Severe Storms

SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1130 AM CDT Sat Sep 14 2019 Valid 141630Z - 151200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS SOUTH-CENTRAL AZ... ...SUMMARY... Isolated to scattered severe wind gusts are possible this afternoon and evening across southern and central Arizona. Isolated severe storms with large hail and damaging wind gusts are possible from the Upper Midwest to the central Great Plains through tonight. ...Southern/central AZ... An MCV over western Chihuahua will drift north-northwestward across southeast AZ through tonight. 50s surface dew points are common across southern AZ amid easterly flow north of this MCV. In conjunction with ample heating northwest of the thicker cloud cover near the MCV, a modestly buoyant air mass with MLCAPE approaching 1000 J/kg should develop by peak heating. 15-25 kt east-northeast 700-500 mb winds around the north side of the MCV will be favorable for cells and semi-organized clusters to spread off the Mogollon Rim into the lower deserts with a threat for severe gusts. Whether more organized clustering can evolve is uncertain compared to the significant severe wind event two weeks ago, but there is at least sufficient damaging wind potential to warrant a Slight Risk across parts of the Gila Valley. ...Upper Midwest to the central Great Plains... Elevated thunderstorms are ongoing in western IA on the leading edge of a low-level warm theta-e advection plume. This plume and attendant zone of ascent will spread east-northeast across the Upper MS Valley into tonight in advance of a low-amplitude shortwave trough near the ND/MB border that will move east-southeast into Lake Superior. This elevated convection will pose a threat for isolated large hail, mainly this evening into tonight with a probable decay cycle this afternoon. A risk for locally damaging winds may also develop tonight towards the IA/IL/WI border region if a cluster can become semi-organized. In the wake of the warm advection regime, storm initiation will depend on weak low-level ascent along a surface trough that extends southwestward across NE/KS. Stronger surface heating and deeper mixing is expected along the trough in KS, with lesser mixing depths and a greater probability of maintaining MLCIN through the afternoon in the warm sector farther northeast. Thus, surface-based thunderstorm development should be sparse and may struggle to be sustained during the late afternoon/early evening. If surface-based storms can form as far northeast as southern MN this afternoon, vertical shear profiles will be sufficient for supercells. Weaker vertical shear is expected with southwestward extent into southwest KS, where high-based storms would pose a threat for isolated severe wind and hail. ...Central Appalachians... A narrow corridor of weak to modest buoyancy is expected with scattered storms along a cold front and over the higher terrain through early evening. Isolated strong downburst winds are possible on the periphery of weak to moderate mid-level southwesterlies. ..Grams/Squitieri.. 09/14/2019 Read more

SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1130 AM CDT Sat Sep 14 2019 Valid 141630Z - 151200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS SOUTH-CENTRAL AZ... ...SUMMARY... Isolated to scattered severe wind gusts are possible this afternoon and evening across southern and central Arizona. Isolated severe storms with large hail and damaging wind gusts are possible from the Upper Midwest to the central Great Plains through tonight. ...Southern/central AZ... An MCV over western Chihuahua will drift north-northwestward across southeast AZ through tonight. 50s surface dew points are common across southern AZ amid easterly flow north of this MCV. In conjunction with ample heating northwest of the thicker cloud cover near the MCV, a modestly buoyant air mass with MLCAPE approaching 1000 J/kg should develop by peak heating. 15-25 kt east-northeast 700-500 mb winds around the north side of the MCV will be favorable for cells and semi-organized clusters to spread off the Mogollon Rim into the lower deserts with a threat for severe gusts. Whether more organized clustering can evolve is uncertain compared to the significant severe wind event two weeks ago, but there is at least sufficient damaging wind potential to warrant a Slight Risk across parts of the Gila Valley. ...Upper Midwest to the central Great Plains... Elevated thunderstorms are ongoing in western IA on the leading edge of a low-level warm theta-e advection plume. This plume and attendant zone of ascent will spread east-northeast across the Upper MS Valley into tonight in advance of a low-amplitude shortwave trough near the ND/MB border that will move east-southeast into Lake Superior. This elevated convection will pose a threat for isolated large hail, mainly this evening into tonight with a probable decay cycle this afternoon. A risk for locally damaging winds may also develop tonight towards the IA/IL/WI border region if a cluster can become semi-organized. In the wake of the warm advection regime, storm initiation will depend on weak low-level ascent along a surface trough that extends southwestward across NE/KS. Stronger surface heating and deeper mixing is expected along the trough in KS, with lesser mixing depths and a greater probability of maintaining MLCIN through the afternoon in the warm sector farther northeast. Thus, surface-based thunderstorm development should be sparse and may struggle to be sustained during the late afternoon/early evening. If surface-based storms can form as far northeast as southern MN this afternoon, vertical shear profiles will be sufficient for supercells. Weaker vertical shear is expected with southwestward extent into southwest KS, where high-based storms would pose a threat for isolated severe wind and hail. ...Central Appalachians... A narrow corridor of weak to modest buoyancy is expected with scattered storms along a cold front and over the higher terrain through early evening. Isolated strong downburst winds are possible on the periphery of weak to moderate mid-level southwesterlies. ..Grams/Squitieri.. 09/14/2019 Read more

SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1130 AM CDT Sat Sep 14 2019 Valid 141630Z - 151200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS SOUTH-CENTRAL AZ... ...SUMMARY... Isolated to scattered severe wind gusts are possible this afternoon and evening across southern and central Arizona. Isolated severe storms with large hail and damaging wind gusts are possible from the Upper Midwest to the central Great Plains through tonight. ...Southern/central AZ... An MCV over western Chihuahua will drift north-northwestward across southeast AZ through tonight. 50s surface dew points are common across southern AZ amid easterly flow north of this MCV. In conjunction with ample heating northwest of the thicker cloud cover near the MCV, a modestly buoyant air mass with MLCAPE approaching 1000 J/kg should develop by peak heating. 15-25 kt east-northeast 700-500 mb winds around the north side of the MCV will be favorable for cells and semi-organized clusters to spread off the Mogollon Rim into the lower deserts with a threat for severe gusts. Whether more organized clustering can evolve is uncertain compared to the significant severe wind event two weeks ago, but there is at least sufficient damaging wind potential to warrant a Slight Risk across parts of the Gila Valley. ...Upper Midwest to the central Great Plains... Elevated thunderstorms are ongoing in western IA on the leading edge of a low-level warm theta-e advection plume. This plume and attendant zone of ascent will spread east-northeast across the Upper MS Valley into tonight in advance of a low-amplitude shortwave trough near the ND/MB border that will move east-southeast into Lake Superior. This elevated convection will pose a threat for isolated large hail, mainly this evening into tonight with a probable decay cycle this afternoon. A risk for locally damaging winds may also develop tonight towards the IA/IL/WI border region if a cluster can become semi-organized. In the wake of the warm advection regime, storm initiation will depend on weak low-level ascent along a surface trough that extends southwestward across NE/KS. Stronger surface heating and deeper mixing is expected along the trough in KS, with lesser mixing depths and a greater probability of maintaining MLCIN through the afternoon in the warm sector farther northeast. Thus, surface-based thunderstorm development should be sparse and may struggle to be sustained during the late afternoon/early evening. If surface-based storms can form as far northeast as southern MN this afternoon, vertical shear profiles will be sufficient for supercells. Weaker vertical shear is expected with southwestward extent into southwest KS, where high-based storms would pose a threat for isolated severe wind and hail. ...Central Appalachians... A narrow corridor of weak to modest buoyancy is expected with scattered storms along a cold front and over the higher terrain through early evening. Isolated strong downburst winds are possible on the periphery of weak to moderate mid-level southwesterlies. ..Grams/Squitieri.. 09/14/2019 Read more

SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1130 AM CDT Sat Sep 14 2019 Valid 141630Z - 151200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS SOUTH-CENTRAL AZ... ...SUMMARY... Isolated to scattered severe wind gusts are possible this afternoon and evening across southern and central Arizona. Isolated severe storms with large hail and damaging wind gusts are possible from the Upper Midwest to the central Great Plains through tonight. ...Southern/central AZ... An MCV over western Chihuahua will drift north-northwestward across southeast AZ through tonight. 50s surface dew points are common across southern AZ amid easterly flow north of this MCV. In conjunction with ample heating northwest of the thicker cloud cover near the MCV, a modestly buoyant air mass with MLCAPE approaching 1000 J/kg should develop by peak heating. 15-25 kt east-northeast 700-500 mb winds around the north side of the MCV will be favorable for cells and semi-organized clusters to spread off the Mogollon Rim into the lower deserts with a threat for severe gusts. Whether more organized clustering can evolve is uncertain compared to the significant severe wind event two weeks ago, but there is at least sufficient damaging wind potential to warrant a Slight Risk across parts of the Gila Valley. ...Upper Midwest to the central Great Plains... Elevated thunderstorms are ongoing in western IA on the leading edge of a low-level warm theta-e advection plume. This plume and attendant zone of ascent will spread east-northeast across the Upper MS Valley into tonight in advance of a low-amplitude shortwave trough near the ND/MB border that will move east-southeast into Lake Superior. This elevated convection will pose a threat for isolated large hail, mainly this evening into tonight with a probable decay cycle this afternoon. A risk for locally damaging winds may also develop tonight towards the IA/IL/WI border region if a cluster can become semi-organized. In the wake of the warm advection regime, storm initiation will depend on weak low-level ascent along a surface trough that extends southwestward across NE/KS. Stronger surface heating and deeper mixing is expected along the trough in KS, with lesser mixing depths and a greater probability of maintaining MLCIN through the afternoon in the warm sector farther northeast. Thus, surface-based thunderstorm development should be sparse and may struggle to be sustained during the late afternoon/early evening. If surface-based storms can form as far northeast as southern MN this afternoon, vertical shear profiles will be sufficient for supercells. Weaker vertical shear is expected with southwestward extent into southwest KS, where high-based storms would pose a threat for isolated severe wind and hail. ...Central Appalachians... A narrow corridor of weak to modest buoyancy is expected with scattered storms along a cold front and over the higher terrain through early evening. Isolated strong downburst winds are possible on the periphery of weak to moderate mid-level southwesterlies. ..Grams/Squitieri.. 09/14/2019 Read more

SPC Day 1 Fire Weather Outlook
Day 1 Fire Weather Outlook NWS Storm Prediction Center Norman OK 1049 AM CDT Sat Sep 14 2019 Valid 141700Z - 151200Z The elevated area was expanded slightly southward along the Sierra Front as downslope winds will likely result in elevated conditions. Otherwise, the forecast remains on track, and please see the discussion below for more details. ..Nauslar.. 09/14/2019 .PREV DISCUSSION... /ISSUED 1259 AM CDT Sat Sep 14 2019/ ...Synopsis... An upper trough is forecast to approach the Pacific Northwest by late tonight, as a downstream shortwave trough moves quickly across the northern Plains. At the surface, broad low pressure will remain in place across south-central Canada, with a surface trough extending into portions of the central/northern High Plains. ...Southern WY... Low-level westerly flow will become established across southern WY this afternoon, to the west of the surface trough over the central/northern High Plains. Drying/mixing within a westerly flow regime will result in minimum RH values dropping to 10-20% this afternoon, in conjunction with sustained winds of 15-25 mph. These conditions will result in elevated fire weather conditions, with the best chance of locally critical conditions expected across portions of southeast WY. ...Northwest Great Basin and Vicinity... In advance of the upper trough, a gradual increase in low-level southwesterly flow is expected across portions of the northwest Great Basin and vicinity. Sustained winds may approach or exceed 15 mph within a hot and dry airmass characterized by minimum RH values of 10-15%, resulting in the potential for elevated fire weather conditions. As flow continues to increase into Sunday morning, mid/high elevation regions that remain above the nocturnal inversion for a longer period of time may see elevated conditions persist into the overnight hours. ...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 1049 AM CDT Sat Sep 14 2019 Valid 141700Z - 151200Z The elevated area was expanded slightly southward along the Sierra Front as downslope winds will likely result in elevated conditions. Otherwise, the forecast remains on track, and please see the discussion below for more details. ..Nauslar.. 09/14/2019 .PREV DISCUSSION... /ISSUED 1259 AM CDT Sat Sep 14 2019/ ...Synopsis... An upper trough is forecast to approach the Pacific Northwest by late tonight, as a downstream shortwave trough moves quickly across the northern Plains. At the surface, broad low pressure will remain in place across south-central Canada, with a surface trough extending into portions of the central/northern High Plains. ...Southern WY... Low-level westerly flow will become established across southern WY this afternoon, to the west of the surface trough over the central/northern High Plains. Drying/mixing within a westerly flow regime will result in minimum RH values dropping to 10-20% this afternoon, in conjunction with sustained winds of 15-25 mph. These conditions will result in elevated fire weather conditions, with the best chance of locally critical conditions expected across portions of southeast WY. ...Northwest Great Basin and Vicinity... In advance of the upper trough, a gradual increase in low-level southwesterly flow is expected across portions of the northwest Great Basin and vicinity. Sustained winds may approach or exceed 15 mph within a hot and dry airmass characterized by minimum RH values of 10-15%, resulting in the potential for elevated fire weather conditions. As flow continues to increase into Sunday morning, mid/high elevation regions that remain above the nocturnal inversion for a longer period of time may see elevated conditions persist into the overnight hours. ...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 1049 AM CDT Sat Sep 14 2019 Valid 141700Z - 151200Z The elevated area was expanded slightly southward along the Sierra Front as downslope winds will likely result in elevated conditions. Otherwise, the forecast remains on track, and please see the discussion below for more details. ..Nauslar.. 09/14/2019 .PREV DISCUSSION... /ISSUED 1259 AM CDT Sat Sep 14 2019/ ...Synopsis... An upper trough is forecast to approach the Pacific Northwest by late tonight, as a downstream shortwave trough moves quickly across the northern Plains. At the surface, broad low pressure will remain in place across south-central Canada, with a surface trough extending into portions of the central/northern High Plains. ...Southern WY... Low-level westerly flow will become established across southern WY this afternoon, to the west of the surface trough over the central/northern High Plains. Drying/mixing within a westerly flow regime will result in minimum RH values dropping to 10-20% this afternoon, in conjunction with sustained winds of 15-25 mph. These conditions will result in elevated fire weather conditions, with the best chance of locally critical conditions expected across portions of southeast WY. ...Northwest Great Basin and Vicinity... In advance of the upper trough, a gradual increase in low-level southwesterly flow is expected across portions of the northwest Great Basin and vicinity. Sustained winds may approach or exceed 15 mph within a hot and dry airmass characterized by minimum RH values of 10-15%, resulting in the potential for elevated fire weather conditions. As flow continues to increase into Sunday morning, mid/high elevation regions that remain above the nocturnal inversion for a longer period of time may see elevated conditions persist into the overnight hours. ...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 1049 AM CDT Sat Sep 14 2019 Valid 141700Z - 151200Z The elevated area was expanded slightly southward along the Sierra Front as downslope winds will likely result in elevated conditions. Otherwise, the forecast remains on track, and please see the discussion below for more details. ..Nauslar.. 09/14/2019 .PREV DISCUSSION... /ISSUED 1259 AM CDT Sat Sep 14 2019/ ...Synopsis... An upper trough is forecast to approach the Pacific Northwest by late tonight, as a downstream shortwave trough moves quickly across the northern Plains. At the surface, broad low pressure will remain in place across south-central Canada, with a surface trough extending into portions of the central/northern High Plains. ...Southern WY... Low-level westerly flow will become established across southern WY this afternoon, to the west of the surface trough over the central/northern High Plains. Drying/mixing within a westerly flow regime will result in minimum RH values dropping to 10-20% this afternoon, in conjunction with sustained winds of 15-25 mph. These conditions will result in elevated fire weather conditions, with the best chance of locally critical conditions expected across portions of southeast WY. ...Northwest Great Basin and Vicinity... In advance of the upper trough, a gradual increase in low-level southwesterly flow is expected across portions of the northwest Great Basin and vicinity. Sustained winds may approach or exceed 15 mph within a hot and dry airmass characterized by minimum RH values of 10-15%, resulting in the potential for elevated fire weather conditions. As flow continues to increase into Sunday morning, mid/high elevation regions that remain above the nocturnal inversion for a longer period of time may see elevated conditions persist into the overnight hours. ...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 1049 AM CDT Sat Sep 14 2019 Valid 141700Z - 151200Z The elevated area was expanded slightly southward along the Sierra Front as downslope winds will likely result in elevated conditions. Otherwise, the forecast remains on track, and please see the discussion below for more details. ..Nauslar.. 09/14/2019 .PREV DISCUSSION... /ISSUED 1259 AM CDT Sat Sep 14 2019/ ...Synopsis... An upper trough is forecast to approach the Pacific Northwest by late tonight, as a downstream shortwave trough moves quickly across the northern Plains. At the surface, broad low pressure will remain in place across south-central Canada, with a surface trough extending into portions of the central/northern High Plains. ...Southern WY... Low-level westerly flow will become established across southern WY this afternoon, to the west of the surface trough over the central/northern High Plains. Drying/mixing within a westerly flow regime will result in minimum RH values dropping to 10-20% this afternoon, in conjunction with sustained winds of 15-25 mph. These conditions will result in elevated fire weather conditions, with the best chance of locally critical conditions expected across portions of southeast WY. ...Northwest Great Basin and Vicinity... In advance of the upper trough, a gradual increase in low-level southwesterly flow is expected across portions of the northwest Great Basin and vicinity. Sustained winds may approach or exceed 15 mph within a hot and dry airmass characterized by minimum RH values of 10-15%, resulting in the potential for elevated fire weather conditions. As flow continues to increase into Sunday morning, mid/high elevation regions that remain above the nocturnal inversion for a longer period of time may see elevated conditions persist into the overnight hours. ...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 0735 AM CDT Sat Sep 14 2019 Valid 141300Z - 151200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS THROUGH TONIGHT ACROSS PARTS OF THE CENTRAL PLAINS TO THE UPPER MS VALLEY...AND THIS AFTERNOON/EVENING ACROSS PARTS OF AZ... ...SUMMARY... Isolated severe storms with damaging gusts and large hail will be possible from the upper Mississippi Valley into the central Plains. Isolated damaging gusts will be possible this afternoon/evening in the lower desert regions of Arizona. ...Upper MS Valley to the central Plains through tonight... Elevated thunderstorms are ongoing over northeast NE in a zone of low-level warm advection on the nose of a 45 kt southwesterly low-level jet. This zone of ascent and storms will spread east-northeastward across northern IA/southern MN through the day, immediately in advance of a low-amplitude shortwave trough moving from the Dakotas to the upper MS Valley. In the wake of the warm advection, storm initiation will depend on weak low-level ascent along a surface trough that extends southwestward across NE/KS. Stronger surface heating and deeper mixing is expected along the trough in KS, with lesser mixing depths and a greater probability of maintaining convective inhibition through the afternoon in the warm sector farther northeast. Thus, surface-based thunderstorm development is uncertain this afternoon/evening. The elevated convection could pose a threat for isolated large hail as far east as western WI later today into tonight. If surface-based storms form as far northeast as southern MN this afternoon, vertical shear profiles will be sufficient for supercells. Somewhat weaker vertical shear is expected with southwestward extent into southwest KS, where high-based storms would pose a threat for isolated damaging gusts and large hail. ...Southern AZ this afternoon/evening... An MCV over northwest Mexico will drift north-northwestward toward southeast AZ through tonight. A substantial increase in low-midlevel moisture/PW has occurred across southeast and south central AZ the past 12-24 hours, and the moisture will continue to spread westward today. Stronger surface heating west of the thicker clouds, as well as 10-20 kt east-northeasterly midlevel flow around the north side of the MCV, will provide an environment favorable for storms to form and spread westward into the lower deserts this afternoon/evening. Typical inverted-v profiles and MLCAPE of 500-1000 J/kg will support a threat for hybrid microbursts capable of producing isolated damaging winds. ...Central/southern Appalachians this afternoon... A narrow corridor of weak-moderate buoyancy is expected this afternoon across the central/southern Appalachians, and a few storms are expected along a cold front and over the higher terrain this afternoon. Very isolated strong downburst winds cannot be ruled out, though the threat is too marginal to warrant damaging wind probabilities. ..Thompson/Gleason.. 09/14/2019 Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0735 AM CDT Sat Sep 14 2019 Valid 141300Z - 151200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS THROUGH TONIGHT ACROSS PARTS OF THE CENTRAL PLAINS TO THE UPPER MS VALLEY...AND THIS AFTERNOON/EVENING ACROSS PARTS OF AZ... ...SUMMARY... Isolated severe storms with damaging gusts and large hail will be possible from the upper Mississippi Valley into the central Plains. Isolated damaging gusts will be possible this afternoon/evening in the lower desert regions of Arizona. ...Upper MS Valley to the central Plains through tonight... Elevated thunderstorms are ongoing over northeast NE in a zone of low-level warm advection on the nose of a 45 kt southwesterly low-level jet. This zone of ascent and storms will spread east-northeastward across northern IA/southern MN through the day, immediately in advance of a low-amplitude shortwave trough moving from the Dakotas to the upper MS Valley. In the wake of the warm advection, storm initiation will depend on weak low-level ascent along a surface trough that extends southwestward across NE/KS. Stronger surface heating and deeper mixing is expected along the trough in KS, with lesser mixing depths and a greater probability of maintaining convective inhibition through the afternoon in the warm sector farther northeast. Thus, surface-based thunderstorm development is uncertain this afternoon/evening. The elevated convection could pose a threat for isolated large hail as far east as western WI later today into tonight. If surface-based storms form as far northeast as southern MN this afternoon, vertical shear profiles will be sufficient for supercells. Somewhat weaker vertical shear is expected with southwestward extent into southwest KS, where high-based storms would pose a threat for isolated damaging gusts and large hail. ...Southern AZ this afternoon/evening... An MCV over northwest Mexico will drift north-northwestward toward southeast AZ through tonight. A substantial increase in low-midlevel moisture/PW has occurred across southeast and south central AZ the past 12-24 hours, and the moisture will continue to spread westward today. Stronger surface heating west of the thicker clouds, as well as 10-20 kt east-northeasterly midlevel flow around the north side of the MCV, will provide an environment favorable for storms to form and spread westward into the lower deserts this afternoon/evening. Typical inverted-v profiles and MLCAPE of 500-1000 J/kg will support a threat for hybrid microbursts capable of producing isolated damaging winds. ...Central/southern Appalachians this afternoon... A narrow corridor of weak-moderate buoyancy is expected this afternoon across the central/southern Appalachians, and a few storms are expected along a cold front and over the higher terrain this afternoon. Very isolated strong downburst winds cannot be ruled out, though the threat is too marginal to warrant damaging wind probabilities. ..Thompson/Gleason.. 09/14/2019 Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0735 AM CDT Sat Sep 14 2019 Valid 141300Z - 151200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS THROUGH TONIGHT ACROSS PARTS OF THE CENTRAL PLAINS TO THE UPPER MS VALLEY...AND THIS AFTERNOON/EVENING ACROSS PARTS OF AZ... ...SUMMARY... Isolated severe storms with damaging gusts and large hail will be possible from the upper Mississippi Valley into the central Plains. Isolated damaging gusts will be possible this afternoon/evening in the lower desert regions of Arizona. ...Upper MS Valley to the central Plains through tonight... Elevated thunderstorms are ongoing over northeast NE in a zone of low-level warm advection on the nose of a 45 kt southwesterly low-level jet. This zone of ascent and storms will spread east-northeastward across northern IA/southern MN through the day, immediately in advance of a low-amplitude shortwave trough moving from the Dakotas to the upper MS Valley. In the wake of the warm advection, storm initiation will depend on weak low-level ascent along a surface trough that extends southwestward across NE/KS. Stronger surface heating and deeper mixing is expected along the trough in KS, with lesser mixing depths and a greater probability of maintaining convective inhibition through the afternoon in the warm sector farther northeast. Thus, surface-based thunderstorm development is uncertain this afternoon/evening. The elevated convection could pose a threat for isolated large hail as far east as western WI later today into tonight. If surface-based storms form as far northeast as southern MN this afternoon, vertical shear profiles will be sufficient for supercells. Somewhat weaker vertical shear is expected with southwestward extent into southwest KS, where high-based storms would pose a threat for isolated damaging gusts and large hail. ...Southern AZ this afternoon/evening... An MCV over northwest Mexico will drift north-northwestward toward southeast AZ through tonight. A substantial increase in low-midlevel moisture/PW has occurred across southeast and south central AZ the past 12-24 hours, and the moisture will continue to spread westward today. Stronger surface heating west of the thicker clouds, as well as 10-20 kt east-northeasterly midlevel flow around the north side of the MCV, will provide an environment favorable for storms to form and spread westward into the lower deserts this afternoon/evening. Typical inverted-v profiles and MLCAPE of 500-1000 J/kg will support a threat for hybrid microbursts capable of producing isolated damaging winds. ...Central/southern Appalachians this afternoon... A narrow corridor of weak-moderate buoyancy is expected this afternoon across the central/southern Appalachians, and a few storms are expected along a cold front and over the higher terrain this afternoon. Very isolated strong downburst winds cannot be ruled out, though the threat is too marginal to warrant damaging wind probabilities. ..Thompson/Gleason.. 09/14/2019 Read more

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0352 AM CDT Sat Sep 14 2019 Valid 171200Z - 221200Z ...DISCUSSION... The medium-range models generally suggest that subtropical ridging may remain a prominent influence across much of the south central and southeastern U.S. from the middle of the coming work week into next weekend. However, rather large spread is evident concerning short wave developments within the westerlies, indicative of poor pattern predictability throughout the period. Even early in the period (Tue/Wed), there are substantial differences concerning a compact, but vigorous short wave impulse emerging from the Great Basin, which could potentially contribute to at least some risk for severe storms, from the immediate lee of the northern Rockies through the northern Plains and portions of the Upper Midwest. And uncertainties associated with these differences are compounded by the uncertain influence of a preceding wave, emanating from the lower latitudes, on low-level moisture and instability across this region. Read more

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0352 AM CDT Sat Sep 14 2019 Valid 171200Z - 221200Z ...DISCUSSION... The medium-range models generally suggest that subtropical ridging may remain a prominent influence across much of the south central and southeastern U.S. from the middle of the coming work week into next weekend. However, rather large spread is evident concerning short wave developments within the westerlies, indicative of poor pattern predictability throughout the period. Even early in the period (Tue/Wed), there are substantial differences concerning a compact, but vigorous short wave impulse emerging from the Great Basin, which could potentially contribute to at least some risk for severe storms, from the immediate lee of the northern Rockies through the northern Plains and portions of the Upper Midwest. And uncertainties associated with these differences are compounded by the uncertain influence of a preceding wave, emanating from the lower latitudes, on low-level moisture and instability across this region. Read more

SPC 0730Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0230 AM CDT Sat Sep 14 2019 Valid 161200Z - 171200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS LATE MONDAY NIGHT ACROSS WESTERN UTAH AND ADJACENT PORTIONS OF THE GREAT BASIN... ...SUMMARY... Strong thunderstorms may impact western Utah and adjacent portions of the Great Basin late Monday night, perhaps accompanied by at least some risk for potentially damaging wind gusts. ...Discussion... Within the westerlies, models indicate substantive further amplification of mid-level ridging along an axis from the Upper Midwest into Hudson Bay during this period. As this occurs, downstream troughing is forecast to dig east-southeast of the Canadian Maritimes and north Atlantic coast, with an associated surface cold front advancing as far south as the Mid Atlantic Coast states and Ohio Valley by 12Z Tuesday. Within much weaker troughing off the south Atlantic coast, to the south of this feature, Humberto may intensify to hurricane strength, but is expected to be in the process of accelerating eastward away from the coast, through the western Atlantic. Meanwhile, as another significant short wave impulse digs southeast of the Gulf of Alaska, to the west of the British Columbia coast, initially amplified upper troughing near the Pacific coast is expected to increasingly split. One emerging short wave trough is forecast to accelerate across and northeast of the Canadian Rockies, while a more significant impulse to the south pivots inland of the Oregon and California coast, toward the northern Rockies. Strong forcing for ascent and wind fields/vertical shear associated with the trailing impulse may contribute to the best potential for any appreciable severe weather risk during this period. However, it appears that this probably will be tempered by drying over the Great Basin in the wake of a preceding short wave impulse, emerging from the lower latitudes ahead of the inland advancing troughing. Of most concern at the present time, at least some model output suggests that a return flow of monsoonal moisture could develop in a narrow plume, ahead the vigorous short wave and associated cold front, across western Utah by late Monday night. This could contribute to sufficient destabilization for the initiation of storms prior to 17/09-12Z, west of the Wasatch into the Great Salt Lake vicinity, where southwesterly flow in the 700-500 mb layer may strengthen to 40-70 kt. With relatively dry sub-cloud air contributing to evaporative cooling in downdrafts, downward mixing of higher momentum air may result in strong surface gusts. ..Kerr.. 09/14/2019 Read more

SPC 0730Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0230 AM CDT Sat Sep 14 2019 Valid 161200Z - 171200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS LATE MONDAY NIGHT ACROSS WESTERN UTAH AND ADJACENT PORTIONS OF THE GREAT BASIN... ...SUMMARY... Strong thunderstorms may impact western Utah and adjacent portions of the Great Basin late Monday night, perhaps accompanied by at least some risk for potentially damaging wind gusts. ...Discussion... Within the westerlies, models indicate substantive further amplification of mid-level ridging along an axis from the Upper Midwest into Hudson Bay during this period. As this occurs, downstream troughing is forecast to dig east-southeast of the Canadian Maritimes and north Atlantic coast, with an associated surface cold front advancing as far south as the Mid Atlantic Coast states and Ohio Valley by 12Z Tuesday. Within much weaker troughing off the south Atlantic coast, to the south of this feature, Humberto may intensify to hurricane strength, but is expected to be in the process of accelerating eastward away from the coast, through the western Atlantic. Meanwhile, as another significant short wave impulse digs southeast of the Gulf of Alaska, to the west of the British Columbia coast, initially amplified upper troughing near the Pacific coast is expected to increasingly split. One emerging short wave trough is forecast to accelerate across and northeast of the Canadian Rockies, while a more significant impulse to the south pivots inland of the Oregon and California coast, toward the northern Rockies. Strong forcing for ascent and wind fields/vertical shear associated with the trailing impulse may contribute to the best potential for any appreciable severe weather risk during this period. However, it appears that this probably will be tempered by drying over the Great Basin in the wake of a preceding short wave impulse, emerging from the lower latitudes ahead of the inland advancing troughing. Of most concern at the present time, at least some model output suggests that a return flow of monsoonal moisture could develop in a narrow plume, ahead the vigorous short wave and associated cold front, across western Utah by late Monday night. This could contribute to sufficient destabilization for the initiation of storms prior to 17/09-12Z, west of the Wasatch into the Great Salt Lake vicinity, where southwesterly flow in the 700-500 mb layer may strengthen to 40-70 kt. With relatively dry sub-cloud air contributing to evaporative cooling in downdrafts, downward mixing of higher momentum air may result in strong surface gusts. ..Kerr.. 09/14/2019 Read more

SPC 0730Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0230 AM CDT Sat Sep 14 2019 Valid 161200Z - 171200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS LATE MONDAY NIGHT ACROSS WESTERN UTAH AND ADJACENT PORTIONS OF THE GREAT BASIN... ...SUMMARY... Strong thunderstorms may impact western Utah and adjacent portions of the Great Basin late Monday night, perhaps accompanied by at least some risk for potentially damaging wind gusts. ...Discussion... Within the westerlies, models indicate substantive further amplification of mid-level ridging along an axis from the Upper Midwest into Hudson Bay during this period. As this occurs, downstream troughing is forecast to dig east-southeast of the Canadian Maritimes and north Atlantic coast, with an associated surface cold front advancing as far south as the Mid Atlantic Coast states and Ohio Valley by 12Z Tuesday. Within much weaker troughing off the south Atlantic coast, to the south of this feature, Humberto may intensify to hurricane strength, but is expected to be in the process of accelerating eastward away from the coast, through the western Atlantic. Meanwhile, as another significant short wave impulse digs southeast of the Gulf of Alaska, to the west of the British Columbia coast, initially amplified upper troughing near the Pacific coast is expected to increasingly split. One emerging short wave trough is forecast to accelerate across and northeast of the Canadian Rockies, while a more significant impulse to the south pivots inland of the Oregon and California coast, toward the northern Rockies. Strong forcing for ascent and wind fields/vertical shear associated with the trailing impulse may contribute to the best potential for any appreciable severe weather risk during this period. However, it appears that this probably will be tempered by drying over the Great Basin in the wake of a preceding short wave impulse, emerging from the lower latitudes ahead of the inland advancing troughing. Of most concern at the present time, at least some model output suggests that a return flow of monsoonal moisture could develop in a narrow plume, ahead the vigorous short wave and associated cold front, across western Utah by late Monday night. This could contribute to sufficient destabilization for the initiation of storms prior to 17/09-12Z, west of the Wasatch into the Great Salt Lake vicinity, where southwesterly flow in the 700-500 mb layer may strengthen to 40-70 kt. With relatively dry sub-cloud air contributing to evaporative cooling in downdrafts, downward mixing of higher momentum air may result in strong surface gusts. ..Kerr.. 09/14/2019 Read more

SPC Day 2 Fire Weather Outlook
Day 2 Fire Weather Outlook NWS Storm Prediction Center Norman OK 0100 AM CDT Sat Sep 14 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. Within this region, 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 region of potentially 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%. The onset of critical conditions in these areas may occur as early as late morning, with critical conditions potentially persisting into late Sunday night across the westernmost critical area. ..Dean.. 09/14/2019 ...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 0100 AM CDT Sat Sep 14 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. Within this region, 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 region of potentially 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%. The onset of critical conditions in these areas may occur as early as late morning, with critical conditions potentially persisting into late Sunday night across the westernmost critical area. ..Dean.. 09/14/2019 ...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 0100 AM CDT Sat Sep 14 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. Within this region, 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 region of potentially 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%. The onset of critical conditions in these areas may occur as early as late morning, with critical conditions potentially persisting into late Sunday night across the westernmost critical area. ..Dean.. 09/14/2019 ...Please see www.spc.noaa.gov/fire for graphic product... Read more