SPC Day 3-8 Fire Weather Outlook
Day 3-8 Fire Weather Outlook NWS Storm Prediction Center Norman OK 0400 PM CDT Mon Sep 16 2024 Valid 181200Z - 241200Z Mid-level troughing is expected to persist over much of the western CONUS through the extended forecast period. At the same time, ridging is expected to build over the central and eastern parts of the country keeping the upper-level pattern relatively stagnant. By midweek, a mid-level low associated with broader troughing over the West will eject over the northern Rockies/Plains. Strong surface winds are expected near a deepening low and cold front, but widespread wetting rainfall is also expected. This pattern will continue later in the week and into next weekend as a second trough is forecast to eject over the central and southern Plains. While strong winds are again expected, area fuels are also likely to be tempered by rainfall. Thus, fire-weather concerns appear modest through the next 7 days. ...Plains D3/Wed-D6/Sat... As the aforementioned troughing shifts eastward, several more prominent impulses will move over the Plains D3/Wed and D6/Sat. Strong lee cyclogenesis should accompany each of these upper-level troughs, bolstering surface winds (20-25 mph) over much of the Plains through the week and early weekend. However, ongoing moisture return will support only modestly low diurnal RH values, with widespread wetting rainfall also likely ahead of strong cold fronts associated with the deepening surface lows. This should temper area fuels, and casts significant uncertainty on the areal/temporal overlap of dry and windy conditions. While some risk for elevated fire-weather conditions is possible over parts of the southern and central High Plains, confidence remains too low to introduce probabilities. ..Lyons.. 09/16/2024 ...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 0248 PM CDT Mon Sep 16 2024 Valid 162000Z - 171200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS NORTH DAKOTA INTO NORTHWEST MINNESOTA AND PARTS OF COASTAL NORTH CAROLINA... ...SUMMARY... The threat for a few tornadoes will continue this afternoon and evening over eastern North Carolina and vicinity. Thunderstorms capable of producing severe gusts and large hail should occur today in parts of the northern Plains. Isolated severe wind and hail also appears possible across parts of the Great Basin to Four Corners. ...Four Corners/Arizona... The primary adjustment was to expand the Marginal risk area southward into eastern AZ. Dewpoints in the upper 50s to low 60s are supporting MLCAPE values upwards of 1000 J/kg with negligible inhibition based on latest RAP mesoanalysis estimates. A deepening and expansive cumulus field across the region (including a few early attempts at convective initiation) corroborate these estimates, suggesting that adequate buoyancy resides across the region for robust convection. Regional VWPs are sampling 30-40 knot winds around 2-3 km AGL with stronger flow analyzed aloft in recent upper-air analyses. Consequently, adequate deep-layer wind shear appears to be in place to support organized convection, including a supercell or two with an attendant severe hail/wind threat, though storm coverage should remain somewhat limited due to modest forcing for ascent (largely driven by orographic lift). For additional information regarding near-term convective trends further north across the Four Corners see MCD #2072. ...North Dakota... The forecast largely remains on track across ND with only some northwestward expansion of the Slight risk/15% hail probability line. Latest high-res solutions continue to suggest that robust convection will most likely develop near the vorticity maximum (noted just to the west/southwest of Minot, ND as of 19 UTC) and propagate northeast along the warm front. This scenario aligns well with recent satellite trends with gradual convective development observed ahead of the vort max and along the front amid continued diurnal destabilization. This alignment of observed trends and recent guidance yields sufficiently high confidence to warrant adjusting the risk probabilities. Elsewhere, the previous forecast remains on track. See the prior discussion (below) or MCDs #2071 and #2073 for the latest details regarding convective trends across coastal North Carolina and portions of the Great Basin, respectively. ..Moore.. 09/16/2024 .PREV DISCUSSION... /ISSUED 1130 AM CDT Mon Sep 16 2024/ ...North Dakota into Northwest Minnesota... Elevated thunderstorms which have produced sporadic, marginally severe hail earlier this morning across parts of ND into northwest MN have generally remained sub-severe over the past couple of hours as a southerly low-level jet has gradually weakened. In the wake of this activity, a surface low should consolidate over the northern High Plains, with a front and convectively reinforced outflow expected to lift slowly northward across ND this afternoon/evening as an effective warm front. Airmass recovery is expected along/south of this boundary, with steepening mid-level lapse rates, moistening at low-levels, and daytime heating all contributing to moderate instability by later this afternoon. While low/mid-level flow will not be overly strong for most of the day, strengthening low-level southerly flow is expected again this evening as a low-level jet strengthens across the northern/central Plains. Current expectations are for robust thunderstorms to develop along/near the front late this afternoon and early evening. Enough deep-layer shear should be present to support a threat of large hail with any supercells initially. With time, some clustering should occur. A potentially greater wind threat may exist through the evening as activity spreads east-northeastward across central/eastern ND into northwest MN. A tornado or two also appears possible with any surface-based convection along/south of the front, especially this evening as 0-1 km shear increases with the strengthening low-level jet. ...Eastern North Carolina and Vicinity... The surface low off the NC/SC Coast (Potential Tropical Cyclone 8) is forecast by NHC to move northwest and inland across parts of SC through this evening. A surface trough/weak baroclinic zone extends northeastward from the low just off the NC Coast/Outer Banks. As the system moves inland, enhanced low-level flow should turn more east-southeasterly. Various NAM/RAP forecast soundings suggest that as low 70s surface dewpoints advance inland along the coastal plain of eastern NC, then only modest/filtered daytime heating will be needed to support weak boundary-layer destabilization. Sufficiently enlarged low-level hodographs should support a threat for a few tornadoes with any low-topped supercells that can form offshore and be sustained inland across coastal portions of eastern NC. The Slight Risk for this region has been maintained with only small adjustments based on recent observations and 12Z guidance. ...Great Basin into the Four Corners... A deep, closed upper low centered over CA this morning will advance slowly eastward across parts of the Great Basin through the period. An attendant south-southwesterly mid-level jet will overspread eastern portions of the Great Basin into the Four Corners region this afternoon and evening. Although cloud cover remains prevalent across parts of these areas, some daytime heating will encourage the development of weak instability by mid to late afternoon. Stronger mid-level flow and related deep-layer shear are forecast across the Four Corners vicinity, where marginal supercell structures could pose an isolated hail threat. Even though instability should generally remain weak owing to limited low-level moisture, occasional strong to severe wind gusts should be the main threat with various small clusters that can form/consolidate and subsequently spread north-northeastward through the early evening. This wind threat will be locally maximized where filtered diurnal heating can help steepen low-level lapse rates. ...Central High Plains... Relatively high-based thunderstorms may develop this afternoon across parts of the central High Plains, generally along/east of a weak surface trough. This region will be mostly displaced to the east of large-scale ascent associated with the upper low over the West. Even so, a narrow zone of weak to moderate instability should be in place across parts of central NE into western KS by peak afternoon heating. Although flow through low/mid levels should remain modest for much of the afternoon, a veering wind profile with height should foster around 25-35 kt of deep-layer shear, sufficient for some updraft organization. The primary uncertainty regarding any isolated severe hail/wind threat remains whether convection will initiate or not. Have therefore not added a Marginal Risk across parts of the central High Plains with this update, but trends will continue to be monitored. Read more

SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0248 PM CDT Mon Sep 16 2024 Valid 162000Z - 171200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS NORTH DAKOTA INTO NORTHWEST MINNESOTA AND PARTS OF COASTAL NORTH CAROLINA... ...SUMMARY... The threat for a few tornadoes will continue this afternoon and evening over eastern North Carolina and vicinity. Thunderstorms capable of producing severe gusts and large hail should occur today in parts of the northern Plains. Isolated severe wind and hail also appears possible across parts of the Great Basin to Four Corners. ...Four Corners/Arizona... The primary adjustment was to expand the Marginal risk area southward into eastern AZ. Dewpoints in the upper 50s to low 60s are supporting MLCAPE values upwards of 1000 J/kg with negligible inhibition based on latest RAP mesoanalysis estimates. A deepening and expansive cumulus field across the region (including a few early attempts at convective initiation) corroborate these estimates, suggesting that adequate buoyancy resides across the region for robust convection. Regional VWPs are sampling 30-40 knot winds around 2-3 km AGL with stronger flow analyzed aloft in recent upper-air analyses. Consequently, adequate deep-layer wind shear appears to be in place to support organized convection, including a supercell or two with an attendant severe hail/wind threat, though storm coverage should remain somewhat limited due to modest forcing for ascent (largely driven by orographic lift). For additional information regarding near-term convective trends further north across the Four Corners see MCD #2072. ...North Dakota... The forecast largely remains on track across ND with only some northwestward expansion of the Slight risk/15% hail probability line. Latest high-res solutions continue to suggest that robust convection will most likely develop near the vorticity maximum (noted just to the west/southwest of Minot, ND as of 19 UTC) and propagate northeast along the warm front. This scenario aligns well with recent satellite trends with gradual convective development observed ahead of the vort max and along the front amid continued diurnal destabilization. This alignment of observed trends and recent guidance yields sufficiently high confidence to warrant adjusting the risk probabilities. Elsewhere, the previous forecast remains on track. See the prior discussion (below) or MCDs #2071 and #2073 for the latest details regarding convective trends across coastal North Carolina and portions of the Great Basin, respectively. ..Moore.. 09/16/2024 .PREV DISCUSSION... /ISSUED 1130 AM CDT Mon Sep 16 2024/ ...North Dakota into Northwest Minnesota... Elevated thunderstorms which have produced sporadic, marginally severe hail earlier this morning across parts of ND into northwest MN have generally remained sub-severe over the past couple of hours as a southerly low-level jet has gradually weakened. In the wake of this activity, a surface low should consolidate over the northern High Plains, with a front and convectively reinforced outflow expected to lift slowly northward across ND this afternoon/evening as an effective warm front. Airmass recovery is expected along/south of this boundary, with steepening mid-level lapse rates, moistening at low-levels, and daytime heating all contributing to moderate instability by later this afternoon. While low/mid-level flow will not be overly strong for most of the day, strengthening low-level southerly flow is expected again this evening as a low-level jet strengthens across the northern/central Plains. Current expectations are for robust thunderstorms to develop along/near the front late this afternoon and early evening. Enough deep-layer shear should be present to support a threat of large hail with any supercells initially. With time, some clustering should occur. A potentially greater wind threat may exist through the evening as activity spreads east-northeastward across central/eastern ND into northwest MN. A tornado or two also appears possible with any surface-based convection along/south of the front, especially this evening as 0-1 km shear increases with the strengthening low-level jet. ...Eastern North Carolina and Vicinity... The surface low off the NC/SC Coast (Potential Tropical Cyclone 8) is forecast by NHC to move northwest and inland across parts of SC through this evening. A surface trough/weak baroclinic zone extends northeastward from the low just off the NC Coast/Outer Banks. As the system moves inland, enhanced low-level flow should turn more east-southeasterly. Various NAM/RAP forecast soundings suggest that as low 70s surface dewpoints advance inland along the coastal plain of eastern NC, then only modest/filtered daytime heating will be needed to support weak boundary-layer destabilization. Sufficiently enlarged low-level hodographs should support a threat for a few tornadoes with any low-topped supercells that can form offshore and be sustained inland across coastal portions of eastern NC. The Slight Risk for this region has been maintained with only small adjustments based on recent observations and 12Z guidance. ...Great Basin into the Four Corners... A deep, closed upper low centered over CA this morning will advance slowly eastward across parts of the Great Basin through the period. An attendant south-southwesterly mid-level jet will overspread eastern portions of the Great Basin into the Four Corners region this afternoon and evening. Although cloud cover remains prevalent across parts of these areas, some daytime heating will encourage the development of weak instability by mid to late afternoon. Stronger mid-level flow and related deep-layer shear are forecast across the Four Corners vicinity, where marginal supercell structures could pose an isolated hail threat. Even though instability should generally remain weak owing to limited low-level moisture, occasional strong to severe wind gusts should be the main threat with various small clusters that can form/consolidate and subsequently spread north-northeastward through the early evening. This wind threat will be locally maximized where filtered diurnal heating can help steepen low-level lapse rates. ...Central High Plains... Relatively high-based thunderstorms may develop this afternoon across parts of the central High Plains, generally along/east of a weak surface trough. This region will be mostly displaced to the east of large-scale ascent associated with the upper low over the West. Even so, a narrow zone of weak to moderate instability should be in place across parts of central NE into western KS by peak afternoon heating. Although flow through low/mid levels should remain modest for much of the afternoon, a veering wind profile with height should foster around 25-35 kt of deep-layer shear, sufficient for some updraft organization. The primary uncertainty regarding any isolated severe hail/wind threat remains whether convection will initiate or not. Have therefore not added a Marginal Risk across parts of the central High Plains with this update, but trends will continue to be monitored. Read more

SPC 1930Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0215 PM CDT Mon Sep 16 2024 Valid 181200Z - 191200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... Organized severe thunderstorms are not expected on Wednesday. ...Great Plains... Forecast guidance at 12z remains similar to previous cycles at Day 3/Wed. The cyclone over eastern MT will become stacked through the period and only progress modestly northeast toward ND and southern SK/MB by 12z Thursday. Enhanced southwesterly mid/upper flow ahead of this feature will overspread the northern/central Plains, while southerly low-level flow allows 60s F dewpoints to remain in place from the southern Plains to the MO and Red River (north) Valleys. Convection may be ongoing across parts of the mid-MO Valley vicinity Wednesday morning, with areas of cloud debris expected across the broader Plains. This will result in some uncertainty in airmass recovery/destabilization during the afternoon. While outflow boundaries and pockets of stronger heating may focus mesoscale areas of thunderstorm potential during peak heating through early evening from the eastern Dakotas/MN south/southwest into the TX Panhandle, severe potential is uncertain. Large-scale ascent will remain nebulous across much of the Plains, and midlevel lapse rates will be modest due to relatively warm temperatures aloft. Vertical shear could support some organized/severe risk from eastern SD/NE into KS, but uncertainty and the conditional nature of potential risk precludes low severe probabilities at this time. ..Leitman.. 09/16/2024 Read more

SPC Day 2 Fire Weather Outlook
Day 2 Fire Weather Outlook NWS Storm Prediction Center Norman OK 0212 PM CDT Mon Sep 16 2024 Valid 171200Z - 181200Z ...19z Update... Minimal changes were made to the prior forecast. The latest model guidance has shown increasing humidity and rain chances across much of the High Plains. However, at least a few hours of strong southerly winds (20-25 mph) will likely interact with reasonably dry fuels and RH below 30%. While confidence is not overly high, a few hours of elevated fire-weather conditions are possible before rain and the cold front approach. Dry and breezy conditions are also possible across parts of southwest CO and eastern UT, but fuels here are not receptive. See prior discussion. ..Lyons.. 09/16/2024 .PREV DISCUSSION... /ISSUED 0156 AM CDT Mon Sep 16 2024/ ...Synopsis... Strong deep-layer south-southwesterly flow preceding an amplified large-scale trough over the West will impinge on the central High Plains during the day. Here, a tightening pressure gradient along a pronounced lee trough, and boundary-layer mixing into the strong flow aloft, will favor 20-25 mph sustained southerly surface winds (with higher gusts). These winds should overlap 20-25 percent RH for a few hours, before a cold front and related precipitation overspread the area from the west during the evening. Given receptive fuels across the area, elevated fire-weather conditions are expected during the afternoon (prior to the arrival of precipitation). ...Please see www.spc.noaa.gov/fire for graphic product... Read more

MD 2071 CONCERNING SEVERE POTENTIAL...WATCH UNLIKELY FOR COASTAL SOUTHERN NORTH CAROLINA
Mesoscale Discussion 2071 NWS Storm Prediction Center Norman OK 1211 PM CDT Mon Sep 16 2024 Areas affected...coastal southern North Carolina Concerning...Severe potential...Watch unlikely Valid 161711Z - 162015Z Probability of Watch Issuance...20 percent SUMMARY...While the risk for a brief tornado may not be negligible across the southern North Carolina coastal plain, this potential still appears low. It is possible that it may not increase appreciably either, but trends are being closely monitored. DISCUSSION...The surface cyclone center appears to be slowly approaching coastal areas to the west/west-northwest of Myrtle Beach SC. Forcing for ascent aided by strongest low-level convergence and warm advection has been focused to its north, spreading inland near/south through southwest of Wilmington. This has been contributing to the most vigorous thunderstorm development, supported by inflow of tropically moist boundary-layer air within a narrow offshore plume wrapping around the periphery of the cyclone. Low-level hodographs across coastal southern North Carolina remain sizable and clockwise curved, supporting at least a couple of occasionally intensifying supercell structures over the past hour or two. However, inland of immediate coastal areas, the convection and embedded mesocyclones probably have been based above at least a residual shallow stable surface-based layer, based on surface observations and Rapid Refresh forecast soundings. Beneath a subsident mid-level dry slot wrapping around the southern periphery of the cyclone, model output suggests that low-level warming within a small inland advecting wedge may contribute to modest boundary-layer destabilization through mid to late afternoon, as the cyclone slowly begins to migrate inland. However, with strongest flow around 850 mb forecast to shift into the Carolina Piedmont, model forecast soundings generally indicate that this may coincide with shrinking and less clockwise curved low-level hodographs. Coupled with potentially increasing mid-level inhibition, the risk for convection capable of producing tornadoes remains uncertain. ..Kerr/Gleason.. 09/16/2024 ...Please see www.spc.noaa.gov for graphic product... ATTN...WFO...MHX...ILM... LAT...LON 33957840 34277866 34587686 34207681 33397770 33657804 33957840 Read more

MD 2072 CONCERNING SEVERE POTENTIAL...WATCH UNLIKELY FOR THE FOUR CORNERS REGION
Mesoscale Discussion 2072 NWS Storm Prediction Center Norman OK 0134 PM CDT Mon Sep 16 2024 Areas affected...the Four Corners Region Concerning...Severe potential...Watch unlikely Valid 161834Z - 162030Z Probability of Watch Issuance...20 percent SUMMARY...Some severe gusts and perhaps some severe hail are possible this afternoon near the Four Corners Region. A watch is not anticipated at this time, however trends will be monitored. DISCUSSION...Thunderstorms have developed near the Mogollon Rim over northeastern Arizona this afternoon. These storms are on the southeastern periphery of an expansive upper-level closed low with a seasonably strong mid-level jet (40-50 kts of 500 mb flow). This results in 30-40 kts of effective bulk shear across the region. Additionally, strong heating has warmed temperatures into the mid 70s to near 80 F, resulting in steep low-level lapse rates (8-9 C/km) and 1000+ J/kg of DCAPE per mesoanalysis. The deep-layer shear induced by the upper-level trough is expected to result in multicell clusters of storms with severe gusts being the primary threat. However given the steep lapse rates, straight hodographs, and low freezing levels, some marginally severe hail may occur as well. Given the expected sparse coverage of both of these, a watch is not anticipated. With time, expect clusters to move to the northeast. Some residual cloud cover over the San Juan Mountains is resulting in lingering stable air, so this may limit the longevity of these storms. ..Supinie/Gleason.. 09/16/2024 ...Please see www.spc.noaa.gov for graphic product... ATTN...WFO...ABQ...GJT...FGZ...SLC... LAT...LON 35171077 35791115 37151074 39171018 39540976 39810923 39770877 39590840 39060778 37830774 36580801 35890806 35260856 35030893 34720972 34831031 35171077 Read more

SPC 1730Z Day 2 Outlook
Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1230 PM CDT Mon Sep 16 2024 Valid 171200Z - 181200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE CENTRAL HIGH PLAINS INTO NORTHEAST MONTANA... ...SUMMARY... Isolated to scattered severe gusts and hail are possible Tuesday across a large swath of the High Plains region, mainly from late afternoon into the evening. The greater concentrations of severe storms may occur over the central High Plains into northeast Montana. ...Synopsis... A mid/upper cyclone is forecast over the Great Basin Tuesday morning. This system will pivot northeast across the central Rockies and into the northern High Plains through the forecast period. This will bring a belt of strong south/southwesterly deep-layer flow across CO/WY and adjacent portions of the High Plains. A surface low will deepen over MT through the period, with a surface trough extending southward through the central/southern High Plains. A warm front is forecast to extend west to east from southeast MT into north-central SD during the morning. With time, this boundary will lift northward toward the International border during the nighttime hours. As the system deepens and the low-level baroclinic zone over the Plains strengthens, 850-700 mb flow is forecast to markedly increase during the afternoon/evening to 30-50 kt. While deeper boundary-layer moisture is forecast to remain east of the surface trough axis and north of the warm front, steep midlevel lapse rates will support pockets of weak to moderate instability. An arc of thunderstorm activity, with a mix of line segments and discrete cells, are expected to develop in the vicinity of the surface low/warm front south/southeast along the surface trough during the afternoon and evening hours. ...Eastern MT... Strong ascent will overspread the region as the upper trough pivots northeast during the late afternoon/evening. Boundary-layer moisture will be greatest to the north of the warm front across north-central/northeast MT, but capping will likely remain in place. Storm motion will likely result in convection remaining elevated to the cool side of the warm front. Nevertheless, steep midlevel lapse rates and favorable vertical shear (elongated/straight hodographs) will support some risk for large hail. As stronger forcing and sufficient erosion of capping can overlap during the evening, strong to severe wind gusts also will be possible. ...Northern/Central High Plains Vicinity... Convection is expected to develop over the higher terrain of CO/WY during the afternoon. Given strengthening mid/upper flow and weak instability, some locally strong gusts could occur with this initial activity near the core of the upper low over western/central CO. As convection shifts east/northeast through the afternoon and into the evening, strong heating is expected to result in a steep low-level lapse rate environment across the High Plains. While deep boundary-layer moisture will remain further east across the Plains, steep midlevel lapse rates and surface dewpoints in the 50s F will result in a corridor of around 1000-1500 J/kg MLCAPE from far eastern CO into parts of western NE/SD. Strengthening midlevel flow atop a deeply mixed boundary-layer will likely support severe gusts (isolated gusts to 75 mph possible) with linear segments spreading northeast across the central High Plains during the late afternoon/evening. ...Southern High Plains Vicinity... Further south, large-scale ascent will be weaker, with stronger height falls focused north of the region. Nevertheless, low-level convergence along the surface trough and modest instability (up to 1000 J/kg MLCAPE) will support initial thunderstorm development over the higher terrain of south-central CO into north-central NM. Forecast soundings show supercell wind profiles across the adjacent High Plains by afternoon. Midlevel lapse rates will be somewhat modest (around 6.5-7 C/km), but elongated/straight hodographs and plenty of instability through the 700-300 mb layer suggest isolated hail is possible. Steep low-level lapse rates also will support isolated strong to severe gusts. ..Leitman.. 09/16/2024 Read more

SPC 1730Z Day 2 Outlook
Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1230 PM CDT Mon Sep 16 2024 Valid 171200Z - 181200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE CENTRAL HIGH PLAINS INTO NORTHEAST MONTANA... ...SUMMARY... Isolated to scattered severe gusts and hail are possible Tuesday across a large swath of the High Plains region, mainly from late afternoon into the evening. The greater concentrations of severe storms may occur over the central High Plains into northeast Montana. ...Synopsis... A mid/upper cyclone is forecast over the Great Basin Tuesday morning. This system will pivot northeast across the central Rockies and into the northern High Plains through the forecast period. This will bring a belt of strong south/southwesterly deep-layer flow across CO/WY and adjacent portions of the High Plains. A surface low will deepen over MT through the period, with a surface trough extending southward through the central/southern High Plains. A warm front is forecast to extend west to east from southeast MT into north-central SD during the morning. With time, this boundary will lift northward toward the International border during the nighttime hours. As the system deepens and the low-level baroclinic zone over the Plains strengthens, 850-700 mb flow is forecast to markedly increase during the afternoon/evening to 30-50 kt. While deeper boundary-layer moisture is forecast to remain east of the surface trough axis and north of the warm front, steep midlevel lapse rates will support pockets of weak to moderate instability. An arc of thunderstorm activity, with a mix of line segments and discrete cells, are expected to develop in the vicinity of the surface low/warm front south/southeast along the surface trough during the afternoon and evening hours. ...Eastern MT... Strong ascent will overspread the region as the upper trough pivots northeast during the late afternoon/evening. Boundary-layer moisture will be greatest to the north of the warm front across north-central/northeast MT, but capping will likely remain in place. Storm motion will likely result in convection remaining elevated to the cool side of the warm front. Nevertheless, steep midlevel lapse rates and favorable vertical shear (elongated/straight hodographs) will support some risk for large hail. As stronger forcing and sufficient erosion of capping can overlap during the evening, strong to severe wind gusts also will be possible. ...Northern/Central High Plains Vicinity... Convection is expected to develop over the higher terrain of CO/WY during the afternoon. Given strengthening mid/upper flow and weak instability, some locally strong gusts could occur with this initial activity near the core of the upper low over western/central CO. As convection shifts east/northeast through the afternoon and into the evening, strong heating is expected to result in a steep low-level lapse rate environment across the High Plains. While deep boundary-layer moisture will remain further east across the Plains, steep midlevel lapse rates and surface dewpoints in the 50s F will result in a corridor of around 1000-1500 J/kg MLCAPE from far eastern CO into parts of western NE/SD. Strengthening midlevel flow atop a deeply mixed boundary-layer will likely support severe gusts (isolated gusts to 75 mph possible) with linear segments spreading northeast across the central High Plains during the late afternoon/evening. ...Southern High Plains Vicinity... Further south, large-scale ascent will be weaker, with stronger height falls focused north of the region. Nevertheless, low-level convergence along the surface trough and modest instability (up to 1000 J/kg MLCAPE) will support initial thunderstorm development over the higher terrain of south-central CO into north-central NM. Forecast soundings show supercell wind profiles across the adjacent High Plains by afternoon. Midlevel lapse rates will be somewhat modest (around 6.5-7 C/km), but elongated/straight hodographs and plenty of instability through the 700-300 mb layer suggest isolated hail is possible. Steep low-level lapse rates also will support isolated strong to severe gusts. ..Leitman.. 09/16/2024 Read more

SPC Day 1 Fire Weather Outlook
Day 1 Fire Weather Outlook NWS Storm Prediction Center Norman OK 1138 AM CDT Mon Sep 16 2024 Valid 161700Z - 171200Z ...17z Update... The prior forecast remains largely on track with only minor changes. The Elevated area over parts of NV was expanded northward where gusty winds and pockets of low humidity are expected to be slightly more prevalent. Over the central High Plains, recent rainfall and additional storms are likely to temper fuels somewhat. However, strong southerly winds (gusts as high as 30 mph) may still overlap with areas of drier fuels and humidity below 30%. While uncertain in areal extent, some fire-weather risk will continue this afternoon and evening. Otherwise, see the prior discussion for more information. ..Lyons.. 09/16/2024 .PREV DISCUSSION... /ISSUED 0156 AM CDT Mon Sep 16 2024/ ...Synopsis... Within the base of a deep midlevel cyclone moving eastward across the Great Basin, a related jet streak will overspread the Lower CO River Valley. Here, boundary-layer mixing into the strengthening flow aloft, coupled with a tightening pressure gradient peripheral to an evolving surface cyclone, will favor 20-25 mph sustained southerly surface winds. Despite a gradual increase in moisture/RH, diurnal heating should still support a corridor of around 20 percent RH amid the strong surface winds along the Lower CO River Valley -- favoring elevated fire-weather conditions. Elevated fire-weather conditions are also expected over portions of the central High Plains -- where breezy/gusty southerly surface winds will overlap 20 percent RH near a lee trough during the afternoon. While spotty rainfall during the past 24 hours could limit fuel receptiveness over parts of the area, mostly receptive fuels should still yield some fire-weather risk. Farther east, warm/dry conditions are expected over portions of OH and KY -- along the southwestern periphery of an expansive surface anticyclone. While sustained surface winds around 10 mph should limit the overall fire-weather threat, around 20 percent RH and very dry/receptive fuels will still pose localized fire-weather concerns during the afternoon. ...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 1130 AM CDT Mon Sep 16 2024 Valid 161630Z - 171200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF NORTH DAKOTA INTO NORTHWEST MINNESOTA...AND EASTERN NORTH CAROLINA... ...SUMMARY... The threat for a few tornadoes will continue this afternoon and evening over eastern North Carolina and vicinity. Thunderstorms capable of producing severe gusts and large hail should occur today in parts of the northern Plains. Isolated severe wind and hail also appears possible across parts of the Great Basin to Four Corners. ...North Dakota into Northwest Minnesota... Elevated thunderstorms which have produced sporadic, marginally severe hail earlier this morning across parts of ND into northwest MN have generally remained sub-severe over the past couple of hours as a southerly low-level jet has gradually weakened. In the wake of this activity, a surface low should consolidate over the northern High Plains, with a front and convectively reinforced outflow expected to lift slowly northward across ND this afternoon/evening as an effective warm front. Airmass recovery is expected along/south of this boundary, with steepening mid-level lapse rates, moistening at low-levels, and daytime heating all contributing to moderate instability by later this afternoon. While low/mid-level flow will not be overly strong for most of the day, strengthening low-level southerly flow is expected again this evening as a low-level jet strengthens across the northern/central Plains. Current expectations are for robust thunderstorms to develop along/near the front late this afternoon and early evening. Enough deep-layer shear should be present to support a threat of large hail with any supercells initially. With time, some clustering should occur. A potentially greater wind threat may exist through the evening as activity spreads east-northeastward across central/eastern ND into northwest MN. A tornado or two also appears possible with any surface-based convection along/south of the front, especially this evening as 0-1 km shear increases with the strengthening low-level jet. ...Eastern North Carolina and Vicinity... The surface low off the NC/SC Coast (Potential Tropical Cyclone 8) is forecast by NHC to move northwest and inland across parts of SC through this evening. A surface trough/weak baroclinic zone extends northeastward from the low just off the NC Coast/Outer Banks. As the system moves inland, enhanced low-level flow should turn more east-southeasterly. Various NAM/RAP forecast soundings suggest that as low 70s surface dewpoints advance inland along the coastal plain of eastern NC, then only modest/filtered daytime heating will be needed to support weak boundary-layer destabilization. Sufficiently enlarged low-level hodographs should support a threat for a few tornadoes with any low-topped supercells that can form offshore and be sustained inland across coastal portions of eastern NC. The Slight Risk for this region has been maintained with only small adjustments based on recent observations and 12Z guidance. ...Great Basin into the Four Corners... A deep, closed upper low centered over CA this morning will advance slowly eastward across parts of the Great Basin through the period. An attendant south-southwesterly mid-level jet will overspread eastern portions of the Great Basin into the Four Corners region this afternoon and evening. Although cloud cover remains prevalent across parts of these areas, some daytime heating will encourage the development of weak instability by mid to late afternoon. Stronger mid-level flow and related deep-layer shear are forecast across the Four Corners vicinity, where marginal supercell structures could pose an isolated hail threat. Even though instability should generally remain weak owing to limited low-level moisture, occasional strong to severe wind gusts should be the main threat with various small clusters that can form/consolidate and subsequently spread north-northeastward through the early evening. This wind threat will be locally maximized where filtered diurnal heating can help steepen low-level lapse rates. ...Central High Plains... Relatively high-based thunderstorms may develop this afternoon across parts of the central High Plains, generally along/east of a weak surface trough. This region will be mostly displaced to the east of large-scale ascent associated with the upper low over the West. Even so, a narrow zone of weak to moderate instability should be in place across parts of central NE into western KS by peak afternoon heating. Although flow through low/mid levels should remain modest for much of the afternoon, a veering wind profile with height should foster around 25-35 kt of deep-layer shear, sufficient for some updraft organization. The primary uncertainty regarding any isolated severe hail/wind threat remains whether convection will initiate or not. Have therefore not added a Marginal Risk across parts of the central High Plains with this update, but trends will continue to be monitored. ..Gleason/Supinie.. 09/16/2024 Read more

No Mesoscale Discussions are in effect as of Mon Sep 16 14:31:02 UTC 2024.

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0746 AM CDT Mon Sep 16 2024 Valid 161300Z - 171200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS IN THE EASTERN CAROLINAS AND PARTS OF THE NORTHERN PLAINS... ...SUMMARY... A tornado threat exists in the eastern Carolinas. Thunderstorms capable of severe gusts and large hail are expected today in parts of the northern Plains. Isolated severe wind and hail are expected in parts of the Four Corners and Great Basin. ...Synopsis... A highly amplified pattern is expected in mid/upper levels, anchored by two cyclones: 1. A purely cold-core, midlatitude circulation initially centered over northern CA, with accompanying cyclonic flow covering most of the CONUS from the Rockies westward. Equatorward progression of this feature is about done, and the 500-mb low should pivot eastward across the RNO area by 00Z, then east-northeastward toward EKO overnight. In the downstream difluent flow, a shortwave trough is apparent in moisture-channel imagery over the western Dakotas. This feature should move northeastward to southwestern MB by 00Z, then to westernmost parts of northwest ON overnight. 2. What is now a small, deep-layer circulation just offshore from ILM and MYR, designated Potential Tropical Cyclone 8 by NHC as of this writing. This system may become subtropical or tropical before moving inland later today, per NHC discussions. Regardless of whether it is named, the system will offer some tornado potential (below). The associated mid/upper low is progged to become better defined through the day and moving farther inland, with the low-level center tracking not far behind. As the surface, aside from PTC 8 and its attached frontal zone, the 11Z analysis showed a quasistationary front extending northeastward from a low near SHR, across southeastern MT to north-central ND, behind the outflow of a mass of ongoing convection over ND. The outflow boundary should act as the effective frontal zone for this region, as it moves slowly eastward over ND and north-central SD before likely stalling around midday. ...Eastern Carolinas... A zone of enhanced low-level gradient flow is apparent north through northeast of the center of PTC 8, over coastal sections of NC and westward past MYR. This is related both to the cyclone itself and antecedent/post-frontal high pressure from north of the baroclinic zone upon which this low developed. The synoptically driven baroclinicity is expected to continue to decrease (frontolysis), especially if this low becomes tropical. However, some mesoscale baroclinicity will remain due to persistent rain north of the old front, and a lack of precip -- combined with a high-theta-e, maritime/tropical airmass to its south and southeast. This airmass should shift northward as the low moves inland, and support potential for inland penetration of enough moisture and limited diurnal heating to enable 500-1000 J/kg MLCAPE today, away from areas of continual/persistent rainfall. In an environment where LCLs are low and low-level shear and SRH already are favorable (per VWP from ILM and MHX), the tornado threat will be tied directly to a combination of 1. Sufficient surface-based destabilization on the mesobeta scale, in that transition zone where flow still is backed enough to keep hodographs large, and 2. Formation of supercell(s) and their ability to remain in the favorably buoyant/backed-flow slot long enough to mature and produce. See SPC mesoscale discussion 2070 for marginal, near-term potential near and north of center. Through the day, the effective warm- frontal regime is expected to shift northward up the coastline and, to some extent, areas around the Sounds, so a small unconditional 5%/"slight risk" has been introduced in those areas. Tonight into tomorrow morning, as the center penetrates deeper inland away from the most favorable airmass and weakens considerably, and as diabatic cooling reduces instability at the surface, the tornado potential should diminish. ...Northern Plains... A large area of precip and convection is ongoing across much of west-central/central and northeastern ND, with embedded strong/ isolated severe thunderstorms capable of gusts and hail. This activity is reinforcing/reorienting the antecedent baroclinic zone across the area, and may persist northeastward into the remainder of northeastern ND and northwestern MN through midday with a continued threat for isolated severe. Additional development is possible along the outflow-modulated boundary, both in the near term and through the afternoon, ahead of the shortwave trough, and in the area of related maximized lift (both convective-scale on the boundary, and broader-scale in the midlevel DCVA). The airmass south and east of the boundary should heat diurnally, steepening the low/middle-level lapse rates amidst favorable 60 F surface dewpoints. This should support peak/preconvective MLCAPE in the 1500-2500 J/kg range, along with veering flow with height. However, lack of stronger midlevel flow limits deep shear, keeping progged effective-shear magnitudes generally under 35 kt. The most probable convective mode appears to be a mix of multicells and messy supercells. Convection-allowing progs that most-closely depicted the current state (which has not included the underdone hourly HRRR for most of the night) reasonably show a lack of substantial destabilization north of the boundary, except perhaps for some elevated hail potential this evening. Convective coverage on ether side of the boundary may increase for a few hours this evening in response to enhancement of moisture, shear and storm-relative flow provides by the LLJ. ...4 Corners/Great Basin... A broad arc of combined baroclinic and large-scale ascent is expected to extend across the near-eastern to far-southeastern sectors of the mid/upper cyclone, supporting episodic, widely scattered to scattered thunderstorms throughout much of the period. Where this activity encounters diurnally/diabatically destabilized boundary layers, characterized by deep mixing with related maximization of lapse rates and DCAPE, and at least marginal CAPE above, isolated severe gusts will be a threat. The potential for high-based supercells amidst greater shear to the southeast, across the Four Corners area, suggest isolated severe hail also will be possible there. ..Edwards/Mosier.. 09/16/2024 Read more

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0353 AM CDT Mon Sep 16 2024 Valid 191200Z - 241200Z ...DISCUSSION... ...D4/Upper Midwest... Lower-end severe potential remains evident on Thursday afternoon to evening across a focused portion of the Upper Midwest, centered on the eastern Dakotas to western MN per latest guidance. A shortwave trough over the southern Prairie Provinces into the northern Great Plains should gradually move east. An attendant north/south-oriented cold front should similarly progress across the Dakotas towards western MN. In the mid-levels, a plume of steep lapse rates should be coincident with a belt of enhanced west-southwesterly flow. The warm-moist sector ahead of the front will likely be confined with decreasing boundary-layer moisture along/east of the Upper MS Valley. As such, the overall threat area will probably be fairly narrow and predictability is too low for a 15 percent highlight. ...D6-7/Southern High Plains to Mid-MO Valley... The next shortwave trough that amplifies into the Southwest should remain positive tilt and slow moving, until the weekend when guidance consensus suggests it accelerates northeastward. The attendant belt of enhanced mid-level flow around this trough appears spatially confined, as a ridge dominates from the Lower Rio Grande Valley to southeast Canada. Coupled with muted mid-level lapse rates over most of the Great Plains, severe potential appears marginal. Read more

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0353 AM CDT Mon Sep 16 2024 Valid 191200Z - 241200Z ...DISCUSSION... ...D4/Upper Midwest... Lower-end severe potential remains evident on Thursday afternoon to evening across a focused portion of the Upper Midwest, centered on the eastern Dakotas to western MN per latest guidance. A shortwave trough over the southern Prairie Provinces into the northern Great Plains should gradually move east. An attendant north/south-oriented cold front should similarly progress across the Dakotas towards western MN. In the mid-levels, a plume of steep lapse rates should be coincident with a belt of enhanced west-southwesterly flow. The warm-moist sector ahead of the front will likely be confined with decreasing boundary-layer moisture along/east of the Upper MS Valley. As such, the overall threat area will probably be fairly narrow and predictability is too low for a 15 percent highlight. ...D6-7/Southern High Plains to Mid-MO Valley... The next shortwave trough that amplifies into the Southwest should remain positive tilt and slow moving, until the weekend when guidance consensus suggests it accelerates northeastward. The attendant belt of enhanced mid-level flow around this trough appears spatially confined, as a ridge dominates from the Lower Rio Grande Valley to southeast Canada. Coupled with muted mid-level lapse rates over most of the Great Plains, severe potential appears marginal. Read more

MD 2069 CONCERNING SEVERE POTENTIAL...WATCH UNLIKELY FOR NORTHEAST SD...SOUTHERN/CENTRAL ND
Mesoscale Discussion 2069 NWS Storm Prediction Center Norman OK 0300 AM CDT Mon Sep 16 2024 Areas affected...Northeast SD...Southern/Central ND Concerning...Severe potential...Watch unlikely Valid 160800Z - 161000Z Probability of Watch Issuance...5 percent SUMMARY...Threat for isolated hail and/or strong gusts will continue from northeast South Dakota into central North Dakota for the next few hours. Limited coverage and magnitude will preclude the need for a watch. DISCUSSION...Elevated thunderstorms are ongoing across northwest SD and adjacent far southwest ND, supported by warm-air advection within the localized warm conveyor associated with the mesoscale convective vortex currently over far northwest SD. These thunderstorms are forecast to continue north-northeastward over the next few hours while gradually weakening in response to decreasing warm-air advection. Even so, the environment downstream across south-central ND appears favorable for evaporatively enhanced downbursts and the potential for some strong gusts. Farther north, a west-to-east oriented band of thunderstorms recently developed in response to persistent warm-air advection near the terminus of the low-level jet that extends across the Plains. Recent radar imagery has shown that the previously more cellular storms may be transitioning into a more clustered mode, with some more easterly motion noted as well. Low-level stability will persist downstream, but enough elevated buoyancy is expected to allow for thunderstorm persistence. Consequently, the developing linear cluster will likely continue east-southeastward with an attendant risk for isolated hail. A strong gust or two may be able to reach the surface as well. ..Mosier/Edwards.. 09/16/2024 ...Please see www.spc.noaa.gov for graphic product... ATTN...WFO...FGF...ABR...BIS...UNR... LAT...LON 45300399 46450319 47720207 48300017 48079831 46729969 44880093 44820309 45300399 Read more

SPC 0730Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0211 AM CDT Mon Sep 16 2024 Valid 181200Z - 191200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... Organized severe thunderstorms are not expected on Wednesday. ...Great Plains... In the wake of extensive convective overturning on D2 across the High Plains, remnant outflows should be present over the lower plains as convection decays Wednesday morning. The northern High Plains shortwave trough and parent mid-level circulation should become vertically stacked with the attendant surface cyclone over eastern MT. This will slow its advance considerably on Wednesday, as it eventually drifts towards far southeast SK. Where a confined plume of moderate buoyancy may develop on Wednesday afternoon from the Mid-MO Valley to the TX Panhandle, 500-mb temperatures will be relatively warm, from -4 to -8 C southwest to northeast. This will foster weak 700-500 mb lapse rates. Beyond weakly convergent convective outflows, large-scale ascent appears nebulous, and convective signals across most models seem limited and mesoscale-focused. While low-end supercell wind profiles could develop during the late afternoon to early evening, the aforementioned limiting factors suggest severe hail/wind potential may be subdued and very localized. As such, will defer to later outlooks for any level 1-MRGL risk highlights. ..Grams.. 09/16/2024 Read more

SPC Day 2 Fire Weather Outlook
Day 2 Fire Weather Outlook NWS Storm Prediction Center Norman OK 0156 AM CDT Mon Sep 16 2024 Valid 171200Z - 181200Z ...Synopsis... Strong deep-layer south-southwesterly flow preceding an amplified large-scale trough over the West will impinge on the central High Plains during the day. Here, a tightening pressure gradient along a pronounced lee trough, and boundary-layer mixing into the strong flow aloft, will favor 20-25 mph sustained southerly surface winds (with higher gusts). These winds should overlap 20-25 percent RH for a few hours, before a cold front and related precipitation overspread the area from the west during the evening. Given receptive fuels across the area, elevated fire-weather conditions are expected during the afternoon (prior to the arrival of precipitation). ..Weinman.. 09/16/2024 ...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 0156 AM CDT Mon Sep 16 2024 Valid 161200Z - 171200Z ...Synopsis... Within the base of a deep midlevel cyclone moving eastward across the Great Basin, a related jet streak will overspread the Lower CO River Valley. Here, boundary-layer mixing into the strengthening flow aloft, coupled with a tightening pressure gradient peripheral to an evolving surface cyclone, will favor 20-25 mph sustained southerly surface winds. Despite a gradual increase in moisture/RH, diurnal heating should still support a corridor of around 20 percent RH amid the strong surface winds along the Lower CO River Valley -- favoring elevated fire-weather conditions. Elevated fire-weather conditions are also expected over portions of the central High Plains -- where breezy/gusty southerly surface winds will overlap 20 percent RH near a lee trough during the afternoon. While spotty rainfall during the past 24 hours could limit fuel receptiveness over parts of the area, mostly receptive fuels should still yield some fire-weather risk. Farther east, warm/dry conditions are expected over portions of OH and KY -- along the southwestern periphery of an expansive surface anticyclone. While sustained surface winds around 10 mph should limit the overall fire-weather threat, around 20 percent RH and very dry/receptive fuels will still pose localized fire-weather concerns during the afternoon. ..Weinman.. 09/16/2024 ...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 1259 AM CDT Mon Sep 16 2024 Valid 171200Z - 181200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS IN THE CENTRAL HIGH PLAINS AND EASTERN MT... ...SUMMARY... Isolated to scattered severe gusts and hail are possible Tuesday across a large swath of the High Plains region, mainly from late afternoon into the evening. The greater concentrations of severe storms may occur over the central High Plains and eastern Montana. ...High Plains... A mid/upper-level shortwave trough initially over the eastern Great Basin will take on a negative tilt as it advances towards the northern High Plains. Deep lee cyclogenesis is expected over far northeast WY/southeast MT, with a warm front arcing east across parts of the Dakotas. This low will advance north then northwestward across eastern MT through 12Z Wednesday. Large-scale ascent will be pronounced within this synoptic regime, with favorable upper-level difluence, mid-level height falls, and low-level convergence. However, weak buoyancy and modest mid-level lapse rates will characterize much of the environment to the south of the surface cyclone and warm front. Aided by a subtropical moisture plume over the Southwest, morning convection near the Four Corners region should move across the higher terrain and expand in coverage into the afternoon. High-based storms over the central and southern High Plains will progress into a well-mixed boundary layer that may initially be devoid of appreciable CAPE. This lack of greater buoyancy during the late afternoon to early evening (outside of areas north of the warm front) yields some uncertainty regarding the degree of storm intensity into the lower elevations. But with scattered to eventually widespread convection expected with time, extensive outflows are expected to push east. The most likely corridor for severe gusts appears to be over the central High Plains where the most pronounced 700-500 mb flow should advance ahead of the negative-tilt shortwave trough. Farther south, a few supercells may initially develop from parts of NM into southeast CO. Modest mid-level lapse rates should temper updraft vigor, but marginally severe hail along with isolated severe gusts will be possible. More favorable low-level moisture with steep mid-level lapse rates will reside near/north of the warm front, supporting moderate buoyancy from northeast MT into ND. While stronger ascent and deep-layer flow may not impinge upon areas north of the front until near sunset, organized storms should develop over the higher terrain by late afternoon and spread north within a backed mid-level flow regime. A few supercells along with an organized cluster or two may impinge on the greater downstream buoyancy plume, maintaining threats for large hail and severe gusts into Tuesday night. ...Eastern NC and southeast VA... While confidence is modest with the probable inland evolution of PTC 8, the bulk signal across guidance is for a weakening low-level wind field by Tuesday morning across the NC/VA coastal plain. The potential for low-topped supercells capable of brief tornadoes appears too low beyond 12Z Tuesday to warrant a risk highlight. ..Grams.. 09/16/2024 Read more