Severe Storms

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0344 AM CDT Sun Sep 15 2019 Valid 181200Z - 231200Z ...DISCUSSION... The medium-range models generally indicate that a large and vigorous short wave trough will dig from the Pacific Northwest into and through the intermountain west during the middle to latter portion of the coming work week, before accelerating northeast of the Rockies through the Upper Midwest by early next weekend. Accompanied by deepening lee surface troughing across the northern and central Plains, and perhaps at least modest embedded cyclogenesis across North Dakota into Ontario, it appears that a risk for organized severe thunderstorms could develop, particularly across the Plains on Friday (Day 6). However, while there appears better consensus concerning these developments in the latest model runs, compared to prior runs, the overall pattern predictability may still be relatively low. Coupled with continuing uncertainties concerning smaller-scale developments which could impact the extent and degree of destabilization, severe weather probabilities are being maintained at less than 15 percent. However, this could change in later outlooks for this time period Read more

SPC 0730Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0225 AM CDT Sun Sep 15 2019 Valid 171200Z - 181200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS TUESDAY INTO TUESDAY EVENING ACROSS PARTS OF THE NORTHERN ROCKIES INTO THE NORTHERN PLAINS AND PORTIONS OF THE UPPER MIDWEST... ...SUMMARY... Strong thunderstorms may impact parts of the northern Rockies into the adjacent northern High Plains, as well as parts of the Upper Midwest, Tuesday, accompanied by at least some potential for severe weather. ...Synopsis... While mid-level ridging within the westerlies remains prominent along an axis across the Great Lakes into Hudson Bay, large-scale troughing may continue to evolve across the northwestern U.S. into the central Canadian/U.S. border area, in association with several progressive short wave troughs. The most significant of these perturbations, including an embedded close low, is forecast to dig into the Pacific Northwest Tuesday through Tuesday night, while a compact but vigorous downstream impulse accelerates northeastward out of the northern Great Basin through the Dakotas by 12Z Wednesday. The lead impulse will be preceded by another perturbation of lower latitude origins, which is generally forecast to undergo considerable deformation while progressing northeast of the Dakotas through portions of northwestern Ontario and the upper Great Lakes region. In association with this regime, modestly deep surface troughing, to the lee of the northern Rockies at the outset of the period, appears likely to shift eastward across the northern and central Plains, while an embedded surface cyclone migrates from eastern Montana into Manitoba. This is expected to be trailed by a cold front, which probably will begin to overtake the surface troughing across the northern Plains by late Tuesday night. Seasonably moist boundary layer air supportive of moderate large CAPE may initially be focused along the western periphery of low-level ridging, across eastern portions of the northern Plains. Little change appears likely through the period, with a 30-50 kt south-southwesterly 850 mb jet being maintained along an axis from Kansas into Minnesota. ...Wyoming through the northern High Plains... Although low-level moisture may be rather limited, lower/mid tropospheric lapse rates are expected to become steep with fairly strong daytime heating and boundary layer mixing. Coupled with mid-level forcing for ascent and cooling associated with the vigorous short wave trough progressing out of the Great Basin, destabilization is expected to become sufficient to support thunderstorm development. This may initiate by midday Tuesday across the higher terrain of western into central Wyoming, before perhaps organizing and propagating northeastward and eastward into the high Plains by the evening. Substantial sub-cloud evaporative cooling probably will aid downward mixing of higher momentum air, including 30-70 kt southwesterly flow in the 700-500 mb layer, resulting in at least scattered strong to severe surface gusts, before the onset of diurnal cooling across the Plains. ...Northern and central Minnesota... More uncertainty exists across this area, but the development of moderately large CAPE in the presence of 30-50 kt south-southwesterly flow in the 850-700 mb layer offers at least conditional severe weather potential. Lower/mid tropospheric warm advection, either early in the day in association with the lead perturbation, or during the evening in advance of the more vigorous approaching impulse, may support the initiation of storms. If this occurs, potential exists for the evolution of an upscale growing cluster of storms which could pose a risk for severe hail and wind. ..Kerr.. 09/15/2019 Read more

SPC 0730Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0225 AM CDT Sun Sep 15 2019 Valid 171200Z - 181200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS TUESDAY INTO TUESDAY EVENING ACROSS PARTS OF THE NORTHERN ROCKIES INTO THE NORTHERN PLAINS AND PORTIONS OF THE UPPER MIDWEST... ...SUMMARY... Strong thunderstorms may impact parts of the northern Rockies into the adjacent northern High Plains, as well as parts of the Upper Midwest, Tuesday, accompanied by at least some potential for severe weather. ...Synopsis... While mid-level ridging within the westerlies remains prominent along an axis across the Great Lakes into Hudson Bay, large-scale troughing may continue to evolve across the northwestern U.S. into the central Canadian/U.S. border area, in association with several progressive short wave troughs. The most significant of these perturbations, including an embedded close low, is forecast to dig into the Pacific Northwest Tuesday through Tuesday night, while a compact but vigorous downstream impulse accelerates northeastward out of the northern Great Basin through the Dakotas by 12Z Wednesday. The lead impulse will be preceded by another perturbation of lower latitude origins, which is generally forecast to undergo considerable deformation while progressing northeast of the Dakotas through portions of northwestern Ontario and the upper Great Lakes region. In association with this regime, modestly deep surface troughing, to the lee of the northern Rockies at the outset of the period, appears likely to shift eastward across the northern and central Plains, while an embedded surface cyclone migrates from eastern Montana into Manitoba. This is expected to be trailed by a cold front, which probably will begin to overtake the surface troughing across the northern Plains by late Tuesday night. Seasonably moist boundary layer air supportive of moderate large CAPE may initially be focused along the western periphery of low-level ridging, across eastern portions of the northern Plains. Little change appears likely through the period, with a 30-50 kt south-southwesterly 850 mb jet being maintained along an axis from Kansas into Minnesota. ...Wyoming through the northern High Plains... Although low-level moisture may be rather limited, lower/mid tropospheric lapse rates are expected to become steep with fairly strong daytime heating and boundary layer mixing. Coupled with mid-level forcing for ascent and cooling associated with the vigorous short wave trough progressing out of the Great Basin, destabilization is expected to become sufficient to support thunderstorm development. This may initiate by midday Tuesday across the higher terrain of western into central Wyoming, before perhaps organizing and propagating northeastward and eastward into the high Plains by the evening. Substantial sub-cloud evaporative cooling probably will aid downward mixing of higher momentum air, including 30-70 kt southwesterly flow in the 700-500 mb layer, resulting in at least scattered strong to severe surface gusts, before the onset of diurnal cooling across the Plains. ...Northern and central Minnesota... More uncertainty exists across this area, but the development of moderately large CAPE in the presence of 30-50 kt south-southwesterly flow in the 850-700 mb layer offers at least conditional severe weather potential. Lower/mid tropospheric warm advection, either early in the day in association with the lead perturbation, or during the evening in advance of the more vigorous approaching impulse, may support the initiation of storms. If this occurs, potential exists for the evolution of an upscale growing cluster of storms which could pose a risk for severe hail and wind. ..Kerr.. 09/15/2019 Read more

SPC 0730Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0225 AM CDT Sun Sep 15 2019 Valid 171200Z - 181200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS TUESDAY INTO TUESDAY EVENING ACROSS PARTS OF THE NORTHERN ROCKIES INTO THE NORTHERN PLAINS AND PORTIONS OF THE UPPER MIDWEST... ...SUMMARY... Strong thunderstorms may impact parts of the northern Rockies into the adjacent northern High Plains, as well as parts of the Upper Midwest, Tuesday, accompanied by at least some potential for severe weather. ...Synopsis... While mid-level ridging within the westerlies remains prominent along an axis across the Great Lakes into Hudson Bay, large-scale troughing may continue to evolve across the northwestern U.S. into the central Canadian/U.S. border area, in association with several progressive short wave troughs. The most significant of these perturbations, including an embedded close low, is forecast to dig into the Pacific Northwest Tuesday through Tuesday night, while a compact but vigorous downstream impulse accelerates northeastward out of the northern Great Basin through the Dakotas by 12Z Wednesday. The lead impulse will be preceded by another perturbation of lower latitude origins, which is generally forecast to undergo considerable deformation while progressing northeast of the Dakotas through portions of northwestern Ontario and the upper Great Lakes region. In association with this regime, modestly deep surface troughing, to the lee of the northern Rockies at the outset of the period, appears likely to shift eastward across the northern and central Plains, while an embedded surface cyclone migrates from eastern Montana into Manitoba. This is expected to be trailed by a cold front, which probably will begin to overtake the surface troughing across the northern Plains by late Tuesday night. Seasonably moist boundary layer air supportive of moderate large CAPE may initially be focused along the western periphery of low-level ridging, across eastern portions of the northern Plains. Little change appears likely through the period, with a 30-50 kt south-southwesterly 850 mb jet being maintained along an axis from Kansas into Minnesota. ...Wyoming through the northern High Plains... Although low-level moisture may be rather limited, lower/mid tropospheric lapse rates are expected to become steep with fairly strong daytime heating and boundary layer mixing. Coupled with mid-level forcing for ascent and cooling associated with the vigorous short wave trough progressing out of the Great Basin, destabilization is expected to become sufficient to support thunderstorm development. This may initiate by midday Tuesday across the higher terrain of western into central Wyoming, before perhaps organizing and propagating northeastward and eastward into the high Plains by the evening. Substantial sub-cloud evaporative cooling probably will aid downward mixing of higher momentum air, including 30-70 kt southwesterly flow in the 700-500 mb layer, resulting in at least scattered strong to severe surface gusts, before the onset of diurnal cooling across the Plains. ...Northern and central Minnesota... More uncertainty exists across this area, but the development of moderately large CAPE in the presence of 30-50 kt south-southwesterly flow in the 850-700 mb layer offers at least conditional severe weather potential. Lower/mid tropospheric warm advection, either early in the day in association with the lead perturbation, or during the evening in advance of the more vigorous approaching impulse, may support the initiation of storms. If this occurs, potential exists for the evolution of an upscale growing cluster of storms which could pose a risk for severe hail and wind. ..Kerr.. 09/15/2019 Read more

SPC 0730Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0225 AM CDT Sun Sep 15 2019 Valid 171200Z - 181200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS TUESDAY INTO TUESDAY EVENING ACROSS PARTS OF THE NORTHERN ROCKIES INTO THE NORTHERN PLAINS AND PORTIONS OF THE UPPER MIDWEST... ...SUMMARY... Strong thunderstorms may impact parts of the northern Rockies into the adjacent northern High Plains, as well as parts of the Upper Midwest, Tuesday, accompanied by at least some potential for severe weather. ...Synopsis... While mid-level ridging within the westerlies remains prominent along an axis across the Great Lakes into Hudson Bay, large-scale troughing may continue to evolve across the northwestern U.S. into the central Canadian/U.S. border area, in association with several progressive short wave troughs. The most significant of these perturbations, including an embedded close low, is forecast to dig into the Pacific Northwest Tuesday through Tuesday night, while a compact but vigorous downstream impulse accelerates northeastward out of the northern Great Basin through the Dakotas by 12Z Wednesday. The lead impulse will be preceded by another perturbation of lower latitude origins, which is generally forecast to undergo considerable deformation while progressing northeast of the Dakotas through portions of northwestern Ontario and the upper Great Lakes region. In association with this regime, modestly deep surface troughing, to the lee of the northern Rockies at the outset of the period, appears likely to shift eastward across the northern and central Plains, while an embedded surface cyclone migrates from eastern Montana into Manitoba. This is expected to be trailed by a cold front, which probably will begin to overtake the surface troughing across the northern Plains by late Tuesday night. Seasonably moist boundary layer air supportive of moderate large CAPE may initially be focused along the western periphery of low-level ridging, across eastern portions of the northern Plains. Little change appears likely through the period, with a 30-50 kt south-southwesterly 850 mb jet being maintained along an axis from Kansas into Minnesota. ...Wyoming through the northern High Plains... Although low-level moisture may be rather limited, lower/mid tropospheric lapse rates are expected to become steep with fairly strong daytime heating and boundary layer mixing. Coupled with mid-level forcing for ascent and cooling associated with the vigorous short wave trough progressing out of the Great Basin, destabilization is expected to become sufficient to support thunderstorm development. This may initiate by midday Tuesday across the higher terrain of western into central Wyoming, before perhaps organizing and propagating northeastward and eastward into the high Plains by the evening. Substantial sub-cloud evaporative cooling probably will aid downward mixing of higher momentum air, including 30-70 kt southwesterly flow in the 700-500 mb layer, resulting in at least scattered strong to severe surface gusts, before the onset of diurnal cooling across the Plains. ...Northern and central Minnesota... More uncertainty exists across this area, but the development of moderately large CAPE in the presence of 30-50 kt south-southwesterly flow in the 850-700 mb layer offers at least conditional severe weather potential. Lower/mid tropospheric warm advection, either early in the day in association with the lead perturbation, or during the evening in advance of the more vigorous approaching impulse, may support the initiation of storms. If this occurs, potential exists for the evolution of an upscale growing cluster of storms which could pose a risk for severe hail and wind. ..Kerr.. 09/15/2019 Read more

SPC Day 2 Fire Weather Outlook
Day 2 Fire Weather Outlook NWS Storm Prediction Center Norman OK 0113 AM CDT Sun Sep 15 2019 Valid 161200Z - 171200Z ...CRITICAL FIRE WEATHER AREA FOR MUCH OF NV...WESTERN UT...EXTREME NORTHWEST AZ... ...Synopsis... A strong upper trough is forecast to move across the Great Basin into portions of the Intermountain West from Monday into Monday night. In conjunction with this trough, a cold front will sweep across portions of the interior Northwest and Great Basin. ...Great Basin and vicinity... A broad area of elevated to critical conditions is again expected over portions of the Great Basin and vicinity on Monday, with the area of greatest threat shifted eastward compared to D1/Sunday. Poor overnight RH recovery into Monday morning may allow critical conditions to develop early in the day ahead of the cold front. Critical conditions will become widespread across much of NV into portions of western UT and perhaps northwest AZ by the afternoon, as sustained winds increase to 20-30 mph and RH values drop below 15%. The northwestern extent of critical conditions will be determined by the timing of the cold front. Some areas northwest of the current critical delineation may see at least brief critical conditions before the front passes. An abrupt wind shift will accompany the front, which will impact the behavior of any ongoing fires, though RH values should rise fairly quickly in the wake of the front. The eastern portion of the critical area, where the front is not expected until Monday night, will see poor RH recovery during the evening and a more prolonged period of critical conditions. ..Dean.. 09/15/2019 ...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 0113 AM CDT Sun Sep 15 2019 Valid 161200Z - 171200Z ...CRITICAL FIRE WEATHER AREA FOR MUCH OF NV...WESTERN UT...EXTREME NORTHWEST AZ... ...Synopsis... A strong upper trough is forecast to move across the Great Basin into portions of the Intermountain West from Monday into Monday night. In conjunction with this trough, a cold front will sweep across portions of the interior Northwest and Great Basin. ...Great Basin and vicinity... A broad area of elevated to critical conditions is again expected over portions of the Great Basin and vicinity on Monday, with the area of greatest threat shifted eastward compared to D1/Sunday. Poor overnight RH recovery into Monday morning may allow critical conditions to develop early in the day ahead of the cold front. Critical conditions will become widespread across much of NV into portions of western UT and perhaps northwest AZ by the afternoon, as sustained winds increase to 20-30 mph and RH values drop below 15%. The northwestern extent of critical conditions will be determined by the timing of the cold front. Some areas northwest of the current critical delineation may see at least brief critical conditions before the front passes. An abrupt wind shift will accompany the front, which will impact the behavior of any ongoing fires, though RH values should rise fairly quickly in the wake of the front. The eastern portion of the critical area, where the front is not expected until Monday night, will see poor RH recovery during the evening and a more prolonged period of critical conditions. ..Dean.. 09/15/2019 ...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 0113 AM CDT Sun Sep 15 2019 Valid 161200Z - 171200Z ...CRITICAL FIRE WEATHER AREA FOR MUCH OF NV...WESTERN UT...EXTREME NORTHWEST AZ... ...Synopsis... A strong upper trough is forecast to move across the Great Basin into portions of the Intermountain West from Monday into Monday night. In conjunction with this trough, a cold front will sweep across portions of the interior Northwest and Great Basin. ...Great Basin and vicinity... A broad area of elevated to critical conditions is again expected over portions of the Great Basin and vicinity on Monday, with the area of greatest threat shifted eastward compared to D1/Sunday. Poor overnight RH recovery into Monday morning may allow critical conditions to develop early in the day ahead of the cold front. Critical conditions will become widespread across much of NV into portions of western UT and perhaps northwest AZ by the afternoon, as sustained winds increase to 20-30 mph and RH values drop below 15%. The northwestern extent of critical conditions will be determined by the timing of the cold front. Some areas northwest of the current critical delineation may see at least brief critical conditions before the front passes. An abrupt wind shift will accompany the front, which will impact the behavior of any ongoing fires, though RH values should rise fairly quickly in the wake of the front. The eastern portion of the critical area, where the front is not expected until Monday night, will see poor RH recovery during the evening and a more prolonged period of critical conditions. ..Dean.. 09/15/2019 ...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 0113 AM CDT Sun Sep 15 2019 Valid 161200Z - 171200Z ...CRITICAL FIRE WEATHER AREA FOR MUCH OF NV...WESTERN UT...EXTREME NORTHWEST AZ... ...Synopsis... A strong upper trough is forecast to move across the Great Basin into portions of the Intermountain West from Monday into Monday night. In conjunction with this trough, a cold front will sweep across portions of the interior Northwest and Great Basin. ...Great Basin and vicinity... A broad area of elevated to critical conditions is again expected over portions of the Great Basin and vicinity on Monday, with the area of greatest threat shifted eastward compared to D1/Sunday. Poor overnight RH recovery into Monday morning may allow critical conditions to develop early in the day ahead of the cold front. Critical conditions will become widespread across much of NV into portions of western UT and perhaps northwest AZ by the afternoon, as sustained winds increase to 20-30 mph and RH values drop below 15%. The northwestern extent of critical conditions will be determined by the timing of the cold front. Some areas northwest of the current critical delineation may see at least brief critical conditions before the front passes. An abrupt wind shift will accompany the front, which will impact the behavior of any ongoing fires, though RH values should rise fairly quickly in the wake of the front. The eastern portion of the critical area, where the front is not expected until Monday night, will see poor RH recovery during the evening and a more prolonged period of critical conditions. ..Dean.. 09/15/2019 ...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 0112 AM CDT Sun Sep 15 2019 Valid 151200Z - 161200Z ...CRITICAL FIRE WEATHER AREA FOR NORTHWEST NV...NORTHEAST CA...SOUTHEAST OR...SOUTHWEST ID... ...CRITICAL FIRE WEATHER AREA FOR CENTRAL/EASTERN NV... ...Synopsis... A vigorous upper trough is forecast to amplify and shift eastward across the Pacific Coast into the Great Basin/interior Northwest by Monday morning. At the surface, low pressure will deepen from the northern Great Basin into portions of the northern High Plains, with a surface trough extending southward into the central/southern High Plains. ...Great Basin and vicinity... As low/midlevel flow increases in advance of the strong upper trough, a broad area of elevated to potentially critical fire weather conditions is forecast to develop from the Great Basin and vicinity eastward into portions of southern WY. High-end critical conditions are likely over northwest NV and adjacent portions of northeast CA, southeast OR, and far southwest ID. In this area, sustained winds of 20-30 mph will combine with minimum RH values of 8-15%, with localized areas of extremely critical conditions possible. Another area of critical conditions is forecast over portions of central/eastern NV, where sustained winds of 15-25 mph are forecast in conjunction with minimum RH values of 10-15%. Poor overnight RH recovery is expected across both critical areas, and critical conditions may persist through late tonight in some areas. Elsewhere, critically low RH is expected over the remainder of the elevated area, though slightly weaker winds and/or less receptive fuels preclude any critical upgrade for those regions. Elevated to locally critical wind/RH will also likely develop across portions of eastern ID into southwest MT, but fuels are currently expected to be mostly unreceptive, so no delineation was included for that area. ..Dean.. 09/15/2019 ...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 0112 AM CDT Sun Sep 15 2019 Valid 151200Z - 161200Z ...CRITICAL FIRE WEATHER AREA FOR NORTHWEST NV...NORTHEAST CA...SOUTHEAST OR...SOUTHWEST ID... ...CRITICAL FIRE WEATHER AREA FOR CENTRAL/EASTERN NV... ...Synopsis... A vigorous upper trough is forecast to amplify and shift eastward across the Pacific Coast into the Great Basin/interior Northwest by Monday morning. At the surface, low pressure will deepen from the northern Great Basin into portions of the northern High Plains, with a surface trough extending southward into the central/southern High Plains. ...Great Basin and vicinity... As low/midlevel flow increases in advance of the strong upper trough, a broad area of elevated to potentially critical fire weather conditions is forecast to develop from the Great Basin and vicinity eastward into portions of southern WY. High-end critical conditions are likely over northwest NV and adjacent portions of northeast CA, southeast OR, and far southwest ID. In this area, sustained winds of 20-30 mph will combine with minimum RH values of 8-15%, with localized areas of extremely critical conditions possible. Another area of critical conditions is forecast over portions of central/eastern NV, where sustained winds of 15-25 mph are forecast in conjunction with minimum RH values of 10-15%. Poor overnight RH recovery is expected across both critical areas, and critical conditions may persist through late tonight in some areas. Elsewhere, critically low RH is expected over the remainder of the elevated area, though slightly weaker winds and/or less receptive fuels preclude any critical upgrade for those regions. Elevated to locally critical wind/RH will also likely develop across portions of eastern ID into southwest MT, but fuels are currently expected to be mostly unreceptive, so no delineation was included for that area. ..Dean.. 09/15/2019 ...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 0112 AM CDT Sun Sep 15 2019 Valid 151200Z - 161200Z ...CRITICAL FIRE WEATHER AREA FOR NORTHWEST NV...NORTHEAST CA...SOUTHEAST OR...SOUTHWEST ID... ...CRITICAL FIRE WEATHER AREA FOR CENTRAL/EASTERN NV... ...Synopsis... A vigorous upper trough is forecast to amplify and shift eastward across the Pacific Coast into the Great Basin/interior Northwest by Monday morning. At the surface, low pressure will deepen from the northern Great Basin into portions of the northern High Plains, with a surface trough extending southward into the central/southern High Plains. ...Great Basin and vicinity... As low/midlevel flow increases in advance of the strong upper trough, a broad area of elevated to potentially critical fire weather conditions is forecast to develop from the Great Basin and vicinity eastward into portions of southern WY. High-end critical conditions are likely over northwest NV and adjacent portions of northeast CA, southeast OR, and far southwest ID. In this area, sustained winds of 20-30 mph will combine with minimum RH values of 8-15%, with localized areas of extremely critical conditions possible. Another area of critical conditions is forecast over portions of central/eastern NV, where sustained winds of 15-25 mph are forecast in conjunction with minimum RH values of 10-15%. Poor overnight RH recovery is expected across both critical areas, and critical conditions may persist through late tonight in some areas. Elsewhere, critically low RH is expected over the remainder of the elevated area, though slightly weaker winds and/or less receptive fuels preclude any critical upgrade for those regions. Elevated to locally critical wind/RH will also likely develop across portions of eastern ID into southwest MT, but fuels are currently expected to be mostly unreceptive, so no delineation was included for that area. ..Dean.. 09/15/2019 ...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 0112 AM CDT Sun Sep 15 2019 Valid 151200Z - 161200Z ...CRITICAL FIRE WEATHER AREA FOR NORTHWEST NV...NORTHEAST CA...SOUTHEAST OR...SOUTHWEST ID... ...CRITICAL FIRE WEATHER AREA FOR CENTRAL/EASTERN NV... ...Synopsis... A vigorous upper trough is forecast to amplify and shift eastward across the Pacific Coast into the Great Basin/interior Northwest by Monday morning. At the surface, low pressure will deepen from the northern Great Basin into portions of the northern High Plains, with a surface trough extending southward into the central/southern High Plains. ...Great Basin and vicinity... As low/midlevel flow increases in advance of the strong upper trough, a broad area of elevated to potentially critical fire weather conditions is forecast to develop from the Great Basin and vicinity eastward into portions of southern WY. High-end critical conditions are likely over northwest NV and adjacent portions of northeast CA, southeast OR, and far southwest ID. In this area, sustained winds of 20-30 mph will combine with minimum RH values of 8-15%, with localized areas of extremely critical conditions possible. Another area of critical conditions is forecast over portions of central/eastern NV, where sustained winds of 15-25 mph are forecast in conjunction with minimum RH values of 10-15%. Poor overnight RH recovery is expected across both critical areas, and critical conditions may persist through late tonight in some areas. Elsewhere, critically low RH is expected over the remainder of the elevated area, though slightly weaker winds and/or less receptive fuels preclude any critical upgrade for those regions. Elevated to locally critical wind/RH will also likely develop across portions of eastern ID into southwest MT, but fuels are currently expected to be mostly unreceptive, so no delineation was included for that area. ..Dean.. 09/15/2019 ...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 1200 AM CDT Sun Sep 15 2019 Valid 161200Z - 171200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS THE GREAT SALT LAKE VICINITY LATE MONDAY NIGHT... ...SUMMARY... Strong thunderstorms may impact portions of the Great Basin near the Great Salt Lake late Monday night, perhaps accompanied by at least some risk for potentially damaging wind gusts. ...Synopsis... Within the westerlies, initially amplified mid-level troughing near/inland of the Pacific coast may already be in the process of splitting at the outset of the period. Models indicate that this will continue into early Tuesday, as another significant short wave trough digs southeast of the Gulf of Alaska, just to the west of the British Columbia coast, and downstream ridging builds along an axis from the Upper Midwest into areas as far north as western Hudson Bay. It appears that one emerging short wave impulse will gradually accelerate north and northeast of the Canadian Rockies, while another more vigorous perturbation pivots inland of the Pacific coast, into northern portions of the Great Basin by 12Z Tuesday. This latter feature will be preceded by a perturbation emanating from the lower latitudes, which may accelerate northeast of the Colorado Rockies, toward the eastern Dakotas Monday through Monday night. East of the ridging, large-scale troughing is forecast to continue digging east-southeast of the Canadian Maritimes and north Atlantic coast. An associated cold front may advance southward through the lower Ohio Valley, Mid Atlantic Coast states and adjacent portions of the western Atlantic. However, it is expected to remain well to the north of Humberto, which is forecast to reach hurricane strength well east of the Florida coast, while slowly accelerating eastward away from the coast. Although seasonably high (tropical) moisture content appears likely to remain largely confined to the Gulf of Mexico and western Atlantic, residual boundary layer moisture, in a corridor along the remnant western flank of the cold front across the lower/mid Missouri Valley, into deepening surface troughing across the northern Plains, may contribute to moderate CAPE with daytime heating Monday. However, at least some combination of weak forcing for ascent and mid-level inhibition, associated with a plume of warm elevated mixed-layer air advecting northeast of the northern Rockies, and across the international border area, is expected to limit convective potential. The development of any appreciable risk for severe weather still seems most probable with strong forcing for ascent and wind fields/shear associated with the short wave trough progressing into the Great Basin Monday night. ...Great Salt Lake vicinity... In the wake of the lead perturbation (of lower latitude origins), boundary layer moisture across western portions of the Great Basin may not be supportive of more than very weak CAPE. However, some northward moisture return appears at least possible to the west of the Wasatch by late Monday night, ahead of the vigorous approaching short wave and associated cold front. Coupled with strong forcing for ascent and mid-level cooling, destabilization may become sufficient to support scattered thunderstorm development across the Great Salt Lake vicinity by 17/09-12Z, in the presence of strengthening (40-70 kt) southwesterly flow in the 700-500 mb layer. This regime may become conducive to the development of potentially damaging wind gusts in stronger convection. ...MAXIMUM RISK BY HAZARD... Tornado: <2% - None Wind: 5% - Marginal Hail: <5% - None ..Kerr.. 09/15/2019 Read more

SPC 0600Z Day 2 Outlook
Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1200 AM CDT Sun Sep 15 2019 Valid 161200Z - 171200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS THE GREAT SALT LAKE VICINITY LATE MONDAY NIGHT... ...SUMMARY... Strong thunderstorms may impact portions of the Great Basin near the Great Salt Lake late Monday night, perhaps accompanied by at least some risk for potentially damaging wind gusts. ...Synopsis... Within the westerlies, initially amplified mid-level troughing near/inland of the Pacific coast may already be in the process of splitting at the outset of the period. Models indicate that this will continue into early Tuesday, as another significant short wave trough digs southeast of the Gulf of Alaska, just to the west of the British Columbia coast, and downstream ridging builds along an axis from the Upper Midwest into areas as far north as western Hudson Bay. It appears that one emerging short wave impulse will gradually accelerate north and northeast of the Canadian Rockies, while another more vigorous perturbation pivots inland of the Pacific coast, into northern portions of the Great Basin by 12Z Tuesday. This latter feature will be preceded by a perturbation emanating from the lower latitudes, which may accelerate northeast of the Colorado Rockies, toward the eastern Dakotas Monday through Monday night. East of the ridging, large-scale troughing is forecast to continue digging east-southeast of the Canadian Maritimes and north Atlantic coast. An associated cold front may advance southward through the lower Ohio Valley, Mid Atlantic Coast states and adjacent portions of the western Atlantic. However, it is expected to remain well to the north of Humberto, which is forecast to reach hurricane strength well east of the Florida coast, while slowly accelerating eastward away from the coast. Although seasonably high (tropical) moisture content appears likely to remain largely confined to the Gulf of Mexico and western Atlantic, residual boundary layer moisture, in a corridor along the remnant western flank of the cold front across the lower/mid Missouri Valley, into deepening surface troughing across the northern Plains, may contribute to moderate CAPE with daytime heating Monday. However, at least some combination of weak forcing for ascent and mid-level inhibition, associated with a plume of warm elevated mixed-layer air advecting northeast of the northern Rockies, and across the international border area, is expected to limit convective potential. The development of any appreciable risk for severe weather still seems most probable with strong forcing for ascent and wind fields/shear associated with the short wave trough progressing into the Great Basin Monday night. ...Great Salt Lake vicinity... In the wake of the lead perturbation (of lower latitude origins), boundary layer moisture across western portions of the Great Basin may not be supportive of more than very weak CAPE. However, some northward moisture return appears at least possible to the west of the Wasatch by late Monday night, ahead of the vigorous approaching short wave and associated cold front. Coupled with strong forcing for ascent and mid-level cooling, destabilization may become sufficient to support scattered thunderstorm development across the Great Salt Lake vicinity by 17/09-12Z, in the presence of strengthening (40-70 kt) southwesterly flow in the 700-500 mb layer. This regime may become conducive to the development of potentially damaging wind gusts in stronger convection. ...MAXIMUM RISK BY HAZARD... Tornado: <2% - None Wind: 5% - Marginal Hail: <5% - None ..Kerr.. 09/15/2019 Read more

SPC 0600Z Day 2 Outlook
Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1200 AM CDT Sun Sep 15 2019 Valid 161200Z - 171200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS THE GREAT SALT LAKE VICINITY LATE MONDAY NIGHT... ...SUMMARY... Strong thunderstorms may impact portions of the Great Basin near the Great Salt Lake late Monday night, perhaps accompanied by at least some risk for potentially damaging wind gusts. ...Synopsis... Within the westerlies, initially amplified mid-level troughing near/inland of the Pacific coast may already be in the process of splitting at the outset of the period. Models indicate that this will continue into early Tuesday, as another significant short wave trough digs southeast of the Gulf of Alaska, just to the west of the British Columbia coast, and downstream ridging builds along an axis from the Upper Midwest into areas as far north as western Hudson Bay. It appears that one emerging short wave impulse will gradually accelerate north and northeast of the Canadian Rockies, while another more vigorous perturbation pivots inland of the Pacific coast, into northern portions of the Great Basin by 12Z Tuesday. This latter feature will be preceded by a perturbation emanating from the lower latitudes, which may accelerate northeast of the Colorado Rockies, toward the eastern Dakotas Monday through Monday night. East of the ridging, large-scale troughing is forecast to continue digging east-southeast of the Canadian Maritimes and north Atlantic coast. An associated cold front may advance southward through the lower Ohio Valley, Mid Atlantic Coast states and adjacent portions of the western Atlantic. However, it is expected to remain well to the north of Humberto, which is forecast to reach hurricane strength well east of the Florida coast, while slowly accelerating eastward away from the coast. Although seasonably high (tropical) moisture content appears likely to remain largely confined to the Gulf of Mexico and western Atlantic, residual boundary layer moisture, in a corridor along the remnant western flank of the cold front across the lower/mid Missouri Valley, into deepening surface troughing across the northern Plains, may contribute to moderate CAPE with daytime heating Monday. However, at least some combination of weak forcing for ascent and mid-level inhibition, associated with a plume of warm elevated mixed-layer air advecting northeast of the northern Rockies, and across the international border area, is expected to limit convective potential. The development of any appreciable risk for severe weather still seems most probable with strong forcing for ascent and wind fields/shear associated with the short wave trough progressing into the Great Basin Monday night. ...Great Salt Lake vicinity... In the wake of the lead perturbation (of lower latitude origins), boundary layer moisture across western portions of the Great Basin may not be supportive of more than very weak CAPE. However, some northward moisture return appears at least possible to the west of the Wasatch by late Monday night, ahead of the vigorous approaching short wave and associated cold front. Coupled with strong forcing for ascent and mid-level cooling, destabilization may become sufficient to support scattered thunderstorm development across the Great Salt Lake vicinity by 17/09-12Z, in the presence of strengthening (40-70 kt) southwesterly flow in the 700-500 mb layer. This regime may become conducive to the development of potentially damaging wind gusts in stronger convection. ...MAXIMUM RISK BY HAZARD... Tornado: <2% - None Wind: 5% - Marginal Hail: <5% - None ..Kerr.. 09/15/2019 Read more

SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1207 AM CDT Sun Sep 15 2019 Valid 151200Z - 161200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... Organized severe thunderstorms are not expected across the U.S. today. ...Synopsis... The upper level pattern over the U.S. will become more amplified today. A deepening upper trough will move southeast to the Pacific Northwest coast. In response, an upper ridge will build over the Plains today, while shifting eastward toward the Mississippi Valley by Monday morning. Further east, a shortwave trough over the upper Great Lakes will progress east, overspreading the northeastern states by the end of the period. Thunderstorms should be ongoing along a cold front attendant to the Great Lakes upper shortwave trough from northern IL/IN into lower MI. This activity will be elevated and is expected to remain sub-severe through the afternoon as the downstream environment will not be conducive to intense convection. While moisture will stream northward across the Plains today beneath the amplifying upper ridge, limited forcing and capping will preclude thunderstorm activity. Further west, a weak mid/upper level low over southern AZ/NM will drift northward while weakening. Still, this feature will provide support for diurnally driven thunderstorms across the Four Corners region. Weak deep layer shear and modest instability will preclude organized/long-lived convection, though a dry boundary layer could result in some gusty outflow winds with the strongest cells. Additional thunderstorms are possible in the vicinity of the central and western Gulf coasts as a weak low migrates westward across the Gulf of Mexico. Further east, the National Hurricane Center forecast keeps Tropical Storm Humberto well offshore from FL, though isolated thunderstorms are possible in areas of convergent low level flow from FL through the eastern Carolinas. ..Leitman/Dean.. 09/15/2019 Read more

SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1207 AM CDT Sun Sep 15 2019 Valid 151200Z - 161200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... Organized severe thunderstorms are not expected across the U.S. today. ...Synopsis... The upper level pattern over the U.S. will become more amplified today. A deepening upper trough will move southeast to the Pacific Northwest coast. In response, an upper ridge will build over the Plains today, while shifting eastward toward the Mississippi Valley by Monday morning. Further east, a shortwave trough over the upper Great Lakes will progress east, overspreading the northeastern states by the end of the period. Thunderstorms should be ongoing along a cold front attendant to the Great Lakes upper shortwave trough from northern IL/IN into lower MI. This activity will be elevated and is expected to remain sub-severe through the afternoon as the downstream environment will not be conducive to intense convection. While moisture will stream northward across the Plains today beneath the amplifying upper ridge, limited forcing and capping will preclude thunderstorm activity. Further west, a weak mid/upper level low over southern AZ/NM will drift northward while weakening. Still, this feature will provide support for diurnally driven thunderstorms across the Four Corners region. Weak deep layer shear and modest instability will preclude organized/long-lived convection, though a dry boundary layer could result in some gusty outflow winds with the strongest cells. Additional thunderstorms are possible in the vicinity of the central and western Gulf coasts as a weak low migrates westward across the Gulf of Mexico. Further east, the National Hurricane Center forecast keeps Tropical Storm Humberto well offshore from FL, though isolated thunderstorms are possible in areas of convergent low level flow from FL through the eastern Carolinas. ..Leitman/Dean.. 09/15/2019 Read more

SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1207 AM CDT Sun Sep 15 2019 Valid 151200Z - 161200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... Organized severe thunderstorms are not expected across the U.S. today. ...Synopsis... The upper level pattern over the U.S. will become more amplified today. A deepening upper trough will move southeast to the Pacific Northwest coast. In response, an upper ridge will build over the Plains today, while shifting eastward toward the Mississippi Valley by Monday morning. Further east, a shortwave trough over the upper Great Lakes will progress east, overspreading the northeastern states by the end of the period. Thunderstorms should be ongoing along a cold front attendant to the Great Lakes upper shortwave trough from northern IL/IN into lower MI. This activity will be elevated and is expected to remain sub-severe through the afternoon as the downstream environment will not be conducive to intense convection. While moisture will stream northward across the Plains today beneath the amplifying upper ridge, limited forcing and capping will preclude thunderstorm activity. Further west, a weak mid/upper level low over southern AZ/NM will drift northward while weakening. Still, this feature will provide support for diurnally driven thunderstorms across the Four Corners region. Weak deep layer shear and modest instability will preclude organized/long-lived convection, though a dry boundary layer could result in some gusty outflow winds with the strongest cells. Additional thunderstorms are possible in the vicinity of the central and western Gulf coasts as a weak low migrates westward across the Gulf of Mexico. Further east, the National Hurricane Center forecast keeps Tropical Storm Humberto well offshore from FL, though isolated thunderstorms are possible in areas of convergent low level flow from FL through the eastern Carolinas. ..Leitman/Dean.. 09/15/2019 Read more

MD 1979 CONCERNING SEVERE THUNDERSTORM WATCH 653... FOR AZ
Mesoscale Discussion 1979 NWS Storm Prediction Center Norman OK 0940 PM CDT Sat Sep 14 2019 Areas affected...AZ Concerning...Severe Thunderstorm Watch 653... Valid 150240Z - 150415Z The severe weather threat for Severe Thunderstorm Watch 653 continues. SUMMARY...Severe threat is decreasing across ww653. DISCUSSION...Earlier convection that developed over the higher terrain of central AZ has propagated southwest across the lower deserts. This activity has struggled to organize, though gusty winds have likely been noted with the strongest storms. Even so, overall severe threat appears to be waning as diurnal cooling and boundary-layer stabilization appears to be negatively influencing convection. ..Darrow.. 09/15/2019 ...Please see www.spc.noaa.gov for graphic product... ATTN...WFO...TWC...PSR... LAT...LON 31931330 33451331 33621227 32461180 31931330 Read more