associated with large hail and damaging wind gusts 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... A shortwave ridge is forecast to move northeastward into the Upper Mississippi Valley on Wednesday as an upper-level trough moves across the Intermountain West. Southwest mid-level flow will be in place across the central and northern Plains as a surface low moves eastward into the central High Plains. A well-defined warm front is forecast to extend eastward from the surface low from southern South Dakota into far northern Iowa. Surface dewpoints south of the front should be in the upper 60s to near 70 F, aiding the development of an east to west axis of moderate instability by afternoon. The latest model runs continue to develop elevated convection during the day to the north of the warm front and have the strongest instability further to the west in southeastern South Dakota. The current thinking is that surface-based thunderstorms will develop in the late afternoon on the western edge of this pocket of strong instability from south-central South Dakota into north-central Nebraska. This convection should spread east-northeastward across southeastern South Dakota from late afternoon to mid evening. NAM and GFS forecast soundings to the west of Sioux Falls for early Wednesday evening continue to show a favorable environment for severe storms with strong instability, moderate deep-layer shear and steep mid-level lapse rates. This environment should support supercells with large hail. Wind damage may also occur especially if an MCS can develop during the evening as the GFS and ECMWF suggest. Although a capping inversion will limit convective development across the mid Missouri Valley, confidence is higher that a cluster of strong to severe thunderstorms will develop in southeastern South Dakota. For this reason, a 15 percent contour has been continued in that area for this outlook. ..Broyles.. 09/09/2019 Read more

SPC 0730Z Day 3 Outlook
Day 3 Convective Outlook RESENT 1 NWS Storm Prediction Center Norman OK 0302 AM CDT Mon Sep 09 2019 Valid 111200Z - 121200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE CENTRAL AND NORTHERN PLAINS INTO THE UPPER MISSISSIPPI VALLEY... ...SUMMARY... Thunderstorms associated with large hail and damaging wind gusts 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... A shortwave ridge is forecast to move northeastward into the Upper Mississippi Valley on Wednesday as an upper-level trough moves across the Intermountain West. Southwest mid-level flow will be in place across the central and northern Plains as a surface low moves eastward into the central High Plains. A well-defined warm front is forecast to extend eastward from the surface low from southern South Dakota into far northern Iowa. Surface dewpoints south of the front should be in the upper 60s to near 70 F, aiding the development of an east to west axis of moderate instability by afternoon. The latest model runs continue to develop elevated convection during the day to the north of the warm front and have the strongest instability further to the west in southeastern South Dakota. The current thinking is that surface-based thunderstorms will develop in the late afternoon on the western edge of this pocket of strong instability from south-central South Dakota into north-central Nebraska. This convection should spread east-northeastward across southeastern South Dakota from late afternoon to mid evening. NAM and GFS forecast soundings to the west of Sioux Falls for early Wednesday evening continue to show a favorable environment for severe storms with strong instability, moderate deep-layer shear and steep mid-level lapse rates. This environment should support supercells with large hail. Wind damage may also occur especially if an MCS can develop during the evening as the GFS and ECMWF suggest. Although a capping inversion will limit convective development across the mid Missouri Valley, confidence is higher that a cluster of strong to severe thunderstorms will develop in southeastern South Dakota. For this reason, a 15 percent contour has been continued in that area for this outlook. ..Broyles.. 09/09/2019 Read more