Severe Storms

SPC Day 1 Fire Weather Outlook
Day 1 Fire Weather Outlook NWS Storm Prediction Center Norman OK 1126 AM CDT Wed Aug 24 2022 Valid 241700Z - 251200Z ...NO CRITICAL AREAS... The previous forecast reasoning (see below) remains the same, and no changes were needed with this update. ..Weinman.. 08/24/2022 .PREV DISCUSSION... /ISSUED 0153 AM CDT Wed Aug 24 2022/ ...Synopsis... A mid-level trough will traverse the Northwest U.S. as broad but weak cyclonic upper flow remains in place east of the Rockies today. Ahead of the mid-level trough, adequate lift and buoyancy will support scattered thunderstorm development, with at least isolated thunderstorms capable of producing strong to severe wind gusts. Fuel beds are receptive to wildfire spread on a spotty basis. However, the combination of dry strikes away from precipitation cores into dry fuel beds, and strong wind gusts exacerbating ongoing fires suggests that at least localized wildfire-spread concerns exist, especially along the Idaho/Montana border. Farther south across the northern Great Basin, locally Elevated dry and windy conditions are possible by afternoon peak heating. Please see the Day 1 Convective Outlook for more details on the severe threat. ...Please see www.spc.noaa.gov/fire for graphic product... Read more

SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1121 AM CDT Wed Aug 24 2022 Valid 241630Z - 251200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM THE NORTHERN ROCKIES TO UPPER THE MISSISSIPPI VALLEY... ...SUMMARY... Marginally severe gusts and/or hail will be possible in a corridor from portions of the northern Rockies to the upper Mississippi Valley. ...Northern Rockies to upper Mississippi Valley... Modest west-northwest mid-level flow will prevail from the Northern Rockies into the upper Great Lakes through tonight. An upper low over WA will drift east, while a low-amplitude impulse over western MN moves slowly southeast. A surface front, extending from the MI Upper Peninsula west/southwest through western NE and southern MT, will serve as a focus for isolated severe potential as thunderstorms develop/intensify this afternoon. Two areas with potentially greater thunderstorm coverage remain evident, over portions of southeast MN/northern IA/southern WI associated with a weak surface low along the front over southern MN, and over western MT in association with the eastward-migrating upper low. Relatively greater boundary-layer moisture exists over IA/southern MN late this morning (surface dew points mid 60s), and this will contribute to pockets of moderate MLCAPE where heating can be maximized. Generally weak low/mid-level wind fields will result in effective shear below 30 kts, though this may support organized multicell structures capable of isolated damaging gusts and hail late this afternoon through early evening. Across western MT, steeper mid-level lapse rates will contribute moderate buoyancy, and effective shear values will average 30-40 kts. Scattered thunderstorms should develop this afternoon, aided by post-frontal upslope flow and ascent with the approaching upper low. A mix of multicell and transient supercell storm modes is possible with a risk for isolated severe wind and hail with the strongest storms. A focused Slight Risk was considered over portions of western MT, however with existing cloud cover some uncertainty remains regarding the degree of destabilization and spatial extent of any greater severe threat. Elsewhere along the front, storm coverage is expected to be more isolated overall, though with perhaps slightly greater coverage in the upslope region of the Black Hills in western SD. A well-mixed boundary layer and marginal low-level moisture will support at least some risk for strong wind gusts. ..Bunting/Wendt.. 08/24/2022 Read more

No watches are valid as of Tue Aug 23 17:41:01 UTC 2022.

No Mesoscale Discussions are in effect as of Tue Aug 23 17:41:01 UTC 2022.

SPC Day 2 Fire Weather Outlook
Day 2 Fire Weather Outlook NWS Storm Prediction Center Norman OK 1235 PM CDT Tue Aug 23 2022 Valid 241200Z - 251200Z ...NO CRITICAL AREAS... The previous forecast (see below) remains on track, and no changes were needed with this update. Isolated dry thunderstorms will also be possible over parts of central into eastern NV during the afternoon, though current indications are that fuels are generally not receptive to wildfire spread over this area. ..Weinman.. 08/23/2022 .PREV DISCUSSION... /ISSUED 0151 AM CDT Tue Aug 23 2022/ ...Synopsis... Broad cyclonic flow will prevail across the eastern U.S., while the western CONUS will remain under the influence of weak upper ridging tomorrow/Wednesday. A weak mid-level cutoff low will also meander around the northern Rockies to the north of the upper ridge. South of this upper low, locally dry and breezy conditions may occur across portions of far southeast Oregon into northern and central Nevada around afternoon peak heating. A greater concentration of dry thunderstorms is also likely across portions of the northern Rockies (particularly central into eastern Idaho) compared to Day 1. As in Day 1 though, dry thunderstorm highlights were withheld given questionable fuel receptiveness to fire spread. ...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 1222 PM CDT Tue Aug 23 2022 Valid 241200Z - 251200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... Organized severe thunderstorms are not currently forecast for Wednesday across the contiguous United States. ...Synopsis... A flattened mid- to upper-level ridge will reside over the Four Corners while a weak upper low remains over the Pacific Northwest. A subtle shortwave trough is expected to move northeastward in the corridor between the upper ridging and upper low, moving across northern NV/southern ID into southwest MT. ...Northern Rockies/High Plains into the Upper Midwest... A weak area of low pressure will gradually move east across southern MN during the day while an attendant cool front becomes draped from NE and becoming more diffuse over parts of the northern Rockies. Isolated thunderstorms are anticipated across southern MN, northern/central IA, and eastern NE along the cold front. Weak vertical shear will limit storm intensity. Some additional thunderstorm development is possible over eastern WY, where low-level convergence between the post-frontal easterly flow and the lee trough is maximized. Vertical shear will be slightly stronger here compared to areas farther east, largely as a result of low-level easterly flow veering to northwesterly aloft. Model guidance continues to indicate instability will be modest, thereby tempering the risk for strong/locally severe thunderstorms. Perhaps the area with the highest relative concern for a stronger thunderstorm will be over parts of western MT. Strong gusty winds may accompany the more intense thunderstorms during the early evening. ...Southeast... A convectively augmented shortwave trough and attendant surface low will continue to slowly drift eastward across the Southeast states, with numerous thunderstorms expected over the region throughout the day. Uncertainty remains high whether mesoscale enhancement to the wind profile will occur in a very moist airmass. ..Smith.. 08/23/2022 Read more

SPC Day 1 Fire Weather Outlook
Day 1 Fire Weather Outlook NWS Storm Prediction Center Norman OK 1120 AM CDT Tue Aug 23 2022 Valid 231700Z - 241200Z ...NO CRITICAL AREAS... The forecast remains on track, and no changes were made with this update. For details, see the previous discussion below. ..Weinman.. 08/23/2022 .PREV DISCUSSION... /ISSUED 0151 AM CDT Tue Aug 23 2022/ ...Synopsis... While broad cyclonic upper flow will prevail east of the Rockies, and a mid-level shortwave trough impinges on the West Coast today, deep-layer winds/forcing should be weak, with dry and windy conditions expected to remain constrained to terrain-favoring areas. While isolated to scattered thunderstorms are possible across parts of the Pacific Northwest into the northern Rockies, several of the storms are expected to be wet. Spotty fuel beds may support isolated lightning-induced ignitions. However, many earlier fire starts have yet to grow rapidly, suggesting that fuels are modestly receptive at best to significant wildfire spread. As such, dry thunderstorm highlights have been withheld this outlook. ...Please see www.spc.noaa.gov/fire for graphic product... Read more

SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1113 AM CDT Tue Aug 23 2022 Valid 231630Z - 241200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS CENTERED ON PARTS OF AZ...ND...AND SOUTHERN NEW ENGLAND... ...SUMMARY... Isolated severe thunderstorms are possible into this evening, centered on portions of Arizona, North Dakota, and southern New England. ...Lower CO Valley to south-central AZ... Full insolation this morning in conjunction with steep mid-level lapse rates of 7-7.5 C/km will yield a moderately unstable air mass with MLCAPE of 1500-2500 J/kg south of the Mogollon Rim by late afternoon. Scattered thunderstorms are expected to develop off the Rim and drift to the south-southwest within a belt of 10-15 kt 500-600 mb flow. Localized severe gusts will be possible as convection spreads into the lower deserts including the greater Phoenix metro area. The lack of stronger shear should limit potential for a more organized severe wind event. ...Central/northern ND... 16Z surface analysis placed a couple of 1013-mb lows near the MT/ND border and the SK/MB/ND border along a weak quasi-stationary front. A minor mid-level vort max attendant to the latter wave should drift southeast, aiding in scattered thunderstorm development later this afternoon across northern to central ND. A compact belt of enhanced upper-level flow may be adequate for a couple stronger cells given moderate mid-level lapse rates sampled by the 12Z Bismarck sounding. These cells will be capable of marginally severe hail and localized strong to marginally severe gusts. ...Southern New England... Scattered thunderstorms are underway across the Hudson Valley downstream of a mid-level trough centered on the Upper St. Lawrence Valley, with more isolated activity farther south. Boundary-layer heating has been more robust across the Tri-State area in the NYC vicinity, with stratus still holding across most of MA/RI. This should result in a confined corridor having a modest combination of buoyancy and mid-level flow over southern New England. In this area, a few wet microbursts capable of locally damaging winds are possible through the rest of the afternoon. ..Grams/Wendt.. 08/23/2022 Read more

No watches are valid as of Mon Aug 22 17:51:01 UTC 2022.

No Mesoscale Discussions are in effect as of Mon Aug 22 17:51:01 UTC 2022.

SPC 1730Z Day 2 Outlook
Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1227 PM CDT Mon Aug 22 2022 Valid 231200Z - 241200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... A few strong thunderstorms will be possible across parts of Arizona, the northern Rockies and northern Plains, and parts of New England on Tuesday, but the organized severe-thunderstorm threat appears relatively low at this time. ...Arizona... Substantial convective overturning occurred across parts of AZ and adjacent portions of southern CA/NV on Sunday. This may tend to suppress convection somewhat on D1/Monday, which in turn may allow for more substantial recovery by D2/Tuesday. If this scenario occurs, then some threat for strong/locally severe wind gusts (and perhaps some hail across higher elevations) may materialize on Tuesday along the Mogollon Rim into portions of the lower deserts. Severe probabilities may need to be added sometime during the Day 1 outlook cycle, depending on shorter-term trends regarding destabilization and the strength of midlevel steering flow. ...Northern Rockies/Great Plains... A few strong storms will be possible Tuesday across parts of the northern Rockies, near and east of a midlevel low moving slowly from southern BC into eastern WA and northern ID. With only modest instability and generally weak deep-layer shear, the severe threat still appears too low to include probabilities. Farther east into the northern Great Plains, isolated to widely scattered storms will be possible during the afternoon and evening, as a midlevel shortwave trough moves eastward and interacts with a weak surface boundary. Moderate instability could support some stronger updrafts, but rather weak deep-layer flow/shear may limit the threat for organized severe storms. ...New England... A weakening mid/upper-level low and associated trough are forecast to move across New England on Tuesday. Modestly enhanced midlevel southwesterly flow could support some occasional storm organization as convection redevelops during the afternoon, though weak midlevel lapse rates will tend to limit updraft intensity to some extent. Any severe threat will likely be dependent on the extent of diurnal heating and destabilization, which remains uncertain at this time due to the potential for widespread early-day cloudiness. ..Dean.. 08/22/2022 Read more

SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1131 AM CDT Mon Aug 22 2022 Valid 221630Z - 231200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS THE MID-ATLANTIC/CAROLINAS AND FROM CENTRAL TEXAS EAST THROUGH CENTRAL LOUISIANA AND SOUTHWEST MISSISSIPPI... ...SUMMARY... A few severe thunderstorms will be possible across parts of central/east Texas to Louisiana/southwest Mississippi, with additional locally severe storms possible across parts of the Mid-Atlantic states and Carolinas. ..Central/east Texas Louisiana/southern Mississippi... Widespread/persistent convection across North Texas this morning should result in a slow southward movement of an east-west baroclinic zone into central TX east to northern/central LA this afternoon as a broad/weak surface low near the DFW area moves slowly east. Diurnal heating of a very moist air mass characterized by PW values of 2-2.4 inches will contribute to moderate destabilization within a largely uncapped environment, and a few stronger storms will be capable of damaging downburst winds. Some potential for transient low-level rotation will continue east of the surface low near an effective warm front across east TX into central LA, where subtle low-level veering in forecast wind profiles will exist. ...Mid-Atlantic States/Carolinas... Variable cloud cover across the area has led to steady heating/destabilization through 16z, with moderate SBCAPE expected by afternoon within a largely uncapped environment. Scattered thunderstorm development is expected ahead of a cold front and over the higher terrain, with storms generally moving east through early evening. West/southwest mid-level flow of 20-30 kts will be sufficient for multicell storm structures capable of strong/locally severe gusts. ...Arizona/Lower Colorado River Valley... While a couple of stronger storms could materialize mainly along the Mogollon Rim late this afternoon through early evening, the overall convective potential across the region should be lower in the wake of Sunday night's MCS. ...Idaho/far western Montana... Upper trough and associated large-scale ascent over the Pacific Northwest/British Columbia will contribute to increasing (mostly dry) thunderstorms across the region this afternoon and evening. A warm and well-mixed boundary layer and modest strengthening of mid-level westerly flow may result in very isolated stronger wind gusts, although the potential for organized severe storms is currently expected to remain low. Please refer to the SPC Day 1 Fire Outlook for additional details. ..Bunting/Wendt.. 08/22/2022 Read more

SPC Day 1 Fire Weather Outlook
Day 1 Fire Weather Outlook NWS Storm Prediction Center Norman OK 1133 AM CDT Mon Aug 22 2022 Valid 221700Z - 231200Z ...CRITICAL FIRE WEATHER AREA FOR PORTIONS OF CENTRAL IDAHO AND SOUTHWESTERN MONTANA... The forecast remains on track, and only minor adjustments were made to the ongoing Dry Thunderstorm highlights based on the latest observations and high-resolution guidance. In addition to the fire-weather concerns described below, 10-15 percent RH and breezy westerly surface winds could result in locally elevated conditions over portions of southeast OR, southwest ID, and north-central NV this afternoon. ..Weinman.. 08/22/2022 .PREV DISCUSSION... /ISSUED 0201 AM CDT Mon Aug 22 2022/ ...Synopsis... A shortwave trough evident in satellite imagery this morning near the Pacific Northwest coast is forecast to move eastward through the day. This trough will act to break down the upper-level ridge over the northern Intermountain West. Ahead of this trough, thunderstorms are expected to be ongoing early in the day across northeastern Oregon and southeastern Washington, where a mix of wet and dry thunderstorms are probable with PW values over 0.75". Farther east, strong heating will lead to warm, deeply mixed boundary layers across Idaho and southwestern Montana. By the afternoon, the shortwave trough will help to initiate scattered thunderstorms in an environment characterized by RH values below 20% and PW values less than 0.75". Given the dry fuels across the region, scattered coverage of dry thunderstorms warrants a critical fire-weather highlight. ...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 1256 PM CDT Sun Aug 21 2022 Valid 221200Z - 231200Z Only minor adjustments were made to the Dry Thunderstorm highlights based on the latest high-resolution guidance consensus. For details, see the previous discussion below. ..Weinman.. 08/21/2022 .PREV DISCUSSION... /ISSUED 0154 AM CDT Sun Aug 21 2022/ ...Synopsis... Upper ridging will weaken some across the Interior West as a mid-level trough traverses the Pacific Northwest and approaches the northern Rockies tomorrow/Monday. Ahead of the mid-level trough, lifting of mid-level monsoonal air across the northern Rockies will support at least isolated high-based thunderstorm development by late afternoon. Given the presence of patchy dry fuels, isolated dry thunderstorm highlights have been introduced. Locally Elevated dry and breezy conditions are also possible across the Harney Basin in southeast Oregon into southwest Idaho around afternoon peak heating. ...Please see www.spc.noaa.gov/fire for graphic product... Read more

No watches are valid as of Sun Aug 21 17:58:02 UTC 2022.

SPC 1730Z Day 2 Outlook
Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1206 PM CDT Sun Aug 21 2022 Valid 221200Z - 231200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... The organized severe-thunderstorm threat is expected to be low on Monday. ...Mid Atlantic/Southern New England into the Carolinas... Convection is expected across a broad region of the eastern CONUS on Monday, within a moist and generally uncapped environment east of a weakening mid/upper-level trough. 20-30 kt midlevel southwesterly flow may sporadically support some modest storm organization, but weak midlevel lapse rates and potentially widespread cloudiness should limit buoyancy and updraft intensity. A threat for locally damaging wind gusts may eventually evolve in areas where stronger heating and steepening of low-level lapse rates can occur between rounds of convection. ...Northern Plains... While low-level moisture will remain relatively limited, diurnal heating will support weak to locally moderate destabilization across parts of the northern Great Plains Monday afternoon. Development and coverage of surface-based storms remain uncertain, and could be tied to convectively enhanced vorticity maxima emanating out of the northern Rockies. If surface-based storms develop, modest deep-layer shear within the weak northwesterly flow regime could support a couple stronger cells or clusters, though the severity of any such development remains uncertain and could be relatively limited. ...TX into LA/southern MS... Widespread convection is expected on Monday across much of TX into the ArkLaMiss region, as a low-amplitude mid/upper-level trough slowly traverses a very moist environment. The organized severe threat appears limited within this regime, due to weak midlevel lapse rates and deep-layer shear, with heavy rain expected to be the primary concern. However, isolated wet microbursts and/or outflow-driven clusters may produce localized gusty winds, especially from central TX into parts of the Rio Grande Valley, where somewhat stronger heating/destabilization may occur prior to storm arrival. ..Dean.. 08/21/2022 Read more

MD 1707 CONCERNING SEVERE POTENTIAL...WATCH UNLIKELY FOR PORTIONS OF MID/UPPER OHIO VALLEY
Mesoscale Discussion 1707 NWS Storm Prediction Center Norman OK 1158 AM CDT Sun Aug 21 2022 Areas affected...Portions of mid/upper Ohio Valley Concerning...Severe potential...Watch unlikely Valid 211658Z - 211830Z Probability of Watch Issuance...20 percent SUMMARY...Storm coverage and intensity will increase gradually this afternoon. Isolated damaging winds and marginally severe hail (in the strongest storms) are the primary hazards. Convective trends will be monitored, but a watch is not currently anticipated this afternoon. DISCUSSION...Cloud breaks within the region have allowed a few thunderstorms to develop ahead of the cold front within a weakly capped environment. The front itself remains farther to the west near the IN/OH border. Continued heating within broken cloud cover will continue to promote greater boundary layer destabilization where around 1500 J/kg MLCAPE may continue to build northeastward into parts of eastern Ohio. Additional storms are likely to develop this afternoon given the upper-level support from the shortwave trough. Effective shear is modest 25-30 kts and will support multicell storms with perhaps isolated, marginal supercells storms. These storms will primarily pose a threat for damaging wind gusts, though the strongest storms could produce marginally severe hail given cold temperatures aloft. Some guidance shows other development occurring along the cold front later in the afternoon. The intensity of this activity is more uncertain as it will be impacted by convection that is occurring currently. The coverage of severe-caliber storms is the greatest source of uncertainty. Whether or not a watch is necessary will depend on convective trends regarding storm coverage and intensity this afternoon. At present, a watch is not anticipated. ..Wendt/Kerr.. 08/21/2022 ...Please see www.spc.noaa.gov for graphic product... ATTN...WFO...PBZ...RLX...CLE...JKL...ILN...LMK... LAT...LON 38548495 40278388 40818276 40848116 40498072 39588064 38308213 38098274 37908441 38118502 38548495 Read more

SPC Day 1 Fire Weather Outlook
Day 1 Fire Weather Outlook NWS Storm Prediction Center Norman OK 1128 AM CDT Sun Aug 21 2022 Valid 211700Z - 221200Z There are no changes to the outlook. In addition to the fire-weather concerns described below, scattered diurnally driven thunderstorms are expected over the northern Rockies this afternoon into the evening where fuels are critically dry. While isolated ignitions will be possible away from the heavier precipitation, 0.75-1.0+ inch PW (sampled by regional 12z soundings/GOES-16 derived PW) and slow storm motions will favor a mixed wet-dry to wet storm mode -- precluding Dry Thunderstorm highlights. ..Weinman.. 08/21/2022 .PREV DISCUSSION... /ISSUED 0152 AM CDT Sun Aug 21 2022/ ...Synopsis... Upper ridging will be in place across the western U.S. as broad cyclonic flow aloft envelops the eastern two-thirds of the CONUS today. By evening, a pronounced mid-level trough will impinge on the Pacific Northwest and lift a monsoonal airmass across Oregon, fostering isolated high-based thunderstorm development. While some of the storms will be slow moving, enough potential exists for strikes to occur away from storm cores into dry fuel beds, warranting the continuation of isolated dry thunderstorm highlights. ...Please see www.spc.noaa.gov/fire for graphic product... Read more

SPC Day 1 Fire Weather Outlook
Day 1 Fire Weather Outlook NWS Storm Prediction Center Norman OK 1128 AM CDT Sun Aug 21 2022 Valid 211700Z - 221200Z There are no changes to the outlook. In addition to the fire-weather concerns described below, scattered diurnally driven thunderstorms are expected over the northern Rockies this afternoon into the evening where fuels are critically dry. While isolated ignitions will be possible away from the heavier precipitation, 0.75-1.0+ inch PW (sampled by regional 12z soundings/GOES-16 derived PW) and slow storm motions will favor a mixed wet-dry to wet storm mode -- precluding Dry Thunderstorm highlights. ..Weinman.. 08/21/2022 .PREV DISCUSSION... /ISSUED 0152 AM CDT Sun Aug 21 2022/ ...Synopsis... Upper ridging will be in place across the western U.S. as broad cyclonic flow aloft envelops the eastern two-thirds of the CONUS today. By evening, a pronounced mid-level trough will impinge on the Pacific Northwest and lift a monsoonal airmass across Oregon, fostering isolated high-based thunderstorm development. While some of the storms will be slow moving, enough potential exists for strikes to occur away from storm cores into dry fuel beds, warranting the continuation of isolated dry thunderstorm highlights. ...Please see www.spc.noaa.gov/fire for graphic product... Read more

SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1120 AM CDT Sun Aug 21 2022 Valid 211630Z - 221200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON ACROSS PARTS OF THE OHIO VALLEY... ...SUMMARY... Isolated strong to briefly severe thunderstorms are expected this afternoon, mainly across parts of the Ohio and Tennessee River Valleys. ...Synopsis... Mid/upper ridging remains generally suppressed across the southern mid- and subtropical latitudes of the eastern Pacific into parts of the Southwest, and across the northern Mexican Plateau and Gulf Basin into the Atlantic. Much of the U.S. will remain under the influence of a weak branch of westerlies, well downstream of large, deep troughing centered over the mid-latitude Pacific, roughly between 140-170 W. This regime includes mean ridging across the Pacific coast into the Rockies, with an embedded short wave trough approaching the Pacific Northwest coast. Downstream, broad mean troughing prevails east of the Rockies, with the most substantive embedded short wave troughing forecast to continue slowly digging east-southeast of the mid/upper Mississippi Valley toward the Appalachians. Another weaker perturbation likely will very slowly progress across the southern Great Plains. Milder and, particularly, drier air has already infiltrated much of the northern Great Plains into Upper Midwest, and will gradually overspread much of the Ohio Valley, while a similar environment remains entrenched across much of New England. Seasonably high moisture content will continue to gradually become increasingly confined to parts of the Southwest, and Gulf into southern and mid Atlantic Coast states, by the end of the period. ...East of the Rockies... The lingering seasonably moist air, coupled with weak mid-level inhibition and large-scale forcing for ascent, is already contributing to considerable pre-frontal thunderstorm development across parts of the southern Great Plains into the Ohio Valley, lower Great Lakes region and Mid Atlantic. This will continue, with a further increase in storm coverage with boundary-layer heating through late afternoon. While the remnants of elevated mixed-layer air might enhance potential for localized downbursts across parts of north central and northeastern Texas by late afternoon, lower/mid tropospheric lapse rates across most areas are generally weak. Deep-layer mean flow and shear is also rather weak, but heavy precipitation loading and downward mixing of 20-30 kt southwesterly to westerly flow in the 850-500 mb layer, to the south and east of the digging short wave trough, might be enough to contribute to locally damaging downbursts in stronger storms, mainly across parts of the Ohio Valley. ...Southwest... Boundary-layer heating and mixing are forecast to remain somewhat modest for the time of year, with the stronger heating and deeper mixing mostly confined to the lower Colorado Valley. However, this may be sufficient, given the relatively moist conditions, to support sizable CAPE by late this afternoon. Aided by 10-20 kt northerly mid-level flow, if thunderstorms can cluster/consolidate sufficiently along the Rim late this afternoon, there appears to be potential for convection to gradually propagate off the higher terrain (and particularly toward the Colorado Valley) accompanied by a risk for strong surface gusts into this evening. ..Kerr/Wendt.. 08/21/2022 Read more