WW 0650 Status Updates
STATUS REPORT ON WW 650 SEVERE WEATHER THREAT CONTINUES RIGHT OF A LINE FROM 25 NE TOR TO 35 SW 2WX. ..THORNTON..08/26/24 ATTN...WFO...BYZ...CYS...LBF...UNR...FSD... STATUS REPORT FOR WS 650 SEVERE WEATHER THREAT CONTINUES FOR THE FOLLOWING AREAS MTC011-262240- MT . MONTANA COUNTIES INCLUDED ARE CARTER NEC013-015-017-031-045-089-103-149-161-165-262240- NE . NEBRASKA COUNTIES INCLUDED ARE BOX BUTTE BOYD BROWN CHERRY DAWES HOLT KEYA PAHA ROCK SHERIDAN SIOUX SDC007-019-023-033-047-053-055-071-081-093-095-102-103-121-123- 262240- SD . SOUTH DAKOTA COUNTIES INCLUDED ARE Read more

WW 650 SEVERE TSTM MT NE SD WY 262010Z - 270400Z
URGENT - IMMEDIATE BROADCAST REQUESTED Severe Thunderstorm Watch Number 650 NWS Storm Prediction Center Norman OK 210 PM MDT Mon Aug 26 2024 The NWS Storm Prediction Center has issued a * Severe Thunderstorm Watch for portions of Far Southeast Montana Northern Nebraska Western and Southern South Dakota Northeast Wyoming * Effective this Monday afternoon and evening from 210 PM until 1000 PM MDT. * Primary threats include... Scattered damaging winds and isolated significant gusts to 80 mph likely Scattered large hail and isolated very large hail events to 2.5 inches in diameter likely A tornado or two possible SUMMARY...Strong to severe thunderstorms including supercells will continue to develop this afternoon across northeast Wyoming/far southeast Montana into western South Dakota, with additional and more isolated development possible along the South Dakota/Nebraska border vicinity. Clusters of eastward-moving storms should evolve by evening, potentially as a severe-wind producing linear convective system that should move across southern South Dakota and northern Nebraska. The severe thunderstorm watch area is approximately along and 80 statute miles north and south of a line from 90 miles west of Rapid City SD to 50 miles north northeast of Oneill NE. For a complete depiction of the watch see the associated watch outline update (WOUS64 KWNS WOU0). PRECAUTIONARY/PREPAREDNESS ACTIONS... REMEMBER...A Severe Thunderstorm Watch means conditions are favorable for 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. Severe thunderstorms can and occasionally do produce tornadoes. && OTHER WATCH INFORMATION...CONTINUE...WW 648...WW 649... AVIATION...A few severe thunderstorms with hail surface and aloft to 2.5 inches. Extreme turbulence and surface wind gusts to 70 knots. A few cumulonimbi with maximum tops to 500. Mean storm motion vector 25030. ...Guyer Read more

SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0258 PM CDT Mon Aug 26 2024 Valid 262000Z - 271200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS THE NORTH-CENTRAL PLAINS AND UPPER MIDWEST... ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS SOUTHERN NEW ENGLAND... ...SUMMARY... Severe thunderstorm wind gusts, large to very large hail and a couple of tornadoes are possible this afternoon through tonight especially across parts of South Dakota, northern Nebraska, central/southern Minnesota, and into Wisconsin. ...20z Update... The primary change with this outlook update was to expand the Marginal Risk southward across Virginia to account for ongoing convection that will track southward with potential risk for damaging wind. Instability will gradually weaken, however modest shear for organization may sustain this threat further south than previously forecast. The previous forecast remains on track with no changes needed based on recent observations and trends in guidance for the Enhanced Risk across the north-central Plains to Upper Midwest. A few initial supercells have developed across Minnesota. See MCD#2000 for more information. Further west across WY/SD, severe threat along the primary cold front continues with potential for enhancement of the earlier MCS moving eastward out of Wyoming. See MCD#1999 for more details on evolution of this severe threat. ..Thornton/Guyer.. 08/26/2024 .PREV DISCUSSION... /ISSUED 1141 AM CDT Mon Aug 26 2024/ ...North-central Plains to Upper Midwest... A relatively active severe-weather day is expected regionally, especially late this afternoon through tonight, with multiple rounds of severe storms possible potentially including eastern South Dakota and parts of central/southern Minnesota into far western Wisconsin. Strong to locally severe storms have already occurred this morning across interior Wyoming, in relatively close proximity to the northeastward-ejecting shortwave trough that will cross the northern High Plains toward the Dakotas through tonight. This convection is thought to be harbinger of a broader/increasing severe risk that should develop this afternoon from far northeast/east-central Wyoming into southwest South Dakota including the Black Hills/Pine Ridge vicinities. Some initial supercells capable of large hail will be possible, but these storms should organize into an MCS and expand/intensify as activity proceeds into greater moisture, instability and post-frontal low-level flow to the east. These storms could persist eastward this evening across southern South Dakota/far northern Nebraska, and all the way into southern Minnesota/far northern Iowa overnight through the predawn hours. Another area of potential severe thunderstorm development including supercells will be across eastern South Dakota east-northeastward into central Minnesota early as mid/late afternoon near the front, where a very moist (middle to upper 70s F surface dewpoints) and very unstable (4000+ J/kg MLCAPE) air mass will reside. This could somewhat relate to ongoing thunderstorms across central South Dakota at late morning, or perhaps more likely, ahead of it into central Minnesota. While potentially intense severe storms/supercells are plausible, some uncertainty exists regarding the diurnal extent of deep convective development given the likelihood of residual mid-level capping. Even if diurnally related development through peak heating is more limited, severe-weather potential should steadily increase from west-to-east across east/southeast South Dakota, southern Minnesota/northern Iowa into western Wisconsin tonight via likely upstream MCS development. ...Northeast States/Mid-Atlantic... A belt of generally strengthening northerly flow aloft, along with modestly cool mid-level temperatures, will reside across the region on the western periphery on offshore-shifting upper-level trough. Coincident with low/some middle 60s F surface dewpoints, moderate destabilization (1000-1500 J/kg MLCAPE) is expected this afternoon across southern New England/eastern New York southwestward toward the Delmarva/coastal Mid-Atlantic. Multiple corridors of at least widely scattered south/southeastward-moving storms should evolve this afternoon, including southern New England/southeast New York as well as the Pennsylvania/Maryland/Virginia border vicinity. Isolated severe wind and hail will be possible this afternoon through early/mid-evening. For additional short-term information, see Mesoscale Discussion 1995. Read more

SPC 1930Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0228 PM CDT Mon Aug 26 2024 Valid 281200Z - 291200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE MID-ATLANTIC TO THE MIDWEST...AND OVER THE NORTHERN PLAINS... ...SUMMARY... Severe storms are expected across portions of the Midwest and Northeast/Mid-Atlantic area, and over portions of the northern Plains. ...Synopsis... A positive-tilt upper trough will move east across southern Quebec Province and northern New England Wednesday, as a surface front moves south and extends from southern New England west into the mid-Mississippi Valley by Wednesday afternoon. Farther west, an upstream cold front, associated with a strong upper low along the international border/MT, will move east across the northern High Plains and western Dakotas. ...Midwest to southern New England, and south across the central Appalachians and into the Mid-Atlantic... A very moist air mass is expected to be in place along and south of the front Wednesday afternoon, contributing to moderate/strong afternoon surface-based instability across the Midwest/OH Valley, and moderate instability farther east. Frontal position remains somewhat uncertain due, in part, to possible influence of early day storms, but the current risk areas remain well aligned with the greatest severe potential. Thunderstorms should develop or re-intensify during the afternoon along and south of the front and pose a risk for damaging gusts. The greater severe hail potential should exist across western portions of the risk areas where MLCAPE may exceed 3000 J/kg. Storms should evolve into east/southeast-moving clusters and continue into the evening. ...Northern Plains... Low-level moisture will increase ahead of the cold front during the day, with a corridor of 60s dew points beneath steepening mid-level lapse rates contributing to moderate instability. Strengthening low-level warm advection and ascent with the approaching upper low should result in a favorable environment for thunderstorms to develop near the front, and within the warm advection zone. Deep-layer shear will become supportive of severe storms capable of severe hail and damaging wind gusts during the evening and overnight hours. ..Bunting.. 08/26/2024 Read more

SPC Day 2 Fire Weather Outlook
Day 2 Fire Weather Outlook NWS Storm Prediction Center Norman OK 0158 PM CDT Mon Aug 26 2024 Valid 271200Z - 281200Z Along the southeastern periphery of the midlevel trough (described below) and related southwesterly jet, 15-20 mph sustained south-southwesterly surface winds amid 15-20 percent RH is expected over the higher terrain from southwest MT into east-central ID. While this may promote locally elevated fire-weather conditions during the afternoon/early evening, the threat appears too localized/marginal for highlights -- especially given modestly receptive fuels. Elsewhere, the previous forecast (see below) remains on track. ..Weinman.. 08/26/2024 .PREV DISCUSSION... /ISSUED 0140 AM CDT Mon Aug 26 2024/ ...Synopsis... A mid-level trough will amplify and traverse the northern Rockies tomorrow (Tuesday), encouraging strong surface gradient winds over the Pacific Northwest in response to a deepening surface lee trough. Dry and windy conditions are likely along and to the lee of the Cascades, where fuels are at least modestly receptive to wildfire spread. Here, 15-25 mph sustained westerly surface winds may overlap with dry fuels and 15-25 percent RH for at least a few hours. As such, Elevated highlights have been added to address the regionally favorable wildfire-spread threat. ...Please see www.spc.noaa.gov/fire for graphic product... Read more

MD 1996 CONCERNING SEVERE POTENTIAL...WATCH LIKELY FOR NORTHEAST WY...SOUTHEAST MT...WESTERN SD...AND WESTERN NE
Mesoscale Discussion 1996 NWS Storm Prediction Center Norman OK 1215 PM CDT Mon Aug 26 2024 Areas affected...northeast WY...southeast MT...western SD...and western NE Concerning...Severe potential...Watch likely Valid 261715Z - 261915Z Probability of Watch Issuance...95 percent SUMMARY...Severe thunderstorm potential will increase over the next few hours across eastern Wyoming into far southeast Montana, western South Dakota and western Nebraska. Large hail and severe wind gusts possible with this activity. A severe thunderstorm watch will likely be needed for portions of the region in the next couple of hours. DISCUSSION...A strong mid/upper trough will continue to eject east/northeast across WY/MT this afternoon, providing ample large-scale ascent for thunderstorm development. Boundary-layer moisture will remain modest, but cool temperatures aloft/steep lapse rates will foster MLCAPE from 1000-2000 J/kg. Effective shear greater than 40 kt will favor organized updrafts, with a mix of supercells and line segments possible. Elongated/straight hodographs combined with a favorable thermodynamic and kinematic environment will support large hail, with some potential for isolated hail stones in the 2-3 inch diameter range in the strongest cells. Additional heating will result in steepening low-level lapse rates, enhancing severe gust potential, particularly across parts of eastern WY into far southwest SD and northwest NE, where a few gusts greater than 70 mph are possible. Some uncertainty exists on the north/east extent of severe potential as morning convection across central SD has left lingering cloud cover while reinforcing a more southward position of a surface baroclinic zone near the SD/NE border. Nevertheless, a severe thunderstorm watch will likely be needed for portions of the MCD area within the next couple of hours. ..Leitman/Guyer.. 08/26/2024 ...Please see www.spc.noaa.gov for graphic product... ATTN...WFO...LBF...UNR...CYS...BYZ...RIW... LAT...LON 44420658 45310621 45620539 45600423 45250310 44400151 43620098 42350143 41960182 41650245 41570361 41790478 42240588 43870665 44420658 Read more

MD 1997 CONCERNING SEVERE POTENTIAL...WATCH POSSIBLE FOR PORTIONS OF CENTRAL MINNESOTA
Mesoscale Discussion 1997 NWS Storm Prediction Center Norman OK 1235 PM CDT Mon Aug 26 2024 Areas affected...Portions of central Minnesota Concerning...Severe potential...Watch possible Valid 261735Z - 261900Z Probability of Watch Issuance...40 percent SUMMARY...Initial storm development in central Minnesota may be elevated to marginally surface based and struggle against residual capping. Should storms mature, large hail and wind damage are possible. A watch is possible, but this will depend on trends in convective evolution. DISCUSSION...Convection has developed in west-central Minnesota, likely aided by weak warm advection at lower levels. This mornings soundings from Aberdeen/Minneapolis showed a warm nose within the 850-700 mb layer. It appears that convection is struggling to intensify/organize with this capping in place. Furthermore, large-scale ascent is currently weak. Should this activity mature, large hail and isolated wind damage would be possible. Short-term guidance is not consistent in how this activity will evolve, with some suggesting it will weaken in the next few hours and others showing cold pool development that spurs new convection farther south where greater buoyancy resides. From a large-scale perspective, greater ascent/mid-level cooling is not expected until later in the afternoon, though an MCV moving through eastern South Dakota could potentially supplement ascent locally earlier. The most probable scenario is that more robust convection will develop by mid/late afternoon near an area of surface convergence in central Minnesota. The need for a watch in the short term is uncertain; however, trends will continue to be closely monitored this afternoon. ..Wendt/Guyer.. 08/26/2024 ...Please see www.spc.noaa.gov for graphic product... ATTN...WFO...DLH...MPX...FGF...ABR... LAT...LON 45449550 45369626 45559646 46069663 46529636 47109448 46939347 46459331 45849401 45449550 Read more

MD 1998 CONCERNING SEVERE THUNDERSTORM WATCH 648... FOR PORTIONS OF SOUTHERN NEW ENGLAND
Mesoscale Discussion 1998 NWS Storm Prediction Center Norman OK 0126 PM CDT Mon Aug 26 2024 Areas affected...Portions of southern New England Concerning...Severe Thunderstorm Watch 648... Valid 261826Z - 262030Z The severe weather threat for Severe Thunderstorm Watch 648 continues. SUMMARY...Large hail and isolated wind damage will remain possible until storms move offshore. Should additional storms develop to the north, the severe risk will likely be more marginal. DISCUSSION...Scattered storms continue across parts of southern New England. Thus far, 1-1.5 inch hail has been the primary observed hazard over the past 90 minutes. The environment will remain supportive of large hail and isolated wind damage before storms move offshore within the next few hours. Given the position of the greatest mid-level ascent on water vapor imagery, additional development to the north of the current activity will likely be more isolated in nature. With shear and buoyancy weaker with northern extent, the severe threat should remain more marginal. ..Wendt.. 08/26/2024 ...Please see www.spc.noaa.gov for graphic product... ATTN...WFO...GYX...BOX...OKX...ALY... LAT...LON 42347325 42927289 42817232 42307167 41827085 41616978 41426943 41226949 41147021 40877203 40737280 40867308 42347325 Read more

WW 0648 Status Updates
STATUS REPORT ON WW 648 THE SEVERE WEATHER THREAT CONTINUES ACROSS THE ENTIRE WATCH AREA. FOR ADDITIONAL INFORMATION SEE MESOSCALE DISCUSSION 1998 ..WENDT..08/26/24 ATTN...WFO...OKX...BOX...ALY...GYX... STATUS REPORT FOR WS 648 SEVERE WEATHER THREAT CONTINUES FOR THE FOLLOWING AREAS CTC001-003-005-007-009-011-013-015-261940- CT . CONNECTICUT COUNTIES INCLUDED ARE FAIRFIELD HARTFORD LITCHFIELD MIDDLESEX NEW HAVEN NEW LONDON TOLLAND WINDHAM MAC001-003-005-007-009-011-013-015-017-019-021-023-025-027- 261940- MA . MASSACHUSETTS COUNTIES INCLUDED ARE BARNSTABLE BERKSHIRE BRISTOL DUKES ESSEX FRANKLIN HAMPDEN HAMPSHIRE MIDDLESEX NANTUCKET NORFOLK PLYMOUTH SUFFOLK WORCESTER NHC005-011-013-015-261940- Read more

SPC 1730Z Day 2 Outlook
Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1230 PM CDT Mon Aug 26 2024 Valid 271200Z - 281200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER MUCH OF THE GREAT LAKES REGION... ...SUMMARY... Severe thunderstorms will be possible on Tuesday, primarily across the Great Lakes region and portions of the Midwest. ...Synopsis... An upper-level trough will progress steadily east across the Great Lakes region on Tuesday as an associated cold front moves south across the upper Midwest and western Great Lakes. A strong upper low will move across the Pacific Northwest, while an expansive upper-level anticyclone remains centered in the vicinity of the mid-Mississippi Valley. ...Great Lakes/Upper Midwest and portions of the OH Valley/Northeast... Thunderstorms may be in progress across portions of WI/MI Upper Peninsula at 12z Tuesday, aided by low-level warm advection in advance of the upper-level trough. Substantial destabilization (MLCAPE in excess of 2000 J/kg) is expected to develop by afternoon in advance of the cold front, reinforced by convective outflows from early day storms. Although the front should move south of the stronger mid-level flow before becoming quasi-stationary, sufficient shear should be in place to support organized storms including a mix of multicell and supercell structures. Thunderstorms are expected to develop or intensify across eastern/southern WI/lower MI during the afternoon, as well as farther south along the front across IA and eventually the northeast KS vicinity. Aided by modest southwest/west mid-level flow, storms should move east and merge into one or more clusters with time posing a risk for damaging gusts as the primary severe hazard. Isolated instances of large hail will also be possible with the strongest updrafts. The potential does exist for a corridor of greater coverage of damaging winds Tuesday afternoon/evening, but uncertainty remains on the location given the effects of early storms and varied hi-res guidance solutions. This potential will be addressed in future outlooks. ..Bunting.. 08/26/2024 Read more

SPC 1730Z Day 2 Outlook
Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1230 PM CDT Mon Aug 26 2024 Valid 271200Z - 281200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER MUCH OF THE GREAT LAKES REGION... ...SUMMARY... Severe thunderstorms will be possible on Tuesday, primarily across the Great Lakes region and portions of the Midwest. ...Synopsis... An upper-level trough will progress steadily east across the Great Lakes region on Tuesday as an associated cold front moves south across the upper Midwest and western Great Lakes. A strong upper low will move across the Pacific Northwest, while an expansive upper-level anticyclone remains centered in the vicinity of the mid-Mississippi Valley. ...Great Lakes/Upper Midwest and portions of the OH Valley/Northeast... Thunderstorms may be in progress across portions of WI/MI Upper Peninsula at 12z Tuesday, aided by low-level warm advection in advance of the upper-level trough. Substantial destabilization (MLCAPE in excess of 2000 J/kg) is expected to develop by afternoon in advance of the cold front, reinforced by convective outflows from early day storms. Although the front should move south of the stronger mid-level flow before becoming quasi-stationary, sufficient shear should be in place to support organized storms including a mix of multicell and supercell structures. Thunderstorms are expected to develop or intensify across eastern/southern WI/lower MI during the afternoon, as well as farther south along the front across IA and eventually the northeast KS vicinity. Aided by modest southwest/west mid-level flow, storms should move east and merge into one or more clusters with time posing a risk for damaging gusts as the primary severe hazard. Isolated instances of large hail will also be possible with the strongest updrafts. The potential does exist for a corridor of greater coverage of damaging winds Tuesday afternoon/evening, but uncertainty remains on the location given the effects of early storms and varied hi-res guidance solutions. This potential will be addressed in future outlooks. ..Bunting.. 08/26/2024 Read more

SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1141 AM CDT Mon Aug 26 2024 Valid 261630Z - 271200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS THE NORTH-CENTRAL PLAINS AND UPPER MIDWEST... ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS SOUTHERN NEW ENGLAND... ...SUMMARY... Severe thunderstorm wind gusts, large to very large hail and a couple of tornadoes are possible this afternoon through tonight especially across parts of South Dakota, northern Nebraska, central/southern Minnesota, and into Wisconsin. ...North-central Plains to Upper Midwest... A relatively active severe-weather day is expected regionally, especially late this afternoon through tonight, with multiple rounds of severe storms possible potentially including eastern South Dakota and parts of central/southern Minnesota into far western Wisconsin. Strong to locally severe storms have already occurred this morning across interior Wyoming, in relatively close proximity to the northeastward-ejecting shortwave trough that will cross the northern High Plains toward the Dakotas through tonight. This convection is thought to be harbinger of a broader/increasing severe risk that should develop this afternoon from far northeast/east-central Wyoming into southwest South Dakota including the Black Hills/Pine Ridge vicinities. Some initial supercells capable of large hail will be possible, but these storms should organize into an MCS and expand/intensify as activity proceeds into greater moisture, instability and post-frontal low-level flow to the east. These storms could persist eastward this evening across southern South Dakota/far northern Nebraska, and all the way into southern Minnesota/far northern Iowa overnight through the predawn hours. Another area of potential severe thunderstorm development including supercells will be across eastern South Dakota east-northeastward into central Minnesota early as mid/late afternoon near the front, where a very moist (middle to upper 70s F surface dewpoints) and very unstable (4000+ J/kg MLCAPE) air mass will reside. This could somewhat relate to ongoing thunderstorms across central South Dakota at late morning, or perhaps more likely, ahead of it into central Minnesota. While potentially intense severe storms/supercells are plausible, some uncertainty exists regarding the diurnal extent of deep convective development given the likelihood of residual mid-level capping. Even if diurnally related development through peak heating is more limited, severe-weather potential should steadily increase from west-to-east across east/southeast South Dakota, southern Minnesota/northern Iowa into western Wisconsin tonight via likely upstream MCS development. ...Northeast States/Mid-Atlantic... A belt of generally strengthening northerly flow aloft, along with modestly cool mid-level temperatures, will reside across the region on the western periphery on offshore-shifting upper-level trough. Coincident with low/some middle 60s F surface dewpoints, moderate destabilization (1000-1500 J/kg MLCAPE) is expected this afternoon across southern New England/eastern New York southwestward toward the Delmarva/coastal Mid-Atlantic. Multiple corridors of at least widely scattered south/southeastward-moving storms should evolve this afternoon, including southern New England/southeast New York as well as the Pennsylvania/Maryland/Virginia border vicinity. Isolated severe wind and hail will be possible this afternoon through early/mid-evening. For additional short-term information, see Mesoscale Discussion 1995. ..Guyer/Wendt.. 08/26/2024 Read more

SPC Day 1 Fire Weather Outlook
Day 1 Fire Weather Outlook NWS Storm Prediction Center Norman OK 1142 AM CDT Mon Aug 26 2024 Valid 261700Z - 271200Z ...NO CRITICAL AREAS... The forecast remains on track. For details, see the previous discussion below. ..Weinman.. 08/26/2024 .PREV DISCUSSION... /ISSUED 0134 AM CDT Mon Aug 26 2024/ ...Synopsis... A mid-level trough traversing the northern Rockies is poised to eject into the Plains states while a second mid-level trough grazes the Pacific Northwest today. Surface high pressure will dominate the Intermountain West, while a surface lee trough will become established to the east of the Cascades. The net result will be relatively quiescent fire weather conditions across much of the western CONUS, though locally dry and windy conditions could manifest in terrain-favoring areas. ...Please see www.spc.noaa.gov/fire for graphic product... Read more

No watches are valid as of Mon Aug 26 13:48:02 UTC 2024.

No Mesoscale Discussions are in effect as of Mon Aug 26 13:48:02 UTC 2024.

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0758 AM CDT Mon Aug 26 2024 Valid 261300Z - 271200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF SOUTH DAKOTA...EXTREME NORTHERN NEBRASKA...MINNESOTA...AND WISCONSIN... ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS SURROUNDING THE ENHANCED RISK...AND ACROSS PORTIONS OF NEW ENGLAND... ...SUMMARY... Severe thunderstorm gusts, large to very large hail and a few tornadoes are possible today and tonight across parts of South Dakota, extreme northern Nebraska, Minnesota, and Wisconsin. ...Synopsis... In mid/upper levels, a persistent and large anticyclone has shifted its center across the southern Plains to the lower Missouri Valley, with ridging northeastward across the Lake Superior and James Bay regions. The ridge will shift eastward across the Upper Great Lakes and southern QC through the period. This will occur in response to these developments on either side: 1. A broad but not very intense cyclone -- initially centered near the western ME/QC border -- will pivot roughly eastward to the adjoining parts and the Canadian Maritimes through the period. As this occurs, a shortwave trough/vorticity lobe -- now in the western semicircle of the cyclone over the St. Lawrence Valley -- should dig southward across eastern NY and extreme western New England today, then weaken and move offshore from the southern New England Coast tonight. 2. A strong shortwave trough -- initially over western MT, southeastern ID and northern UT -- should move to eastern MT and central WY by 00Z, then to the western Dakotas within 12 more hours. This will foster the northeastward ejection of two weak perturbations, now apparent in moisture-channel imagery over the western NE Panhandle/southeastern WY region into southwestern SD, the other over central/eastern CO. By 00Z, these features should reach eastern ND and eastern/southern SD, respectively. At the surface, 11Z analysis showed a low near FSD, with cold front arching southwestward across the NE Sandhills then northwestward to another low over east-central WY near CPR. A quasistationary frontal zone was drawn from the low northeastward over western/ northern MN. The low should move slowly eastward today while the poleward frontal extension moves little, and the cold front moves southeastward into northwestern IA and eastern/central NE. The western segment of that front should hang up over northwestern NE and east-central WY amid mass response to the approaching shortwave trough, which also should induce a surface trough and perhaps secondary/reinforcing baroclinic zone across the lee of the north-central Rockies over eastern WY and into southeastern MT. ...North-central Plains to Upper Midwest... Two main rounds of severe-thunderstorm potential are apparent today, each crossing portions of the main risk area, which represents an aggregated severe potential from both complexes. From east to west: 1. Strong-severe thunderstorms should develop over eastern SD near or north/northwest of the surface low this afternoon -- perhaps arising as early and far west as central SD during midday. This activity will be related to maximized low-level lift associated with the low, and a plume of large-scale ascent preceding the weaker shortwave troughs, and already supporting convection at this time over western SD. Whether the ongoing convection will be continuous with later activity is uncertain. In either event, this eastern complex should intensify substantially over the southeastern SD/southwestern MN/northwestern IA vicinity as it crosses the low-level baroclinic zone and encounters a strongly unstable, richly moist boundary layer, with upper 60s to mid 70s surface dewpoints. Beneath steep lower-middle-level lapse rates, this should contribute to a corridor of 3500-5000 J/kg MLCAPE near I-90 from the FSD area to near the Mississippi River, decreasing to a still-favorable 2000-4000 J/kg in central MN. Supercells with destructive hail, potentially significant-severe gusts, and a few tornadoes are possible, though so is fairly quick upscale expansion. 2. An area of convection may develop as early as late morning to midday well behind the surface cold front, in higher terrain of northern/central WY, initially with a marginal severe threat. This convection should be supported by at least modest low/middle-level moisture, and strong cooling/destabilization aloft, related to the swath of strong large-scale DCVA/ascent immediately preceding the northern Rockies shortwave trough. This activity may be an outgrowth or extension of nonsevere thunderstorms now over extreme western WY near the Star and Hams Fork Valleys and adjacent ranges. These thunderstorms should organize into an MCS and expand/intensify as activity proceeds into greater moisture, instability and storm-relative/post-frontal low-level flow to the east, on the High Plains and near the Black Hills. Northeasterly to easterly flow behind the front and near the trough, beneath strengthening southwest flow aloft, will support 45-60 kt effective-shear magnitudes. Buoyancy will increase eastward as the convection -- which may already have evolve into an outflow-dominant arc by the time it gets into greater moisture east of the Black Hills -- further intensifies into the northern part of a corridor of 1500-2000 J/kg MLCAPE and still-favorable storm-relative boundary- layer flow. Some of this convection may be supercellular to the extent it can remain at least somewhat discrete, with severe wind and large to very large hail possible. With time, wind will dominate as the main threat. This activity should encounter the outflow from the other complex somewhere over southeastern SD or southern MN tonight. Mesoscale uncertainty over the positioning and strength of the outflow (and thus threat of severe to its poleward side) preclude greater unconditional probabilities at this time. Still, a focused corridor of destructive winds remains a possibility across southern parts of SD/MN, some of it potentially affecting areas struck by the first complex. ...Northeastern CONUS... Widely scattered to scattered thunderstorms should develop over portions of eastern NY and New England, as well as parts of western/central PA and northwestern MD -- each moving southward to southeastward through a favorable airmass for organized convection. Strong to locally severe gusts are possible, along with severe hail. Over the New England part of the outlook, cold air aloft, overlying low-level moisture represented by mid/upper 50s F surface dewpoints, should combine with limited diurnal heating to remove MLCINH, and support peak/preconvective MLCAPE ion the 1000-1500 J/kg range. Though low-level flow will be modest, relatively straight/lengthy hodographs will support some hail potential. Further southwest, greater low-level moisture (dewpoints mostly mid/upper 60s to near 70 F at lower elevations) but weaker mid/upper-level lapse rates will be present, yielding similar CAPE values but with different vertical distribution of buoyancy (more skewed to low levels). Still, enough deep/speed shear will be present to support organized multicells and at least transient/isolated supercells. ..Edwards/Bentley.. 08/26/2024 Read more

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0344 AM CDT Mon Aug 26 2024 Valid 291200Z - 031200Z ...DISCUSSION... An upper low is forecast to move across the Canadian Prairie and north-central U.S. through the first half of the Day 4/Thursday period, before being shunted a bit northeastward into Ontario due to pronounced downstream ridging. Timing differences amongst the medium-range global models with the advance of this feature, similarly result in positional differences with the surface front. Thus, while some severe risk may manifest during the afternoon/evening hours across the Upper Midwest region given a likely-to-be-sufficient kinematic and thermodynamic environment ahead of the front, no risk areas will be highlighted at this time. Similarly on Day 5/Friday, timing differences are evident as upper troughing and the associated surface front shift across the Upper Great Lakes/Midwest region. While some severe risk would again be possible within this general region, too much positional uncertainty exists for areal outlines. Beyond Day 5, a gradual expansion of cyclonic flow aloft is forecast across roughly the eastern half of the country -- though to different degrees in the various models. As this occurs, the more favorably moist low-level airmass will gradually be suppressed southward, south of the faster belt of flow aloft, and thus a general decrease in severe risk is expected across the U.S. overall. This trend should continue through the end of the period, as a pronounced intrusion of Canadian air gradually spreads across the eastern two-thirds of the country through Labor Day and beyond. Read more

SPC 0730Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0243 AM CDT Mon Aug 26 2024 Valid 281200Z - 291200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM LOWER MICHIGAN EASTWARD TO SOUTHERN NEW ENGLAND...AND ACROSS PORTIONS OF THE DAKOTAS... ...SUMMARY... Severe storms are expected across portions of the Midwest and Northeast/Mid-Atlantic area, and over portions of the northern Plains. ...Synopsis... Upper troughing is forecast to shift into the Northeast Wednesday, as a short-wave trough cresting the central and eastern U.S. ridge moves across the Great Lakes region and southeastern Canada -- partially merging with a more substantial trough crossing Quebec and moving into the Canadian Maritimes. Upstream, a strong upper low is forecast to move eastward across the Canadian Prairie and adjacent northern Intermountain Region through the period. At the surface, a west-to-east quasi-stationary front is forecast to extend from southern New England across the Midwest, while retreating northward as a warm front across the central and into the northern Plains. This retreat will occur as a cold front shifts into the northern Plains and western Nebraska during the afternoon and evening. By the end of the period, this cold front should extend from the eastern Dakotas to the central High Plains. ...Midwest to southern New England, and south across the central Appalachians and into the Mid-Atlantic... Uncertainty with evolution of convection persists across the region at this time, as substantial model differences exist with respect to early-day/ongoing convection, as well as timing/position of synoptic features -- both surface and aloft. While the risk areas will likely require adjustment in subsequent outlooks, current indications are that storms should reintensify/develop during the afternoon as the airmass near and south of a west-to-east surface baroclinic zone becomes moderately unstable. The most favorable kinematic environment is expected to extend from lower Michigan to southern New England, but greater instability is expected westward across the Upper Ohio Valley and Midwest. As such, damaging winds would likely be the primary threat over northern and eastern portions of the region, with large hail potentially more prevalent into the Midwest. Storms -- and at least some severe risk -- will likely continue well into the evening and possibly into the overnight hours, spreading southeastward through the end of the period. ...Northern Plains... As the upper low advances eastward across the Canadian Prairie and northern Intermountain Region during the day, northward return of the surface baroclinic zone and associated moist low-level airmass into the Dakotas is expected to occur. Afternoon heating will support moderate destabilization, with storms expected to develop by late afternoon near the retreating baroclinic zone, and a cold front shifting across the northern High Plains into the Dakotas. While some risk for damaging winds may evolve, the main risk will likely be large hail -- particularly with elevated storms across North Dakota during the evening, and spreading into Minnesota overnight. ..Goss.. 08/26/2024 Read more

SPC 0730Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0243 AM CDT Mon Aug 26 2024 Valid 281200Z - 291200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM LOWER MICHIGAN EASTWARD TO SOUTHERN NEW ENGLAND...AND ACROSS PORTIONS OF THE DAKOTAS... ...SUMMARY... Severe storms are expected across portions of the Midwest and Northeast/Mid-Atlantic area, and over portions of the northern Plains. ...Synopsis... Upper troughing is forecast to shift into the Northeast Wednesday, as a short-wave trough cresting the central and eastern U.S. ridge moves across the Great Lakes region and southeastern Canada -- partially merging with a more substantial trough crossing Quebec and moving into the Canadian Maritimes. Upstream, a strong upper low is forecast to move eastward across the Canadian Prairie and adjacent northern Intermountain Region through the period. At the surface, a west-to-east quasi-stationary front is forecast to extend from southern New England across the Midwest, while retreating northward as a warm front across the central and into the northern Plains. This retreat will occur as a cold front shifts into the northern Plains and western Nebraska during the afternoon and evening. By the end of the period, this cold front should extend from the eastern Dakotas to the central High Plains. ...Midwest to southern New England, and south across the central Appalachians and into the Mid-Atlantic... Uncertainty with evolution of convection persists across the region at this time, as substantial model differences exist with respect to early-day/ongoing convection, as well as timing/position of synoptic features -- both surface and aloft. While the risk areas will likely require adjustment in subsequent outlooks, current indications are that storms should reintensify/develop during the afternoon as the airmass near and south of a west-to-east surface baroclinic zone becomes moderately unstable. The most favorable kinematic environment is expected to extend from lower Michigan to southern New England, but greater instability is expected westward across the Upper Ohio Valley and Midwest. As such, damaging winds would likely be the primary threat over northern and eastern portions of the region, with large hail potentially more prevalent into the Midwest. Storms -- and at least some severe risk -- will likely continue well into the evening and possibly into the overnight hours, spreading southeastward through the end of the period. ...Northern Plains... As the upper low advances eastward across the Canadian Prairie and northern Intermountain Region during the day, northward return of the surface baroclinic zone and associated moist low-level airmass into the Dakotas is expected to occur. Afternoon heating will support moderate destabilization, with storms expected to develop by late afternoon near the retreating baroclinic zone, and a cold front shifting across the northern High Plains into the Dakotas. While some risk for damaging winds may evolve, the main risk will likely be large hail -- particularly with elevated storms across North Dakota during the evening, and spreading into Minnesota overnight. ..Goss.. 08/26/2024 Read more

SPC Day 2 Fire Weather Outlook
Day 2 Fire Weather Outlook NWS Storm Prediction Center Norman OK 0140 AM CDT Mon Aug 26 2024 Valid 271200Z - 281200Z ...Synopsis... A mid-level trough will amplify and traverse the northern Rockies tomorrow (Tuesday), encouraging strong surface gradient winds over the Pacific Northwest in response to a deepening surface lee trough. Dry and windy conditions are likely along and to the lee of the Cascades, where fuels are at least modestly receptive to wildfire spread. Here, 15-25 mph sustained westerly surface winds may overlap with dry fuels and 15-25 percent RH for at least a few hours. As such, Elevated highlights have been added to address the regionally favorable wildfire-spread threat. ..Squitieri.. 08/26/2024 ...Please see www.spc.noaa.gov/fire for graphic product... Read more