SPC Day 1 Fire Weather Outlook
Day 1 Fire Weather Outlook NWS Storm Prediction Center Norman OK 1136 AM CDT Wed Aug 21 2024 Valid 211700Z - 221200Z ...17z Update... Minimal changes were made to the valid outlook. Elevated to near critical fire-weather conditions are possible from the southern Great Basin into parts of WY. Dry thunderstorms are also possible over parts of the Rockies where fuels have trended drier. At least some risk for isolated dry and breezy conditions are also possible over parts of the southern Plains this afternoon, though the coverage of 15+ mph surface winds and RH below 20% appears limited. See the prior discussion for more info. ..Lyons.. 08/21/2024 .PREV DISCUSSION... /ISSUED 0141 AM CDT Wed Aug 21 2024/ ...Synopsis... Broad mid-level southwesterly flow will overspread much of the Great Basin and portions of the Pacific Northwest in advance of a southward-moving shortwave trough approaching the Washington coast. This will result in pockets of elevated fire-weather conditions across Nevada, Idaho, and Wyoming, with an additional risk for isolated dry thunderstorms across eastern and central Wyoming. ...Dry/Windy... Deep boundary-layer mixing beneath 40-45kt mid-level flow will result in elevated to locally critical fire-weather conditions across portions of Nevada, eastern Idaho, and northern Wyoming. The best overlap of elevated fire-weather conditions with receptive fuels will be across northern Wyoming and central Nevada, where fuels guidance suggest ERCs are above the 90th annual percentile. Across eastern Idaho in the Snake River Plain, meteorological conditions are expected to exceed Elevated criteria, but recent wetting rainfall and current fuels guidance suggests a narrower corridor supporting wildfire spread. ...Dry Thunderstorms... Isolated dry thunderstorms are expected across central and eastern Wyoming, where ERC fuels are in the 90th-98th annual percentile range and thunderstorms are expected to develop in deeply mixed, dry boundary-layer profiles. Storm motion estimates of 30 kts and PWAT values < 0.8 in should limit wetting rainfall except for in the strongest cores, and some overlap with elevated fire-weather conditions could pose a risk for wildfire spread with any new ignitions. ...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 Wed Aug 21 2024 Valid 211630Z - 221200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF EASTERN MONTANA AND THE WESTERN DAKOTAS.... ...SUMMARY... Severe hail and thunderstorm gusts are most probable today over parts of eastern Montana and the western Dakotas. ...Northern High Plains... Morning water vapor imagery shows a fast-moving shortwave trough over ID/NV tracking northeastward. Lift associated with this system will overspread parts of MT/WY/Dakotas later this afternoon and evening. This will help to initiate scattered thunderstorms over the higher terrain of southern MT and WY, building eastward into the Plains during the evening. Instability in the mountains is quite weak with dewpoints only in the 40s, but with steep low/mid level lapse rates and moderately strong westerly flow aloft posing a risk of gusty winds. Storms will eventually move/develop eastward into a more moist/unstable air mass across eastern MT and western SD/ND where more robust/severe storms are expected, capable of damaging winds and large hail. ...CO/NE/KS... Ample mid-level moisture will result in scattered afternoon thunderstorms over the mountains of central CO and southern WY. This area will be on the fringe of the stronger westerly flow aloft, and with pockets of strong daytime heating helping to steepen low-level lapse rates. This will promote a risk of gusty/damaging winds in the strongest cells. As the activity spreads eastward into the Plains, further intensification is possible with a few cells continuing a risk of gusty winds and hail during the evening. ...Southeast AZ... Afternoon thunderstorms have been occurring daily over southeast AZ, with isolated strong cells capable of gusty winds. Today will be similar as daytime heating dewpoints in the 60s promote storms over the higher terrain that track slowly northwestward during the late afternoon and early evening. ..Hart/Thornton.. 08/21/2024 Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0751 AM CDT Wed Aug 21 2024 Valid 211300Z - 221200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PARTS OF EASTERN MONTANA AND WESTERN NORTH DAKOTA... ...SUMMARY... Severe hail and thunderstorm gusts are most probable over parts of eastern Montana and western North Dakota. ...Synopsis... The CONUS portion of the large-scale, mid/upper-level pattern this period will be characterized by mean troughing over the East and West Coasts, and ridging extending northward over the Great Plains States from a high over west TX. A strong cyclone -- initially centered just south of the AK Panhandle -- is expected to dig south-southeastward, with its 500-mb center moving to around 200 nm west of UIL by 12Z tomorrow. As this process reinforces the mean western trough, a series of mostly low-amplitude shortwave perturbations will eject through the foregoing southwest flow. The best-defined and potentially most important of those perturbations evident in moisture-channel imagery over portions of northern CA, northwestern NV and southeastern OR. This feature should reach southeastern ID and west-central MT around 00Z, before ejecting northeastward across the northern High Plains and losing definition tonight. Meanwhile, in the subtropical easterlies, a shortwave trough will continue to drift westward across parts of Sonora, the Gulf of California, and central/northern Baja. At the surface, 11Z analysis showed rich Gulf-origin moisture still confined near and south of a slowly weakening synoptic front over northern FL, the northern Gulf shelf waters, and southeast to north-central TX. Nonetheless, a plume of mainly 60s F surface dewpoints was analyzed from much of OK north-northwestward across western/central portions of KS, NE and the Dakotas. A lee trough was drawn farther west, over eastern portions of MT/WY/CO. This trough should intensify through the day as ridging aloft shifts somewhat eastward, and southwest flow aloft spreads over more of the High Plains. As part of that process, surface cyclogenesis is expected over the northeastern WY/southeastern MT region, with the resulting low shifting eastward into northwestern SD around 06Z. ...Northern Plains... Widely scattered to scattered thunderstorms are expected to develop initially over the higher terrain of south-central/southwestern MT by midafternoon. In this area, heating of greater elevations preferentially removes MLCINH first, as large-scale lift ahead of the ejecting shortwave begins to move overhead. This activity should move northeastward into parts of central MT atop a boundary layer that is diurnally destabilizing/mixing, yet still favorably moist. Additional thunderstorms may develop by late afternoon near the surface trough, where strong surface heating and the western rim of the corridor of greatest moisture (surface dewpoints commonly in the upper 50s to mid 60s F) will remove capping at lower elevations. Convection of both origins may merge near the trough, over eastern MT. Along the way, activity should produce at least occasional large hail (mainly with any sustained supercells) and damaging gusts. Some aggregation of convection should occur, leading to forward-propagational clustering and increased potential for swath(s) of severe to potentially significant (65+ kt) gusts from late afternoon through much of the evening, as activity moves through a lingering, deep, well-mixed layer left by diurnal heating. A well-heated and deep boundary layer west of the moist plume will support MLCAPE in the 500-1500 J/kg range, with 1000-1500 J/kg DCAPE as well. This will foster high-based convection for the first few hours, with some potential for activity to cluster and become collectively outflow-dominant before reaching the grater moisture. weak low-level winds are expected, beneath 50-80 kt flow in the upper half of the buoyant profile, contributing to favorable deep shear (40-50 kt effective) for supercells, and long, relatively straight hodographs supporting splitting storms and hail potential where convection doesn't produce too much outflow too soon. Thunderstorms will move into larger nominal CAPE and greater near- surface moisture over easternmost MT into western ND, where the moist axis should be found, with MLCAPE of 2000-3000 J/kg. Though MLCINH also will be stronger in the higher-CAPE corridor than farther west, forced ascent that is driven by cold-pool processes should sustain some of the strong-severe convection well into ND this evening. Activity should peak near the moist/buoyancy axis and weaken afterword tonight, as it moves into progressively more-stable low-level profile, both with lower ambient theta-e and nocturnal diabatic cooling/stabilization near the surface. ...Central High Plains... Widely scattered to scattered thunderstorms should develop this afternoon over higher terrain from the Black Hills to the Laramie Range and southward over the Front Range, its foothills, and adjoining ridges such as the Cheyenne Ridge and Palmer Divide. This convection should move east toward the lee trough and low-level moist axis, while crossing over a hot, deeply mixed boundary layer. Isolated severe gusts are expected, and severe hail also may be a concern with relatively discrete cells. While vertical shear will be weaker than farther north, strong veering of flow with height (especially near the trough) should contribute enough deep shear (30-40 kt effective mainly north of I-70) for at least brief supercell potential. Aggregation of outflows may foster one or more eastward-surging clusters into this evening from western KS to central SD, and a relatively concentrated local severe-wind threat will exist in any such cluster. However, guidance is too inconsistent in convective evolution and longevity, and in location/number of such clusters, to assign greater unconditional probabilities within the long "marginal" area at this time. ...Southeastern AZ... Scattered thunderstorms are expected to develop this afternoon, at first over higher terrain then across deserts/valleys as outflow/ differential-heating boundaries develop. With a relatively deep layer of south-southeasterly midlevel flow, activity should move generally northwestward. Though most progs keep the flow aloft modest (15 kt or less), some mesoscale enhancement is possible east of the track of a northwestward-moving MCV -- evident in IR satellite imagery over north-central Sonora. The most intense convection will be capable of isolated severe gusts. Clouds related both to earlier/overnight convection over southern AZ, as well as to activity over MX, are south and west of this region already, portending essentially a full day of insolation over the outlook area. Residual lower-elevation surface dewpoints in the 50s to mid 60s should decrease only slightly through the diurnal heating/mixing cycle, offset to some extent by moist advection. MLCAPE in the 1000-2000 J/kg range should develop through early/mid afternoon, atop the well-mixed subcloud/boundary layer. ..Edwards/Mosier.. 08/21/2024 Read more

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0355 AM CDT Wed Aug 21 2024 Valid 241200Z - 291200Z ...DISCUSSION... ...Saturday/Day 4 to Monday/Day 6... Heights within an upper-level ridge are forecast to rise across the central and northern U.S over the weekend, as an upper-level trough moves across the western U.S. Isolated severe-thunderstorm development will be possible across the Dakotas in the afternoon and evening both Saturday and Sunday. The best chance for severe storms would be on Sunday as large-scale ascent and deep-layer shear both increase across the northern Plains due to the approach of the trough. The severe threat is forecast to shift eastward into the upper Mississippi Valley on Monday, as the upper-level trough and its associated cold front advance eastward from the northern Plains into the upper Mississippi Valley. ...Tuesday/Day 7 and Wednesday/Day 8... On Tuesday and Wednesday, the upper-level trough is forecast to deamplify as it moves through the Great Lakes region. Another upper-level trough is forecast to move through the western U.S on Tuesday and Wednesday. The best chance for severe storm development would be on Wednesday afternoon along an instability axis, most likely in either eastern parts of the northern Plains or in the upper Mississippi Valley. At this range, large model spread concerning the timing of the trough and distribution of instability suggests uncertainty is substantial. Read more

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0355 AM CDT Wed Aug 21 2024 Valid 241200Z - 291200Z ...DISCUSSION... ...Saturday/Day 4 to Monday/Day 6... Heights within an upper-level ridge are forecast to rise across the central and northern U.S over the weekend, as an upper-level trough moves across the western U.S. Isolated severe-thunderstorm development will be possible across the Dakotas in the afternoon and evening both Saturday and Sunday. The best chance for severe storms would be on Sunday as large-scale ascent and deep-layer shear both increase across the northern Plains due to the approach of the trough. The severe threat is forecast to shift eastward into the upper Mississippi Valley on Monday, as the upper-level trough and its associated cold front advance eastward from the northern Plains into the upper Mississippi Valley. ...Tuesday/Day 7 and Wednesday/Day 8... On Tuesday and Wednesday, the upper-level trough is forecast to deamplify as it moves through the Great Lakes region. Another upper-level trough is forecast to move through the western U.S on Tuesday and Wednesday. The best chance for severe storm development would be on Wednesday afternoon along an instability axis, most likely in either eastern parts of the northern Plains or in the upper Mississippi Valley. At this range, large model spread concerning the timing of the trough and distribution of instability suggests uncertainty is substantial. Read more

SPC 0730Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0225 AM CDT Wed Aug 21 2024 Valid 231200Z - 241200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE CENTRAL AND NORTHERN PLAINS...AND IN PARTS OF THE INTERMOUNTAIN WEST AND CENTRAL ROCKIES... ...SUMMARY... Marginally severe storms with hail and isolated severe gusts will be possible on Friday across parts of the central and northern Plains, and in parts of the Intermountain West and central Rockies. ...Central and Northern Plains... An upper-level ridge will remain over eastern parts of the central and northern Plains on Friday. A north-to-south axis of moisture and instability is forecast across Kansas, Nebraska, South Dakota and eastern Montana, where isolated thunderstorm development will be possible during the afternoon and evening. Forecast soundings near the area of strongest instability late Friday afternoon in northern Kansas and southwest Nebraska suggest MLCAPE will peak in the 2000 to 3000 J/kg range and 0-6 km shear will be from 30 to 40 knots. This, combined with steep low to mid-level lapse rates should support an isolated severe threat. However, large-scale ascent is forecast to be absent across much of the region. For this reason, updrafts may struggle to intensify due to subsidence in the wake of the ridge, keeping any severe threat marginal. ...Eastern Utah/Western Colorado/Far Southwest Wyoming... An upper-level low is forecast to approach the coast of Oregon on Friday as southwest mid-level flow remains over much of the Intermountain West. A shortwave trough is forecast to move through the western U.S., which will likely aid the development of scattered thunderstorms in the afternoon from eastern Utah eastward into the central Rockies. The models suggest that weak instability, moderate deep-layer shear and steep low to mid-level lapse rates will be in place, which would be sufficient for marginal severe threat. Hail and isolated severe gusts will be possible mainly during the mid to late afternoon. ..Broyles.. 08/21/2024 Read more

SPC Day 2 Fire Weather Outlook
Day 2 Fire Weather Outlook NWS Storm Prediction Center Norman OK 0145 AM CDT Wed Aug 21 2024 Valid 221200Z - 231200Z ...CRITICAL FIRE WEATHER AREA FOR SOUTHWEST INTO CENTRAL NEVADA... ...Synopsis... A southward-moving shortwave trough is forecast to approach the Oregon/Washington coasts on Thursday, before moving east on Friday. This will result in an intensified height gradient across the Great Basin and a deepening surface low over Oregon that will bring widespread dry/windy conditions to portions of Oregon, Nevada, and Idaho. ...Dry/Windy... Critical fire-weather conditions are forecast across southwestern and central Nevada, where single-digit relative humidity values and winds of 25-30 MPH will overlap with ERC values exceeding the 80th-98th annual percentiles. Uncertainty exists in the eastward extent of the Critical area due to recent wetting rainfall and a tight gradient in fuel receptiveness to wildfire spread, and some areal expansion may be needed in future updates. Elevated fire-weather conditions are expected on the periphery of the Critical highlight area, as well as portions of northwestern Nevada into southeastern Oregon. Southeastern Oregon and northwestern Nevada will have slightly higher boundary-layer relative humidity values of 10-15%, and slightly slower wind speeds of 20-25 MPH. However, fuels in the region are widely receptive to wildfire spread, and if surface winds trend higher, a subsequent upgrade to Critical may be needed in this area. ..Halbert/Squitieri.. 08/21/2024 ...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 0141 AM CDT Wed Aug 21 2024 Valid 211200Z - 221200Z ...Synopsis... Broad mid-level southwesterly flow will overspread much of the Great Basin and portions of the Pacific Northwest in advance of a southward-moving shortwave trough approaching the Washington coast. This will result in pockets of elevated fire-weather conditions across Nevada, Idaho, and Wyoming, with an additional risk for isolated dry thunderstorms across eastern and central Wyoming. ...Dry/Windy... Deep boundary-layer mixing beneath 40-45kt mid-level flow will result in elevated to locally critical fire-weather conditions across portions of Nevada, eastern Idaho, and northern Wyoming. The best overlap of elevated fire-weather conditions with receptive fuels will be across northern Wyoming and central Nevada, where fuels guidance suggest ERCs are above the 90th annual percentile. Across eastern Idaho in the Snake River Plain, meteorological conditions are expected to exceed Elevated criteria, but recent wetting rainfall and current fuels guidance suggests a narrower corridor supporting wildfire spread. ...Dry Thunderstorms... Isolated dry thunderstorms are expected across central and eastern Wyoming, where ERC fuels are in the 90th-98th annual percentile range and thunderstorms are expected to develop in deeply mixed, dry boundary-layer profiles. Storm motion estimates of 30 kts and PWAT values < 0.8 in should limit wetting rainfall except for in the strongest cores, and some overlap with elevated fire-weather conditions could pose a risk for wildfire spread with any new ignitions. ..Halbert/Squitieri.. 08/21/2024 ...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 1235 AM CDT Wed Aug 21 2024 Valid 221200Z - 231200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE CENTRAL AND NORTHERN PLAINS... ...SUMMARY... Thunderstorms with hail and a few marginally severe gusts will be possible on Thursday across parts of the central and northern Plains. ...Central and Northern Plains... An upper-level ridge over the central Plains and upper Mississippi Valley is forecast to move eastward on Thursday, as a shortwave trough moves through the northern Plains. In association with the trough, elevated morning thunderstorms appear likely in parts of North Dakota. As the convective cluster moves eastward into Minnesota, an axis of moderate instability is expected to develop in its wake across central and eastern North Dakota. The instability axis should be located from the Dakotas south-southwestward into western Nebraska and far western Kansas. During the day, isolated severe thunderstorm development will be possible along and near the instability axis. Most locations near the instability axis have 0-6 km shear forecast in the 25 to 35 knot range. This combined with steep low to mid-level lapse rates will support a marginal severe threat during the late afternoon. Hail and a few severe gusts will be possible. During the evening, the focus is expected to shift southward into far eastern Colorado and western Kansas, as the low-level jet ramps up. A small cluster of thunderstorms with severe potential is expected to develop and move across the central High Plains during the early to mid evening. Model solutions differ on the exact location of this cluster, and have widely varying instability distributions suggesting uncertainty is substantial. For this reason, Marginal seems to be appropriate category at this time. ..Broyles.. 08/21/2024 Read more

SPC 0600Z Day 2 Outlook
Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1235 AM CDT Wed Aug 21 2024 Valid 221200Z - 231200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE CENTRAL AND NORTHERN PLAINS... ...SUMMARY... Thunderstorms with hail and a few marginally severe gusts will be possible on Thursday across parts of the central and northern Plains. ...Central and Northern Plains... An upper-level ridge over the central Plains and upper Mississippi Valley is forecast to move eastward on Thursday, as a shortwave trough moves through the northern Plains. In association with the trough, elevated morning thunderstorms appear likely in parts of North Dakota. As the convective cluster moves eastward into Minnesota, an axis of moderate instability is expected to develop in its wake across central and eastern North Dakota. The instability axis should be located from the Dakotas south-southwestward into western Nebraska and far western Kansas. During the day, isolated severe thunderstorm development will be possible along and near the instability axis. Most locations near the instability axis have 0-6 km shear forecast in the 25 to 35 knot range. This combined with steep low to mid-level lapse rates will support a marginal severe threat during the late afternoon. Hail and a few severe gusts will be possible. During the evening, the focus is expected to shift southward into far eastern Colorado and western Kansas, as the low-level jet ramps up. A small cluster of thunderstorms with severe potential is expected to develop and move across the central High Plains during the early to mid evening. Model solutions differ on the exact location of this cluster, and have widely varying instability distributions suggesting uncertainty is substantial. For this reason, Marginal seems to be appropriate category at this time. ..Broyles.. 08/21/2024 Read more

SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1252 AM CDT Wed Aug 21 2024 Valid 211200Z - 221200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF EASTERN MONTANA AND WESTERN NORTH DAKOTA.... ...SUMMARY... Scattered thunderstorms, some with severe hail and damaging gusts, are expected to develop today over parts of far eastern Montana and western North Dakota. ...Synopsis... A mid-level shortwave trough over north-central California early this morning will move across the Great Basin and emerge across eastern Montana this afternoon. This shortwave trough will be the focus for a severe weather threat this afternoon/evening across eastern Montana and western North Dakota. Farther east, a mid-level trough centered over the Plains will start to break down during the day today. As this occurs, surface troughing is forecast to develop from the northern Plains to the central High Plains. Scattered strong to potentially severe storms are expected along the extent of this surface trough from western South Dakota to eastern Colorado. ...Eastern Montana and western North Dakota... Significant heating is forecast across eastern Montana this afternoon with temperatures forecast to warm into the mid to upper 90s (depending on the degree of mixing). This will result in moderate instability and a mostly uncapped atmosphere by mid to late afternoon. DCVA ahead of the approaching mid-level trough will result in sufficient deep-layer ascent for thunderstorm development by mid to late afternoon. These storms will likely be supercellular in nature as mid-level flow strengthens to near 50 knots while the associated mid-level jet streak overspreads the region. The long-straight hodograph may also support some splitting storms. Large hail (up to golf ball size) and severe wind gusts of 60 to 80 mph will be the primary threats associated with this activity. ...Western South Dakota to eastern Colorado... Scattered thunderstorm activity is expected within a broad surface trough from western South Dakota to eastern Colorado where moderate to strong instability will be in place by mid-afternoon. Mid-level flow will be mostly weak across this region (15 to 20 knots) which will limit the overall shear magnitude. However, moderate southeasterly flow ahead of this surface trough, coupled with the westerly mid-level flow may result in adequate shear for storm organization and perhaps a few slow-moving supercells. The deeply mixed boundary layer across this zone will support a threat for severe wind gusts with isolated hail as a lesser threat (predominantly associated with any more robust supercell development which may occur). A few regions within the marginal risk may have a greater threat (southwest South Dakota/northern Nebraska and northeast Colorado), but it is not clear at this time whether coverage/intensity will be sufficient for a slight risk. ...Southeast Arizona... A surge of monsoon moisture across southern Arizona will result in moderate (1500-2000 J/kg MLCAPE) instability and scattered to widespread thunderstorm development this afternoon. Storm organization will likely be somewhat weak given the weak shear (~15 knots). However, the moderate instability in a deeply mixed boundary layer will support an isolated severe-wind threat. In addition, the widespread nature of the convection will likely result in numerous outflow boundary collisions which may locally enhance updraft intensity and support a few stronger cells. ..Bentley.. 08/21/2024 Read more

SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1252 AM CDT Wed Aug 21 2024 Valid 211200Z - 221200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF EASTERN MONTANA AND WESTERN NORTH DAKOTA.... ...SUMMARY... Scattered thunderstorms, some with severe hail and damaging gusts, are expected to develop today over parts of far eastern Montana and western North Dakota. ...Synopsis... A mid-level shortwave trough over north-central California early this morning will move across the Great Basin and emerge across eastern Montana this afternoon. This shortwave trough will be the focus for a severe weather threat this afternoon/evening across eastern Montana and western North Dakota. Farther east, a mid-level trough centered over the Plains will start to break down during the day today. As this occurs, surface troughing is forecast to develop from the northern Plains to the central High Plains. Scattered strong to potentially severe storms are expected along the extent of this surface trough from western South Dakota to eastern Colorado. ...Eastern Montana and western North Dakota... Significant heating is forecast across eastern Montana this afternoon with temperatures forecast to warm into the mid to upper 90s (depending on the degree of mixing). This will result in moderate instability and a mostly uncapped atmosphere by mid to late afternoon. DCVA ahead of the approaching mid-level trough will result in sufficient deep-layer ascent for thunderstorm development by mid to late afternoon. These storms will likely be supercellular in nature as mid-level flow strengthens to near 50 knots while the associated mid-level jet streak overspreads the region. The long-straight hodograph may also support some splitting storms. Large hail (up to golf ball size) and severe wind gusts of 60 to 80 mph will be the primary threats associated with this activity. ...Western South Dakota to eastern Colorado... Scattered thunderstorm activity is expected within a broad surface trough from western South Dakota to eastern Colorado where moderate to strong instability will be in place by mid-afternoon. Mid-level flow will be mostly weak across this region (15 to 20 knots) which will limit the overall shear magnitude. However, moderate southeasterly flow ahead of this surface trough, coupled with the westerly mid-level flow may result in adequate shear for storm organization and perhaps a few slow-moving supercells. The deeply mixed boundary layer across this zone will support a threat for severe wind gusts with isolated hail as a lesser threat (predominantly associated with any more robust supercell development which may occur). A few regions within the marginal risk may have a greater threat (southwest South Dakota/northern Nebraska and northeast Colorado), but it is not clear at this time whether coverage/intensity will be sufficient for a slight risk. ...Southeast Arizona... A surge of monsoon moisture across southern Arizona will result in moderate (1500-2000 J/kg MLCAPE) instability and scattered to widespread thunderstorm development this afternoon. Storm organization will likely be somewhat weak given the weak shear (~15 knots). However, the moderate instability in a deeply mixed boundary layer will support an isolated severe-wind threat. In addition, the widespread nature of the convection will likely result in numerous outflow boundary collisions which may locally enhance updraft intensity and support a few stronger cells. ..Bentley.. 08/21/2024 Read more

WW 0641 Status Updates
STATUS REPORT ON WW 641 SEVERE WEATHER THREAT CONTINUES RIGHT OF A LINE FROM 30 ENE SHR TO 65 N SHR TO 70 SSW GGW TO 70 NE LWT TO 65 NE HVR. ..HALBERT..08/21/24 ATTN...WFO...TFX...BYZ...GGW... STATUS REPORT FOR WS 641 SEVERE WEATHER THREAT CONTINUES FOR THE FOLLOWING AREAS MTC033-071-087-105-210340- MT . MONTANA COUNTIES INCLUDED ARE GARFIELD PHILLIPS ROSEBUD VALLEY THE WATCH STATUS MESSAGE IS FOR GUIDANCE PURPOSES ONLY. PLEASE REFER TO WATCH COUNTY NOTIFICATION STATEMENTS FOR OFFICIAL INFORMATION ON COUNTIES...INDEPENDENT CITIES AND MARINE ZONES CLEARED FROM SEVERE THUNDERSTORM AND TORNADO WATCHES. Read more

WW 641 SEVERE TSTM MT 202040Z - 210400Z
URGENT - IMMEDIATE BROADCAST REQUESTED Severe Thunderstorm Watch Number 641 NWS Storm Prediction Center Norman OK 240 PM MDT Tue Aug 20 2024 The NWS Storm Prediction Center has issued a * Severe Thunderstorm Watch for portions of Southwest and Central Montana * Effective this Tuesday afternoon and evening from 240 PM until 1000 PM MDT. * Primary threats include... Scattered damaging wind gusts to 70 mph possible Isolated large hail events to 1.5 inches in diameter possible SUMMARY...Thunderstorms will develop over the mountains of southwest Montana this afternoon and spread quickly eastward across the watch area through the evening. Damaging wind gusts are the main threat with the strongest storms. The severe thunderstorm watch area is approximately along and 85 statute miles north and south of a line from 20 miles north of Dillon MT to 125 miles east northeast of Lewistown MT. For a complete depiction of the watch see the associated watch outline update (WOUS64 KWNS WOU1). 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 1.5 inches. Extreme turbulence and surface wind gusts to 60 knots. A few cumulonimbi with maximum tops to 500. Mean storm motion vector 25030. ...Hart Read more

SPC 0100Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0747 PM CDT Tue Aug 20 2024 Valid 210100Z - 211200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF MONTANA... ...SUMMARY... Severe thunderstorms with some severe wind gusts are possible this evening across parts of Montana. A few storms capable of large hail and severe wind gusts are possible across southeast Colorado for a few hours this evening. ...Montana... Thunderstorms associated with a fast-moving mid-level shortwave trough across Montana will continue northeast through the evening. These storms will continue to pose some threat for severe wind gusts before weakening below severe thresholds by late evening as the boundary layer cools and inhibition increases. ...Southeast Colorado... A few supercells have developed near Colorado Springs with at least one report of severe hail. These storms may persist for a few more hours and could congeal into a cluster with an increasing severe wind threat. Elsewhere across southeast Colorado, numerous mostly sub-severe thunderstorms have developed with many outflow boundaries present. Collision of these boundaries could result in a few additional strong to severe storms with a threat for large hail and severe wind gusts. Overall, inhibition is forecast to increase across southeast Colorado this evening as the boundary layer cools. This should result in a decreasing severe weather threat by late evening. ..Bentley.. 08/21/2024 Read more

WW 0641 Status Updates
STATUS REPORT ON WW 641 SEVERE WEATHER THREAT CONTINUES RIGHT OF A LINE FROM 25 SSE MQM TO 20 N DLN TO 25 WNW BZN TO 30 NW GTF. ..HALBERT..08/20/24 ATTN...WFO...TFX...BYZ...GGW... STATUS REPORT FOR WS 641 SEVERE WEATHER THREAT CONTINUES FOR THE FOLLOWING AREAS MTC003-005-007-009-013-015-027-031-033-037-041-045-057-059-065- 067-069-071-087-095-097-103-105-107-111-210040- MT . MONTANA COUNTIES INCLUDED ARE BIG HORN BLAINE BROADWATER CARBON CASCADE CHOUTEAU FERGUS GALLATIN GARFIELD GOLDEN VALLEY HILL JUDITH BASIN MADISON MEAGHER MUSSELSHELL PARK PETROLEUM PHILLIPS ROSEBUD STILLWATER SWEET GRASS TREASURE VALLEY WHEATLAND YELLOWSTONE THE WATCH STATUS MESSAGE IS FOR GUIDANCE PURPOSES ONLY. PLEASE REFER TO WATCH COUNTY NOTIFICATION STATEMENTS FOR OFFICIAL INFORMATION ON COUNTIES...INDEPENDENT CITIES AND MARINE ZONES CLEARED FROM SEVERE THUNDERSTORM AND TORNADO WATCHES. Read more

SPC Day 3-8 Fire Weather Outlook
Day 3-8 Fire Weather Outlook NWS Storm Prediction Center Norman OK 0500 PM CDT Tue Aug 20 2024 Valid 221200Z - 281200Z An upper low over the West Coast is forecast to move south and linger over parts of the Northwest through the weekend. Stronger southwesterly flow east of the low will overspread a modestly dry air mass across parts of the Great Basin and Northwest through the weekend. This should support elevated to critical fire-weather potential and some risk for isolated dry thunderstorms. ...Northwest and Great Basin... As the aforementioned upper low approaches from the northwest D3/Thursday and D4/Friday, stronger flow on the eastern side will gradually overspread a warm and fairly dry air mass across parts of OR/ID and into the Great Basin. Several days of dry and breezy conditions are expected with the potential for elevated to near-critical fire-weather concerns. Winds are expected to be strongest D4/Friday over parts of southern NV and western UT with gusts to 35 mph possible. Area fuels should continue to dry and be at least partially receptive to fire spread heading into the weekend. Fire-weather concerns should continue through the weekend as stronger flow aloft begins to extend into the northern/central Rockies. Confidence in more widespread elevated fire-weather potential is highest for D5/Saturday, though some risk may continue across parts of WY/CO/MT into early next week. ...Southern Plains... Periodic dry return flow is possible over parts of the southern Plains late this week into the weekend. Gusty southerly flow ahead of the upper low to the west may support occasional 10-15 mph winds and RH below 20% over parts of west TX and eastern NM. Confidence remains low in the coverage and duration of elevated to critical fire-weather potential. ...Dry thunderstorm potential... Mid-level moisture should increase ahead of the low over much of the Western US beginning D3/Thursday. Medium-range guidance shows a plume of 0.6 to 0.8 inch PWATs moving into the Pacific Northwest ahead of the upper low into OR and WA. Some dry lightning will be possible Thursday, though the best storm coverage may remain away from the driest fuels. Confidence in dry thunderstorm and lightning potential over dry fuels is higher in southeast OR and western ID beginning D4/Friday as the upper low continues south and moisture depth increases. At least some risk for occasional dry storms will continue through the weekend, though the increase in moisture should gradually limit fuels as temperatures cool and chances for wetting rains increase beneath the upper low. ..Lyons.. 08/20/2024 ...Please see www.spc.noaa.gov/fire for graphic product... Read more

MD 1964 CONCERNING SEVERE POTENTIAL...WATCH POSSIBLE FOR SOUTHWEST INTO CENTRAL MT
Mesoscale Discussion 1964 NWS Storm Prediction Center Norman OK 0311 PM CDT Tue Aug 20 2024 Areas affected...southwest into central MT Concerning...Severe potential...Watch possible Valid 202011Z - 202215Z Probability of Watch Issuance...60 percent SUMMARY...Isolated to widely scattered thunderstorms could produce strong/damaging gusts and isolated hail into early evening across parts of southeast into central Montana. Area is being monitored for possible severe thunderstorm watch issuance. DISCUSSION...Isolated thunderstorms have developed this afternoon over the higher terrain of southwest Montana. This area has quickly warmed into the 80s F as earlier cloud cover has shifted northeast. Additional convection is expected to develop further east near the Beartooth/Absarokas over the next couple of hours. Collectively this convection will spread northeast into this evening. Modest instability, mainly supported by steep midlevel lapse rates/cool temps aloft, and effective shear magnitudes greater than 35 kt will support organized/robust updrafts. Forecast hodographs along with regional VWP data also indicate shear favorable for supercells. Given high-based storms and steepening low-level lapse rates, strong/damaging gusts are possible with this activity as it becomes better organized with time and northeastward extent into the high Plains. A few instances of hail up to 1.25 inch diameter is also possible. A severe thunderstorm watch may be needed this afternoon. ..Leitman/Hart.. 08/20/2024 ...Please see www.spc.noaa.gov for graphic product... ATTN...WFO...BYZ...GGW...TFX...MSO... LAT...LON 45531289 46451251 46751218 47121145 47421034 47500949 47450855 47020732 46200683 45770694 45210755 45210863 44971202 45041265 45231284 45531289 Read more

WW 0641 Status Updates
STATUS FOR WATCH 0641 HAS NOT BEEN ISSUED YET Read more

WW 641 SEVERE TSTM MT 202040Z - 210400Z
URGENT - IMMEDIATE BROADCAST REQUESTED Severe Thunderstorm Watch Number 641 NWS Storm Prediction Center Norman OK 240 PM MDT Tue Aug 20 2024 The NWS Storm Prediction Center has issued a * Severe Thunderstorm Watch for portions of Southwest and Central Montana * Effective this Tuesday afternoon and evening from 240 PM until 1000 PM MDT. * Primary threats include... Scattered damaging wind gusts to 70 mph possible Isolated large hail events to 1.5 inches in diameter possible SUMMARY...Thunderstorms will develop over the mountains of southwest Montana this afternoon and spread quickly eastward across the watch area through the evening. Damaging wind gusts are the main threat with the strongest storms. The severe thunderstorm watch area is approximately along and 85 statute miles north and south of a line from 20 miles north of Dillon MT to 125 miles east northeast of Lewistown MT. For a complete depiction of the watch see the associated watch outline update (WOUS64 KWNS WOU1). 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 1.5 inches. Extreme turbulence and surface wind gusts to 60 knots. A few cumulonimbi with maximum tops to 500. Mean storm motion vector 25030. ...Hart Read more