SPC MD 1650

2 years 11 months ago
MD 1650 CONCERNING SEVERE POTENTIAL...WATCH UNLIKELY FOR PARTS OF THE CENTRAL APPALACHIANS INTO THE MID ATLANTIC
Mesoscale Discussion 1650 NWS Storm Prediction Center Norman OK 1214 PM CDT Thu Aug 04 2022 Areas affected...Parts of the central Appalachians into the Mid Atlantic Concerning...Severe potential...Watch unlikely Valid 041714Z - 041915Z Probability of Watch Issuance...20 percent SUMMARY...Storms capable of isolated damaging winds will increase in coverage this afternoon. DISCUSSION...Convection is increasing early this afternoon across eastern WV and northwest VA, with some increasing cumulus also noted across southern VA. Strong diurnal heating and rich low-level moisture will support MLCAPE increasing to near or above 2000 J/kg across the region this afternoon, as MLCINH erodes and storm coverage continues to increase with time. Deep-layer shear is generally expected to remain weak, but the thermodynamic environment will support a threat of isolated and potentially damaging downburst winds in association with the strongest storms. Midlevel cloudiness associated with an approaching MCV may result in a relative minimum in storm coverage across parts of western VA, but some potential exists for a loosely organized storm cluster to develop and spread across northern VA into adjacent portions of MD, as outflows consolidate with time. Due to the generally disorganized nature of the threat, watch issuance is considered unlikely at this time. ..Dean/Grams.. 08/04/2022 ...Please see www.spc.noaa.gov for graphic product... ATTN...WFO...AKQ...LWX...RNK...PBZ...RLX... LAT...LON 38468071 39207948 39657882 39687754 39667714 38847666 38137656 37767666 37707725 37777777 37937799 38157825 38397869 38507916 38277993 38188027 38098056 38068093 38248100 38468071 Read more

SPC Aug 4, 2022 1730 UTC Day 2 Convective Outlook

2 years 11 months ago
SPC 1730Z Day 2 Outlook
Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1209 PM CDT Thu Aug 04 2022 Valid 051200Z - 061200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF THE NORTHERN PLAINS AS WELL AS THE MID-ATLANTIC... ...SUMMARY... Isolated severe wind gusts or marginal hail will be possible Friday afternoon across parts of the northern Plains, and over parts of Virginia and Maryland. ...Synopsis... Upper ridging is forecast to prevail across the southern half of the CONUS on Friday, with the center of the ridge drifting northeastward into the central Plains. A shortwave trough is expected to progress eastward across the Canadian Prairie Provinces into Ontario. The gradient between the southern CONUS upper ridging and this shortwave trough will act to enhanced the westerly flow aloft from the Pacific Northwest into the Upper MS Valley. A surface low will precede the Canadian shortwave, beginning the period over central Manitoba before moving northeastward into northern Ontario and the Hudson Bay. An attendant cold front is expected to sweep southeastward across the northern Plains and Upper Midwest, leading to thunderstorms development during the afternoon and evening. ...Northern Plains... Strong diurnal heating is anticipated ahead of the front across the northern Plains on Friday, with temperatures reaching the upper 90s and low 100s. Despite deep boundary-layer mixing associated with this heating, dewpoints are expected to remain in the 60s, which will support moderate to strong instability within the pre-frontal air mass. Late afternoon thunderstorm initiation is anticipated along the front, with robust updrafts developing quickly. Some of the enhanced mid-level flow discussed in the synopsis will extend over the region, supporting around 30 to 40 kt of deep-layer vertical shear, which is enough for occasional supercell storm structures. However, the linear character of the forcing for ascent along the front coupled with high storm coverage suggests a discrete, supercellular mode would be difficult to maintain. These factors, coupled with the high-based character of the storms, suggest a mainly multicellular/outflow-dominant mode, with damaging wind gusts as the main severe threat. There is enough overlap between the buoyancy and shear to support a hail threat as well, particularly early in the storm life cycle. ...Mid-Atlantic... Afternoon thunderstorm development is expected over much of the Mid-Atlantic, fostered by diurnal heating, ample low-level moisture, and modest ascent. The ascent over the region will be a combination of low-level confluence and weak large-scale lift attendant to any convectively inducted vorticity maxima from overnight activity farther west. All of these factors maximize over northern VA and vicinity, where the greatest probability for a few damaging wind gusts exists. ..Mosier.. 08/04/2022 Read more

SPC MD 1649

2 years 11 months ago
MD 1649 CONCERNING SEVERE POTENTIAL...WATCH UNLIKELY FOR PARTS OF CENTRAL/EASTERN OH...WESTERN PA...NORTHERN WV PANHANDLE
Mesoscale Discussion 1649 NWS Storm Prediction Center Norman OK 1158 AM CDT Thu Aug 04 2022 Areas affected...Parts of central/eastern OH...western PA...northern WV Panhandle Concerning...Severe potential...Watch unlikely Valid 041658Z - 041900Z Probability of Watch Issuance...5 percent SUMMARY...Thunderstorms capable of isolated damaging wind gusts are possible this afternoon. DISCUSSION...Convection is gradually increasing in coverage and intensity early this afternoon, along and ahead of a weak surface boundary draped from northern OH into northwest PA. With deep-layer shear expected to remain weak, convection is expected to remain relatively disorganized. However, as MLCAPE increases into the 1500-2000 J/kg range and low-level lapse rates steepen with time, the strongest cells/clusters may be capable of producing isolated damaging wind as they spread northeastward this afternoon. Watch issuance is not expected at this time. ..Dean/Grams.. 08/04/2022 ...Please see www.spc.noaa.gov for graphic product... ATTN...WFO...CTP...PBZ...RLX...CLE...ILN... LAT...LON 40348335 40848174 41368018 41767927 41147927 40028049 39708171 39658264 39688299 39848355 40138366 40348335 Read more

SPC Day 1 Fire Weather Outlook

2 years 11 months ago
SPC Day 1 Fire Weather Outlook
Day 1 Fire Weather Outlook NWS Storm Prediction Center Norman OK 1127 AM CDT Thu Aug 04 2022 Valid 041700Z - 051200Z ...CRITICAL FIRE WEATHER AREA FOR PORTIONS OF WESTERN MONTANA... The previous forecast remains valid with only minor adjustments for the latest hi-res guidance. Critical fire weather conditions are expected with a strong frontal passage across portions of northern MT. Isolated dry thunderstorms are also expected within dry fuels across southern MT. Otherwise, please see the prior discussion for more details. ..Lyons.. 08/04/2022 .PREV DISCUSSION... /ISSUED 0141 AM CDT Thu Aug 04 2022/ ...Synopsis... A midlevel shortwave trough is forecast to move eastward across the northern Rockies today. Strong west-southwesterly flow aloft associated with this feature will overspread the Pacific Northwest and northern Idaho/Montana. In response at the surface, low pressure will deepen over Alberta and Saskatchewan. ...Northern Rockies and adjacent High Plains... Along the southern periphery of the surface low, a swath of 20-25 mph sustained westerly surface winds are expected across parts of north-central MT. These strong winds, coupled with a hot/deeply-mixed boundary layer (10-15 percent minimum RH) will lead to critical fire-weather conditions. In addition, mixed wet-dry thunderstorms should spread eastward across the northern Rockies, accompanied by locally strong outflow winds. Given the expected high cloud bases and relatively fast storm motions (over 30 mph), limited rainfall accumulation is expected, supporting isolated dry thunderstorm potential. ...Pacific Northwest... Deep boundary-layer mixing in the presence of strong westerly flow aloft combined with downslope warming/drying in the lee of the Cascades will result in 15-20 mph sustained westerly surface winds and 15-20 percent RH. Given receptive fuels from WA into OR, elevated to locally critical conditions can be expected. ...Please see www.spc.noaa.gov/fire for graphic product... Read more

SPC Aug 4, 2022 1630 UTC Day 1 Convective Outlook

2 years 11 months ago
SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1121 AM CDT Thu Aug 04 2022 Valid 041630Z - 051200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS PARTS OF THE CONUS... ...SUMMARY... Isolated severe thunderstorms, mainly in the form of damaging winds, are possible into early evening from the Ohio Valley into parts of the Mid-Atlantic and New England, western portions of South Dakota and Nebraska, Montana, and the western Colorado Plateau. ...NE/SD... Strong surface heating and deep mixing will occur along a surface lee trough across from the NE Panhandle into southwest SD. Though boundary-layer moisture will be somewhat marginal, a narrow corridor of MLCAPE approaching 1500 J/kg should develop with minimal MLCIN. Most CAM guidance suggest a few storms should form near the surface trough during the late afternoon. Inverted-v thermodynamic profiles and moderately elongated hodographs could support a couple high-based supercells capable of isolated severe wind and hail for a few hours into the early evening. ...MT... An amplified upper trough centered on BC will shift east across the Canadian Rockies towards SK through 12Z tomorrow. As this occurs, a surface cyclone will deepen over southeast AB into southern SK, with a trailing cold front sharpening over MT. With PW values largely between 0.5 to 0.75 inches this morning, boundary-layer moisture will be quite limited. Very deep boundary-layer mixing with meager buoyancy atop that along the surface front should be just enough to promote very high-based convection from southwest to central MT. While the bulk of stronger mid-level westerlies will be confined to the cool side of the surface front, adequate strengthening will support semi-organized skeletal clusters capable of isolated severe outflow gusts spreading east-northeast. ...OH Valley into the Mid-Atlantic and New England... A remnant MCV over far southern IL should drift east into western KY. To the northeast of this MCV, broad but weak mid-level southwesterlies will exist within a seasonably rich PW moisture plume. The persistence of weak convective outflows, differential surface heating, and terrain will support a broad swath of scattered thunderstorms. Relatively greater potential for damaging microbursts in predominately pulse and slow-moving multicell clusters should exist from the Upper OH Valley into the Northeast/Mid-Atlantic where MLCAPE can exceed 2000 J/kg. But the lack of greater vertical shear will be detrimental to an organized severe threat. See MCD 1648 and later MCDs this afternoon for additional short-term forecast information. ...Western CO Plateau vicinity... A belt of enhanced mid-level easterlies becoming more southeasterly later today will persist to the north of an MCV drifting west across the Lower CO Valley. Scattered thunderstorms are expected to develop northwestward off the Mogollon Rim across the western CO Plateau and spread towards the southern Great Basin. Marginally severe hail will possible in initial updrafts transitioning to mainly a marginally severe wind threat later. ..Grams/Smith.. 08/04/2022 Read more

SPC MD 1648

2 years 11 months ago
MD 1648 CONCERNING SEVERE POTENTIAL...WATCH UNLIKELY FOR NORTH-CENTRAL PA INTO SOUTHERN/CENTRAL NY
Mesoscale Discussion 1648 NWS Storm Prediction Center Norman OK 1119 AM CDT Thu Aug 04 2022 Areas affected...North-central PA into southern/central NY Concerning...Severe potential...Watch unlikely Valid 041619Z - 041815Z Probability of Watch Issuance...20 percent SUMMARY...Locally damaging winds are possible as thunderstorms spread northeastward this afternoon. DISCUSSION...An arc of convection has moved from western into north-central PA through the morning, with occasional 30-35 kt gusts noted. While deep-layer shear is generally weak across the region, unidirectional southwesterly flow may be sufficient to maintain loosely organized convection in association with this arc and related cold pool as it moves northeastward into a destabilizing environment, with an attendant threat of locally damaging wind gusts. Additional storm development is expected downstream into parts of southern/central NY this afternoon, which may also pose a localized damaging wind threat as low-level lapse rates steepen with time. With the threat expected to remain relatively isolated and disorganized, watch issuance is considered unlikely. ..Dean/Grams.. 08/04/2022 ...Please see www.spc.noaa.gov for graphic product... ATTN...WFO...ALY...BGM...BUF...CTP... LAT...LON 42647697 43107539 43147492 42867454 42197508 41507610 41137662 40967706 40777809 41447879 41787899 42647697 Read more

SPC Aug 3, 2022 1730 UTC Day 2 Convective Outlook

2 years 11 months ago
SPC 1730Z Day 2 Outlook
Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1213 PM CDT Wed Aug 03 2022 Valid 041200Z - 051200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF THE OH VALLEY...AND CENTRAL MT... ...SUMMARY... Thunderstorms capable of isolated damaging wind gusts are expected over portions of the Ohio Valley as well as over central Montana on Thursday. ...Synopsis... Expansive upper ridging is forecast to be centered over the southern High Plains early Thursday morning, covering much of the southern half of the CONUS. This upper ridging is expected to persist throughout the period, relegating any stronger westerly flow to the northern CONUS, in particular the corridor from the Pacific Northwest into the Upper MS Valley/Upper Great Lakes. A shortwave trough will progress through this westerly flow aloft, remaining mainly on the Canadian side of the international border. Afternoon/evening thunderstorms are possible across MT as the ascent and increasing mid-level moisture attendant to this shortwave foster thunderstorm development. The central and eastern CONUS will be devoid of any large-scale synoptic features, but a convectively induced shortwave trough may be in place over the Mid MS Valley early in the period, induced by overnight thunderstorms. This shortwave is then forecast to progress northeastward through the OH Valley during the day. ...OH Valley... Overnight thunderstorms upstream of the region will greatly influence the overall severe potential Thursday, contributing significantly to both the strength of the shortwave trough expected to move through the region as well as the position of any outflow boundaries. Current expectation is for the convectively induced shortwave trough to track northeastward through the region during the afternoon, interacting with the moist and buoyant air mass to foster the development of numerous to widespread thunderstorms. Modestly enhanced low to mid-level flow may accompany this shortwave, supporting the potential for a few stronger, more organized storms capable of damaging wind gusts. ...Central MT... Strong boundary-layer mixing is anticipated ahead of the approaching shortwave trough. Destabilization resultant from this mixing as well as increasing mid-level moisture will result in meager buoyancy. Afternoon thunderstorm development is anticipated as the southern periphery of the shortwave glances the region. Moderate vertical shear will aid in updraft persistence, with the high-based character of these storms contributing to a risk for damaging wind gusts. ...Great Basin/Four Corners... Scattered to numerous thunderstorms are expected within the moist Monsoonal regime beneath the expansive upper ridge. Modest vertical shear should result in a predominantly pulse/multicellular storm mode, limiting updraft duration and overall strength. The only exception is over northern AZ, where the combination of shear and buoyancy may be enough to support a severe storm or two. However, uncertainty regarding coverage precludes introducing any severe probabilities with this outlook. ...Northern ME... Southern periphery of a shortwave trough moving through Quebec will contribute to increased forcing for ascent as well as stronger mid-level flow across the region. Scattered thunderstorm development is anticipated during afternoon, with the deep westerly flow aloft contributing to the potential for a few stronger storms capable of damaging wind gusts. Current expectation is for overall severe coverage too remain less than 5%. ..Mosier.. 08/03/2022 Read more

SPC Aug 3, 2022 1630 UTC Day 1 Convective Outlook

2 years 11 months ago
SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1122 AM CDT Wed Aug 03 2022 Valid 031630Z - 041200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS LOWER MO VALLEY TO THE GREAT LAKES... ...SUMMARY... Scattered damaging winds will be possible from the Great Lakes to the Lower Missouri Valley through this evening. ...Northern IL/southeast WI to Lower MI... An MCV evident in east-central IA will move into Lower MI by early evening. A broken swath of stratiform and deep convection is ongoing immediately ahead of this MCV in eastern IA, northeast across northern/central Lower MI. Robust boundary-layer heating is underway ahead of large-scale convective outflow still spreading east of this midday activity in IL, with a plume of large buoyancy anticipated as MLCAPE increases to 3000-4000 J/kg. Much of the convection may remain to the cool side of the large-scale convective outflow (at least in the short-term), but there is potential for clusters to eventually consolidate along the leading edge of the differential heating corridor. While stronger mid-level westerlies will generally reside over Lower MI (with a gradient from north to south), the DMX VWP sampled 40-45 kt 700-500 mb westerlies in the wake of the MCV. This should support increasingly organized convection this afternoon, even behind the broader large-scale convective outflow. Sporadic strong to severe wind gusts producing swaths of scattered damage appears possible this afternoon. This threat should linger into early evening with line segments that spread eastward. ...Mid-MS/Lower MO Valleys... Most morning guidance suggest ongoing showers and isolated thunderstorms in the wake of the leading east-central IA MCV should hold off on intensifying until the early evening time frame. A low-amplitude shortwave impulse over the Mid-MO Valley should drift east-southeast, while low-level convergence should tend to strengthen towards early evening along southern portion of a bifurcated frontal zone. Weaker but a more northwesterly component to mid-level flow should yield slower storm motions in multicell clusters that tend to propagate south-southeast in MO/IL. With a plume of large buoyancy in the warm/moist sector, scattered damaging wind gusts will be possible well into the evening, before gradually waning overnight. ...Southern AZ... Late morning convection is ongoing across parts of southeast AZ and this lowers confidence in the degree of boundary-layer heating and convective redevelopment off the higher terrain later today. Morning CAM guidance generally provides mixed signals on the degree of convective coverage during the late afternoon and evening. Conditionally, adequate speed shear from the mid to upper levels within a belt of east-southeasterlies around the Four Corners anticyclone could support a threat for marginally severe wind and some hail this evening. ...Southeast States... Very localized damaging winds are possible within pulse microbursts over a large swath of the Southeast. Minimal deep-layer shear will mitigate potential for organized clustering. ..Grams/Lyons.. 08/03/2022 Read more

SPC Day 1 Fire Weather Outlook

2 years 11 months ago
SPC Day 1 Fire Weather Outlook
Day 1 Fire Weather Outlook NWS Storm Prediction Center Norman OK 1042 AM CDT Wed Aug 03 2022 Valid 031700Z - 041200Z ...CRITICAL FIRE WEATHER AREA FOR NORTH-CENTRAL MONTANA... The previous forecast remains on track with only minor adjustments needed based on recent guidance and morning observations. Elevated conditions are already ongoing across north-central MT, and should continue to deteriorate through the remainder of the day. See the previous discussion below for additional details. ..Moore.. 08/03/2022 .PREV DISCUSSION... /ISSUED 0159 AM CDT Wed Aug 03 2022/ ...Synopsis... An expansive large-scale ridge will be centered over the Great Basin, while a belt of moderate midlevel westerly flow extends from the Pacific Northwest into the northern Rockies/adjacent High Plains along the northern periphery of the ridge. Within the westerly midlevel flow, a shortwave trough will track east-southeastward into the Pacific Northwest, while an attendant surface low deepens over southern AB. ...Northern Rockies and adjacent High Plains... Deep boundary-layer mixing and downslope flow from the northern Rockies into the adjacent High Plains will result in 10-15 percent minimum RH during the afternoon. At the same time, the tightening surface pressure gradient along the southern periphery of the surface low will support 20-25 mph sustained westerly surface winds over parts of north-central MT -- where Critical highlights remain in place. ...Pacific Northwest... The enhanced westerly flow will lead to warming/drying in the lee of the Cascades from northern WA into central OR. Sustained westerly surface winds of 15-20 mph amid 10-15 percent RH will yield elevated to locally critical fire-weather conditions. ...Dry Thunderstorms... Along the northern periphery of the monsoonal moisture plume, diurnal heating and orographic circulations along the higher terrain in OR into northern CA will support isolated high-based thunderstorm development. While many of these storms may be a mixed wet-dry mode (0.75-1.0 in PW), lightning strikes on the periphery of precipitation cores could lead to new fire starts given receptive fuels over the area. Additionally, adequate deep-layer shear could support a few loosely organized storms capable of strong/erratic outflow winds. ...Please see www.spc.noaa.gov/fire for graphic product... Read more

SPC MD 1631

2 years 11 months ago
MD 1631 CONCERNING SEVERE POTENTIAL...WATCH UNLIKELY FOR NORTHERN MINNESOTA INTO FAR NORTHWEST WISCONSIN
Mesoscale Discussion 1631 NWS Storm Prediction Center Norman OK 1241 PM CDT Tue Aug 02 2022 Areas affected...northern Minnesota into far northwest Wisconsin Concerning...Severe potential...Watch unlikely Valid 021741Z - 021845Z Probability of Watch Issuance...20 percent SUMMARY...Isolated hail will be possible with elevated storms early this afternoon. A weather watch is not expected. DISCUSSION...As of 1730 UTC, regional radar showed isolated thunderstorms developing along and north of a warm front across portions of northern MN and WI. Driven predominately by warm advection, these storms are rooted above the surface with unstable parcels near 850 mb. Model soundings show 500-1000 J/kg of MUCAPE along with 40-50 kt of effective shear within northwesterly flow aloft. Some organization potential into elevated supercell structures is possible given the favorable CAPE/shear overlap. Isolated marginally severe hail will be the primary risk given the relatively isolated nature of storms and favorable deep-layer shear. However, the marginal buoyancy/mid-level lapse rates should limit updraft strength and hail production. Storms should gradually weaken as they drift eastward away from the frontal zone and ascent. While isolated instances of hail will remain possible through this afternoon, the limited potential for more organized severe storms suggests a watch is unlikely. ..Lyons/Grams.. 08/02/2022 ...Please see www.spc.noaa.gov for graphic product... ATTN...WFO...DLH...FGF... LAT...LON 48399399 48569491 48489559 48259581 47949606 47599562 47089475 46779398 46529289 46259222 46319103 46689064 46929067 47069110 47249178 47499238 47899328 48399399 Read more

SPC Aug 2, 2022 1730 UTC Day 2 Convective Outlook

2 years 11 months ago
SPC 1730Z Day 2 Outlook
Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1214 PM CDT Tue Aug 02 2022 Valid 031200Z - 041200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF LOWER MI AND THE MID MS VALLEY... ...SUMMARY... Scattered storms, some severe, are most likely from Lower Michigan into the Mid Mississippi Valley Wednesday, with at least isolated severe possible extending southwestward across Missouri and into eastern Kansas. ...Synopsis... Upper ridging is forecast to persist across the southern half of the CONUS throughout the period, keeping any stronger westerly flow aloft confined to the northern CONUS. A shortwave trough is expected to move through this western flow, beginning the period extended from western Ontario through the Upper Midwest. This shortwave should then progress eastward through the remainder of Ontario and the adjacent Upper Great Lakes, and into Quebec. Surface low attendant to this shortwave will take a similar track, moving just ahead of the parent shortwave, as associated cold front pushes southeastward through the Upper/Middle MS Valley and Upper Great Lakes. This cold front will interact with the warm and moist air mass covering the MS Valley, Upper Great Lakes, and OH Valley, triggering scattered to widespread thunderstorms across the region. ...Upper Great Lakes into the Lower MO Valley... Showers and thunderstorms will likely be ongoing within the warm-air advection regime preceding the front over northern Lower MI and adjacent portions of far eastern Upper MI. Stable low-levels will limit surface-based storms, but cold mid-level temperatures and low to mid-level moisture advection will support elevated thunderstorms, a few of which could be strong enough produce hail. The low-level stable layer will be relatively shallow, so a few downbursts could be strong enough to reach the surface. These storms should move east into northeastern Ontario throughout the morning, allowing for destabilization in their wake across northern Lower MI. Additional destabilization is anticipated ahead the front within the warm and very moist air mass through the Mid MS Valley and into the Ozark Plateau. By the afternoon, strong to very strong instability (i.e. MLCAPE from 2000-4000 J/kg) will likely be in place over this region, with little to no convective inhibition. Rapid thunderstorm development is expected as the front interacts with this airmass. The strongest mid-level flow is expected over Lower MI, decreasing with southward/southwestward extent. As a result, the highest potential for supercells is over Lower MI, with greater shear/outflow balance possible here as well. A more outflow-dominant, multicellular mode is likely farther south, from the Mid MS Valley to the Lower MO Valley. Damaging wind gusts will be the primary severe threat across the entire region, but potential for supercells and stronger low-level hodograph curvature suggests a tornado or two is possible across northern Lower MI. ...Southern AZ... Deep easterly flow is expected over the region, as the upper ridge shifts slightly northward towards the Four Corners vicinity. Thunderstorm development is anticipated over the higher terrain, with the deep easterly flow then favoring motion off the terrain in the well-mixing boundary layer of adjacent desert. Thermodynamic conditions favor strong outflow, and the potential for a few severe wind gusts. ..Mosier.. 08/02/2022 Read more

SPC Aug 2, 2022 1630 UTC Day 1 Convective Outlook

2 years 11 months ago
SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1117 AM CDT Tue Aug 02 2022 Valid 021630Z - 031200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS NORTHERN UPPER MIDWEST... ...SUMMARY... Scattered large hail and damaging winds are possible across a portion of the northern Upper Midwest this evening into tonight. ...Northeast ND to northern WI/Upper MI... A vigorous shortwave trough will progress east across the southern Prairie Provinces into northwest ON through 12Z tomorrow. A deep surface cyclone will similarly track from southern SK to far northwest ON. A cold front arcing southwest from this cyclone will sweep into the Red River Valley by evening and likely reach western Lake Superior in the early morning. Initial severe potential should be focused near this boundary in the northeast ND vicinity during the early evening. Here, the trailing portion of supercell development may spread across the international border (more likely in eastern MB) as MLCIN wanes on the western periphery of upper 60s boundary-layer dew points. This activity may occur within a confined corridor of large buoyancy (MLCAPE of 2500-3000 J/kg), steep mid-level lapse rates (8-8.5 C/km from 700-500 mb), and an elongated/straight-line hodograph. These will conditionally favor a discrete supercell or two capable of producing very large hail and locally damaging wind gusts into northwest MN during the evening. Farther east, a leading mid-level perturbation near the MB/ND border in conjunction with low-level warm theta-e advection should support a separate corridor of severe potential from the St. Croix Valley to western Upper MI this evening into tonight. The environment along the northwest/southeast-oriented warm front will be conditionally favorable for intense supercells. However, confidence is low in whether surface-based supercells will develop and be sustained given the presence of the upstream elevated mixed-layer and warming 700-mb temperatures (near 14 C this evening over the Twin Cities). The more probable scenario is for elevated convection later this evening into the overnight. With ample upstream buoyancy and effective bulk shear, organized clusters with embedded supercell structures should pose a threat for both severe hail and damaging winds. ...Lower OH Valley/Mid-South... Thunderstorm clusters are ongoing but largely decaying in southern IL. Broader convective outflow has spread out well ahead of these clusters near the confluence of the MS/OH rivers and should be a limiting factor to a more robust threat. But strong boundary-layer heating to the south and west of this outflow could support resurgence of convective remnants into the Mid-South region later this afternoon amid modest mid to upper-level north-northwesterlies. Morning guidance such as the 12Z NAM and HRRR runs have terribly simulated ongoing convection, lowering confidence in areal extent of the isolated damaging wind threat today. ...Northern ME... Scattered showers are ongoing along and just ahead of a surface cold front shifting east from the St. Lawrence Valley. This activity should deepen somewhat as it impinges on the warming boundary layer across northern New England. Weak mid-level lapse rates will limit updraft intensity, although a modest combination of buoyancy/shear could favor some threat for isolated damaging winds. ...Central/southern FL Peninsula... Numerous thunderstorms will develop along the sea breezes and should eventually coalesce over the interior peninsula as they slowly spread inland later this afternoon. Light winds through 400 mb will limit potential for storm-scale organization with ambient effective bulk shear expected to only reach 8-15 kts. But large buoyancy and storm-scale mergers should support a threat for sporadic wet microbursts and localized strong gusts. ..Grams/Lyons.. 08/02/2022 Read more

SPC Day 1 Fire Weather Outlook

2 years 11 months ago
SPC Day 1 Fire Weather Outlook
Day 1 Fire Weather Outlook NWS Storm Prediction Center Norman OK 1041 AM CDT Tue Aug 02 2022 Valid 021700Z - 031200Z ...CRITICAL FIRE WEATHER AREA FOR CENTRAL MONTANA INTO THE WESTERN DAKOTAS... The main adjustment for this update is to expand the Elevated risk area into portions of northwest South Dakota and to introduce an isolated dry-thunderstorm risk to portions of central/northern NE. The 12 UTC UNR sounding sampled very dry boundary-layer conditions atop a shallow nocturnal inversion. Latest surface observations show temperatures quickly warming into the mid 80s as the inversion begins to mix out. Relative humidity should quickly fall through the afternoon as mixing continues (though this may be hindered to a degree by increasing cloud cover). As pressure gradient winds increase this afternoon, elevated conditions appear probable. To the south across NE, richer moisture content is noted in morning soundings, which will help support adequate instability for high-based thunderstorms later this afternoon. Forecast soundings suggest a deep, well-mixed boundary layer will be in place as temperatures warm into the upper 90s and low 100s. A 2-3 km deep sub-cloud layer coupled with steep low-level lapse rates should be supportive of a few dry thunderstorms as well as gusty outflow winds. With ERCs across the region near the 90th percentile and 10-hour fuel moisture between 5-8%, a lightning-driven fire weather threat appears probable. ..Moore.. 08/02/2022 .PREV DISCUSSION... /ISSUED 0201 AM CDT Tue Aug 02 2022/ ...Synopsis... Along the northern periphery of a large-scale ridge centered over the western CONUS, a belt of deep/enhanced westerly flow will extend from the Pacific Northwest into the northern Rockies and adjacent High Plains. Multiple shortwave troughs will move through the westerly flow aloft during the day, with the strongest midlevel flow expected across parts of northern MT into northwest ND. ...Wind/RH... Deep boundary-layer mixing into the belt of strong flow aloft will result in a swath of 20-25 mph sustained westerly surface winds amid 15-20 percent RH across portions of MT into far western ND this afternoon. Given highly receptive fuels over this area, critical conditions are expected. Farther west, westerly downslope flow will favor warming/drying in the lee of the Cascades in WA into northern OR. Here, 15-20 mph sustained westerly surface winds coupled with 15-20 percent minimum RH will yield elevated to locally critical conditions. ...Dry Thunderstorms... Large-scale ascent accompanying the shortwave troughs and sufficient midlevel moisture/instability will support high-based thunderstorm development along and east of the Cascades in OR into northern CA and farther east in the northern Rockies. While many of these storms will be associated with accumulating rainfall given 1.0-1.2 in PW, isolated lightning-induced ignitions will still be possible on the periphery of precipitation cores. ...Please see www.spc.noaa.gov/fire for graphic product... Read more

SPC Aug 1, 2022 1730 UTC Day 2 Convective Outlook

3 years ago
SPC 1730Z Day 2 Outlook
Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1227 PM CDT Mon Aug 01 2022 Valid 021200Z - 031200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PARTS OF THE UPPER MIDWEST NEAR THE INTERNATIONAL BORDER AND LAKE SUPERIOR... ...SUMMARY... Large hail and damaging to severe thunderstorm gusts are most likely Tuesday evening and night over parts of the Upper Midwest near the international border and Lake Superior. ...Synopsis... The large-scale pattern will continue to be characterized by an anticyclone over AZ/NM and vicinity, with ridging eastward over the southern Plains and Gulf Coast States. Mean troughing will persist over the Lower Great Lakes and central Appalachians, south of a strong synoptic cyclone moving erratically over the northern Hudson Bay region. However, that troughing should deamplify as heights fall in the upstream west-northwest flow belt, across the northwestern/north-central CONUS and adjoining Canada. Those height falls will be related largely to two strong shortwave troughs, the trailing one forecast to move from AK into BC. The leading shortwave trough, and most relevant for this forecast, is apparent in moisture-channel imagery from northwestern NC southward off the coast of Vancouver Island. This perturbation is forecast to move east-southeastward to the northern Rockies by the start of the period (02/12Z), penetrate a low-amplitude mean ridge during the day, followed by entering the confluent-flow belt south of the Hudson Bay cyclone. By 03/12Z, the trough should reach the southern part of the MB/ON provincial border, southward over western MN. There it should phase with an initially separate/weaker perturbation currently evident over parts of central CA and southern NV, that will be entrained into the northern-stream westerlies early day 2. At the surface, a cold front -- initially located over Lake Michigan, northern IL and southern IA -- should move eastward into the Lower Great Lakes and Northeast early day-2. The western segment of this frontal zone should become a warm front by the start of the period, extending from central IL northwestward to a frontal- wave low over eastern/southeastern ND, then northwestward to a primary low over southern SK. By 03/00Z, the latter low should move eastward to southern MB, with warm front over northwestern MN, southeastern MN/western WI, and central IL. A cold front will extend from the low across parts of northeastern ND, northwestern SD and central/southern WY. By 12Z, the warm front should reach the western U.P., central Lake Michigan, southwestern Lower MI, near the IN/OH line, to central KY. ...Upper Midwest... During the afternoon, a corridor of strong buoyancy will develop in the warm sector over southern/eastern MN, with strong diurnal heating and rich low-level moisture fostering MLCAPE in the 3000-4000 J/kg range. Still-favorable but lower values will extend northwestward toward the main surface low, with 1500-2500 J/kg possible over northeastern ND. However, strong MLCINH and nebulous deep-layer forcing cast great uncertainty on diurnal development near the warm front, over the eastern MN/WI area. Thunderstorms may develop during the afternoon and evening over northeastern ND and northwestern MN, as well as the Boundary Waters, MN Arrowhead and western Lake Superior region. Activity northeast of the warm front will be elevated, but still pose a threat for severe hail and isolated damaging gusts. Development over the warm sector is more uncertain in timing/coverage due to strong EML-related capping, but the potential for at least isolated to widely scattered surface-based thunderstorms will increase as the mid/upper trough approaches and associated mass response strengthens overnight. That mass response also will include strengthening of the associated zone of low-level warm advection, moisture transport and isentropic lift to LFC over the warm-frontal zone. The entire convective regime is expected to shift eastward or east- southeastward across the lake, and perhaps northern/eastern parts of the Upper Peninsula, through the period. Forecast soundings early in the episode suggest very steep low/ middle level lapse rates above the warm-frontal surface, supporting MLCAPE and elevated MUCAPE increasing to the 2500-3500 J/kg range, amidst effective-shear magnitudes of 40-50 kt (perhaps higher). This will support supercell and large-hail potential, especially early in the convective cycle and along the inflow (south to southwest sides) of any resulting complex, where relatively unimpeded access persists to the 45-55-kt nocturnal LLJ. The track of this convective regime remains somewhat uncertain, but it should outpace the advance of the warm front and become more elevated with time. Unconditional probabilities are being extended eastward over more of the U.P. to accommodate the threat from this activity. ...Northeastern Plains... A conditional threat exists for strong-severe gusts with thunderstorms that may form during the evening and overnight, ahead of the cold front over eastern parts of SD and northeastern NE. While moisture/buoyancy will be less than areas farther northeast near the warm front, increasing large-scale ascent and cooling aloft will occur ahead of the southern/phased branch of the shortwave trough. A residual very warm and deeply mixed boundary layer from prior diurnal heating will foster the potential for strong-severe gusts with any convection that can develop; however, storm coverage appears too uncertain for more than marginal unconditional probabilities at this time. ...Lower Ohio Valley to Ozarks... Scattered showers and thunderstorms may be ongoing over northern and/or eastern parts of this region from prior/overnight MCS activity discussed in more detail in the day-1 outlook. This convection should leave outflow/differential-heating boundaries to focus additional, diurnal development. Though deep-layer shear will be weak, strong diabatic heating away from any persistent cloud cover, combined with very rich low-level moisture (dewpoints commonly in the 70s F) will underlie moderately steep midlevel lapse rates of around 6.5 deg C/km, within a deep troposphere. The result should be areas of 3000-4000 J/kg MLCAPE. MLCINH will be weak east of the EML, supporting diurnal development and perhaps upscale growth into one or more wind-producing clusters. Any more-focused area of potential within the broader outlook will be very dependent on mesoscale processes yet to evolve, and this outlook area may shift or change shape substantially as time gets closer. ..Edwards.. 08/01/2022 Read more
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