Severe Storms

SPC Day 2 Fire Weather Outlook
Day 2 Fire Weather Outlook NWS Storm Prediction Center Norman OK 0132 PM CDT Thu Aug 24 2023 Valid 251200Z - 261200Z The previous forecast (see below) remains on track, with no changes or additions made. ..Squitieri.. 08/24/2023 .PREV DISCUSSION... /ISSUED 1234 AM CDT Thu Aug 24 2023/ ...Synopsis... Thunderstorms may be ongoing on Day 2/Friday morning across parts of the Pacific Northwest -- in association with a midlevel impulse lifting northward along the Cascades in WA/OR. While these storms could be relatively wet (0.80 to 1.0 inch PW), fast storm motions (and minimal rainfall accumulations) will still support a risk of lightning-induced ignitions over dry fuels. By the afternoon, lingering midlevel moisture/instability atop a dry/well-mixed boundary layer could favor another round of diurnally driven, high-based storms along the Cascades. Fire starts will also be a concern with this activity given limited expected rainfall and dry fuels. ...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 0132 PM CDT Thu Aug 24 2023 Valid 251200Z - 261200Z The previous forecast (see below) remains on track, with no changes or additions made. ..Squitieri.. 08/24/2023 .PREV DISCUSSION... /ISSUED 1234 AM CDT Thu Aug 24 2023/ ...Synopsis... Thunderstorms may be ongoing on Day 2/Friday morning across parts of the Pacific Northwest -- in association with a midlevel impulse lifting northward along the Cascades in WA/OR. While these storms could be relatively wet (0.80 to 1.0 inch PW), fast storm motions (and minimal rainfall accumulations) will still support a risk of lightning-induced ignitions over dry fuels. By the afternoon, lingering midlevel moisture/instability atop a dry/well-mixed boundary layer could favor another round of diurnally driven, high-based storms along the Cascades. Fire starts will also be a concern with this activity given limited expected rainfall and dry fuels. ...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 1224 PM CDT Thu Aug 24 2023 Valid 251200Z - 261200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM PARTS OF THE CENTRAL PLAINS EASTWARD ACROSS THE OHIO VALLEY AND VIRGINIA... ...SUMMARY... Scattered strong thunderstorms may impact a corridor from the Mid Atlantic and lower Ohio Valley through the lower Missouri Valley and central Great Plains Friday afternoon into Friday night, accompanied by a risk of damaging wind gusts and sporadic marginal hail. ...MO/IL eastward toward VA... Strong instability will develop from the lower MS Valley across the OH Valley on Friday, with a weak front/surface trough extending from PA into IL. This area will exist beneath generally weak northwest flow aloft from MO/IL into the OH Valley, with midlevel winds on the order of 20-30 kt from OH into PA by 00Z. A dying MCS with cooling outflow will likely affect parts of WV, eastern KY and VA early in the day, but westerly winds around 850 mb will likely result in destabilization later. Otherwise, strong heating to the west and weak convergence should yield scattered storms along the length of the front, and perhaps in association with the earlier outflow which will affect KY during the afternoon. Any of these diurnal storms will have locally damaging gust potential given MLCAPE over 2000-3000 J/kg, with little organization due to weak winds aloft. However, the evolution of the early day MCS will need to be monitored, and a small corridor of higher probabilities for wind could be added in subsequent outlooks depending on trends. ...Central Plains to IL... Afternoon storms will be likely from CO eastward across southern NE/northern KS and into parts of IA near the stalled boundary. Strong heating and hot temperatures will aid development despite modest instability levels, with cooler yet still moist upslope flow over CO. Generally small to marginally severe hail will be possible as well as directional shear with height aids cellular storm mode. Stronger flow aloft on the southwest fringe of the Great Lakes upper trough may aid isolated hail potential as well from IA into IL due to slightly better shear. ..Jewell.. 08/24/2023 Read more

WW 0653 Status Updates
STATUS FOR WATCH 0653 HAS NOT BEEN ISSUED YET Read more

WW 653 SEVERE TSTM ND 232155Z - 240500Z
URGENT - IMMEDIATE BROADCAST REQUESTED Severe Thunderstorm Watch Number 653 NWS Storm Prediction Center Norman OK 455 PM CDT Wed Aug 23 2023 The NWS Storm Prediction Center has issued a * Severe Thunderstorm Watch for portions of North Central North Dakota * Effective this Wednesday afternoon from 455 PM until Midnight CDT. * Primary threats include... Scattered large hail and isolated very large hail events to 2 inches in diameter possible Scattered damaging wind gusts to 70 mph possible SUMMARY...Thunderstorms are intensifying over northwest North Dakota. This activity will track eastward this evening, with a few storms capable of large hail and damaging wind gusts. The severe thunderstorm watch area is approximately along and 40 statute miles north and south of a line from 70 miles west of Minot ND to 80 miles east of Minot ND. For a complete depiction of the watch see the associated watch outline update (WOUS64 KWNS WOU3). 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. && AVIATION...A few severe thunderstorms with hail surface and aloft to 2 inches. Extreme turbulence and surface wind gusts to 60 knots. A few cumulonimbi with maximum tops to 500. Mean storm motion vector 27025. ...Hart Read more

SPC Day 3-8 Fire Weather Outlook
Day 3-8 Fire Weather Outlook NWS Storm Prediction Center Norman OK 0358 PM CDT Wed Aug 23 2023 Valid 251200Z - 311200Z An upper ridge will slowly meander westward from the Plains states toward the Rockies as an upper trough amplifies over the eastern CONUS through the remainder of this week into early next week. Broad upper troughing will also prevail across the Pacific Northwest into next week, with the possibility of a more pronounced, progressive mid-level trough overspreading the region sometime after the upcoming weekend. Amid the aforementioned synoptic pattern/evolution, two primary areas of concern exist. Prolonged hot conditions (with RH dipping into the 20-35 percent range by afternoon peak heating) will persist each day across the south-central CONUS, with little beneficial rainfall in the forecast. Though differences in timing exist in medium-range guidance, there is a consensus among the GFS and ECMWF in the passage of a cold front across the southern Plains into the lower Mississippi Valley sometime in the Days 6-8/Monday-Wednesday period. Current indications are that this front may be dry, accompanied by little (if any) rainfall, breezy northwesterly surface flow, and fairly dry low-level air. Given highly receptive fuels, Critical conditions may occur, and Critical probabilities may be added in future outlooks pending model agreement in the timing of frontal passage. Across the Pacific Northwest, west of the Cascades, appreciable widespread rainfall has been largely absent, and is expected to remain so into next week. Fuels west of the Cascades are highly receptive to wildfire spread, supportive of efficient fire ignitions for any lightning that occurs away from soaking rain. Multiple instances of showers and thunderstorms are possible across the Pacific Northwest late this week into the weekend. However, questions remain regarding coverage, especially west of the Cascades, given scant buoyancy. As such, dry thunderstorm probabilities/highlights may be added in future outlooks if details regarding the timing of thunderstorm development and available buoyancy are resolved. ..Squitieri.. 08/23/2023 ...Please see www.spc.noaa.gov/fire for graphic product... Read more

SPC Day 3-8 Fire Weather Outlook
Day 3-8 Fire Weather Outlook NWS Storm Prediction Center Norman OK 0358 PM CDT Wed Aug 23 2023 Valid 251200Z - 311200Z An upper ridge will slowly meander westward from the Plains states toward the Rockies as an upper trough amplifies over the eastern CONUS through the remainder of this week into early next week. Broad upper troughing will also prevail across the Pacific Northwest into next week, with the possibility of a more pronounced, progressive mid-level trough overspreading the region sometime after the upcoming weekend. Amid the aforementioned synoptic pattern/evolution, two primary areas of concern exist. Prolonged hot conditions (with RH dipping into the 20-35 percent range by afternoon peak heating) will persist each day across the south-central CONUS, with little beneficial rainfall in the forecast. Though differences in timing exist in medium-range guidance, there is a consensus among the GFS and ECMWF in the passage of a cold front across the southern Plains into the lower Mississippi Valley sometime in the Days 6-8/Monday-Wednesday period. Current indications are that this front may be dry, accompanied by little (if any) rainfall, breezy northwesterly surface flow, and fairly dry low-level air. Given highly receptive fuels, Critical conditions may occur, and Critical probabilities may be added in future outlooks pending model agreement in the timing of frontal passage. Across the Pacific Northwest, west of the Cascades, appreciable widespread rainfall has been largely absent, and is expected to remain so into next week. Fuels west of the Cascades are highly receptive to wildfire spread, supportive of efficient fire ignitions for any lightning that occurs away from soaking rain. Multiple instances of showers and thunderstorms are possible across the Pacific Northwest late this week into the weekend. However, questions remain regarding coverage, especially west of the Cascades, given scant buoyancy. As such, dry thunderstorm probabilities/highlights may be added in future outlooks if details regarding the timing of thunderstorm development and available buoyancy are resolved. ..Squitieri.. 08/23/2023 ...Please see www.spc.noaa.gov/fire for graphic product... Read more

MD 2029 CONCERNING SEVERE POTENTIAL...WATCH POSSIBLE FOR NORTHWEST/NORTH-CENTRAL ND
Mesoscale Discussion 2029 NWS Storm Prediction Center Norman OK 0343 PM CDT Wed Aug 23 2023 Areas affected...Northwest/North-Central ND Concerning...Severe potential...Watch possible Valid 232043Z - 232315Z Probability of Watch Issuance...60 percent SUMMARY...Isolated supercells are possible this afternoon and evening across northwest/north-central ND. Primary severe risks with any mature storms are large hail and damaging gusts. DISCUSSION...Recent surface analysis places a low in far northwest ND, approximately 50 miles north of ISN. Visible satellite shows some deeper cumulus in the vicinity of this low, with some additional shallower cumulus ahead of it. The air mass across the region continues to destabilize amid strong heating and dewpoints in the upper 60s/low 70s. Recent mesoanalysis estimates MLCAPE is near 1500 J/kg just downstream of the surface low. Moderate mid-level flow stretches across this region as well, which is contributing to moderate/strong vertical shear. Recent mesoanalysis estimates effective bulk shear around 40-45 kt is currently in place. This moderate mid-level flow and associated moderate/strong shear is expected to persist across the region through the evening. Given these environmental conditions, a conditional risk of a supercell or two exists. Main uncertainty is whether or not updrafts can be maintained amid the potential entrainment of moderately warm and dry mid-level air. Current expectation is that at least a few storms should be able to persist, although, given the subtle forcing, it could be a few hours before updrafts are able to mature. Any storms that do mature/persist would likely become supercellular with a subsequent risk for large hail and/or damaging gusts. ..Mosier/Grams.. 08/23/2023 ...Please see www.spc.noaa.gov for graphic product... ATTN...WFO...FGF...BIS... LAT...LON 48450383 49030342 49009924 47529992 47300149 47380238 47710309 48450383 Read more

SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0256 PM CDT Wed Aug 23 2023 Valid 232000Z - 241200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS LOWER GREAT LAKES...NORTHERN NORTH DAKOTA... ...SUMMARY... Scattered damaging winds and large hail, and a tornado or two will be possible across parts of the Lower Great Lakes and northern North Dakota, centered on this evening into tonight. ...Discussion... Only minor changes were made to the previous convective outlook. 1) Extension of 5-percent and 15-percent wind probabilities farther south into southeast OH and WV. The 12z NSSL WRF had the best depiction of storm activity across eastern OH compared to other 12z CAMS and recent HRRR runs. The northerly flow across the upper OH Valley will aid in storm motions to the south. Some moisture advection into eastern OH in the 925-850 mb layer will act to destabilize the airmass downstream of the ongoing storms in eastern OH. 2) Remove a tier of counties in northern Lower MI from 5-percent hail probabilities. A considerable spatial extent of stratus will likely be maintained across northern Lower MI and this will likely limit overall destabilization and the hail risk. ..Smith.. 08/23/2023 .PREV DISCUSSION... /ISSUED 1128 AM CDT Wed Aug 23 2023/ ...Lower Great Lakes... A relatively low confidence but conditionally favorable environment for severe storms is expected through tonight with above-average spread in potential outcomes from minimal coverage to a mesoscale-focused swath of fairly numerous reports. Elevated convection is ongoing across eastern Lower MI to southern ON. This may not entirely decay during the afternoon, with a threat for isolated, marginally severe hail and strong wind gusts potentially persisting southeastward in eastern OH/western PA. To the west, a very unstable air mass will gradually advect east across much of southern Lower MI through western OH in tandem with an EML expanding from the Upper Midwest. A substantial baroclinic zone supported by pronounced differential boundary-layer heating will yield a sizable thermal gradient across the northwest to southeast-oriented warm front. The surface warm sector should remain capped but there are a few models, namely the 12Z ARW-NSSL and 00Z ECMWF which suggest convection should develop along the warm front and into the warm sector. The more probable scenario is for regenerative elevated convection to increase again after sunset. Forecast soundings suggest that deep-layer flow may remain relatively constant with height near the warm front which would limit cloud-bearing shear, with more favorable deep-layer shear farther east coincident with lesser instability. As such, a cluster convective mode will likely dominate with relatively equal threats for large hail and damaging winds. ...ND... An MCV over southeast SK will move east across southern MB into northwest ON tonight. While the bulk of convection attendant to this MCV may remain north of the international border, trailing development into ND will become increasingly likely towards early evening along the apex of a differential boundary-layer heating corridor centered over central ND. There should be favorable zone for a couple supercells across a portion of north-central to northeast ND within the MLCAPE/CIN gradient that should orient from northwest to southeast. Large hail, isolated severe wind gusts, and a tornado or two will be possible during the evening before convection tends to weaken overnight closer to the Red River Valley. Read more

SPC Day 2 Fire Weather Outlook
Day 2 Fire Weather Outlook NWS Storm Prediction Center Norman OK 1253 PM CDT Wed Aug 23 2023 Valid 241200Z - 251200Z Elevated highlights were added to portions of northern Montana, where a surface cold front will sweep across the state while a mid-level trough traverses the international border. Along and behind the cold front, RH may drop into the 15-20 percent range as widespread 15+ mph sustained northwesterly surface winds overspread fine fuels that are becoming receptive to wildfire spread. Isolated dry thunderstorm highlights have also been added to the Oregon/California border region, where an embedded mid-level impulse will promote deep-layer ascent amid a marginally buoyant airmass. Thunderstorm coverage should be quite sparse. However, any thunderstorms that develop will be fast-moving, and will pass over highly receptive fuels which have missed the benefits of recent rainfall from TC Hilary. ..Squitieri.. 08/23/2023 .PREV DISCUSSION... /ISSUED 0158 AM CDT Wed Aug 23 2023/ ...Synopsis... Within the base of a closed midlevel low off the Pacific Northwest coast, an embedded shortwave impulse should lift north-northeastward across OR during the evening/overnight hours. The related large-scale ascent and gradually increasing midlevel moisture/instability could support isolated thunderstorm development. While lightning-induced ignitions cannot be ruled out with any storms that develop over dry fuels, weak instability casts uncertainty on storm coverage and the overall risk -- precluding an Isolated Dry Thunderstorm area at this time. Farther east, boundary-layer mixing into a belt of enhanced deep-layer westerly flow over northern MT could favor dry/breezy conditions during the afternoon. While locally elevated fire-weather conditions are possible, recent rainfall could limit the overall risk. ...Please see www.spc.noaa.gov/fire for graphic product... Read more

SPC 1730Z Day 2 Outlook
Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1230 PM CDT Wed Aug 23 2023 Valid 241200Z - 251200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FOR THE SOUTHERN GREAT LAKES...CENTRAL APPALACHIANS...AND NORTH DAKOTA... ...SUMMARY... Isolated severe thunderstorms are possible across the southern Great Lakes and central Appalachians, and North Dakota late Thursday afternoon into Thursday night. ...Southern Great Lakes into the central Appalachians... A mid-level high over southern OK will maintain a suppressive influence on deep convective development across much of the central U.S. eastward towards the TN Valley. A belt of moderate west-northwesterly mid-level flow will extend from the Upper Great Lakes east-southeastward to the northern portion of the Mid-Atlantic region. In the low levels, a cold front will push southeast across the central Great Lakes into the Lower Great Lakes and provide a focus for thunderstorm development. Very warm mid-level temperatures on the northeast periphery of the mid-level anticyclone will likely inhibit convective development for much of the day. However, associated with the elevated mixed layer over the southern Great Lakes, steep 700-500 mb lapse rates and a very moisture-rich airmass will contribute to moderate to extreme instability developing by mid afternoon. Model guidance indicates at least isolated to scattered storms will develop near the Lake Erie vicinity on the northeast periphery of stronger capping. It remains unclear on the overall coverage/placement and subsequent evolution of storms in the Lower Great Lakes/upper OH Valley. If a cluster can develop and become surface-based, a potentially greater risk for severe may occur (i.e., upper OH Valley/Lake Erie vicinity). This activity will probably grow upscale into the central Appalachians during the evening into the overnight and perhaps maintain a risk for damaging gusts/large hail. Farther west across the southern Great Lakes, the surface boundary will become more diffuse with west extent near the MS River. Very hot conditions may overcome the weakly forced setup and result in a few storms from Michiana westward into far eastern IA. Severe gusts and perhaps large hail will be the primary threats with these potential storms. ...ND... A mid-level shortwave trough over Alberta/Saskatchewan will pivot southeast towards the Canadian/ND border by early evening and into northern MN by daybreak Friday. A weak front will push southeast into ND by mid afternoon. Steep low- to mid-level lapse rates and dewpoints ranging from the 50s west to low-mid 60s over eastern ND, will result in weak to moderate buoyancy. The latest model guidance indicates isolated to scattered storms developing near the boundary by early evening. Elongated hodographs will aid in storm organization (i.e., organized multicells and a few supercells). Isolated large hail and severe gusts are the primary risks with the stronger storms. Some of this activity may linger into the overnight as it moves east across ND late. ..Smith.. 08/23/2023 Read more

No watches are valid as of Tue Aug 22 22:28:01 UTC 2023.

No Mesoscale Discussions are in effect as of Tue Aug 22 22:28:01 UTC 2023.

SPC Day 3-8 Fire Weather Outlook
Day 3-8 Fire Weather Outlook NWS Storm Prediction Center Norman OK 0348 PM CDT Tue Aug 22 2023 Valid 241200Z - 301200Z A broad upper ridge will prevail across much of the southern and central CONUS through this week into early next week, with medium-range guidance depicting a pronounced mid-level trough impinging on the Pacific Northwest by Days 7-8/Monday-Tuesday. Hot and occasionally dry conditions will continue beneath the upper ridge across portions of the central and southern Plains into the lower MS Valley through the extended period, with no appreciable rainfall accumulations in the forecast. Surface winds should remain relatively weak across the southern CONUS, precluding the addition of Critical probabilities, though fire weather highlights may be needed if regional increases in surface winds become apparent. While several areas near and west of the Rockies will benefit from appreciable rainfall produced by the remnants of Hilary and perhaps Harold, fuels should remain dry and highly receptive to wildfire spread west of the Cascades (i.e. extreme northwest California into western Oregon and Washington). Isolated thunderstorms are possible along and west of the Cascades as a mid-level impulse tracks across the region Days 3-4/Thursday-Friday. However, uncertainty regarding dry thunderstorm coverage precludes dry thunderstorm probabilities this outlook. Medium range guidance is also in agreement that potentially dry and windy surface conditions may develop across portions of the Pacific Northwest by early next week with the approach of a more pronounced mid-level trough. However, the exact placement and timing of favorable dry/windy conditions remains unclear this far in advance and more guidance consistency is needed for the addition of Critical probabilities. ..Squitieri.. 08/22/2023 ...Please see www.spc.noaa.gov/fire for graphic product... Read more

SPC Day 3-8 Fire Weather Outlook
Day 3-8 Fire Weather Outlook NWS Storm Prediction Center Norman OK 0348 PM CDT Tue Aug 22 2023 Valid 241200Z - 301200Z A broad upper ridge will prevail across much of the southern and central CONUS through this week into early next week, with medium-range guidance depicting a pronounced mid-level trough impinging on the Pacific Northwest by Days 7-8/Monday-Tuesday. Hot and occasionally dry conditions will continue beneath the upper ridge across portions of the central and southern Plains into the lower MS Valley through the extended period, with no appreciable rainfall accumulations in the forecast. Surface winds should remain relatively weak across the southern CONUS, precluding the addition of Critical probabilities, though fire weather highlights may be needed if regional increases in surface winds become apparent. While several areas near and west of the Rockies will benefit from appreciable rainfall produced by the remnants of Hilary and perhaps Harold, fuels should remain dry and highly receptive to wildfire spread west of the Cascades (i.e. extreme northwest California into western Oregon and Washington). Isolated thunderstorms are possible along and west of the Cascades as a mid-level impulse tracks across the region Days 3-4/Thursday-Friday. However, uncertainty regarding dry thunderstorm coverage precludes dry thunderstorm probabilities this outlook. Medium range guidance is also in agreement that potentially dry and windy surface conditions may develop across portions of the Pacific Northwest by early next week with the approach of a more pronounced mid-level trough. However, the exact placement and timing of favorable dry/windy conditions remains unclear this far in advance and more guidance consistency is needed for the addition of Critical probabilities. ..Squitieri.. 08/22/2023 ...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 Tue Aug 22 2023 Valid 222000Z - 231200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FOR PARTS OF SOUTH TX...THE EASTERN GREAT BASIN TO NORTHERN ROCKIES...AND MI... ...SUMMARY... A brief tornado or two will remain possible through the rest of the afternoon across a portion of South Texas. Isolated severe wind gusts will be the primary threat later this afternoon across parts of the eastern Great Basin to the northern Rockies. Isolated severe hail will be possible across parts of Michigan early Wednesday. ...20Z Update... The 2% tornado probabilities in south TX have been trimmed to more closely align with an arc of convection to the east/northeast of TC Harold's center. While low-level shear/SRH will tend to gradually decrease with time as Harold weakens, transient low-topped supercells capable of a brief tornado or two will remain possible through the remainder of the afternoon to the north/northeast of Harold's track, as it continues to move west-northwestward. Elsewhere, no changes have been made to the Marginal Risk areas. See the previous discussion below for more information, and also see MCD 2025 for more information regarding the short-term threat from parts of UT into southwest WY. ..Dean.. 08/22/2023 .PREV DISCUSSION... /ISSUED 1130 AM CDT Tue Aug 22 2023/ ...South TX... TC Harold near the Lower Texas Coastal Plain will move west-northwest and weaken across South TX into this evening. Potential for a brief tornado or two should linger to the west-northwest through north relative to the center circulation. Low-topped convection along the western extent of surface dew points at or above 76 F should remain coupled with adequate low-level SRH for a few more hours inland before the environment conducive to tornadoes diminishes spatially and in magnitude late this afternoon. ...Eastern Great Basin to the northern Rockies... Similar to yesterday, a moisture plume coincident with a belt of enhanced mid-level southerlies will support sporadic strong storms, focused on central to eastern UT and western WY. A few multicells and transitory/weak supercell structures should evolve this afternoon, mainly within a corridor where differential boundary-layer heating is most pronounced. While deep-layer shear will be sufficient for storm organization, moist profiles will render weak mid-level lapse rates, limiting the overall magnitude of destabilization and the severe wind threat. ...Upper Great Lakes... A repeat scenario of elevated thunderstorm development is expected during the early morning Wednesday shifted a bit farther east relative to this morning across parts of MI. With a stronger low-level jet overnight and deeper updrafts regenerating within the zone of isentropic ascent along the fringe of an EML expanding east from northern MN to western Upper MI, a cluster convective mode should largely dominate. This will probably marginalize the severe hail risk, while severe wind gusts appear unlikely given the stable boundary layer where storms are expected to occur. Read more

SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0256 PM CDT Tue Aug 22 2023 Valid 222000Z - 231200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FOR PARTS OF SOUTH TX...THE EASTERN GREAT BASIN TO NORTHERN ROCKIES...AND MI... ...SUMMARY... A brief tornado or two will remain possible through the rest of the afternoon across a portion of South Texas. Isolated severe wind gusts will be the primary threat later this afternoon across parts of the eastern Great Basin to the northern Rockies. Isolated severe hail will be possible across parts of Michigan early Wednesday. ...20Z Update... The 2% tornado probabilities in south TX have been trimmed to more closely align with an arc of convection to the east/northeast of TC Harold's center. While low-level shear/SRH will tend to gradually decrease with time as Harold weakens, transient low-topped supercells capable of a brief tornado or two will remain possible through the remainder of the afternoon to the north/northeast of Harold's track, as it continues to move west-northwestward. Elsewhere, no changes have been made to the Marginal Risk areas. See the previous discussion below for more information, and also see MCD 2025 for more information regarding the short-term threat from parts of UT into southwest WY. ..Dean.. 08/22/2023 .PREV DISCUSSION... /ISSUED 1130 AM CDT Tue Aug 22 2023/ ...South TX... TC Harold near the Lower Texas Coastal Plain will move west-northwest and weaken across South TX into this evening. Potential for a brief tornado or two should linger to the west-northwest through north relative to the center circulation. Low-topped convection along the western extent of surface dew points at or above 76 F should remain coupled with adequate low-level SRH for a few more hours inland before the environment conducive to tornadoes diminishes spatially and in magnitude late this afternoon. ...Eastern Great Basin to the northern Rockies... Similar to yesterday, a moisture plume coincident with a belt of enhanced mid-level southerlies will support sporadic strong storms, focused on central to eastern UT and western WY. A few multicells and transitory/weak supercell structures should evolve this afternoon, mainly within a corridor where differential boundary-layer heating is most pronounced. While deep-layer shear will be sufficient for storm organization, moist profiles will render weak mid-level lapse rates, limiting the overall magnitude of destabilization and the severe wind threat. ...Upper Great Lakes... A repeat scenario of elevated thunderstorm development is expected during the early morning Wednesday shifted a bit farther east relative to this morning across parts of MI. With a stronger low-level jet overnight and deeper updrafts regenerating within the zone of isentropic ascent along the fringe of an EML expanding east from northern MN to western Upper MI, a cluster convective mode should largely dominate. This will probably marginalize the severe hail risk, while severe wind gusts appear unlikely given the stable boundary layer where storms are expected to occur. Read more

SPC Day 2 Fire Weather Outlook
Day 2 Fire Weather Outlook NWS Storm Prediction Center Norman OK 0205 PM CDT Tue Aug 22 2023 Valid 231200Z - 241200Z ...NO CRITICAL AREAS... The previous forecast (see below) remains on track, with no changes or additions made. ..Squitieri.. 08/22/2023 .PREV DISCUSSION... /ISSUED 0205 AM CDT Tue Aug 22 2023/ ...Synopsis... An expansive midlevel anticyclone will persist over the central CONUS on Day 2/Wednesday. Along its northern periphery, a belt of enhanced low/mid-level flow is expected from parts of the central Plains into the Midwest -- where a tightening pressure gradient will develop in the vicinity of surface low pressure. While breezy/gusty surface winds are expected through this corridor, somewhat marginal RH reductions and modestly receptive fuels should generally limit the fire-weather risk -- precluding highlights at this time. Farther south along the southwestern periphery of the anticyclone, breezy/gusty southeasterly surface winds are expected across southwest TX, though heating and related RH reductions could also be limited here. ...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 0205 PM CDT Tue Aug 22 2023 Valid 231200Z - 241200Z ...NO CRITICAL AREAS... The previous forecast (see below) remains on track, with no changes or additions made. ..Squitieri.. 08/22/2023 .PREV DISCUSSION... /ISSUED 0205 AM CDT Tue Aug 22 2023/ ...Synopsis... An expansive midlevel anticyclone will persist over the central CONUS on Day 2/Wednesday. Along its northern periphery, a belt of enhanced low/mid-level flow is expected from parts of the central Plains into the Midwest -- where a tightening pressure gradient will develop in the vicinity of surface low pressure. While breezy/gusty surface winds are expected through this corridor, somewhat marginal RH reductions and modestly receptive fuels should generally limit the fire-weather risk -- precluding highlights at this time. Farther south along the southwestern periphery of the anticyclone, breezy/gusty southeasterly surface winds are expected across southwest TX, though heating and related RH reductions could also be limited here. ...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 1223 PM CDT Tue Aug 22 2023 Valid 231200Z - 241200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FOR NORTHEAST ND INTO NORTHERN MN...AND ALSO FOR LOWER MI...NORTHERN OH...WESTERN PA/NY... ...SUMMARY... Isolated to widely scattered strong to severe storms are possible Wednesday across Lower Michigan into the Lake Erie and western Lake Ontario vicinity, and also from northeast North Dakota into northern Minnesota. ...Lower Great Lakes region... Multiple rounds of thunderstorms will be possible Wednesday across the lower Great Lakes region. Elevated convection will likely be ongoing Wednesday morning across parts of lower MI, aided by a moderate low-level jet and associated warm advection to the east of a north-south oriented baroclinic zone. Moderate MUCAPE may support an isolated hail threat before storms weaken by late morning. The baroclinic zone will move eastward as a warm front Wednesday afternoon, though its progress will be modulated by how quickly morning convection abates across lower MI. Diurnal heating of a moist low-level environment will support strong destabilization along/west of the warm front by late afternoon. Surface-based storm development cannot be ruled out during the late afternoon into the early evening across the warm sector as MLCINH diminishes. Sufficient deep-layer shear would support a conditional supercell risk with all severe hazards if surface-based development occurs, but this remains a low-probability scenario with large-scale ascent expected to generally weaken through the day as low-level warm advection shifts eastward. Another round of elevated convection associated with nocturnal strengthening of the low-level jet is expected Wednesday night into Thursday morning. Initial development will tend to occur over southern Ontario, perhaps extending into eastern lower MI, with storms potentially evolving into a loosely organized MCS and spreading into parts of northern OH and western PA/NY with time. Moderate to strong elevated buoyancy (MUCAPE of 2000 J/kg or greater) will support some hail potential with stronger embedded cells, while isolated strong/damaging gusts will be possible if more organized upscale growth occurs by early Thursday morning. ...Northern ND/MN... A weakening midlevel shortwave trough (the remnant of a trough that persisted for several days over the West) will move across parts of the northern Plains on Wednesday, around the periphery of the upper ridge. While richer low-level moisture will likely stay south of the region, some modest moistening and destabilization will be possible through the day into eastern ND and northern MN. While MLCINH will likely prohibit diurnal surface-based storm development, ascent attendant to the shortwave and continued moistening in the 850-700 mb layer may result in slightly elevated storm development during the evening. Favorable deep-layer shear will support potential for an elevated supercell or two, with an attendant threat of isolated hail and localized strong/damaging gusts. ..Dean.. 08/22/2023 Read more