SPC Day 1 Fire Weather Outlook
Day 1 Fire Weather Outlook NWS Storm Prediction Center Norman OK 1201 PM CDT Mon Sep 02 2024 Valid 021700Z - 031200Z ...CRITICAL FIRE WEATHER AREA FOR SOUTHERN OREGON INTO FAR NORTHEAST CALIFORNIA AND FAR NORTHWEST NEVADA... ...CRITICAL FIRE WEATHER AREA FOR SOUTHEAST OREGON AND SOUTHWEST IDAHO...NORTHEAST NEVADA...AND FAR NORTHWEST UTAH... ...CRITICAL FIRE WEATHER AREA FOR NORTHWEST NEBRASKA INTO WESTERN SOUTH DAKOTA... An active day of fire weather is anticipated across the Pacific Northwest, Great Basin, and portions of the High Plains. Morning 12z observed soundings from SLC (Salt Lake City, UT) and LKN (Elko, NV) indicate precipitable water values around 0.60". Midlevel moisture should increase through the day ahead of forcing for ascent with a midlevel wave currently just offshore in the Pacific Northwest. A mix of isolated to scattered wet/dry thunderstorms is expected by the afternoon with potential for new ignitions from lightning. In addition, Critical conditions are likely in the lee of the Sierra across Nevada and in the High Plains. No changes have been made to this forecast. See previous discussion for more information below. ..Thornton.. 09/02/2024 .PREV DISCUSSION... /ISSUED 0150 AM CDT Mon Sep 02 2024/ ...Synopsis... An active fire weather day is anticipated across the High Plains and Pacific Northwest/northern Great Basin. Fire weather concerns across the West will be associated with a progressive upper wave currently moving onshore along the northern CA coast, which is forecast to migrate into the interior Pacific Northwest over the next 24 hours. As this occurs, strengthening low-level winds will support dry/windy conditions, and lift ahead of the wave will promote isolated to scattered thunderstorms. To the east, flow across the northern to central Rockies is forecast to strengthen slightly within the apex of an upper ridge. This will result in modest surface pressure falls along the High Plains, which when juxtaposed with a building surface high over the Midwest will yield strong southerly winds and dry conditions. Fuels across both regions remain very dry (ERCs at or above the 90th percentile) after multiple days of dry conditions, which will support the fire weather concerns. ...Pacific Northwest/Great Basin... Regional VWPs along the West Coast are beginning to observe the influence of the approaching wave with winds in the lowest few kilometers slowly strengthening since 00 UTC. Further intensification of the low-level wind field is anticipated, which will strengthen downslope flow off the central to northern Sierra Nevada. Dry conditions are already in place and will be maintained within the augmented downslope regime. Latest ensemble guidance continues to show a strong signal for afternoon RH values to fall into the teens with 15-25 mph winds. The strongest winds (and highest probability for sustained critical conditions) are expected from northeast CA into southern OR and far northwest NV as the mid-level jet max passes overhead around peak heating. Over the past several days, a plume of monsoonal moisture has been tracked from southern AZ into northern NV and central to eastern OR. The 00 UTC MFR sounding sampled this air mass well, which is characterized by sufficient mid-level moisture to support weak convection, but a very dry boundary layer favorable for dry thunderstorms. Over the past two days, thunderstorms within this air mass across the Great Basin have been predominantly dry, and are expected to mainly be dry once again today for much of the region (one exception is from the Blue Mountains in northeast OR to the Salmon River Mountains in central ID where orographic ascent should support more prolonged convection with a higher probability for wetting rainfall). Stronger synoptic-scale forcing for ascent should result in greater thunderstorm coverage compared to previous days, warranting a scattered dry thunderstorm risk area from eastern OR into ID, northeast NV, and far northwest UT where latest CAM guidance shows the best convective signal. ...High Plains... A recent frontal intrusion into the Plains/Midwest has shunted seasonally rich moisture southward into the southern Plains. A strong surface high in the wake of the front will shift east through the day concurrent with the deepening of a weak lee trough. A dry return flow regime will become established through the day as winds become more southerly. Latest deterministic and ensemble solutions show a fairly strong signal for 20-25 mph winds (gusting to 35 mph) across western NE into western SD with RH values falling into the low 20s to teens. Consequently, confidence in sustained critical conditions over an appreciable area has increased enough to warrant introducing a Critical risk area. ...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 1118 AM CDT Mon Sep 02 2024 Valid 021630Z - 031200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE INTERIOR PACIFIC NORTHWEST INTO THE NORTHERN GREAT BASIN/ROCKIES... ...SUMMARY... Isolated to scattered thunderstorms across the northern Great Basin and parts of the interior Pacific Northwest may be capable of occasional strong to severe wind gusts this afternoon and evening. ...Interior Pacific Northwest into the Northern Great Basin/Rockies... Water-vapor imagery this morning shows a closed low near the northern CA/southern OR coast. This upper feature will move east through OR and be situated along the OR/ID border by daybreak Tuesday. A belt of stronger flow (30-50 kt 500-mb winds) will move through the base of the larger-scale mid-level trough and overspread northern NV into southwestern ID and eastern OR this afternoon into the early evening. Large-scale ascent associated with the upper disturbance and the development of weak buoyancy (mainly via heating), will facilitate the development of isolated to scattered high-based thunderstorms beginning later this afternoon and persisting into the evening. Forecast soundings show large surface temperature-dewpoint spreads (50 degrees F) with 9+ degrees C lapse rates into the mid levels and a dry sub-cloud layer. Evaporative cooling of the more intense downdrafts will probably yield a risk for isolated 60-70 mph gusts before weakening later this evening. ..Smith/Squitieri.. 09/02/2024 Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0738 AM CDT Mon Sep 02 2024 Valid 021300Z - 031200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE INTERIOR PACIFIC NORTHWEST INTO THE NORTHERN GREAT BASIN/ROCKIES... ...SUMMARY... Isolated to scattered thunderstorms across the northern Great Basin and parts of the interior Pacific Northwest may be capable of occasional strong to severe wind gusts this afternoon and evening. ...Interior Pacific Northwest into the Northern Great Basin/Rockies... A closed upper low approaching the northern CA and OR Coast will continue eastward today across the Pacific Northwest and northern Great Basin. Associated 35-50 kt mid-level south-southwesterlies will overspread these regions through the afternoon and evening. Large-scale ascent attendant to the upper low has already encouraged weak, elevated convection this morning across pats of eastern OR and vicinity. Current expectations are for additional showers and thunderstorms to develop later this afternoon as daytime heating occurs, mainly across parts of central/eastern OR into ID and northern NV/northwest UT. This convection will likely be rather high-based (LCLs around 3-4 km AGL), as latest surface observations and area 12Z soundings show very limited low-level moisture, and total PWAT values generally 0.5-0.7 inches. Even with rather weak buoyancy forecast across much of this area, a deeply mixed boundary layer should encourage efficient evaporative cooling of convective downdrafts. An isolated risk for strong/gusty winds approaching and occasionally exceeding severe levels remains apparent with this high-based convection as it spreads generally north-northeastward through the afternoon/evening before eventually weakening. ..Gleason/Leitman.. 09/02/2024 Read more

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0400 AM CDT Mon Sep 02 2024 Valid 051200Z - 101200Z ...DISCUSSION... Global models have come into a bit better agreement with each other, through late next week, with respect to their handling of the large-scale features. Day 4 (Thursday), the upper trough crossing central portions of Canada and the north-central U.S. is progged to continue digging southeastward -- reaching a roughly upper Mississippi Valley to Mid-Missouri Valley position by Friday morning. As this occurs, a corresponding eastward/southward advance of a surface cold front will occur, crossing the Upper Great Lakes/Upper Midwest and drifting as far south as the central Plains overnight. Preceding the front, limited low-level moisture is expected, with Gulf moisture remaining restricted to the southern-tier states. Thus, while a few strong/severe storms may evolve within a southern Upper Great Lakes to central Plains corridor, potential for a more widespread severe event appears limited at this time. Day 5 (Friday), a continued southeastward advance/amplification of the upper trough is anticipated, shifting across the Great Lakes and Midwest through the day, and with cyclonic flow surrounding the trough to encompass the entire eastern half of the country by Saturday morning. The associated cold front -- crossing the central U.S. through the day, is expected to reach a Lower Great Lakes to Lower Mississippi Valley to Texas position overnight. Meanwhile, the height falls associated with this trough into the southeastern U.S. may support frontal wave development along the remnant baroclinic zone likely to be lingering over the northern Gulf/Gulf Coast area. While still uncertain, this low may shift across the Southeast Friday, reaching the eastern Carolinas vicinity by Sunday morning. While it is not out of the question that -- with this front/low marking the northward extent of tropical low-level air, that low-end severe risk could evolve overnight. However, this scenario is uncertain, and would seem likely to remain limited in terms of significance. Day 6, some negative tilt of the upper trough is expected as it advances across the Midwest and Lower Great Lakes area, with models suggesting evolution into a closed low over the eastern Ontario vicinity with time. Meanwhile, the advancing cold front is progged to begin to overtake the remnant baroclinic zone and frontal wave, with the combined front to linger near -- and eventually move off -- the Atlantic Seaboard as the frontal low moves toward/into southern New England overnight. Again, some severe potential may manifest ahead of the consolidating surface front, but at this time, models suggest that destabilization will remain largely just offshore. By Sunday (Day 7) and continuing through the end of the period, model divergence increases -- with evolution/positioning of the deepening closed low over eastern NOAM, and -- as a result, the upstream flow pattern over the western half of the country. Overall severe risk would appear to be low overall however, with general ridging likely over the western half of the country. Read more

SPC 0730Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0230 AM CDT Mon Sep 02 2024 Valid 041200Z - 051200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF THE NORTH-CENTRAL U.S. AND INTO THE ROCKIES... ...SUMMARY... Risk for isolated strong to severe storms -- capable of producing gusty/locally damaging winds -- will be possible from parts of Montana/Wyoming/Colorado into the northern Plains Wednesday/Wednesday night. Marginal hail with stronger storms may also occur across the northern Plains region. ...Synopsis... The main upper feature of interest with respect to convective/local severe risk will be a short-wave trough initially situated from the northern Intermountain region to the Great Basin. As this feature advances eastward toward -- and eventually into -- the northern and central Plains, it is expected to gradually phase with larger-scale trough digging southeastward into the Canadian Prairie. This will result in slow amplification of the upper pattern over Canada and the adjacent northern half of the U.S. through Thursday morning. At the surface, a baroclinic zone is forecast to linger in the vicinity of the Gulf Coast/northern Gulf of Mexico, at the southern fringe of a drier Continental airmass represented by a large area of high pressure over the eastern and into the central states. Meanwhile, a second cold front -- ahead of the evolving northern U.S. upper trough -- will shift eastward across the northern Plains and southward into the central Plains through the period. By Thursday morning, the front should extend from Minnesota southwestward to the Far West Texas vicinity. ...Northern Plains into parts of Montana/Wyoming/Colorado... Diurnal heating in the wake of the advancing cold front/beneath the upper trough will result in modest destabilization across portions of Montana/Wyoming/Colorado during the afternoon -- resulting in development of isolated thunderstorms. With a belt of moderate mid-level west-southwesterlies supporting locally stronger updrafts, and a deep mixed layer suggesting some evaporative enhancement potential in the sub-cloud layer, a few instances of strong/severe outflow winds are expected. Farther east, destabilization near/ahead of the advancing from should support isolated storm by late afternoon, and continuing into the evening hours. With shear becoming sufficient for organized updrafts, a few stronger storms during the afternoon and evening should prove capable of producing strong/gusty winds and marginal hail, before nocturnally weakening. ..Goss.. 09/02/2024 Read more

SPC 0730Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0230 AM CDT Mon Sep 02 2024 Valid 041200Z - 051200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF THE NORTH-CENTRAL U.S. AND INTO THE ROCKIES... ...SUMMARY... Risk for isolated strong to severe storms -- capable of producing gusty/locally damaging winds -- will be possible from parts of Montana/Wyoming/Colorado into the northern Plains Wednesday/Wednesday night. Marginal hail with stronger storms may also occur across the northern Plains region. ...Synopsis... The main upper feature of interest with respect to convective/local severe risk will be a short-wave trough initially situated from the northern Intermountain region to the Great Basin. As this feature advances eastward toward -- and eventually into -- the northern and central Plains, it is expected to gradually phase with larger-scale trough digging southeastward into the Canadian Prairie. This will result in slow amplification of the upper pattern over Canada and the adjacent northern half of the U.S. through Thursday morning. At the surface, a baroclinic zone is forecast to linger in the vicinity of the Gulf Coast/northern Gulf of Mexico, at the southern fringe of a drier Continental airmass represented by a large area of high pressure over the eastern and into the central states. Meanwhile, a second cold front -- ahead of the evolving northern U.S. upper trough -- will shift eastward across the northern Plains and southward into the central Plains through the period. By Thursday morning, the front should extend from Minnesota southwestward to the Far West Texas vicinity. ...Northern Plains into parts of Montana/Wyoming/Colorado... Diurnal heating in the wake of the advancing cold front/beneath the upper trough will result in modest destabilization across portions of Montana/Wyoming/Colorado during the afternoon -- resulting in development of isolated thunderstorms. With a belt of moderate mid-level west-southwesterlies supporting locally stronger updrafts, and a deep mixed layer suggesting some evaporative enhancement potential in the sub-cloud layer, a few instances of strong/severe outflow winds are expected. Farther east, destabilization near/ahead of the advancing from should support isolated storm by late afternoon, and continuing into the evening hours. With shear becoming sufficient for organized updrafts, a few stronger storms during the afternoon and evening should prove capable of producing strong/gusty winds and marginal hail, before nocturnally weakening. ..Goss.. 09/02/2024 Read more

SPC Day 2 Fire Weather Outlook
Day 2 Fire Weather Outlook NWS Storm Prediction Center Norman OK 0218 AM CDT Mon Sep 02 2024 Valid 031200Z - 041200Z ...Synopsis... Fire weather concerns will continue into Tuesday as an upper wave (currently moving onshore along the northern CA coast) translates east across the northern Rockies. However, fire weather conditions are not expected to be as intense or widespread as compared to Monday across on either side of the continental divide. ...Nevada into Idaho... Portions of northeast NV and central ID are forecast to remain within the dry slot of the maturing upper-level low. This will maintain clear skies/warm conditions across the region, but will also support broad scale subsidence/drying and windy conditions across the region. Regional orographic influences - namely the Snake River Plain in eastern ID as well as the Independence and Ruby mountains of northeast NV, will augment the dry/windy conditions and should support several hours of elevated fire weather conditions. Isolated to scattered thunderstorms are also anticipated across northern ID, MT, and WY by late afternoon as the low shifts east. While a few dry thunderstorms are possible based on forecast thermal profiles, recent ensemble guidance shows a stronger signal for wetting rainfall compared to Monday, limiting confidence in the dry-lightning threat. ...Central/Northern Plains... A lee trough is expected to become established over the next 24 hours, but will see more substantial deepening through Tuesday afternoon amid increasing synoptic-scale ascent ahead of the approaching upper wave. This will result in not only strengthening westerly downslope flow across eastern WY, but will also bolster pressure gradient winds across central NE into SD. Recent ensemble guidance shows reasonably high confidence in maintaining at least a few hours of elevated fire weather conditions for both regions with 15-20 mph winds and RH reductions into the teens and low 20s. Persistent southerly flow overnight Monday into Tuesday will support some degree of moisture return into the Plains, which is expected to limit the spatial coverage of elevated fire weather conditions. That said, guidance typically struggles to accurately capture boundary-layer mixing/RH reductions in such return flow regimes, and fire weather conditions may be more widespread across NE/SD than currently depicted. ..Moore.. 09/02/2024 ...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 0218 AM CDT Mon Sep 02 2024 Valid 031200Z - 041200Z ...Synopsis... Fire weather concerns will continue into Tuesday as an upper wave (currently moving onshore along the northern CA coast) translates east across the northern Rockies. However, fire weather conditions are not expected to be as intense or widespread as compared to Monday across on either side of the continental divide. ...Nevada into Idaho... Portions of northeast NV and central ID are forecast to remain within the dry slot of the maturing upper-level low. This will maintain clear skies/warm conditions across the region, but will also support broad scale subsidence/drying and windy conditions across the region. Regional orographic influences - namely the Snake River Plain in eastern ID as well as the Independence and Ruby mountains of northeast NV, will augment the dry/windy conditions and should support several hours of elevated fire weather conditions. Isolated to scattered thunderstorms are also anticipated across northern ID, MT, and WY by late afternoon as the low shifts east. While a few dry thunderstorms are possible based on forecast thermal profiles, recent ensemble guidance shows a stronger signal for wetting rainfall compared to Monday, limiting confidence in the dry-lightning threat. ...Central/Northern Plains... A lee trough is expected to become established over the next 24 hours, but will see more substantial deepening through Tuesday afternoon amid increasing synoptic-scale ascent ahead of the approaching upper wave. This will result in not only strengthening westerly downslope flow across eastern WY, but will also bolster pressure gradient winds across central NE into SD. Recent ensemble guidance shows reasonably high confidence in maintaining at least a few hours of elevated fire weather conditions for both regions with 15-20 mph winds and RH reductions into the teens and low 20s. Persistent southerly flow overnight Monday into Tuesday will support some degree of moisture return into the Plains, which is expected to limit the spatial coverage of elevated fire weather conditions. That said, guidance typically struggles to accurately capture boundary-layer mixing/RH reductions in such return flow regimes, and fire weather conditions may be more widespread across NE/SD than currently depicted. ..Moore.. 09/02/2024 ...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 0150 AM CDT Mon Sep 02 2024 Valid 021200Z - 031200Z ...CRITICAL FIRE WEATHER AREA FOR SOUTHERN OREGON INTO FAR NORTHEAST CALIFORNIA AND FAR NORTHWEST NEVADA... ...CRITICAL FIRE WEATHER AREA FOR SOUTHEAST OREGON INTO SOUTHWEST IDAHO...NORTHEAST NEVADA...AND FAR NORTHWEST UTAH... ...CRITICAL FIRE WEATHER AREA FOR NORTHWEST NEBRASKA INTO WESTERN SOUTH DAKOTA... ...Synopsis... An active fire weather day is anticipated across the High Plains and Pacific Northwest/northern Great Basin. Fire weather concerns across the West will be associated with a progressive upper wave currently moving onshore along the northern CA coast, which is forecast to migrate into the interior Pacific Northwest over the next 24 hours. As this occurs, strengthening low-level winds will support dry/windy conditions, and lift ahead of the wave will promote isolated to scattered thunderstorms. To the east, flow across the northern to central Rockies is forecast to strengthen slightly within the apex of an upper ridge. This will result in modest surface pressure falls along the High Plains, which when juxtaposed with a building surface high over the Midwest will yield strong southerly winds and dry conditions. Fuels across both regions remain very dry (ERCs at or above the 90th percentile) after multiple days of dry conditions, which will support the fire weather concerns. ...Pacific Northwest/Great Basin... Regional VWPs along the West Coast are beginning to observe the influence of the approaching wave with winds in the lowest few kilometers slowly strengthening since 00 UTC. Further intensification of the low-level wind field is anticipated, which will strengthen downslope flow off the central to northern Sierra Nevada. Dry conditions are already in place and will be maintained within the augmented downslope regime. Latest ensemble guidance continues to show a strong signal for afternoon RH values to fall into the teens with 15-25 mph winds. The strongest winds (and highest probability for sustained critical conditions) are expected from northeast CA into southern OR and far northwest NV as the mid-level jet max passes overhead around peak heating. Over the past several days, a plume of monsoonal moisture has been tracked from southern AZ into northern NV and central to eastern OR. The 00 UTC MFR sounding sampled this air mass well, which is characterized by sufficient mid-level moisture to support weak convection, but a very dry boundary layer favorable for dry thunderstorms. Over the past two days, thunderstorms within this air mass across the Great Basin have been predominantly dry, and are expected to mainly be dry once again today for much of the region (one exception is from the Blue Mountains in northeast OR to the Salmon River Mountains in central ID where orographic ascent should support more prolonged convection with a higher probability for wetting rainfall). Stronger synoptic-scale forcing for ascent should result in greater thunderstorm coverage compared to previous days, warranting a scattered dry thunderstorm risk area from eastern OR into ID, northeast NV, and far northwest UT where latest CAM guidance shows the best convective signal. ...High Plains... A recent frontal intrusion into the Plains/Midwest has shunted seasonally rich moisture southward into the southern Plains. A strong surface high in the wake of the front will shift east through the day concurrent with the deepening of a weak lee trough. A dry return flow regime will become established through the day as winds become more southerly. Latest deterministic and ensemble solutions show a fairly strong signal for 20-25 mph winds (gusting to 35 mph) across western NE into western SD with RH values falling into the low 20s to teens. Consequently, confidence in sustained critical conditions over an appreciable area has increased enough to warrant introducing a Critical risk area. ..Moore.. 09/02/2024 ...Please see www.spc.noaa.gov/fire for graphic product... Read more

SPC 0600Z Day 2 Outlook
Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 0101 AM CDT Mon Sep 02 2024 Valid 031200Z - 041200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF THE NORTHERN INTERMOUNTAIN REGION AND GREAT BASIN... ...SUMMARY... Scattered strong/a few severe storms capable of producing damaging wind gusts, and possibly marginal hail, are expected from the northern Intermountain region eastward into the northern High Plains, and southward into Utah. ...Synopsis... As a large-scale upper trough continues to vacate the northeastern U.S. Tuesday, a second/short-wave trough initially situated over the Pacific Northwest will advance eastward across the northern Intermountain region/Great Basin. At the surface, a cold front will shift eastward across the northwestern quarter of the country, in conjunction with the advancing upper trough, while westerly flow aloft will maintain a High-Plains lee trough. Meanwhile, a remnant baroclinic zone will linger from the southern Atlantic coastal area westward across the Gulf Coast/northern Gulf of Mexico through the period, as a large area of high pressure prevails north of the front, across the central and eastern U.S., through the period. ...Montana to the western Dakotas, and southward to northwestern Colorado and Utah... As the upper system advances eastward across Idaho/western Montana and the Great Basin during the afternoon, daytime heating/mixing will eventually result in 500 to 1000 J/kg mixed-layer CAPE atop a deep/dry boundary layer. This will support development of scattered thunderstorms from western Montana/eastern Idaho southward across Utah and adjacent portions of eastern Nevada. The strongest storms are expected to evolve from southwestern Montana south to northern Utah, where CAPE should be maximized ahead of the trough, and a belt of 30 to 40 kt west-southwesterly mid-level flow on the southeastern periphery of the upper trough should reside. Here, a couple of the strongest -- potentially rotating -- storms will be capable of producing both strong/severe outflow winds and possibly marginal hail. Surrounding this area, where instability and/or shear should remain a bit weaker, the primary risk will be isolated strong wind gusts. Through late afternoon and into the evening, convection -- and local risk for strong/damaging winds -- will spread eastward toward/into the High Plains, before weakening into the overnight hours. ..Goss.. 09/02/2024 Read more

SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1241 AM CDT Mon Sep 02 2024 Valid 021200Z - 031200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS CENTRAL TO WESTERN IDAHO AND ADJACENT PORTIONS OF NEVADA AND OREGON... ...SUMMARY... Isolated to scattered thunderstorms across the northern Great Basin and parts of the Pacific Northwest may be capable of strong to severe wind gusts this afternoon and evening. ...Synopsis... Recent water-vapor imagery depicts a dominant upper ridge centered over the central CONUS. Flanking the ridge is a departing upper trough across the lower Great Lakes/Northeast and a more compact shortwave trough off the northern California coast. This upper-air regime will largely remain intact for the next 24 hours as the Northeast upper wave continues to move into the western Atlantic and the CA shortwave migrates towards the northern Rockies. At the surface, a slowing cold front draped from the Northeast into the southern Plains will continue to meander south through the day as a surface high builds over the Midwest. Isolated to scattered thunderstorms will be possible along this front and in the vicinity of a weak mid-level disturbance over western TX; however, weak flow aloft will hinder the potential for organized convection. Across the West, thunderstorms, including a few strong to severe storms, are expected ahead of the upper trough as it moves onshore over the next 24 hours. ...Nevada into eastern Oregon and Idaho... A modest plume of monsoonal moisture has been tracked from southern AZ into northern NV/eastern OR over the past few days, and has resulted in multiple rounds of thunderstorms across the Great Basin despite very limited low-level moisture and only modestly cool mid-level temperatures. These conditions were well-sampled by the 00 UTC MFR sounding, which depicts around 250 J/kg MLCAPE atop a very deep, dry boundary layer. This profile will be typical this afternoon across the region as ascent associated with the approaching wave overspreads the northern Great Basin/Pacific Northwest. Despite minimal buoyancy, LCL heights between 3-4 km will foster ample evaporative cooling of convective downdrafts that will support strong downburst winds. Increasing flow throughout the column will improve wind shear within the CAPE-bearing layer, promoting better storm longevity and organization (and hence a higher potential for producing strong/severe wind gusts) compared to previous days. Recent CAM solutions also hint at this potential with several HREF members showing isolated swaths of severe winds across northern NV into central and western ID and eastern OR. ..Moore/Kerr.. 09/02/2024 Read more

SPC 0100Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0742 PM CDT Sun Sep 01 2024 Valid 020100Z - 021200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... Isolated to scattered thunderstorms will continue into the late evening and overnight hours from the Mid-Atlantic region into the southern CONUS, Four Corners region, and Pacific Northwest. ...Summary... Isolated to scattered thunderstorms are expected to persist into the early morning hours across parts of the Mid-Atlantic, but the overall severe threat appears sufficiently low to remove risk probabilities. ...Mid-Atlantic... Thunderstorms across the Mid-Atlantic region have shown signs of steady weakening over the past hour based on regional reflectivity imagery, MRMS echo-top heights, and cloud-top temperatures. 00 UTC soundings along the East Coast, and downstream from ongoing multicell clusters, sampled around 500-1000 J/kg MLCAPE with around 20 knots of mid-level flow. A sporadic strong updraft or two will remain possible this evening along the outflow boundaries of ongoing convection given these environmental conditions. However, the onset of nocturnal cooling will continue to modulate mixed-layer buoyancy (with an attendance increase in inhibition), which should maintain the overall weakening trend. Latest CAM solutions support this scenario with increasingly sparse thunderstorm coverage heading into the early morning hours. Consequently, the overall severe potential appears sufficiently low to warrant removing risk probabilities. ..Moore.. 09/02/2024 Read more

No Mesoscale Discussions are in effect as of Sun Sep 1 22:16:01 UTC 2024.

No watches are valid as of Sun Sep 1 22:16:01 UTC 2024.

SPC Day 3-8 Fire Weather Outlook
Day 3-8 Fire Weather Outlook NWS Storm Prediction Center Norman OK 0416 PM CDT Sun Sep 01 2024 Valid 031200Z - 091200Z A midlevel trough and accompanying midlevel speed max will move across the northern Rockies on D3/Tue, bringing an increase in surface winds across portions of Idaho and Wyoming. High pressure will build in across the western US D4/Wednesday through D8/Saturday, with a warming and drying trend. As this occurs, monsoonal moisture will gradually shift southward with drying conditions extending into the desert Southwest through D7/Friday. Winds will remain mostly light where fuels are dry, keeping fire weather concerns low. ...Dry/Windy... As a midlevel speed max moves across Idaho into Montana D3/Tuesday, Critical conditions will be likely in the Snake River Plain, where relative humidity in the teens and sustained westerly winds around 20 mph will overlap critically dry fuels. Across eastern Wyoming, Elevated to Critical fire weather conditions will be possible as a surface low deepens and westerly gradients increase across the Dakotas. Downslope warming and drying will result in relative humidity reductions into the upper teens to 20s amid sustained winds at 15-20 mph. A 40 percent delineation was added with this outlook. ...Isolated Dry Thunderstorms... Thunderstorm potential will continue across the northern Rockies on D3/Tuesday, though gradually increasing moisture and precipitation cast uncertainty on the overall fire-weather risk, which precludes Isolated Dry Thunderstorm probabilities. ..Thornton.. 09/01/2024 ...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 0255 PM CDT Sun Sep 01 2024 Valid 012000Z - 021200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FOR PARTS OF UPSTATE NEW YORK AND SOUTHERN NEW ENGLAND INTO THE CAROLINAS AND SOUTHERN APPALACHIANS... ...SUMMARY... Strong to severe thunderstorms capable of producing isolated damaging winds may still occur this afternoon across parts of the southern Appalachians into the Mid-Atlantic and southern New England. ...20Z Update... The previous forecast remains on track, with only slight changes made to the thunder line to reflect the latest guidance consensus and observations. ..Squitieri.. 09/01/2024 .PREV DISCUSSION... /ISSUED 1125 AM CDT Sun Sep 01 2024/ ...Southern Appalachians into the Mid-Atlantic and Southern New England... Thunderstorms should gradually increase in coverage this afternoon along/south of a diffuse front that extends from the Mid-South/lower OH Valley into the Mid-Atlantic. Late morning visible satellite imagery shows substantial cloud cover in the vicinity of the boundary. Nevertheless, daytime heating of a moist low-level air mass should allow at least weak/pockets of moderate instability to develop by early to mid afternoon along and south/east of the front. Modest ascent with an upper trough over eastern Canada and adjacent Great Lakes/Northeast U.S., in combination with orographic ascent, will likely contribute to thunderstorm development through the afternoon and early evening. Mid-level flow and related deep-layer shear will remain fairly modest, especially with southward extent across the Mid-Atlantic into the Carolinas and southern Appalachians. Mid-level flow should still prove sufficient to support modest thunderstorm organization. Multiple loosely organized multicell clusters may eventually develop and consolidate by late afternoon and early evening, posing some threat for isolated strong to damaging winds while moving generally eastward. The greatest concentration of thunderstorms should exist across parts of southern VA into NC and upstate SC where greater instability (MLCAPE on the order of 2000-2500 J/kg) is forecast this afternoon. ...Western/Northern New York into Northern New England... The upper-level trough and associated surface cold front will move east today across Ontario/Quebec provinces and Northeast U.S., with weak surface-based instability possibly developing in advance of the front. This may result in a narrow, low-topped line of convection (possibly with little lightning) moving east and accompanied by some risk for strong/locally damaging gusts. Read more

SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0255 PM CDT Sun Sep 01 2024 Valid 012000Z - 021200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FOR PARTS OF UPSTATE NEW YORK AND SOUTHERN NEW ENGLAND INTO THE CAROLINAS AND SOUTHERN APPALACHIANS... ...SUMMARY... Strong to severe thunderstorms capable of producing isolated damaging winds may still occur this afternoon across parts of the southern Appalachians into the Mid-Atlantic and southern New England. ...20Z Update... The previous forecast remains on track, with only slight changes made to the thunder line to reflect the latest guidance consensus and observations. ..Squitieri.. 09/01/2024 .PREV DISCUSSION... /ISSUED 1125 AM CDT Sun Sep 01 2024/ ...Southern Appalachians into the Mid-Atlantic and Southern New England... Thunderstorms should gradually increase in coverage this afternoon along/south of a diffuse front that extends from the Mid-South/lower OH Valley into the Mid-Atlantic. Late morning visible satellite imagery shows substantial cloud cover in the vicinity of the boundary. Nevertheless, daytime heating of a moist low-level air mass should allow at least weak/pockets of moderate instability to develop by early to mid afternoon along and south/east of the front. Modest ascent with an upper trough over eastern Canada and adjacent Great Lakes/Northeast U.S., in combination with orographic ascent, will likely contribute to thunderstorm development through the afternoon and early evening. Mid-level flow and related deep-layer shear will remain fairly modest, especially with southward extent across the Mid-Atlantic into the Carolinas and southern Appalachians. Mid-level flow should still prove sufficient to support modest thunderstorm organization. Multiple loosely organized multicell clusters may eventually develop and consolidate by late afternoon and early evening, posing some threat for isolated strong to damaging winds while moving generally eastward. The greatest concentration of thunderstorms should exist across parts of southern VA into NC and upstate SC where greater instability (MLCAPE on the order of 2000-2500 J/kg) is forecast this afternoon. ...Western/Northern New York into Northern New England... The upper-level trough and associated surface cold front will move east today across Ontario/Quebec provinces and Northeast U.S., with weak surface-based instability possibly developing in advance of the front. This may result in a narrow, low-topped line of convection (possibly with little lightning) moving east and accompanied by some risk for strong/locally damaging gusts. Read more

SPC Day 2 Fire Weather Outlook
Day 2 Fire Weather Outlook NWS Storm Prediction Center Norman OK 0252 PM CDT Sun Sep 01 2024 Valid 021200Z - 031200Z ...CRITICAL FIRE WEATHER AREA FOR NORTHEAST CALIFORNIA INTO SOUTHERN OREGON AND NORTHWEST NEVADA... Minor adjustments were made to extend isolated dry thunderstorm chances further north into Washington/Idaho and to bring the Critical fire weather area further north into Oregon. This is in agreement with latest conditional probabilities from the HREF for sustained Critical wind/RH as well as conditional probability of thunder. See previous discussion for more information. ..Thornton.. 09/01/2024 .PREV DISCUSSION... /ISSUED 0210 AM CDT Sun Sep 01 2024/ ...Synopsis... Fire weather concerns are expected across parts of the Pacific Northwest/Great Basin as well as central to northern High Plains on Monday afternoon. ...Pacific Northwest/Great Basin... South/southwest mid-level flow along the West Coast will gradually increase over the next 24-48 hours with the approach of an upper wave currently off the northern CA coast. This will act to strengthen downslope flow off the northern Sierra Nevada with most deterministic and ensemble solutions indicating that winds between 15-25 mph will be common by peak heating Monday afternoon when RH values will fall into the teens. Elevated to critical fire weather conditions appear likely - especially across the CA/NV/OR tri-state region where the strongest winds are expected under the mid-level jet max. A warming trend over the past week (featuring multiple days of sub-20% RH minimums) has maintained ERC values well within the 80-90th percentiles across much of the Pacific Northwest and Great Basin. While thunderstorms are anticipated across parts of the region today (Sunday), little rain accumulation is expected, and holdover fires from dry-lightning starts may become more active Monday as winds increase. Dry thunderstorms will also be a concern across much of NV, central to eastern OR, and western ID. A plume of mid-level moisture (noted in 00z soundings and water-vapor imagery across NV into southern OR) is expected to continue spreading north through Monday afternoon. Lift associated with the wave should support another day of isolated thunderstorms. Dry boundary-layer conditions will promote limited rainfall and an attendant threat of dry lightning. While thunderstorms are possible across a broader swath of the region, the dry-lightning risk area was confined to areas with receptive fuels and low probability for wetting rainfall per ensemble guidance. ...High Plains... A surface high currently building across the northern Plains in the wake of a cold front is forecast to shift east towards the Midwest by Monday afternoon. Modest lee troughing juxtaposed with the nearby surface high will bolster southerly pressure gradient winds across northeast CO and western NE/SD. The displacement of richer low-level moisture to the south across the southern Plains will promote a dry return flow regime with afternoon RH values falling to near 20%. When combined with 15-20 mph winds and very dry fuels (ERCs are currently estimated to be above the 90th percentile), elevated to locally critical fire weather conditions appear probable. ...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 0252 PM CDT Sun Sep 01 2024 Valid 021200Z - 031200Z ...CRITICAL FIRE WEATHER AREA FOR NORTHEAST CALIFORNIA INTO SOUTHERN OREGON AND NORTHWEST NEVADA... Minor adjustments were made to extend isolated dry thunderstorm chances further north into Washington/Idaho and to bring the Critical fire weather area further north into Oregon. This is in agreement with latest conditional probabilities from the HREF for sustained Critical wind/RH as well as conditional probability of thunder. See previous discussion for more information. ..Thornton.. 09/01/2024 .PREV DISCUSSION... /ISSUED 0210 AM CDT Sun Sep 01 2024/ ...Synopsis... Fire weather concerns are expected across parts of the Pacific Northwest/Great Basin as well as central to northern High Plains on Monday afternoon. ...Pacific Northwest/Great Basin... South/southwest mid-level flow along the West Coast will gradually increase over the next 24-48 hours with the approach of an upper wave currently off the northern CA coast. This will act to strengthen downslope flow off the northern Sierra Nevada with most deterministic and ensemble solutions indicating that winds between 15-25 mph will be common by peak heating Monday afternoon when RH values will fall into the teens. Elevated to critical fire weather conditions appear likely - especially across the CA/NV/OR tri-state region where the strongest winds are expected under the mid-level jet max. A warming trend over the past week (featuring multiple days of sub-20% RH minimums) has maintained ERC values well within the 80-90th percentiles across much of the Pacific Northwest and Great Basin. While thunderstorms are anticipated across parts of the region today (Sunday), little rain accumulation is expected, and holdover fires from dry-lightning starts may become more active Monday as winds increase. Dry thunderstorms will also be a concern across much of NV, central to eastern OR, and western ID. A plume of mid-level moisture (noted in 00z soundings and water-vapor imagery across NV into southern OR) is expected to continue spreading north through Monday afternoon. Lift associated with the wave should support another day of isolated thunderstorms. Dry boundary-layer conditions will promote limited rainfall and an attendant threat of dry lightning. While thunderstorms are possible across a broader swath of the region, the dry-lightning risk area was confined to areas with receptive fuels and low probability for wetting rainfall per ensemble guidance. ...High Plains... A surface high currently building across the northern Plains in the wake of a cold front is forecast to shift east towards the Midwest by Monday afternoon. Modest lee troughing juxtaposed with the nearby surface high will bolster southerly pressure gradient winds across northeast CO and western NE/SD. The displacement of richer low-level moisture to the south across the southern Plains will promote a dry return flow regime with afternoon RH values falling to near 20%. When combined with 15-20 mph winds and very dry fuels (ERCs are currently estimated to be above the 90th percentile), elevated to locally critical fire weather conditions appear probable. ...Please see www.spc.noaa.gov/fire for graphic product... Read more

SPC 1930Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0223 PM CDT Sun Sep 01 2024 Valid 031200Z - 041200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM PARTS OF EASTERN IDAHO INTO SOUTHWEST MONTANA AND WESTERN WYOMING... ...SUMMARY... A few strong storms may produce hail and gusty winds over parts of eastern Idaho, southwest Montana, and western Wyoming on Tuesday. ...Synopsis... On Tuesday, an upper trough will move east across ID into MT and WY, weakening during that time. Cooling aloft will still accompany this wave, with 500 mb wind speeds around 30-35 kt. Meanwhile, a larger upper trough will quickly exit the Northeast, with height rises over the Great Lakes and upper MS Valley. At the surface, a prominent high will affect much of the eastern CONUS, providing relatively stable conditions. A trough will develop during the afternoon over the northern High Plains, with the primary cold front affecting parts of the northern Rockies in association with the a shortwave trough moving across ID, MT, and WY. ...ID into MT and WY... Cool temperatures aloft will support early/ongoing showers and a few thunderstorms on Tuesday, with increasing coverage as heating occurs into parts of eastern ID, southwest MT and western WY. As the trough progresses east, scattered strong to marginally severe storms may develop as instability increases with heating. Steeper lapse rates aloft as well as elongated hodographs with effective deep-layer shear around 40 kt will favor cellular storm mode with hail, perhaps to severe levels. Veering winds with height and perhaps 100 m2/s2 SRH may support a supercell or two as well. ..Jewell.. 09/01/2024 Read more