SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0248 PM CDT Sun Sep 15 2024 Valid 152000Z - 161200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE NORTHERN/CENTRAL PLAINS... ...SUMMARY... Thunderstorms capable of producing isolated severe gusts and hail may occur today and tonight across parts of the northern/central Plains. ...20z Update... Only minor adjustments were made to the D1 Convective Outlook to account for latest observational trends. See previous discussion below for more information. ..Thornton/Gleason.. 09/15/2024 .PREV DISCUSSION... /ISSUED 1128 AM CDT Sun Sep 15 2024/ ...Northern/Central Plains... An amplified upper trough along/near the West Coast this morning will further evolve into a closed upper low over northern CA and vicinity by late tonight. Ahead of this feature, modestly enhanced south-southwesterly mid-level flow will be in place over much of the western states and Rockies through the period. Although low-level moisture is expected to remain limited over much of this region, isolated strong to severe gusts may occur with any thunderstorms that can develop in a deeply mixed boundary layer favorable for gusty downdraft winds. Latest guidance continues to suggest that a relatively greater concentration of severe potential will be focused across parts of the northern/central Plains late this afternoon through tonight. Across this area, a weak surface lee trough and greater low-level moisture to its east should support weak to moderate instability with daytime heating. Steep mid-level lapse rates should also aid updraft accelerations/intensities, with around 20-30 kt of deep-layer shear supporting modest thunderstorm organization. Isolated severe hail may occur with initially more discrete convection, but a tendency for clustering should lead to a relatively greater wind threat with time as convection spreads generally east-northeastward through the evening. Regardless, the overall severe threat from northeast CO into western NE/SD and vicinity should remain fairly isolated/marginal given the modest deep-layer shear. Low-level warm advection is forecast to increase across much of the northern/central Plains tonight as a southerly low-level jet strengthens. A surface warm front is also expected to lift northward over ND late tonight into early Monday morning. With steepening mid-level lapse rates overspreading the northern Plains in tandem with increasing low-level moisture, ample MUCAPE should be available. Most guidance shows at least isolated convection developing across parts of ND tonight in this favorable thermodynamic environment. Although deep-layer shear may remain fairly modest, it may still be sufficient for updraft organization and an isolated threat for severe hail with any elevated convection that can form. Have therefore expanded the Marginal Risk northward to account for this potential. ...Coastal Carolinas... Latest NHC forecast continues to indicate some potential for sub-tropical or tropical development of a surface low currently off the SC Coast. Regardless of development, it still appears that the more moist/tropical low-level airmass over the Gulf Stream will struggle to advance inland over coastal portions of NC/SC through the end of the Day 1 forecast period early Monday morning (16/12Z). Accordingly, tornado potential with any low-topped supercells on the north to northeast periphery of the surface low should tend to remain offshore until Day 2/Monday (after 16/12Z). Read more

SPC Day 3-8 Fire Weather Outlook
Day 3-8 Fire Weather Outlook NWS Storm Prediction Center Norman OK 0229 PM CDT Sun Sep 15 2024 Valid 171200Z - 231200Z A broad mid-level trough will progress across the Interior West toward the Rockies this week, with multiple mid-level impulses likely to eject into the Northern Plains as the broader mid-level trough gradually de-amplifies. Spotty rainfall should dampen fuels for several areas west of the Rockies through the week. Potentially Elevated-equivalent fire weather conditions may develop over portions of the High Plains on Day 3/Tuesday and especially Day 4/Wednesday. However, scattered to potentially widespread showers and thunderstorms (with the first in a series of mid-level impulses) may dampen fuels in several locales Tuesday into Tuesday night. As such, no Critical probabilities were introduced this outlook. ..Squitieri.. 09/15/2024 ...Please see www.spc.noaa.gov/fire for graphic product... Read more

SPC Day 3-8 Fire Weather Outlook
Day 3-8 Fire Weather Outlook NWS Storm Prediction Center Norman OK 0229 PM CDT Sun Sep 15 2024 Valid 171200Z - 231200Z A broad mid-level trough will progress across the Interior West toward the Rockies this week, with multiple mid-level impulses likely to eject into the Northern Plains as the broader mid-level trough gradually de-amplifies. Spotty rainfall should dampen fuels for several areas west of the Rockies through the week. Potentially Elevated-equivalent fire weather conditions may develop over portions of the High Plains on Day 3/Tuesday and especially Day 4/Wednesday. However, scattered to potentially widespread showers and thunderstorms (with the first in a series of mid-level impulses) may dampen fuels in several locales Tuesday into Tuesday night. As such, no Critical probabilities were introduced this outlook. ..Squitieri.. 09/15/2024 ...Please see www.spc.noaa.gov/fire for graphic product... Read more

No Mesoscale Discussions are in effect as of Sun Sep 15 19:35:02 UTC 2024.

SPC 1930Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0229 PM CDT Sun Sep 15 2024 Valid 171200Z - 181200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FOR THE HIGH PLAINS... ...SUMMARY... Strong to locally severe thunderstorms will be possible Tuesday across a large swath of the High Plains region, mainly from late afternoon into the evening. Severe gusts should be the primary hazard, though some hail may also be possible. ...High Plains... A mid/upper-level shortwave trough initially over the eastern Great Basin should take on a negative tilt as it advances towards the northern High Plains. Deep lee cyclogenesis is expected over northeast WY/southeast MT, with a warm front extending east-northeast of the low somewhere from eastern MT into the Dakotas during the afternoon and evening. This low will advance north towards the MT/SK border area by 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 low and warm front. Aided by the subtropical moisture plume over the Southwest, morning convection near the Four Corners region may move across the higher terrain toward the High Plains, with additional terrain-driven development possible during the afternoon. High-based storms 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 substantial uncertainty regarding the degree of storm organization into the lower elevations. But with scattered to widespread convection and increasingly extensive outflow expected with time, sporadic severe gusts may occur during the afternoon and evening. Somewhat more favorable low-level moisture and buoyancy may reside near/north of the warm front, from eastern MT into the western Dakotas. While stronger ascent and deep-layer flow may not impinge upon areas north of the front later in the forecast period, there will be some potential for organized convection to develop during the evening as the shortwave trough ejects northeastward. A couple of supercells and/or stronger clusters will be possible within this regime, with a threat of hail and isolated severe gusts. ...Four Corners region... Despite the unfavorable time of day, a few strong storms cannot be ruled out Tuesday morning across the Four Corners region into western CO/NM, in close proximity to the ejecting shortwave trough. Wind profiles will be quite favorable for organized convection, though it remains uncertain if sufficient buoyancy will be present to support any severe threat during the early part of the day. ...Eastern NC/VA... With uncertainty already relatively high regarding evolution of the currently developing offshore low into D2/Monday, confidence remains too low to delineate severe probabilities for D3/Tuesday. Slower and more aggressive ensemble members continue to suggest an adequate SRH/buoyancy combination for low-topped supercells may linger over eastern NC early in the period and shift into parts of eastern VA. However, the bulk of guidance still indicates a general weakening of the low-level wind field during the day. ..Dean.. 09/15/2024 Read more

SPC 1930Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0229 PM CDT Sun Sep 15 2024 Valid 171200Z - 181200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FOR THE HIGH PLAINS... ...SUMMARY... Strong to locally severe thunderstorms will be possible Tuesday across a large swath of the High Plains region, mainly from late afternoon into the evening. Severe gusts should be the primary hazard, though some hail may also be possible. ...High Plains... A mid/upper-level shortwave trough initially over the eastern Great Basin should take on a negative tilt as it advances towards the northern High Plains. Deep lee cyclogenesis is expected over northeast WY/southeast MT, with a warm front extending east-northeast of the low somewhere from eastern MT into the Dakotas during the afternoon and evening. This low will advance north towards the MT/SK border area by 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 low and warm front. Aided by the subtropical moisture plume over the Southwest, morning convection near the Four Corners region may move across the higher terrain toward the High Plains, with additional terrain-driven development possible during the afternoon. High-based storms 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 substantial uncertainty regarding the degree of storm organization into the lower elevations. But with scattered to widespread convection and increasingly extensive outflow expected with time, sporadic severe gusts may occur during the afternoon and evening. Somewhat more favorable low-level moisture and buoyancy may reside near/north of the warm front, from eastern MT into the western Dakotas. While stronger ascent and deep-layer flow may not impinge upon areas north of the front later in the forecast period, there will be some potential for organized convection to develop during the evening as the shortwave trough ejects northeastward. A couple of supercells and/or stronger clusters will be possible within this regime, with a threat of hail and isolated severe gusts. ...Four Corners region... Despite the unfavorable time of day, a few strong storms cannot be ruled out Tuesday morning across the Four Corners region into western CO/NM, in close proximity to the ejecting shortwave trough. Wind profiles will be quite favorable for organized convection, though it remains uncertain if sufficient buoyancy will be present to support any severe threat during the early part of the day. ...Eastern NC/VA... With uncertainty already relatively high regarding evolution of the currently developing offshore low into D2/Monday, confidence remains too low to delineate severe probabilities for D3/Tuesday. Slower and more aggressive ensemble members continue to suggest an adequate SRH/buoyancy combination for low-topped supercells may linger over eastern NC early in the period and shift into parts of eastern VA. However, the bulk of guidance still indicates a general weakening of the low-level wind field during the day. ..Dean.. 09/15/2024 Read more

SPC Day 2 Fire Weather Outlook
Day 2 Fire Weather Outlook NWS Storm Prediction Center Norman OK 0204 PM CDT Sun Sep 15 2024 Valid 161200Z - 171200Z The primary changes to the Day 2 Fire Weather Outlook were to add Elevated highlights to portions of the central High Plains. Surface lee troughing ahead of an approaching broad mid-level trough will encourage 15-20 mph sustained southerly surface winds over the central High Plains (particularly along the KS/CO border), in tandem with 20-25 percent RH. These surface meteorological conditions will overspread modestly dry fuels, warranting Elevated highlights in this region. Surface high pressure over the Northeast will encourage dry easterly surface flow across portions of Ohio and immediate surrounding areas tomorrow, where fuels are anomalously dry and highly supportive of wildfire spread. RH may drop into the 20-25 percent range over these fuels by afternoon peak heating. However, surface sustained wind speeds should be generally under 15 mph, precluding the addition of Elevated highlights this outlook. Nonetheless, given such dry fuels (with a severe to locally extreme drought in place), gusty conditions may support localized brush-fire growth in this regime. ..Squitieri.. 09/15/2024 .PREV DISCUSSION... /ISSUED 0150 AM CDT Sun Sep 15 2024/ ...Synopsis... A highly amplified midlevel trough, accompanied by strong deep-layer south-southwesterly flow, will overspread the Great Basin during the day. This will promote 20-30 mph sustained south-southwesterly surface winds (with higher gusts) across portions of the southern Great Basin. Despite cooling surface temperatures and increasing moisture/RH, diurnal heating should still contribute to a corridor of 15-20 percent RH amid the strong/gusty winds. Therefore, Elevated highlights are in place for the wind-driven fire-weather risk. ...Please see www.spc.noaa.gov/fire for graphic product... Read more

SPC Day 2 Fire Weather Outlook
Day 2 Fire Weather Outlook NWS Storm Prediction Center Norman OK 0204 PM CDT Sun Sep 15 2024 Valid 161200Z - 171200Z The primary changes to the Day 2 Fire Weather Outlook were to add Elevated highlights to portions of the central High Plains. Surface lee troughing ahead of an approaching broad mid-level trough will encourage 15-20 mph sustained southerly surface winds over the central High Plains (particularly along the KS/CO border), in tandem with 20-25 percent RH. These surface meteorological conditions will overspread modestly dry fuels, warranting Elevated highlights in this region. Surface high pressure over the Northeast will encourage dry easterly surface flow across portions of Ohio and immediate surrounding areas tomorrow, where fuels are anomalously dry and highly supportive of wildfire spread. RH may drop into the 20-25 percent range over these fuels by afternoon peak heating. However, surface sustained wind speeds should be generally under 15 mph, precluding the addition of Elevated highlights this outlook. Nonetheless, given such dry fuels (with a severe to locally extreme drought in place), gusty conditions may support localized brush-fire growth in this regime. ..Squitieri.. 09/15/2024 .PREV DISCUSSION... /ISSUED 0150 AM CDT Sun Sep 15 2024/ ...Synopsis... A highly amplified midlevel trough, accompanied by strong deep-layer south-southwesterly flow, will overspread the Great Basin during the day. This will promote 20-30 mph sustained south-southwesterly surface winds (with higher gusts) across portions of the southern Great Basin. Despite cooling surface temperatures and increasing moisture/RH, diurnal heating should still contribute to a corridor of 15-20 percent RH amid the strong/gusty winds. Therefore, Elevated highlights are in place for the wind-driven fire-weather risk. ...Please see www.spc.noaa.gov/fire for graphic product... Read more

SPC 1730Z Day 2 Outlook
Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1225 PM CDT Sun Sep 15 2024 Valid 161200Z - 171200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FOR THE EASTERN GREAT BASIN INTO THE FOUR CORNERS REGION...ND INTO NORTHWEST MN...EASTERN NC AND VICINITY... ...SUMMARY... On Monday, sporadic severe gusts and hail will be possible during the afternoon to early evening across parts of the eastern Great Basin to Four Corners. Isolated severe storms are possible over eastern North Dakota into northwest Minnesota. Some tornado threat may develop over eastern North Carolina and vicinity. ...Eastern Great Basin to the Four Corners... A seasonably strong mid-level low initially near San Francisco Bay Monday morning should move east during the day, before curling northeast Monday night towards the NV/UT/ID border area. This will occur in response to a strong mid-level jet translating through the basal portion of the large-scale trough across the Desert Southwest into the eastern Great Basin. Convection will likely be ongoing at the start of the forecast period near the midlevel low, and also farther east toward the Four Corners region, within the warm/moist conveyor. Relatively strong heating will be possible between these two regimes, from eastern NV into parts of UT. While buoyancy will likely remain quite weak within this warmer and more well-mixed regime, high-based convection will be possible during the afternoon and evening as the midlevel low approaches the region, with increasing meridional flow and a deeply mixed boundary layer supporting isolated severe gusts. Farther southeast into eastern UT and the Four Corners vicinity, increasing southwesterly flow aloft and strengthening deep-layer shear will become conditionally supportive of organized convection. Warmer midlevel temperatures may limit buoyancy to some extent, though sufficient moisture will support afternoon MLCAPE of 500-1000 J/kg. A few supercells will be possible within this regime, with an attendant threat of isolated severe gusts and hail. ...Parts of ND into northern MN... With the primary upper-level trough displaced well to the west, deep-layer shear will remain weak across much of the Great Plains. However, most guidance suggests an MCV will emanate out of central High Plains convection on D1/Sunday and gradually progress northeast towards the Red River Valley during the day on Monday. In conjunction with a strengthening low-level jet, this MCV may help to support relatively vigorous storm redevelopment within a moderately unstable environment during the afternoon and evening. Stronger midlevel flow attendant to the MCV could support some storm organization, and a couple supercells and/or stronger clusters will be possible, with a threat of isolated hail and damaging wind. Somewhat favorable low-level shear/SRH could also support a tornado threat, if a surface-based supercell can be sustained. Uncertainty remains regarding the strength/timing of any MCV moving across the region, along with the most favored corridor for diurnal storm development. ...Eastern NC and vicinity... Guidance generally suggests that an initially offshore surface low will move northward or northwestward from later on D1/Sunday into D2/Monday and D3/Tuesday, and eventually move inland across some part of the Carolinas. However, uncertainty remains regarding the timing, track, and intensity of this low, along with the extent to which it acquires any tropical or subtropical characteristics. If a deepening low does move onshore, then a higher theta-e airmass may move inland, accompanied by increasing low-level shear/SRH along/north of the low track. While the general scenario supports some potential for low-topped supercells, the magnitude of any tornado threat will be dependent on the extent of intensification that occurs with the low (and its attendant wind fields) prior to landfall. The Marginal Risk has been expanded somewhat across eastern NC and vicinity, in response to the various uncertainties. ..Dean.. 09/15/2024 Read more

SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1128 AM CDT Sun Sep 15 2024 Valid 151630Z - 161200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE NORTHERN/CENTRAL PLAINS... ...SUMMARY... Thunderstorms capable of producing isolated severe gusts and hail may occur today and tonight across parts of the northern/central Plains. ...Northern/Central Plains... An amplified upper trough along/near the West Coast this morning will further evolve into a closed upper low over northern CA and vicinity by late tonight. Ahead of this feature, modestly enhanced south-southwesterly mid-level flow will be in place over much of the western states and Rockies through the period. Although low-level moisture is expected to remain limited over much of this region, isolated strong to severe gusts may occur with any thunderstorms that can develop in a deeply mixed boundary layer favorable for gusty downdraft winds. Latest guidance continues to suggest that a relatively greater concentration of severe potential will be focused across parts of the northern/central Plains late this afternoon through tonight. Across this area, a weak surface lee trough and greater low-level moisture to its east should support weak to moderate instability with daytime heating. Steep mid-level lapse rates should also aid updraft accelerations/intensities, with around 20-30 kt of deep-layer shear supporting modest thunderstorm organization. Isolated severe hail may occur with initially more discrete convection, but a tendency for clustering should lead to a relatively greater wind threat with time as convection spreads generally east-northeastward through the evening. Regardless, the overall severe threat from northeast CO into western NE/SD and vicinity should remain fairly isolated/marginal given the modest deep-layer shear. Low-level warm advection is forecast to increase across much of the northern/central Plains tonight as a southerly low-level jet strengthens. A surface warm front is also expected to lift northward over ND late tonight into early Monday morning. With steepening mid-level lapse rates overspreading the northern Plains in tandem with increasing low-level moisture, ample MUCAPE should be available. Most guidance shows at least isolated convection developing across parts of ND tonight in this favorable thermodynamic environment. Although deep-layer shear may remain fairly modest, it may still be sufficient for updraft organization and an isolated threat for severe hail with any elevated convection that can form. Have therefore expanded the Marginal Risk northward to account for this potential. ...Coastal Carolinas... Latest NHC forecast continues to indicate some potential for sub-tropical or tropical development of a surface low currently off the SC Coast. Regardless of development, it still appears that the more moist/tropical low-level airmass over the Gulf Stream will struggle to advance inland over coastal portions of NC/SC through the end of the Day 1 forecast period early Monday morning (16/12Z). Accordingly, tornado potential with any low-topped supercells on the north to northeast periphery of the surface low should tend to remain offshore until Day 2/Monday (after 16/12Z). ..Gleason/Moore.. 09/15/2024 Read more

SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1128 AM CDT Sun Sep 15 2024 Valid 151630Z - 161200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE NORTHERN/CENTRAL PLAINS... ...SUMMARY... Thunderstorms capable of producing isolated severe gusts and hail may occur today and tonight across parts of the northern/central Plains. ...Northern/Central Plains... An amplified upper trough along/near the West Coast this morning will further evolve into a closed upper low over northern CA and vicinity by late tonight. Ahead of this feature, modestly enhanced south-southwesterly mid-level flow will be in place over much of the western states and Rockies through the period. Although low-level moisture is expected to remain limited over much of this region, isolated strong to severe gusts may occur with any thunderstorms that can develop in a deeply mixed boundary layer favorable for gusty downdraft winds. Latest guidance continues to suggest that a relatively greater concentration of severe potential will be focused across parts of the northern/central Plains late this afternoon through tonight. Across this area, a weak surface lee trough and greater low-level moisture to its east should support weak to moderate instability with daytime heating. Steep mid-level lapse rates should also aid updraft accelerations/intensities, with around 20-30 kt of deep-layer shear supporting modest thunderstorm organization. Isolated severe hail may occur with initially more discrete convection, but a tendency for clustering should lead to a relatively greater wind threat with time as convection spreads generally east-northeastward through the evening. Regardless, the overall severe threat from northeast CO into western NE/SD and vicinity should remain fairly isolated/marginal given the modest deep-layer shear. Low-level warm advection is forecast to increase across much of the northern/central Plains tonight as a southerly low-level jet strengthens. A surface warm front is also expected to lift northward over ND late tonight into early Monday morning. With steepening mid-level lapse rates overspreading the northern Plains in tandem with increasing low-level moisture, ample MUCAPE should be available. Most guidance shows at least isolated convection developing across parts of ND tonight in this favorable thermodynamic environment. Although deep-layer shear may remain fairly modest, it may still be sufficient for updraft organization and an isolated threat for severe hail with any elevated convection that can form. Have therefore expanded the Marginal Risk northward to account for this potential. ...Coastal Carolinas... Latest NHC forecast continues to indicate some potential for sub-tropical or tropical development of a surface low currently off the SC Coast. Regardless of development, it still appears that the more moist/tropical low-level airmass over the Gulf Stream will struggle to advance inland over coastal portions of NC/SC through the end of the Day 1 forecast period early Monday morning (16/12Z). Accordingly, tornado potential with any low-topped supercells on the north to northeast periphery of the surface low should tend to remain offshore until Day 2/Monday (after 16/12Z). ..Gleason/Moore.. 09/15/2024 Read more

SPC Day 1 Fire Weather Outlook
Day 1 Fire Weather Outlook NWS Storm Prediction Center Norman OK 1059 AM CDT Sun Sep 15 2024 Valid 151700Z - 161200Z The previous forecast remains on track, with minor changes made to the Elevated areas to reflect the latest guidance consensus. Additionally, a couple of dry strikes may accompany isolated thunderstorms along the Front Range in eastern Colorado (and surrounding areas), but overall modest fuel receptiveness suggests that lightning-induced fire ignitions should remain a localized concern, so no isolated dry thunderstorm highlights have been added. ..Squitieri.. 09/15/2024 .PREV DISCUSSION... /ISSUED 0150 AM CDT Sun Sep 15 2024/ ...Synopsis... Preceding an amplifying large-scale trough over the West Coast, enhanced deep-layer meridional flow will overspread the Great Basin, while a related surface cyclone evolves over northern NV. Deep boundary-layer mixing into the enhanced flow aloft, along with a tightening pressure gradient peripheral to the surface cyclone, will yield 20-25 mph sustained southerly surface winds and 15-20 percent RH over southern/central NV. Given modestly receptive fuels here, elevated fire-weather conditions are expected during the afternoon. Additionally, large-scale ascent accompanying the amplifying midlevel trough will promote a mix of wet/dry thunderstorms across the northern Great Basin/Intermountain West. While quick storm motions and limited precipitation with some of this activity could yield a risk of lightning-induced ignitions, marginal fuels should generally limit the threat. Over the southern High Plains, breezy/gusty southerly surface winds will develop amid a warm/dry boundary layer near a lee trough during the afternoon. This will favor a few hours of elevated fire-weather conditions. ...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 1059 AM CDT Sun Sep 15 2024 Valid 151700Z - 161200Z The previous forecast remains on track, with minor changes made to the Elevated areas to reflect the latest guidance consensus. Additionally, a couple of dry strikes may accompany isolated thunderstorms along the Front Range in eastern Colorado (and surrounding areas), but overall modest fuel receptiveness suggests that lightning-induced fire ignitions should remain a localized concern, so no isolated dry thunderstorm highlights have been added. ..Squitieri.. 09/15/2024 .PREV DISCUSSION... /ISSUED 0150 AM CDT Sun Sep 15 2024/ ...Synopsis... Preceding an amplifying large-scale trough over the West Coast, enhanced deep-layer meridional flow will overspread the Great Basin, while a related surface cyclone evolves over northern NV. Deep boundary-layer mixing into the enhanced flow aloft, along with a tightening pressure gradient peripheral to the surface cyclone, will yield 20-25 mph sustained southerly surface winds and 15-20 percent RH over southern/central NV. Given modestly receptive fuels here, elevated fire-weather conditions are expected during the afternoon. Additionally, large-scale ascent accompanying the amplifying midlevel trough will promote a mix of wet/dry thunderstorms across the northern Great Basin/Intermountain West. While quick storm motions and limited precipitation with some of this activity could yield a risk of lightning-induced ignitions, marginal fuels should generally limit the threat. Over the southern High Plains, breezy/gusty southerly surface winds will develop amid a warm/dry boundary layer near a lee trough during the afternoon. This will favor a few hours of elevated fire-weather conditions. ...Please see www.spc.noaa.gov/fire for graphic product... Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0750 AM CDT Sun Sep 15 2024 Valid 151300Z - 161200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE CENTRAL AND NORTHERN HIGH PLAINS... ...SUMMARY... Thunderstorms capable of isolated severe gusts and hail will be possible today across parts of the central and northern High Plains. ...Synopsis... In mid/upper levels, a blocky longwave pattern will remain over the CONUS, with amplifying troughing in the West and a Rex configuration in the East. Cyclonic flow already covers most of the land west of the Rockies. That will continue but with backing of the flow aloft, as a cyclone now centered over Vancouver Island strengthens and digs south-southeastward down the West Coast. By 12Z tomorrow, the associated 500-mb low should be located near OAK, with strongly difluent flow and modest ridging over the High Plains from eastern NM to MT. The southern part of a weak shortwave trough -- evident in moisture-channel imagery from UT to eastern AZ -- should cross CO today and reach the eastern border of WY to near GLD by 12Z, likely enhanced from this evening onward by convectively generated vorticity. A mid/upper anticyclone now over the Lower Great Lakes will stretch eastward and open up to that direction around the end of the period. The base of the eastern pattern block will be composed of a broad, nearly zonal height weakness anchored by: 1. The decaying remains of Francine, long merged with a mid/upper low, and forecast to drift erratically over the Mid-South while weakening further; 2. An intensifying, deep-layer cyclone with low-level manifestation as a deepening wave cyclone along a frontal zone, offshore from the Carolinas. The 11Z surface analysis showed a wavy, quasistationary frontal zone attached to a strengthening low located roughly south of EWN and east of SAV. The front extended across northern FL to the western FL Panhandle and southwestern AL. A remnant low was drawn well inland over northern MS, connecting to the Gulf boundary via an occluded front. These features should move little through the period, but with further weakening of the western low, and intensification of the eastern one. Elsewhere, a lee trough and dryline either overlapped, or were drawn within less than 100 nm apart, near the eastern border of WY, eastern CO, the northern/ western TX Panhandle, and east-central/southeastern NM. The dryline should shift somewhat eastward today amid diurnal heating. ...Central/northern High Plains... Isolated to widely scattered thunderstorms are possible across a large part of the Rockies, Intermountain West, and Desert Southwest today. Some of this activity will mature atop deep, well-mixed boundary layers of desert valleys and the High Plains, with non-zero potential for a strong-severe gust. The most concentrated/organized potential for gusts near to above severe limits, as well as marginal hail, still appears to be over portions of the central High Plains into the Black Hills and vicinity, near the lee trough/dryline. East of that, low-level moisture will be relatively maximized in a return-flow airmass of predominantly continental origin, with a north-south belt of 50s to mid 60s F surface dewpoints. Where the western part of that moisture coincides with strong surface heating, and underlies the eastern part of the EML, a north-south corridor of MLCAPE in the 1500-2500 J/kg range should develop, with 500-1500 J/kg extending into the more deeply mixed regime nearest the lee trough. East of the trough, considerable veering of winds with height is expected, with some low-level hodograph enhancement potentially moving 0-3-km SRH to near 150 J/kg, but lack of stronger midlevel flow will temper overall shear. ...Coastal NC, extreme eastern SC... Many progs deepen the low-level cyclone and transition it to subtropical or tropical character through the end of day 2, while eroding the frontal zone's baroclinicity; however, inconsistency among models is high. The most aggressive among the synoptic and CAM guidance with the speed of the transition and approach to the coast (e.g., 06Z GFS and 00Z ARW high-res window respectively) show favorably large low-level shear, but barely have surface-based effective inflow onshore at the end of the period, with greatest convective coverage and buoyancy still offshore. As such, the associated coastal tornado threat still appears too low and conditional to outlook until day 2 (after 16/12Z). Potential for faster/deeper development and shoreward translation of the low will continue to be monitored for onshore supercell threat the last few hours of day 1. See latest NHC tropical outlook for guidance on overall development potential with this system. ..Edwards/Mosier.. 09/15/2024 Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0750 AM CDT Sun Sep 15 2024 Valid 151300Z - 161200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE CENTRAL AND NORTHERN HIGH PLAINS... ...SUMMARY... Thunderstorms capable of isolated severe gusts and hail will be possible today across parts of the central and northern High Plains. ...Synopsis... In mid/upper levels, a blocky longwave pattern will remain over the CONUS, with amplifying troughing in the West and a Rex configuration in the East. Cyclonic flow already covers most of the land west of the Rockies. That will continue but with backing of the flow aloft, as a cyclone now centered over Vancouver Island strengthens and digs south-southeastward down the West Coast. By 12Z tomorrow, the associated 500-mb low should be located near OAK, with strongly difluent flow and modest ridging over the High Plains from eastern NM to MT. The southern part of a weak shortwave trough -- evident in moisture-channel imagery from UT to eastern AZ -- should cross CO today and reach the eastern border of WY to near GLD by 12Z, likely enhanced from this evening onward by convectively generated vorticity. A mid/upper anticyclone now over the Lower Great Lakes will stretch eastward and open up to that direction around the end of the period. The base of the eastern pattern block will be composed of a broad, nearly zonal height weakness anchored by: 1. The decaying remains of Francine, long merged with a mid/upper low, and forecast to drift erratically over the Mid-South while weakening further; 2. An intensifying, deep-layer cyclone with low-level manifestation as a deepening wave cyclone along a frontal zone, offshore from the Carolinas. The 11Z surface analysis showed a wavy, quasistationary frontal zone attached to a strengthening low located roughly south of EWN and east of SAV. The front extended across northern FL to the western FL Panhandle and southwestern AL. A remnant low was drawn well inland over northern MS, connecting to the Gulf boundary via an occluded front. These features should move little through the period, but with further weakening of the western low, and intensification of the eastern one. Elsewhere, a lee trough and dryline either overlapped, or were drawn within less than 100 nm apart, near the eastern border of WY, eastern CO, the northern/ western TX Panhandle, and east-central/southeastern NM. The dryline should shift somewhat eastward today amid diurnal heating. ...Central/northern High Plains... Isolated to widely scattered thunderstorms are possible across a large part of the Rockies, Intermountain West, and Desert Southwest today. Some of this activity will mature atop deep, well-mixed boundary layers of desert valleys and the High Plains, with non-zero potential for a strong-severe gust. The most concentrated/organized potential for gusts near to above severe limits, as well as marginal hail, still appears to be over portions of the central High Plains into the Black Hills and vicinity, near the lee trough/dryline. East of that, low-level moisture will be relatively maximized in a return-flow airmass of predominantly continental origin, with a north-south belt of 50s to mid 60s F surface dewpoints. Where the western part of that moisture coincides with strong surface heating, and underlies the eastern part of the EML, a north-south corridor of MLCAPE in the 1500-2500 J/kg range should develop, with 500-1500 J/kg extending into the more deeply mixed regime nearest the lee trough. East of the trough, considerable veering of winds with height is expected, with some low-level hodograph enhancement potentially moving 0-3-km SRH to near 150 J/kg, but lack of stronger midlevel flow will temper overall shear. ...Coastal NC, extreme eastern SC... Many progs deepen the low-level cyclone and transition it to subtropical or tropical character through the end of day 2, while eroding the frontal zone's baroclinicity; however, inconsistency among models is high. The most aggressive among the synoptic and CAM guidance with the speed of the transition and approach to the coast (e.g., 06Z GFS and 00Z ARW high-res window respectively) show favorably large low-level shear, but barely have surface-based effective inflow onshore at the end of the period, with greatest convective coverage and buoyancy still offshore. As such, the associated coastal tornado threat still appears too low and conditional to outlook until day 2 (after 16/12Z). Potential for faster/deeper development and shoreward translation of the low will continue to be monitored for onshore supercell threat the last few hours of day 1. See latest NHC tropical outlook for guidance on overall development potential with this system. ..Edwards/Mosier.. 09/15/2024 Read more

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0334 AM CDT Sun Sep 15 2024 Valid 181200Z - 231200Z ...DISCUSSION... A shortwave trough near the northern High Plains at 12Z Wednesday should slow as it largely progresses across the southern Prairie Provinces. A belt of enhanced mid-level southwesterlies should linger over the northern Great Plains through Thursday, and aid in a recharging and downstream advection of steep mid-level lapse rates over the Dakotas and NE. The low-level moisture plume near the edge of the EML should be confined, as dry conditions persist in the Great Lakes region, on the backside of the low-amplitude mid-level trough over the East. Low-probability severe may occur along a portion of a weak cold front on Thursday in the north-central states. The next shortwave trough that amplifies into the Southwest should remain positive tilt and slow moving, until around next weekend when guidance consensus suggests it accelerates northeastward as another shortwave trough digs into the Northwest. This pattern should yield more muted mid-level lapse rates over most of the Great Plains, especially into next weekend. As such, severe probabilities may remain low through the period. Read more

SPC 0730Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0230 AM CDT Sun Sep 15 2024 Valid 171200Z - 181200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS IN THE HIGH PLAINS... ...SUMMARY... Isolated severe thunderstorms will be possible across a large swath of the High Plains region, mainly from Tuesday late afternoon into the evening. Severe gusts should be the primary hazard. ...High Plains... A shortwave trough over the eastern Great Basin at 12Z Tuesday should take on a negative tilt as it advances towards the northern High Plains. This process will yield a separation of the strong upper-level jet surrounding the trough, from a meridional component shifting north into eastern WY and a zonal component holding over AZ/NM. Guidance has oscillated southward with the evolution of the meridional component relative to yesterday's guidance. Deep lee cyclogenesis is expected over northeast WY/southeast MT. This low will advance north towards the MT/SK border area by 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. But weak buoyancy and modest mid-level lapse rates will characterized much of the environment. The bulk of convective development will occur over the higher terrain, likely aided by the subtropical moisture plume over the Southwest. High-based storms should 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 northeast MT into the Dakotas, yields substantial uncertainty in the degree of strong versus severe storms. But with scattered to widespread convection likely into the evening, sporadic severe gusts may occur. ...Eastern NC and southeast VA... The poor predictability of offshore cyclogenesis amplitude and inland progression on Monday renders minimal confidence in delineating a severe area on Tuesday. Slower and more aggressive ensemble members suggest an adequate SRH/buoyancy combination for low-topped tornado potential may linger over eastern NC early in the period and shift into parts of southeast VA. But overall trends indicate a generalized weakening low-level wind field may occur during the day. ..Grams.. 09/15/2024 Read more

SPC Day 2 Fire Weather Outlook
Day 2 Fire Weather Outlook NWS Storm Prediction Center Norman OK 0150 AM CDT Sun Sep 15 2024 Valid 161200Z - 171200Z ...Synopsis... A highly amplified midlevel trough, accompanied by strong deep-layer south-southwesterly flow, will overspread the Great Basin during the day. This will promote 20-30 mph sustained south-southwesterly surface winds (with higher gusts) across portions of the southern Great Basin. Despite cooling surface temperatures and increasing moisture/RH, diurnal heating should still contribute to a corridor of 15-20 percent RH amid the strong/gusty winds. Therefore, Elevated highlights are in place for the wind-driven fire-weather risk. ..Weinman.. 09/15/2024 ...Please see www.spc.noaa.gov/fire for graphic product... Read more

SPC Day 2 Fire Weather Outlook
Day 2 Fire Weather Outlook NWS Storm Prediction Center Norman OK 0150 AM CDT Sun Sep 15 2024 Valid 161200Z - 171200Z ...Synopsis... A highly amplified midlevel trough, accompanied by strong deep-layer south-southwesterly flow, will overspread the Great Basin during the day. This will promote 20-30 mph sustained south-southwesterly surface winds (with higher gusts) across portions of the southern Great Basin. Despite cooling surface temperatures and increasing moisture/RH, diurnal heating should still contribute to a corridor of 15-20 percent RH amid the strong/gusty winds. Therefore, Elevated highlights are in place for the wind-driven fire-weather risk. ..Weinman.. 09/15/2024 ...Please see www.spc.noaa.gov/fire for graphic product... Read more

SPC Day 1 Fire Weather Outlook
Day 1 Fire Weather Outlook NWS Storm Prediction Center Norman OK 0150 AM CDT Sun Sep 15 2024 Valid 151200Z - 161200Z ...Synopsis... Preceding an amplifying large-scale trough over the West Coast, enhanced deep-layer meridional flow will overspread the Great Basin, while a related surface cyclone evolves over northern NV. Deep boundary-layer mixing into the enhanced flow aloft, along with a tightening pressure gradient peripheral to the surface cyclone, will yield 20-25 mph sustained southerly surface winds and 15-20 percent RH over southern/central NV. Given modestly receptive fuels here, elevated fire-weather conditions are expected during the afternoon. Additionally, large-scale ascent accompanying the amplifying midlevel trough will promote a mix of wet/dry thunderstorms across the northern Great Basin/Intermountain West. While quick storm motions and limited precipitation with some of this activity could yield a risk of lightning-induced ignitions, marginal fuels should generally limit the threat. Over the southern High Plains, breezy/gusty southerly surface winds will develop amid a warm/dry boundary layer near a lee trough during the afternoon. This will favor a few hours of elevated fire-weather conditions. ..Weinman.. 09/15/2024 ...Please see www.spc.noaa.gov/fire for graphic product... Read more