Severe Storms

SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0239 PM CDT Sun Aug 20 2023 Valid 202000Z - 211200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS SOUTHEAST CA INTO THE LOWER CO VALLEY... ...SUMMARY... A couple tornadoes are possible across the Lower Colorado Valley and southern Mojave Desert vicinity through around dusk. ...20z Update... Only minor adjustments have been made to the 2 percent tornado probabilities over AZ. Otherwise, the previous outlook remains on track. See previous discussion below for more details, and reference MCD 2017 for short term severe/tornado hazard information. ..Leitman.. 08/20/2023 .PREV DISCUSSION... /ISSUED 1119 AM CDT Sun Aug 20 2023/ ...Desert Southwest... The conditional TC-tornado environment evident over the northern Gulf of CA and northwest Sonora is expected to spread north-northwest across the Lower CO Valley and southern Mojave Desert vicinity. The primary corridor of concern will be across southeast CA and adjacent portions of western AZ/southern NV this afternoon into early evening. Here, meager MLCAPE from 300-600 J/kg should develop with some thinning of the cloud canopy amid upper 60s to low 70s boundary-layer dewpoints. This will remain coincident with an enlarged low-level hodograph in the northeast quadrant of weakening TC Hilary. Most 12Z HREF guidance struggles to maintain deep convection, but sustained low-topped convection could acquire updraft rotation and be capable of producing a brief tornado. This threat will end from south to north during the evening as low-level drying and decreasing hodograph curvature occurs within the southeast quadrant of the remnant TC. Relatively greater likelihood of deeper convective development is anticipated during the mid to late afternoon along the differential boundary-layer heating corridor from southeast AZ to southwest UT. This zone will be within the pronounced west to east gradient of high to low PW and consequently along the fringe of meager MLCAPE. At least isolated thunderstorms should form off the higher terrain and possess progressively weaker low-level SRH relative to the west/south. Some 12Z HREF members do depict a 2-5 km UH signal which makes sense given adequate shear within this layer. While mid-level rotation will be possible, isolated severe wind gusts should be the primary threat, particularly with any cells/small clusters that can propagate towards the more deeply mixed environment to the north-northeast. Read more

SPC Day 3-8 Fire Weather Outlook
Day 3-8 Fire Weather Outlook NWS Storm Prediction Center Norman OK 0232 PM CDT Sun Aug 20 2023 Valid 221200Z - 281200Z A large-scale upper-level anticyclone will meander across the central U.S. through much of the week before slowly drifting westward toward the Rockies by next weekend. Relatively rich deep-layer moisture pivoting around the upper anticyclone will promote overall cooler/moist conditions across much of the Pacific Northwest into the central Rockies. Meanwhile, hot and dry surface conditions will prevail beneath the upper anticyclone over the central and southern CONUS. The latest guidance consensus suggests that some overlap in dry/windy conditions may occur over eastern Colorado Day 3/Tuesday, with 40% Critical probabilities introduced. Thereafter, overall weaker surface winds are expected on a widespread basis across the southern High Plains into the Southeast, with more focused areas of relatively greater wildfire-spread potential confined locally. ..Squitieri.. 08/20/2023 ...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 0157 PM CDT Sun Aug 20 2023 Valid 211200Z - 221200Z ...CRITICAL FIRE WEATHER AREA FOR PORTIONS OF CENTRAL TEXAS... The previous forecast (see below) remains generally on track. The two main changes in this outlook were to add Elevated highlights to eastern Wyoming and expand the Elevated in Texas eastward to central Louisiana. In Wyoming, 15-25 mph sustained southwesterly surface winds should overlap with 15-20 percent RH during the late morning to late afternoon hours. Grass-based fuels in this area have been exposed to multiple days of relatively dry conditions and have not received appreciable rainfall for at least the last 1-2 weeks. These fuels have become at least marginally receptive to wildfire spread, necessitating the introduction of Elevated highlights. Meanwhile, prolonged dry conditions have materialized across portions of the mid-south, resulting in the curing of fuels in this region. Elevated highlights have been extended into Louisiana to account for the increasingly receptive fuels, RH dipping below 30 percent, and at least locally gusty conditions expected. ..Squitieri.. 08/20/2023 .PREV DISCUSSION... /ISSUED 0218 AM CDT Sun Aug 20 2023/ ...Synopsis... A midlevel anticyclone over the central Plains will shift slightly northeastward on Day 2/Monday, yielding a slight increase in deep-layer easterlies across much of TX. At the same time, a modest increase in the surface pressure gradient is expected along the northwestern periphery of a weather disturbance moving across the Gulf of Mexico. ...Central and north TX... An anomalously warm/dry air mass will remain in place across much of central and north TX -- where 100+ deg afternoon temperatures and around 20 percent RH are expected. Deep boundary-layer mixing into the enhanced easterly low/mid-level flow, coupled with the tightening pressure gradient, will support 15-20 mph sustained east-southeasterly surface winds and locally higher gusts. Given exceptionally dry fuels over the area (95th+ percentile ERCs), critical fire-weather conditions are expected. ...Central High Plains... Similar to Day 1/Sunday, efficient diurnal heating/mixing will yield 15-20 percent minimum RH. At the same time, 15-20 mph sustained southerly surface winds are expected owing to a tightening pressure gradient, with gusts upwards of 30 mph possible. This dry/breezy combination will favor another day of elevated to spotty critical fire-weather conditions. ...Please see www.spc.noaa.gov/fire for graphic product... Read more

No watches are valid as of Sat Aug 19 22:04:01 UTC 2023.

SPC Day 3-8 Fire Weather Outlook
Day 3-8 Fire Weather Outlook NWS Storm Prediction Center Norman OK 0317 PM CDT Sat Aug 19 2023 Valid 211200Z - 271200Z An upper ridge will remain firmly in place across the central/southern CONUS through the upcoming week, promoting hot, dry, and occasionally breezy surface conditions across the central High Plains into Texas. Meanwhile, the remnants of Hilary will traverse the interior west, accompanied and preceded by a rich and deeply moist airmass/precipitation, both of which may prove detrimental to significant, widespread wildfire-spread potential. The best chance for Elevated-equivalent dry/windy surface conditions would be Day 3/Monday across the central High Plains and central Texas, where east-southeasterly winds amid a hot/mixed boundary layer will overspread receptive fuels. Thereafter, medium-range guidance differs on the placement and timing of overlapping favorable surface winds/RH across the south-central CONUS, precluding the addition of Critical probabilities. ..Squitieri.. 08/19/2023 ...Please see www.spc.noaa.gov/fire for graphic product... Read more

MD 2016 CONCERNING SEVERE POTENTIAL...WATCH UNLIKELY FOR SAN JOAQUIN VALLEY INTO THE WESTERN MOJAVE DESERT
Mesoscale Discussion 2016 NWS Storm Prediction Center Norman OK 0319 PM CDT Sat Aug 19 2023 Areas affected...San Joaquin Valley into the western Mojave Desert Concerning...Severe potential...Watch unlikely Valid 192019Z - 192245Z Probability of Watch Issuance...5 percent SUMMARY...Storms capable of isolated strong to severe gusts will be possible later this afternoon. DISCUSSION...Initially steep midlevel lapse rates and increasing moisture in advance of Hurricane Hilary will result in widely scattered thunderstorm development this afternoon across parts of the San Joaquin Valley and western Mojave desert region. Recent thunderstorm development has already been noted across northeast Kern County, with storm coverage expected to increase over lower elevation areas with time. With low-level flow/shear expected to remain weak through the afternoon, storms may quickly become outflow dominant. However, increasing mid/upper-level flow (as noted on the KSOX and KEYX VWPs) may support modestly organized and sustained convection, with one or more outflow-driven clusters possible by late afternoon. Strong to locally severe gusts will be possible as storms spread northward through the afternoon into early evening across the San Joaquin Valley. ..Dean/Grams.. 08/19/2023 ...Please see www.spc.noaa.gov for graphic product... ATTN...WFO...VEF...SGX...HNX...LOX...STO...MTR... LAT...LON 36291776 35181694 34881717 34731770 34651820 35151930 36312069 37072115 37732112 38072037 37501907 36291776 Read more

SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0241 PM CDT Sat Aug 19 2023 Valid 192000Z - 201200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER THE SAN JOAQUIN VALLEY AND WESTERN MOJAVE DESERT... ...SUMMARY... Isolated severe wind gusts are possible over the San Joaquin Valley and western Mojave Desert vicinity the remainder of the afternoon into early evening. ...20z Update -- San Joaquin Valley/Western Mojave Desert... The previous outlook remains unchanged with the 20z update. Convection will increase in coverage over the next 2-3 hours, and sporadic severe thunderstorm gusts are possible into early evening. For more details, see previous outlook below and any forthcoming MCDs. ..Leitman.. 08/19/2023 .PREV DISCUSSION... /ISSUED 1114 AM CDT Sat Aug 19 2023/ ...San Joaquin Valley and western Mojave Desert... Hot temperatures will persist over the Central Valley this afternoon with abundant insolation underway northwest of the extensive cloud canopy downstream of Hurricane Hilary. Convective temperatures will be breached towards early afternoon over the higher terrain across parts of the Transverse Ranges and southern Sierra NV mountains. Isolated to eventually scattered thunderstorms will occur through the afternoon, spreading north-northwest amid south to southeast steering flow that notably strengthens with height in the upper portion of the buoyancy profile. Deeply mixed, inverted-v thermodynamic profiles beneath the moderate storm motions should support a threat for sporadic severe wind gusts before waning during the early evening. ...West... Elsewhere in the West, very localized severe wind gusts will be possible with several areas of scattered thunderstorms this afternoon. Spatial coverage of the severe wind threat appears likely to remain below the 5 percent threshold needed for an areal delineation. Read more

SPC Day 2 Fire Weather Outlook
Day 2 Fire Weather Outlook NWS Storm Prediction Center Norman OK 0219 PM CDT Sat Aug 19 2023 Valid 201200Z - 211200Z The previous forecast (see below) remains on track, with no changes or additions made. ..Squitieri.. 08/19/2023 .PREV DISCUSSION... /ISSUED 0205 AM CDT Sat Aug 19 2023/ ...Synopsis... A broad midlevel anticyclone will remain centered over the central Plains on Day 2/Sunday, with enhanced midlevel flow along its southern and western peripheries. ...West and central TX... Similar to Day 1/Saturday, a continuation of above-average temperatures (100+ deg) and 15-20 percent RH is expected across parts of west and central TX during the afternoon. Boundary-layer mixing into the enhanced easterly flow aloft (along the southern periphery of the midlevel anticyclone) will yield 10-15 mph sustained east-southeasterly surface winds. These winds, coupled with the hot/dry conditions, will support elevated fire-weather conditions given critically dry fuels across the area. ...Central High Plains... Efficient diurnal heating/mixing in the presence of enhanced deep-layer southerly flow (along the western periphery of the midlevel anticyclone) will favor dry/breezy conditions over the central High Plains during the afternoon. 15-20 mph sustained southerly surface winds (with higher gusts) amid 15 percent RH could lead to elevated fire-weather conditions. ...Please see www.spc.noaa.gov/fire for graphic product... Read more

No watches are valid as of Fri Aug 18 22:14:01 UTC 2023.

No Mesoscale Discussions are in effect as of Fri Aug 18 22:14:01 UTC 2023.

SPC Day 3-8 Fire Weather Outlook
Day 3-8 Fire Weather Outlook NWS Storm Prediction Center Norman OK 0256 PM CDT Fri Aug 18 2023 Valid 201200Z - 261200Z A large-scale upper ridge will dominate the central and southern U.S. through the forecast period. Through the early part of the upcoming week, the remnants of Hilary will track northward across portions of the Great Basin into the Pacific Northwest and northern Rockies, potentially accompanied by soaking rainfall and a plummet in fuel receptiveness to wildfire spread. To the west of the Cascades though, the eastward passage of Hilary may encourage dry, downslope easterly winds, where fuels are highly receptive to wildfire spread. Details of such a scenario are highly dependent on the placement and timing of Hilary remnants, hence no fire weather highlights have been introduced. However, several days of dry and windy conditions are possible across the central/southern High Plains into central Texas, where fuels have been steadily curing over the last couple of weeks. Multiple days of dry/windy conditions should prime fine fuels for some wildfire spread potential, especially Days 3-4/Sunday-Monday, where 40 percent Critical probabilities have been added. The probabilities were added across portions of Texas and the Central High Plains, where confidence is highest in the need for Elevated highlights by the Days 1-2 period. ..Squitieri.. 08/18/2023 ...Please see www.spc.noaa.gov/fire for graphic product... Read more

SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0256 PM CDT Fri Aug 18 2023 Valid 182000Z - 191200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FOR PARTS OF THE DESERT SOUTHWEST...MONTANA...AND NEW ENGLAND... ...SUMMARY... Isolated strong to severe wind gusts are possible, mainly from late afternoon to mid-evening across parts of Montana, the Desert Southwest, and New England. ...20Z Update... The general thunderstorm area has been trimmed across New England, but no changes have been made to the Marginal Risk areas. Uncertainty remains regarding potential for substantial redevelopment of deep convection across New England, but isolated damaging gusts cannot be ruled out if any stronger storms can be sustained. Storms capable of producing localized severe gusts remain possible later this afternoon into this evening across parts of MT and the Southwest. See the previous discussion below for more information, and MCD 2013 regarding the near-term threat across Montana. ..Dean.. 08/18/2023 .PREV DISCUSSION... /ISSUED 1129 AM CDT Fri Aug 18 2023/ ...MT... Despite lingering mid-level clouds tempering insolation to some extent, surface temperatures should still heat into the 90s across eastern MT by late afternoon. Large-scale ascent attendant to a shortwave trough tracking east from southern BC to the lee of the Canadian Rockies should largely hold north of the international border. But low-level speed convergence should increase this evening along a trailing surface cold front and this may aid in sustaining isolated thunderstorms off the higher terrain of southwest MT. While MLCAPE should remain meager (at or below 500 J/kg), very deeply mixed profiles east of the terrain will support a threat for isolated severe wind gusts. ...Desert Southwest.... Weak deep-layer shear will be the primary limiting factor to a more organized severe wind threat, with mainly 15-25 kt 500-mb southerlies between a stout anticyclone over the southern Great Plains and a cutoff low off the southern CA coast. Scattered thunderstorms developing over the higher terrain, aided by a high PW air mass emanating north from the Gulf of CA, will pose a threat for sporadic severe wind gusts as they spread/collide northward within the deeply mixed environment across the lower deserts. ...New England... In the wake of this morning's tornadic supercell, low-level winds have substantially veered and weakened ahead of a north to south-oriented cold front pushing east into western New England. With a wedge of greater insolation between it and cloud cover associated with the early-day convection that is now largely off the coast, MLCAPE of 500-1000 J/kg should redevelop over the next few hours and support deepening convection along the front. While adequate deep-layer shear will remain, the increasingly poor low-level wind fields should mitigate an organized damaging wind threat. Still, a few strong gusts remain possible until the front reaches the coast. Read more

SPC Day 2 Fire Weather Outlook
Day 2 Fire Weather Outlook NWS Storm Prediction Center Norman OK 1249 PM CDT Fri Aug 18 2023 Valid 191200Z - 201200Z The main change to this outlook was to add an isolated dry thunderstorm area across portions of northern California into southern and central Oregon. The latest guidance consensus depicts an appreciable risk for at least a few dry thunderstorms, where fuels are also receptive to wildfire spread. Otherwise, the rest of the forecast (see below) remains on track. ..Squitieri.. 08/18/2023 .PREV DISCUSSION... /ISSUED 0209 AM CDT Fri Aug 18 2023/ ...Synopsis... Along the southern periphery of an expansive midlevel anticyclone centered over the central Plains, moderate low/mid-level east-southeasterly flow will overspread parts of southern/central into west TX. Deep boundary-layer mixing into the enhanced flow aloft will support 15 mph sustained southeasterly surface winds. These winds, combined with 100+ deg surface temperatures and around 15 percent RH, will yield elevated fire-weather conditions across parts of central and west TX (where fuels are critically dry). Farther northwest, a mix of wet/dry thunderstorms is possible across parts of southern OR, as a series of midlevel shortwave troughs cross the region. Deep inverted-V thermodynamic profiles could limit rainfall accumulations, though slow storm motions and PW near 0.75 inches cast uncertainty on the dry thunderstorm threat. ...Please see www.spc.noaa.gov/fire for graphic product... Read more

No watches are valid as of Thu Aug 17 21:41:01 UTC 2023.

No Mesoscale Discussions are in effect as of Thu Aug 17 21:41:01 UTC 2023.

SPC Day 3-8 Fire Weather Outlook
Day 3-8 Fire Weather Outlook NWS Storm Prediction Center Norman OK 0327 PM CDT Thu Aug 17 2023 Valid 191200Z - 251200Z Fire weather concerns will primarily be focused on the western periphery of tropical moisture moving northward in association with now Hurricane Hillary. Additional concerns may also develop as winds increase over very dry fuels in parts of Texas. ...West Texas... The proximity of Hurricane Hillary to the Baja Peninsula is expected to have some effect on the surface pressure gradient for the Southwest and perhaps into the southern High Plains. With hot temperatures expected on preceding days, already very dry fuels in western/central Texas will dry further. Given the increase in wind fields expected and the state of fuels, concern for elevated to near-critical fire weather is evident on Saturday and Sunday. ...Thunderstorms... Models differ in the speed of northward moisture transport along with now Hurricane Hillary. The GFS is the more aggressive of the two models and shows cloud cover/cooler temperatures into northern California and the Northwest this weekend. The ECMWF shows more potential for heating. With some lingering mid-level moisture, isolated thunderstorms could develop in parts of northern California into Oregon. Uncertainty remains high, however. The main push of tropical moisture is currently forecast to primarily impact western and central portions of the Great Basin. With a weak trough forecast to remain off the northern California coast there is at least a low conditional probability of thunderstorms for northern California and perhaps parts of the Northwest late this weekend into early next week. Potential will be contingent upon how fuels respond to any cooler/wetter conditions as well as cloud cover on the western flank of the tropical system. ..Wendt.. 08/17/2023 ...Please see www.spc.noaa.gov/fire for graphic product... Read more

SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0258 PM CDT Thu Aug 17 2023 Valid 172000Z - 181200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE CENTRAL/SOUTHERN GREAT LAKES REGION AND ALSO PARTS OF THE NORTHEAST... ...SUMMARY... Isolated strong to severe thunderstorms remain possible late this afternoon across parts of the central/southern Great Lakes region, and later tonight over parts of the Northeast. ...IL/IN/OH/MI... The Marginal Risk has been trimmed slightly from the west across northeast IL, to account for the progression of the cold front. Otherwise, the previous outlook reasoning remains valid. A few strong storms may develop as the cold front moves eastward, with a threat of isolated hail and damaging winds. See the previous discussion below for more information. ...PA/NJ/NY... The 5% wind and 2% tornado probabilities have been expanded slightly eastward, to account for the potential progression of overnight convection through the end of the period. Wind profiles will be favorable for organized convection in the vicinity of a warm front, as storms develop late tonight across eastern PA. The magnitude of the severe threat remains uncertain due to limited instability, but locally damaging winds and perhaps a tornado will be possible as storms move eastward toward southern New England by Friday morning. ..Dean.. 08/17/2023 .PREV DISCUSSION... /ISSUED 1109 AM CDT Thu Aug 17 2023/ ...IN/OH/Lower MI... A large and progressive upper trough is moving across the central Great Lakes region today, with an associated surface cold front digging southeastward across northern IL. A pre-frontal band of thunderstorms extends from central IL into lower MI, and is situated along the axis of the low-level jet. This precipitation will significantly limit daytime heating for much of the day ahead of the front and preclude a more organized severe threat. Nevertheless, a consensus of 12z CAM solutions suggest a narrow corridor of heating in the wake of this pre-frontal activity later this afternoon over parts of IN/OH. Sufficient instability and favorable deep-layer shear will support a few organized storms, with a risk of strong winds and hail in the most intense cells. This threat should end around sunset. ...PA/NJ/NY... Later tonight, large scale forcing associated with the approaching upper trough will spread into eastern PA and vicinity. Greater low-level moisture will be in place across this region as dewpoints in the upper 60s advect northward. Diurnal cooling/de-coupling will likely limit the severe threat. But there is some chance of an occasional rotating storm during the late evening or overnight, capable of gusty winds or perhaps a brief tornado. Read more

SPC Day 2 Fire Weather Outlook
Day 2 Fire Weather Outlook NWS Storm Prediction Center Norman OK 0209 PM CDT Thu Aug 17 2023 Valid 181200Z - 191200Z ...CRITICAL FIRE WEATHER AREA FOR COLUMBIA BASIN... ...CRITICAL FIRE WEATHER AREA FOR PARTS OF NORTHERN MONTANA... No changes to the ongoing forecast. ..Wendt.. 08/17/2023 .PREV DISCUSSION... /ISSUED 0149 AM CDT Thu Aug 17 2023/ ...Synopsis... A mid-level trough over the Pacific Northwest is forecast to intensify and shift eastward, suppressing the strong ridge centered over the southern Plains. At the surface, a cyclone in southern Canada will deepen, enhancing westerly winds along the international border. Very hot and dry conditions are expected over parts of the Plains and Intermountain West. Dry and breezy west winds are expected over parts of the Northwest and northern Rockies with widespread elevated to critical fire-weather conditions likely. ...Northwest and northern Rockies... As the Pacific trough moves inland it is forecast to strengthen, resulting in moderate mid-level westerly flow over much of the Northwest. At the same time, the surface cyclone over southern Alberta should deepen, enhancing low-level flow in its wake. Downslope winds of 20-25 mph are likely in the lee of the Cascades and across the western Columbia Basin. Warm temperatures will also support low afternoon RH of 15-20% from eastern WA to central MT. With area fuels rather dry, widespread critical fire-weather conditions are likely. Dry and windy conditions will extend eastward across the northern Rockies as the surface low approaches later in the day. While slightly cooler in the wake of a prior cold front, strong surface winds of 20-30 mph are expected over parts of northern/western MT. With afternoon RH values of 20-25% critical conditions still appear likely. As westerly winds increase, the monsoon moisture that has lingered over northern CA and southern OR will be shunted eastward. Isolated showers and thunderstorms are possible over parts of central and northeast OR into western ID/MT. Model soundings show relatively high PWAT values near 1 inch, but fast storm motions greater than 30 mph. Lightning strikes are possible outside of the wetter cores with these storms as they move over areas of dry fuels. However, storm coverage and the potential for some wetting rain cast considerable uncertainty on the need for IsoDryT highlights. ...Texas... As the ridge continues to build, extremely hot temperatures are forecast to redevelop over parts of southern and central TX. Highs over 100F along with exceptionally dry fuels will be the primary catalyst for locally elevated fire-weather activity. Southerly surface winds, while not robust, may occasionally reach 10-15 mph further increasing concerns for locally elevated fire-weather conditions over central parts of the state. ...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 1229 PM CDT Thu Aug 17 2023 Valid 181200Z - 191200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FOR PARTS OF NEW ENGLAND AND ARIZONA... ...SUMMARY... Isolated severe thunderstorms with a risk for damaging gusts and perhaps a tornado or two will be possible during the day across portions of New England on Friday. Storms capable of isolated severe gusts will also be possible across parts of Arizona. ...Synopsis... A seasonably deep/strong upper-level trough will move across the Northeast and Mid Atlantic regions on Friday. An associated surface low will move eastward across Quebec, as a trailing cold front moves from the upper Great Lakes into New England through the day. Farther west, a mid/upper-level low will remain nearly stationary off of the California coast. A mid/upper-level shortwave trough and associated surface low will move across the Canadian Prairies, as an attendant cold front moves into the northern Plains. ...Northeast... Multiple rounds of convection are possible across parts of the Northeast/New England on Friday. The initial morning to early afternoon round may be capable of locally damaging gusts and perhaps a tornado or two, with a more isolated threat later Friday afternoon along/ahead of the cold front. One or more storm clusters will likely be ongoing Friday morning somewhere from northern NY into southern New England. Strong deep-layer flow associated with the approaching upper trough will support sufficient effective shear for organized convective elements within these clusters. The strongest buoyancy (with MLCAPE generally 500-1000 J/kg during the morning) is expected near/south of a northward-advancing warm front across southern New England, with weaker instability extending northward into parts of VT/NH. The morning threat will likely be maximized near/south of the warm front, where line-embedded supercells and/or shorter-lived mesovortices will support potential for locally damaging gusts and perhaps a tornado or two, within an environment of favorable low-level shear/SRH. Depending on the extent of heating/destabilization that can occur across southern New England prior to storm arrival, higher severe probabilities may eventually be needed. In the wake of early-day convection, redevelopment along/ahead of the cold front will be possible during the afternoon. Coverage and intensity of convection associated with the cold front remain uncertain, with storms potentially struggling to mature due to generally weak instability and a midlevel dry slot overspreading the region. However, a few strong to locally severe storms will be possible within this frontal regime, with a threat of locally damaging gusts and small to marginally severe hail. ...Arizona... Scattered to numerous thunderstorms are expected Friday from AZ into southern NV/UT, as moisture continues to increase east of the nearly stationary upper-level trough off of the CA coast. Modest southerly midlevel flow will support the potential for loosely organized, north to northwesterly moving clusters during the afternoon and evening. Localized severe gusts will be possible where somewhat stronger preconvective heating/destabilization occurs, which currently appears most likely across the lower elevations of southern/central AZ. Small hail and gusty winds will also be possible into northern AZ, though coverage of any severe threat remains more uncertain across this area. ...Montana... Widely scattered high-based convection is expected across parts of MT Friday afternoon and evening. Hot, deeply mixed boundary layers will support the potential for localized severe gusts, though the threat appears too disorganized and unfocused for severe-wind probabilities at this time. ..Dean.. 08/17/2023 Read more

No watches are valid as of Wed Aug 16 22:12:01 UTC 2023.