Severe Storms

SPC 1730Z Day 2 Outlook
Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1231 PM CDT Sun Sep 01 2019 Valid 021200Z - 031200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE DAKOTAS INTO WESTERN WISCONSIN... ...SUMMARY... Severe thunderstorms are expected over parts of the northern Plains and upper Mississippi Valley Monday through early Tuesday morning. Damaging winds and hail are likely. Isolated severe storms are possible across parts of southern New England and extending southward into northern Virginia. ...Synopsis... The upper ridge will flatten over the northern Rockies/High Plains as a powerful shortwave trough develops southeastward out of Canada. This wave will be located over MT during the day, and will accelerate southeastward across the Dakotas and MN Monday night. At the surface, low pressure will deepen as it moves from ND eastward toward Lake Superior, with a cold front moving from the western Dakotas Monday afternoon to the MS River by early Tuesday morning. Extending east of the low will be a warm front, which will lift north across ND and MN late in the day and overnight. Cooling aloft and southerly low-level winds will result in destabilization over the region, with large-scale lift resulting in a severe hail and wind threat. To the east, a shortwave trough will move across the Northeast, with moderate westerlies and cooling aloft. Southerly winds ahead of a cold front will result in destabilization and may support isolated severe storms, from northern VA into southern New England. ...Dakotas...Minnesota...Wisconsin... Early day storms are possible in the warm advection regime from northeastern MT into ND, with elevated storms producing hail. Lift aided by a strengthening low-level jet will persist throughout the day, with increasing elevated storm coverage from ND into northern MN. Although the boundary layer will be cool there, damaging winds may occur should the storms organize into a substantial MCS with hail-laden outflow. Otherwise, large, perhaps very large, hail is possible. Farther south, the stronger low-level lapse rates will develop over the far western Dakotas and Nebraska. There are questions regarding capping and potential storm coverage from central SD into southern MN and IA, however, there is a high conditional threat of severe hail and wind should storms materialize. The ECMWF model shows substantially more storms than the NAM, for example. Given these uncertainties, will maintain a broad 15% with potential significant hail or wind, but a corridor of higher probabilities may be added as predictability increases, most likely from ND into parts of MN. ...Northern VA into southern New England... Rain and storms are expected to be ongoing Monday morning over parts of NY and PA near a deepening surface trough and aided by low-level warm advection. This will play a role in where the greatest destabilization occurs should areas of outflow exist. In general, destabilization will occur ahead of the morning activity, with increasing storm trends into the afternoon toward New York City and across southern New England. Veering winds with height may even support a supercell or two, though low-level shear values will not be particularly strong. A brief/weak tornado cannot be ruled out, in addition to marginal hail. Farther south into VA and MD, strong heating ahead of the wind shift beneath good mid to upper flow will likely support isolated cells capable of hail. ...Florida East Coast... The center of Hurricane Dorian is currently forecast to remain offshore the east coast of Florida on Monday, including most of the outer convective bands. However, increasing low-level convergence within a moist air mass may allow for at least isolated, southwestward-moving cells late Monday into Tuesday morning generally east of Lake Okeechobee, with a gradual increase in low-level shear. The tornado threat appears too low at this time to introduce typical 5% tornado probabilities, but may increase with time depending on the track. ...MAXIMUM RISK BY HAZARD... Tornado: 5% - Slight Wind: 15% - Slight Hail: 15% SIG - Slight ..Jewell.. 09/01/2019 Read more

SPC 1730Z Day 2 Outlook
Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1231 PM CDT Sun Sep 01 2019 Valid 021200Z - 031200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE DAKOTAS INTO WESTERN WISCONSIN... ...SUMMARY... Severe thunderstorms are expected over parts of the northern Plains and upper Mississippi Valley Monday through early Tuesday morning. Damaging winds and hail are likely. Isolated severe storms are possible across parts of southern New England and extending southward into northern Virginia. ...Synopsis... The upper ridge will flatten over the northern Rockies/High Plains as a powerful shortwave trough develops southeastward out of Canada. This wave will be located over MT during the day, and will accelerate southeastward across the Dakotas and MN Monday night. At the surface, low pressure will deepen as it moves from ND eastward toward Lake Superior, with a cold front moving from the western Dakotas Monday afternoon to the MS River by early Tuesday morning. Extending east of the low will be a warm front, which will lift north across ND and MN late in the day and overnight. Cooling aloft and southerly low-level winds will result in destabilization over the region, with large-scale lift resulting in a severe hail and wind threat. To the east, a shortwave trough will move across the Northeast, with moderate westerlies and cooling aloft. Southerly winds ahead of a cold front will result in destabilization and may support isolated severe storms, from northern VA into southern New England. ...Dakotas...Minnesota...Wisconsin... Early day storms are possible in the warm advection regime from northeastern MT into ND, with elevated storms producing hail. Lift aided by a strengthening low-level jet will persist throughout the day, with increasing elevated storm coverage from ND into northern MN. Although the boundary layer will be cool there, damaging winds may occur should the storms organize into a substantial MCS with hail-laden outflow. Otherwise, large, perhaps very large, hail is possible. Farther south, the stronger low-level lapse rates will develop over the far western Dakotas and Nebraska. There are questions regarding capping and potential storm coverage from central SD into southern MN and IA, however, there is a high conditional threat of severe hail and wind should storms materialize. The ECMWF model shows substantially more storms than the NAM, for example. Given these uncertainties, will maintain a broad 15% with potential significant hail or wind, but a corridor of higher probabilities may be added as predictability increases, most likely from ND into parts of MN. ...Northern VA into southern New England... Rain and storms are expected to be ongoing Monday morning over parts of NY and PA near a deepening surface trough and aided by low-level warm advection. This will play a role in where the greatest destabilization occurs should areas of outflow exist. In general, destabilization will occur ahead of the morning activity, with increasing storm trends into the afternoon toward New York City and across southern New England. Veering winds with height may even support a supercell or two, though low-level shear values will not be particularly strong. A brief/weak tornado cannot be ruled out, in addition to marginal hail. Farther south into VA and MD, strong heating ahead of the wind shift beneath good mid to upper flow will likely support isolated cells capable of hail. ...Florida East Coast... The center of Hurricane Dorian is currently forecast to remain offshore the east coast of Florida on Monday, including most of the outer convective bands. However, increasing low-level convergence within a moist air mass may allow for at least isolated, southwestward-moving cells late Monday into Tuesday morning generally east of Lake Okeechobee, with a gradual increase in low-level shear. The tornado threat appears too low at this time to introduce typical 5% tornado probabilities, but may increase with time depending on the track. ...MAXIMUM RISK BY HAZARD... Tornado: 5% - Slight Wind: 15% - Slight Hail: 15% SIG - Slight ..Jewell.. 09/01/2019 Read more

SPC 1730Z Day 2 Outlook
Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1231 PM CDT Sun Sep 01 2019 Valid 021200Z - 031200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE DAKOTAS INTO WESTERN WISCONSIN... ...SUMMARY... Severe thunderstorms are expected over parts of the northern Plains and upper Mississippi Valley Monday through early Tuesday morning. Damaging winds and hail are likely. Isolated severe storms are possible across parts of southern New England and extending southward into northern Virginia. ...Synopsis... The upper ridge will flatten over the northern Rockies/High Plains as a powerful shortwave trough develops southeastward out of Canada. This wave will be located over MT during the day, and will accelerate southeastward across the Dakotas and MN Monday night. At the surface, low pressure will deepen as it moves from ND eastward toward Lake Superior, with a cold front moving from the western Dakotas Monday afternoon to the MS River by early Tuesday morning. Extending east of the low will be a warm front, which will lift north across ND and MN late in the day and overnight. Cooling aloft and southerly low-level winds will result in destabilization over the region, with large-scale lift resulting in a severe hail and wind threat. To the east, a shortwave trough will move across the Northeast, with moderate westerlies and cooling aloft. Southerly winds ahead of a cold front will result in destabilization and may support isolated severe storms, from northern VA into southern New England. ...Dakotas...Minnesota...Wisconsin... Early day storms are possible in the warm advection regime from northeastern MT into ND, with elevated storms producing hail. Lift aided by a strengthening low-level jet will persist throughout the day, with increasing elevated storm coverage from ND into northern MN. Although the boundary layer will be cool there, damaging winds may occur should the storms organize into a substantial MCS with hail-laden outflow. Otherwise, large, perhaps very large, hail is possible. Farther south, the stronger low-level lapse rates will develop over the far western Dakotas and Nebraska. There are questions regarding capping and potential storm coverage from central SD into southern MN and IA, however, there is a high conditional threat of severe hail and wind should storms materialize. The ECMWF model shows substantially more storms than the NAM, for example. Given these uncertainties, will maintain a broad 15% with potential significant hail or wind, but a corridor of higher probabilities may be added as predictability increases, most likely from ND into parts of MN. ...Northern VA into southern New England... Rain and storms are expected to be ongoing Monday morning over parts of NY and PA near a deepening surface trough and aided by low-level warm advection. This will play a role in where the greatest destabilization occurs should areas of outflow exist. In general, destabilization will occur ahead of the morning activity, with increasing storm trends into the afternoon toward New York City and across southern New England. Veering winds with height may even support a supercell or two, though low-level shear values will not be particularly strong. A brief/weak tornado cannot be ruled out, in addition to marginal hail. Farther south into VA and MD, strong heating ahead of the wind shift beneath good mid to upper flow will likely support isolated cells capable of hail. ...Florida East Coast... The center of Hurricane Dorian is currently forecast to remain offshore the east coast of Florida on Monday, including most of the outer convective bands. However, increasing low-level convergence within a moist air mass may allow for at least isolated, southwestward-moving cells late Monday into Tuesday morning generally east of Lake Okeechobee, with a gradual increase in low-level shear. The tornado threat appears too low at this time to introduce typical 5% tornado probabilities, but may increase with time depending on the track. ...MAXIMUM RISK BY HAZARD... Tornado: 5% - Slight Wind: 15% - Slight Hail: 15% SIG - Slight ..Jewell.. 09/01/2019 Read more

SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1131 AM CDT Sun Sep 01 2019 Valid 011630Z - 021200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS CENTRAL AND SOUTHERN ARIZONA... ...SUMMARY... Scattered severe wind gusts are possible across parts of central and southern Arizona during the late afternoon and evening, with other severe storms possible across the northern High Plains and Ohio Valley. ...Central/southern Arizona... The mid/upper-level ridge will remain centered over the Four Corners area through tonight, with a belt of moderately strong easterly mid-level winds on its immediate southern periphery as sampled by 12Z observed soundings from Phoenix/Tucson. Orographic lift will be the primary driver of isolated to widely scattered thunderstorms by early afternoon across the higher terrain of western New Mexico into central/eastern Arizona. With a belt of 15-25 kt easterlies across the southern half of Arizona, this convection will spread westward over the lower deserts during the late afternoon and evening. Surface dew points should mix into the upper 50s to mid 60s at peak heating across the Lower Colorado and Gila Valleys, yielding at least moderate buoyancy with MLCAPE above 1000 J/kg. One or two clusters may organize off the terrain with a risk for scattered severe-caliber wind gusts, with at least a couple of these storms likely to reach the Lower Colorado River Valley. ...Ohio Valley... A convectively influenced shortwave trough centered over central Indiana at late morning will continue east-northeastward toward the Upper Ohio Valley and western portions of Pennsylvania/New York. Modest ascent ahead of this feature will continue to influence thunderstorm development across the region, with some increase in coverage/intensity this afternoon as MLCAPE reaches 1000-1500 J/kg. The primary risks from multicell clusters should be isolated strong gusts and marginally severe hail. However, guidance is fairly consistent in strengthening low-level winds early this evening from the Upper Ohio Valley to northern Appalachians. A small temporal window may exist for a supercell-related brief tornado risk near the Ohio/Pennsylvania/West Virginia border area as low-level hodographs enlarge prior to surface-based instability decreasing with eastern extent in Pennsylvania. ...Northern High Plains including Montana to Nebraska... No changes warranted for the region. A mid-level ridge will remain prominent across much of the northern Great Plains through the period, although some flattening is anticipated towards 12Z/Monday as a vigorous shortwave trough amplifies over the Canadian Rockies. Isolated thunderstorms may develop along the lee trough from north-central Montana to the Nebraska/Colorado border area. Buoyancy will be weak to the northwest but may be compensated by plentiful mid to upper-level speed shear. A couple cells with mid-level updraft rotation may form but will likely struggle to be sustained eastward given pronounced MLCIN east of the trough. Have expanded/combined the MRGL risk areas to account for this scenario. Otherwise, an arc of 700-mb warm theta-e advection should yield isolated to perhaps scattered elevated thunderstorms overnight across eastern Montana and the Dakotas into Nebraska. Strongest speed shear will be across the northern portion of the region, with MUCAPE increasing as richer 850-mb moisture advects north. It is unclear whether uncapped parcels can become rooted beneath 700-mb prior to 12Z. For now, will maintain MRGL risk, mainly for the potential of isolated severe hail. ..Guyer/Nauslar.. 09/01/2019 Read more

SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1131 AM CDT Sun Sep 01 2019 Valid 011630Z - 021200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS CENTRAL AND SOUTHERN ARIZONA... ...SUMMARY... Scattered severe wind gusts are possible across parts of central and southern Arizona during the late afternoon and evening, with other severe storms possible across the northern High Plains and Ohio Valley. ...Central/southern Arizona... The mid/upper-level ridge will remain centered over the Four Corners area through tonight, with a belt of moderately strong easterly mid-level winds on its immediate southern periphery as sampled by 12Z observed soundings from Phoenix/Tucson. Orographic lift will be the primary driver of isolated to widely scattered thunderstorms by early afternoon across the higher terrain of western New Mexico into central/eastern Arizona. With a belt of 15-25 kt easterlies across the southern half of Arizona, this convection will spread westward over the lower deserts during the late afternoon and evening. Surface dew points should mix into the upper 50s to mid 60s at peak heating across the Lower Colorado and Gila Valleys, yielding at least moderate buoyancy with MLCAPE above 1000 J/kg. One or two clusters may organize off the terrain with a risk for scattered severe-caliber wind gusts, with at least a couple of these storms likely to reach the Lower Colorado River Valley. ...Ohio Valley... A convectively influenced shortwave trough centered over central Indiana at late morning will continue east-northeastward toward the Upper Ohio Valley and western portions of Pennsylvania/New York. Modest ascent ahead of this feature will continue to influence thunderstorm development across the region, with some increase in coverage/intensity this afternoon as MLCAPE reaches 1000-1500 J/kg. The primary risks from multicell clusters should be isolated strong gusts and marginally severe hail. However, guidance is fairly consistent in strengthening low-level winds early this evening from the Upper Ohio Valley to northern Appalachians. A small temporal window may exist for a supercell-related brief tornado risk near the Ohio/Pennsylvania/West Virginia border area as low-level hodographs enlarge prior to surface-based instability decreasing with eastern extent in Pennsylvania. ...Northern High Plains including Montana to Nebraska... No changes warranted for the region. A mid-level ridge will remain prominent across much of the northern Great Plains through the period, although some flattening is anticipated towards 12Z/Monday as a vigorous shortwave trough amplifies over the Canadian Rockies. Isolated thunderstorms may develop along the lee trough from north-central Montana to the Nebraska/Colorado border area. Buoyancy will be weak to the northwest but may be compensated by plentiful mid to upper-level speed shear. A couple cells with mid-level updraft rotation may form but will likely struggle to be sustained eastward given pronounced MLCIN east of the trough. Have expanded/combined the MRGL risk areas to account for this scenario. Otherwise, an arc of 700-mb warm theta-e advection should yield isolated to perhaps scattered elevated thunderstorms overnight across eastern Montana and the Dakotas into Nebraska. Strongest speed shear will be across the northern portion of the region, with MUCAPE increasing as richer 850-mb moisture advects north. It is unclear whether uncapped parcels can become rooted beneath 700-mb prior to 12Z. For now, will maintain MRGL risk, mainly for the potential of isolated severe hail. ..Guyer/Nauslar.. 09/01/2019 Read more

SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1131 AM CDT Sun Sep 01 2019 Valid 011630Z - 021200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS CENTRAL AND SOUTHERN ARIZONA... ...SUMMARY... Scattered severe wind gusts are possible across parts of central and southern Arizona during the late afternoon and evening, with other severe storms possible across the northern High Plains and Ohio Valley. ...Central/southern Arizona... The mid/upper-level ridge will remain centered over the Four Corners area through tonight, with a belt of moderately strong easterly mid-level winds on its immediate southern periphery as sampled by 12Z observed soundings from Phoenix/Tucson. Orographic lift will be the primary driver of isolated to widely scattered thunderstorms by early afternoon across the higher terrain of western New Mexico into central/eastern Arizona. With a belt of 15-25 kt easterlies across the southern half of Arizona, this convection will spread westward over the lower deserts during the late afternoon and evening. Surface dew points should mix into the upper 50s to mid 60s at peak heating across the Lower Colorado and Gila Valleys, yielding at least moderate buoyancy with MLCAPE above 1000 J/kg. One or two clusters may organize off the terrain with a risk for scattered severe-caliber wind gusts, with at least a couple of these storms likely to reach the Lower Colorado River Valley. ...Ohio Valley... A convectively influenced shortwave trough centered over central Indiana at late morning will continue east-northeastward toward the Upper Ohio Valley and western portions of Pennsylvania/New York. Modest ascent ahead of this feature will continue to influence thunderstorm development across the region, with some increase in coverage/intensity this afternoon as MLCAPE reaches 1000-1500 J/kg. The primary risks from multicell clusters should be isolated strong gusts and marginally severe hail. However, guidance is fairly consistent in strengthening low-level winds early this evening from the Upper Ohio Valley to northern Appalachians. A small temporal window may exist for a supercell-related brief tornado risk near the Ohio/Pennsylvania/West Virginia border area as low-level hodographs enlarge prior to surface-based instability decreasing with eastern extent in Pennsylvania. ...Northern High Plains including Montana to Nebraska... No changes warranted for the region. A mid-level ridge will remain prominent across much of the northern Great Plains through the period, although some flattening is anticipated towards 12Z/Monday as a vigorous shortwave trough amplifies over the Canadian Rockies. Isolated thunderstorms may develop along the lee trough from north-central Montana to the Nebraska/Colorado border area. Buoyancy will be weak to the northwest but may be compensated by plentiful mid to upper-level speed shear. A couple cells with mid-level updraft rotation may form but will likely struggle to be sustained eastward given pronounced MLCIN east of the trough. Have expanded/combined the MRGL risk areas to account for this scenario. Otherwise, an arc of 700-mb warm theta-e advection should yield isolated to perhaps scattered elevated thunderstorms overnight across eastern Montana and the Dakotas into Nebraska. Strongest speed shear will be across the northern portion of the region, with MUCAPE increasing as richer 850-mb moisture advects north. It is unclear whether uncapped parcels can become rooted beneath 700-mb prior to 12Z. For now, will maintain MRGL risk, mainly for the potential of isolated severe hail. ..Guyer/Nauslar.. 09/01/2019 Read more

SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1131 AM CDT Sun Sep 01 2019 Valid 011630Z - 021200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS CENTRAL AND SOUTHERN ARIZONA... ...SUMMARY... Scattered severe wind gusts are possible across parts of central and southern Arizona during the late afternoon and evening, with other severe storms possible across the northern High Plains and Ohio Valley. ...Central/southern Arizona... The mid/upper-level ridge will remain centered over the Four Corners area through tonight, with a belt of moderately strong easterly mid-level winds on its immediate southern periphery as sampled by 12Z observed soundings from Phoenix/Tucson. Orographic lift will be the primary driver of isolated to widely scattered thunderstorms by early afternoon across the higher terrain of western New Mexico into central/eastern Arizona. With a belt of 15-25 kt easterlies across the southern half of Arizona, this convection will spread westward over the lower deserts during the late afternoon and evening. Surface dew points should mix into the upper 50s to mid 60s at peak heating across the Lower Colorado and Gila Valleys, yielding at least moderate buoyancy with MLCAPE above 1000 J/kg. One or two clusters may organize off the terrain with a risk for scattered severe-caliber wind gusts, with at least a couple of these storms likely to reach the Lower Colorado River Valley. ...Ohio Valley... A convectively influenced shortwave trough centered over central Indiana at late morning will continue east-northeastward toward the Upper Ohio Valley and western portions of Pennsylvania/New York. Modest ascent ahead of this feature will continue to influence thunderstorm development across the region, with some increase in coverage/intensity this afternoon as MLCAPE reaches 1000-1500 J/kg. The primary risks from multicell clusters should be isolated strong gusts and marginally severe hail. However, guidance is fairly consistent in strengthening low-level winds early this evening from the Upper Ohio Valley to northern Appalachians. A small temporal window may exist for a supercell-related brief tornado risk near the Ohio/Pennsylvania/West Virginia border area as low-level hodographs enlarge prior to surface-based instability decreasing with eastern extent in Pennsylvania. ...Northern High Plains including Montana to Nebraska... No changes warranted for the region. A mid-level ridge will remain prominent across much of the northern Great Plains through the period, although some flattening is anticipated towards 12Z/Monday as a vigorous shortwave trough amplifies over the Canadian Rockies. Isolated thunderstorms may develop along the lee trough from north-central Montana to the Nebraska/Colorado border area. Buoyancy will be weak to the northwest but may be compensated by plentiful mid to upper-level speed shear. A couple cells with mid-level updraft rotation may form but will likely struggle to be sustained eastward given pronounced MLCIN east of the trough. Have expanded/combined the MRGL risk areas to account for this scenario. Otherwise, an arc of 700-mb warm theta-e advection should yield isolated to perhaps scattered elevated thunderstorms overnight across eastern Montana and the Dakotas into Nebraska. Strongest speed shear will be across the northern portion of the region, with MUCAPE increasing as richer 850-mb moisture advects north. It is unclear whether uncapped parcels can become rooted beneath 700-mb prior to 12Z. For now, will maintain MRGL risk, mainly for the potential of isolated severe hail. ..Guyer/Nauslar.. 09/01/2019 Read more

SPC Day 1 Fire Weather Outlook
Day 1 Fire Weather Outlook NWS Storm Prediction Center Norman OK 1049 AM CDT Sun Sep 01 2019 Valid 011700Z - 021200Z The current forecast remains on track, with only minimal changes needed with this forecast update to reflect observations and the latest model guidance. While a few HREFv2 members suggest at least some potential for elevated fire weather conditions this afternoon across portions of far north-central Colorado, recent precipitation (>0.5" over past 48 hours according to AHPS) and brief/spotty nature of any elevated meteorological conditions preclude expanding the elevated fire weather area into Colorado. Please see discussion below for more information on today's fire weather threat. ..Elliott.. 09/01/2019 .PREV DISCUSSION... /ISSUED 1241 AM CDT Sun Sep 01 2019/ ...Synopsis... An upper-level ridge will prevail across the western CONUS throughout the day, with an intensifying mid-level impulse beginning to crest the ridge, across the Pacific Northwest/northern Rockies regions by the end of the period. The resultant strengthening flow aloft by peak heating may be transported downward via a deep, mixed boundary layer, promoting dry and breezy conditions which may foster some threat for wildfire-spread. ...Northern Great Basin into the central Rockies... Downslope flow and boundary layer mixing of the winds aloft will result in 15-20 mph sustained west-southwesterly surface winds and 10-20% RH, from parts of the Snake River Plain into the Great Divide Basin. An elevated area has been maintained for regions where the aforementioned breezy, dry surface conditions are expected to persist for several hours during the afternoon. Fuels across this area are also quite supportive of wildfire-spread potential. Farther west-southwest into parts of the Great Basin, at least localized to briefly widespread elevated conditions may be observed, but the patchy or brief nature of such conditions precludes a delineation at this time. ...Central into southern Colorado and far northwest New Mexico... A couple of thunderstorms may initiate atop the higher terrain of the Rocky Mountains across parts of central Colorado into Northwest New Mexico during the afternoon hours. These storms may be high-based in nature, with a couple of dry strikes possible, and where fuels are marginally to modestly receptive to fire spread. The very sparse nature of dry strikes renders an isolated dry thunderstorm delineation unwarranted at this time. ...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 Sun Sep 01 2019 Valid 011700Z - 021200Z The current forecast remains on track, with only minimal changes needed with this forecast update to reflect observations and the latest model guidance. While a few HREFv2 members suggest at least some potential for elevated fire weather conditions this afternoon across portions of far north-central Colorado, recent precipitation (>0.5" over past 48 hours according to AHPS) and brief/spotty nature of any elevated meteorological conditions preclude expanding the elevated fire weather area into Colorado. Please see discussion below for more information on today's fire weather threat. ..Elliott.. 09/01/2019 .PREV DISCUSSION... /ISSUED 1241 AM CDT Sun Sep 01 2019/ ...Synopsis... An upper-level ridge will prevail across the western CONUS throughout the day, with an intensifying mid-level impulse beginning to crest the ridge, across the Pacific Northwest/northern Rockies regions by the end of the period. The resultant strengthening flow aloft by peak heating may be transported downward via a deep, mixed boundary layer, promoting dry and breezy conditions which may foster some threat for wildfire-spread. ...Northern Great Basin into the central Rockies... Downslope flow and boundary layer mixing of the winds aloft will result in 15-20 mph sustained west-southwesterly surface winds and 10-20% RH, from parts of the Snake River Plain into the Great Divide Basin. An elevated area has been maintained for regions where the aforementioned breezy, dry surface conditions are expected to persist for several hours during the afternoon. Fuels across this area are also quite supportive of wildfire-spread potential. Farther west-southwest into parts of the Great Basin, at least localized to briefly widespread elevated conditions may be observed, but the patchy or brief nature of such conditions precludes a delineation at this time. ...Central into southern Colorado and far northwest New Mexico... A couple of thunderstorms may initiate atop the higher terrain of the Rocky Mountains across parts of central Colorado into Northwest New Mexico during the afternoon hours. These storms may be high-based in nature, with a couple of dry strikes possible, and where fuels are marginally to modestly receptive to fire spread. The very sparse nature of dry strikes renders an isolated dry thunderstorm delineation unwarranted at this time. ...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 Sun Sep 01 2019 Valid 011700Z - 021200Z The current forecast remains on track, with only minimal changes needed with this forecast update to reflect observations and the latest model guidance. While a few HREFv2 members suggest at least some potential for elevated fire weather conditions this afternoon across portions of far north-central Colorado, recent precipitation (>0.5" over past 48 hours according to AHPS) and brief/spotty nature of any elevated meteorological conditions preclude expanding the elevated fire weather area into Colorado. Please see discussion below for more information on today's fire weather threat. ..Elliott.. 09/01/2019 .PREV DISCUSSION... /ISSUED 1241 AM CDT Sun Sep 01 2019/ ...Synopsis... An upper-level ridge will prevail across the western CONUS throughout the day, with an intensifying mid-level impulse beginning to crest the ridge, across the Pacific Northwest/northern Rockies regions by the end of the period. The resultant strengthening flow aloft by peak heating may be transported downward via a deep, mixed boundary layer, promoting dry and breezy conditions which may foster some threat for wildfire-spread. ...Northern Great Basin into the central Rockies... Downslope flow and boundary layer mixing of the winds aloft will result in 15-20 mph sustained west-southwesterly surface winds and 10-20% RH, from parts of the Snake River Plain into the Great Divide Basin. An elevated area has been maintained for regions where the aforementioned breezy, dry surface conditions are expected to persist for several hours during the afternoon. Fuels across this area are also quite supportive of wildfire-spread potential. Farther west-southwest into parts of the Great Basin, at least localized to briefly widespread elevated conditions may be observed, but the patchy or brief nature of such conditions precludes a delineation at this time. ...Central into southern Colorado and far northwest New Mexico... A couple of thunderstorms may initiate atop the higher terrain of the Rocky Mountains across parts of central Colorado into Northwest New Mexico during the afternoon hours. These storms may be high-based in nature, with a couple of dry strikes possible, and where fuels are marginally to modestly receptive to fire spread. The very sparse nature of dry strikes renders an isolated dry thunderstorm delineation unwarranted at this time. ...Please see www.spc.noaa.gov/fire for graphic product... Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0750 AM CDT Sun Sep 01 2019 Valid 011300Z - 021200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS CENTRAL AND SOUTHERN AZ... ...SUMMARY... Scattered severe wind gusts are possible across parts of central and southern Arizona during the late afternoon and evening. ...Central/southern Arizona... A stout mid-level anticyclone will remain centered over the Four Corners area. Orographic lift will be the primary driver of isolated to widely scattered thunderstorms by early afternoon across the higher terrain of western NM into eastern AZ. With a belt of 15-25 kt easterlies across the southern half of AZ, this convection will spread west over the lower deserts during the late afternoon and evening. Surface dew points should mix into the upper 50s to mid 60s at peak heating across the Lower Colorado and Gila Valleys, yielding at least moderate buoyancy with MLCAPE above 1000 J/kg. One or two clusters may organize off the terrain with a risk for scattered severe wind gusts until convection weakens overnight amid increasingly substantial MLCIN in the Mojave Desert. ...OH Valley... Within broadly cyclonic flow over eastern Canada and the Great Lakes, a minor shortwave impulse will eject east from IL towards PA/NY. Modest ascent ahead of this feature has encouraged a couple thunderstorm clusters from central IL to Lower MI and over the Upper OH Valley. This activity should remain weak through midday, but will likely increase in coverage and intensity this afternoon as MLCAPE reaches 1000-1500 J/kg across parts of IN/OH ahead of the IL cluster. The primary risks from multicell clusters should be isolated strong gusts and marginally severe hail. However, guidance is fairly consistent in strengthening low-level winds this evening from the Upper OH Valley to northern Appalachians. A small temporal window should exist for a brief tornado risk near the OH/PA/WV border area as low-level hodographs enlarge prior to surface-based instability decreasing with eastern extent in PA. ...MT to NE... A mid-level ridge will remain prominent across much of the northern Great Plains through the period, although some flattening is anticipated towards 12Z/Monday as a vigorous shortwave trough amplifies over the Canadian Rockies. Considerable uncertainty remains regarding possible convective initiation during the late afternoon and early evening. Isolated thunderstorms may develop along the lee trough from north-central MT to the NE/CO border area. Buoyancy will be weak to the northwest but may be compensated by plentiful mid to upper-level speed shear. A couple cells with mid-level updraft rotation may form but will likely struggle to be sustained eastward given pronounced MLCIN east of the trough. Have expanded/combined the MRGL risk areas to account for this scenario. Otherwise, an arc of 700-mb warm theta-e advection should yield isolated to perhaps scattered elevated thunderstorms overnight across eastern MT and the Dakotas into NE. Strongest speed shear will be across the northern portion of the region, with MUCAPE increasing as richer 850-mb moisture advects north. It is unclear whether uncapped parcels can become rooted beneath 700-mb prior to 12Z. For now, will maintain MRGL risk, mainly for the potential of isolated severe hail. ..Grams/Leitman.. 09/01/2019 Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0750 AM CDT Sun Sep 01 2019 Valid 011300Z - 021200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS CENTRAL AND SOUTHERN AZ... ...SUMMARY... Scattered severe wind gusts are possible across parts of central and southern Arizona during the late afternoon and evening. ...Central/southern Arizona... A stout mid-level anticyclone will remain centered over the Four Corners area. Orographic lift will be the primary driver of isolated to widely scattered thunderstorms by early afternoon across the higher terrain of western NM into eastern AZ. With a belt of 15-25 kt easterlies across the southern half of AZ, this convection will spread west over the lower deserts during the late afternoon and evening. Surface dew points should mix into the upper 50s to mid 60s at peak heating across the Lower Colorado and Gila Valleys, yielding at least moderate buoyancy with MLCAPE above 1000 J/kg. One or two clusters may organize off the terrain with a risk for scattered severe wind gusts until convection weakens overnight amid increasingly substantial MLCIN in the Mojave Desert. ...OH Valley... Within broadly cyclonic flow over eastern Canada and the Great Lakes, a minor shortwave impulse will eject east from IL towards PA/NY. Modest ascent ahead of this feature has encouraged a couple thunderstorm clusters from central IL to Lower MI and over the Upper OH Valley. This activity should remain weak through midday, but will likely increase in coverage and intensity this afternoon as MLCAPE reaches 1000-1500 J/kg across parts of IN/OH ahead of the IL cluster. The primary risks from multicell clusters should be isolated strong gusts and marginally severe hail. However, guidance is fairly consistent in strengthening low-level winds this evening from the Upper OH Valley to northern Appalachians. A small temporal window should exist for a brief tornado risk near the OH/PA/WV border area as low-level hodographs enlarge prior to surface-based instability decreasing with eastern extent in PA. ...MT to NE... A mid-level ridge will remain prominent across much of the northern Great Plains through the period, although some flattening is anticipated towards 12Z/Monday as a vigorous shortwave trough amplifies over the Canadian Rockies. Considerable uncertainty remains regarding possible convective initiation during the late afternoon and early evening. Isolated thunderstorms may develop along the lee trough from north-central MT to the NE/CO border area. Buoyancy will be weak to the northwest but may be compensated by plentiful mid to upper-level speed shear. A couple cells with mid-level updraft rotation may form but will likely struggle to be sustained eastward given pronounced MLCIN east of the trough. Have expanded/combined the MRGL risk areas to account for this scenario. Otherwise, an arc of 700-mb warm theta-e advection should yield isolated to perhaps scattered elevated thunderstorms overnight across eastern MT and the Dakotas into NE. Strongest speed shear will be across the northern portion of the region, with MUCAPE increasing as richer 850-mb moisture advects north. It is unclear whether uncapped parcels can become rooted beneath 700-mb prior to 12Z. For now, will maintain MRGL risk, mainly for the potential of isolated severe hail. ..Grams/Leitman.. 09/01/2019 Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0750 AM CDT Sun Sep 01 2019 Valid 011300Z - 021200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS CENTRAL AND SOUTHERN AZ... ...SUMMARY... Scattered severe wind gusts are possible across parts of central and southern Arizona during the late afternoon and evening. ...Central/southern Arizona... A stout mid-level anticyclone will remain centered over the Four Corners area. Orographic lift will be the primary driver of isolated to widely scattered thunderstorms by early afternoon across the higher terrain of western NM into eastern AZ. With a belt of 15-25 kt easterlies across the southern half of AZ, this convection will spread west over the lower deserts during the late afternoon and evening. Surface dew points should mix into the upper 50s to mid 60s at peak heating across the Lower Colorado and Gila Valleys, yielding at least moderate buoyancy with MLCAPE above 1000 J/kg. One or two clusters may organize off the terrain with a risk for scattered severe wind gusts until convection weakens overnight amid increasingly substantial MLCIN in the Mojave Desert. ...OH Valley... Within broadly cyclonic flow over eastern Canada and the Great Lakes, a minor shortwave impulse will eject east from IL towards PA/NY. Modest ascent ahead of this feature has encouraged a couple thunderstorm clusters from central IL to Lower MI and over the Upper OH Valley. This activity should remain weak through midday, but will likely increase in coverage and intensity this afternoon as MLCAPE reaches 1000-1500 J/kg across parts of IN/OH ahead of the IL cluster. The primary risks from multicell clusters should be isolated strong gusts and marginally severe hail. However, guidance is fairly consistent in strengthening low-level winds this evening from the Upper OH Valley to northern Appalachians. A small temporal window should exist for a brief tornado risk near the OH/PA/WV border area as low-level hodographs enlarge prior to surface-based instability decreasing with eastern extent in PA. ...MT to NE... A mid-level ridge will remain prominent across much of the northern Great Plains through the period, although some flattening is anticipated towards 12Z/Monday as a vigorous shortwave trough amplifies over the Canadian Rockies. Considerable uncertainty remains regarding possible convective initiation during the late afternoon and early evening. Isolated thunderstorms may develop along the lee trough from north-central MT to the NE/CO border area. Buoyancy will be weak to the northwest but may be compensated by plentiful mid to upper-level speed shear. A couple cells with mid-level updraft rotation may form but will likely struggle to be sustained eastward given pronounced MLCIN east of the trough. Have expanded/combined the MRGL risk areas to account for this scenario. Otherwise, an arc of 700-mb warm theta-e advection should yield isolated to perhaps scattered elevated thunderstorms overnight across eastern MT and the Dakotas into NE. Strongest speed shear will be across the northern portion of the region, with MUCAPE increasing as richer 850-mb moisture advects north. It is unclear whether uncapped parcels can become rooted beneath 700-mb prior to 12Z. For now, will maintain MRGL risk, mainly for the potential of isolated severe hail. ..Grams/Leitman.. 09/01/2019 Read more

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0325 AM CDT Sun Sep 01 2019 Valid 041200Z - 091200Z ...DISCUSSION... The extended period will feature a mid-level anticyclone centered over the southern High Plains through the first half before model show this feature weakening by next weekend. A cold front is forecast to move through the Northeast on Wednesday (day 4) with the southwest portion of this boundary becoming nebulous over the south-central U.S. A drier airmass in its wake will tend to limit the magnitude of destabilization later in the week near westerlies over the north-central states. Severe potential seems largely dependent on the eventual track of Hurricane Dorian. Based on National Hurricane Center forecast guidance, it is possible a tornado risk could develop during the early half of the extended period over the coastal Carolinas. However, large uncertainty in this scenario precludes introducing a risk area. Read more

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0325 AM CDT Sun Sep 01 2019 Valid 041200Z - 091200Z ...DISCUSSION... The extended period will feature a mid-level anticyclone centered over the southern High Plains through the first half before model show this feature weakening by next weekend. A cold front is forecast to move through the Northeast on Wednesday (day 4) with the southwest portion of this boundary becoming nebulous over the south-central U.S. A drier airmass in its wake will tend to limit the magnitude of destabilization later in the week near westerlies over the north-central states. Severe potential seems largely dependent on the eventual track of Hurricane Dorian. Based on National Hurricane Center forecast guidance, it is possible a tornado risk could develop during the early half of the extended period over the coastal Carolinas. However, large uncertainty in this scenario precludes introducing a risk area. Read more

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0325 AM CDT Sun Sep 01 2019 Valid 041200Z - 091200Z ...DISCUSSION... The extended period will feature a mid-level anticyclone centered over the southern High Plains through the first half before model show this feature weakening by next weekend. A cold front is forecast to move through the Northeast on Wednesday (day 4) with the southwest portion of this boundary becoming nebulous over the south-central U.S. A drier airmass in its wake will tend to limit the magnitude of destabilization later in the week near westerlies over the north-central states. Severe potential seems largely dependent on the eventual track of Hurricane Dorian. Based on National Hurricane Center forecast guidance, it is possible a tornado risk could develop during the early half of the extended period over the coastal Carolinas. However, large uncertainty in this scenario precludes introducing a risk area. Read more

SPC 0730Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0213 AM CDT Sun Sep 01 2019 Valid 031200Z - 041200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FOR NORTHERN ILLINOIS...EASTERN WISCONSIN...AND PARTS OF LOWER MICHIGAN... ...SUMMARY... Severe thunderstorms are possible across the western and central Great Lakes on Tuesday. ...Synopsis... A mid-level trough and associated speed max will move from the Upper Midwest eastward across the Great Lakes and into southeastern Canada on Tuesday into Tuesday night. A mid-level anticyclone will remain situated over the Four Corners while Hurricane Dorian slowly approaches the Southeast United States. In the low levels, a cold front is forecast to move southeast across the Midwest and into the lower Great Lakes. ...Great Lakes... Ongoing storms are likely in the morning across the Upper Midwest as a southwesterly LLJ and warm advection regime promote moisture transport and ascent in portions of MN/WI and the western U.P. of MI. A severe risk may accompany this activity mainly in the form of isolated damaging gusts. The northeastern extent of an elevated mixed layer with associated capping will probably overspread parts of the middle MS Valley during the day. Isolated diurnal storms are possible along the front with a hail/wind risk. Farther northeast, the magnitude of destabilization is highly dependent on the convective evolution of a possible MCS moving through the western Great Lakes during the morning. Wind fields will likely strengthen across the destabilizing warm sector during the day which will favor organized storm structures including the possibility for supercells and bowing segments. Refinements in severe probabilities will likely be needed due to mesoscale dependencies influencing the severe thunderstorm outlook. ...FL Peninsula (Hurricane Dorian)... Uncertainty remains regarding the eventual track of Hurricane Dorian as it moves into the Gulf Stream waters east of the FL Peninsula Monday night into Tuesday morning. If the northeast quadrant were to overspread the FL Peninsula on Tuesday and/or Tuesday night, then a risk for potential tornadoes would include those areas. At this time, uncertainty is too high to include low-severe probabilities. Please refer to the National Hurricane Center for the latest guidance regarding the forecast track of Hurricane Dorian. ..Smith.. 09/01/2019 Read more

SPC 0730Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0213 AM CDT Sun Sep 01 2019 Valid 031200Z - 041200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FOR NORTHERN ILLINOIS...EASTERN WISCONSIN...AND PARTS OF LOWER MICHIGAN... ...SUMMARY... Severe thunderstorms are possible across the western and central Great Lakes on Tuesday. ...Synopsis... A mid-level trough and associated speed max will move from the Upper Midwest eastward across the Great Lakes and into southeastern Canada on Tuesday into Tuesday night. A mid-level anticyclone will remain situated over the Four Corners while Hurricane Dorian slowly approaches the Southeast United States. In the low levels, a cold front is forecast to move southeast across the Midwest and into the lower Great Lakes. ...Great Lakes... Ongoing storms are likely in the morning across the Upper Midwest as a southwesterly LLJ and warm advection regime promote moisture transport and ascent in portions of MN/WI and the western U.P. of MI. A severe risk may accompany this activity mainly in the form of isolated damaging gusts. The northeastern extent of an elevated mixed layer with associated capping will probably overspread parts of the middle MS Valley during the day. Isolated diurnal storms are possible along the front with a hail/wind risk. Farther northeast, the magnitude of destabilization is highly dependent on the convective evolution of a possible MCS moving through the western Great Lakes during the morning. Wind fields will likely strengthen across the destabilizing warm sector during the day which will favor organized storm structures including the possibility for supercells and bowing segments. Refinements in severe probabilities will likely be needed due to mesoscale dependencies influencing the severe thunderstorm outlook. ...FL Peninsula (Hurricane Dorian)... Uncertainty remains regarding the eventual track of Hurricane Dorian as it moves into the Gulf Stream waters east of the FL Peninsula Monday night into Tuesday morning. If the northeast quadrant were to overspread the FL Peninsula on Tuesday and/or Tuesday night, then a risk for potential tornadoes would include those areas. At this time, uncertainty is too high to include low-severe probabilities. Please refer to the National Hurricane Center for the latest guidance regarding the forecast track of Hurricane Dorian. ..Smith.. 09/01/2019 Read more

SPC 0730Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0213 AM CDT Sun Sep 01 2019 Valid 031200Z - 041200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FOR NORTHERN ILLINOIS...EASTERN WISCONSIN...AND PARTS OF LOWER MICHIGAN... ...SUMMARY... Severe thunderstorms are possible across the western and central Great Lakes on Tuesday. ...Synopsis... A mid-level trough and associated speed max will move from the Upper Midwest eastward across the Great Lakes and into southeastern Canada on Tuesday into Tuesday night. A mid-level anticyclone will remain situated over the Four Corners while Hurricane Dorian slowly approaches the Southeast United States. In the low levels, a cold front is forecast to move southeast across the Midwest and into the lower Great Lakes. ...Great Lakes... Ongoing storms are likely in the morning across the Upper Midwest as a southwesterly LLJ and warm advection regime promote moisture transport and ascent in portions of MN/WI and the western U.P. of MI. A severe risk may accompany this activity mainly in the form of isolated damaging gusts. The northeastern extent of an elevated mixed layer with associated capping will probably overspread parts of the middle MS Valley during the day. Isolated diurnal storms are possible along the front with a hail/wind risk. Farther northeast, the magnitude of destabilization is highly dependent on the convective evolution of a possible MCS moving through the western Great Lakes during the morning. Wind fields will likely strengthen across the destabilizing warm sector during the day which will favor organized storm structures including the possibility for supercells and bowing segments. Refinements in severe probabilities will likely be needed due to mesoscale dependencies influencing the severe thunderstorm outlook. ...FL Peninsula (Hurricane Dorian)... Uncertainty remains regarding the eventual track of Hurricane Dorian as it moves into the Gulf Stream waters east of the FL Peninsula Monday night into Tuesday morning. If the northeast quadrant were to overspread the FL Peninsula on Tuesday and/or Tuesday night, then a risk for potential tornadoes would include those areas. At this time, uncertainty is too high to include low-severe probabilities. Please refer to the National Hurricane Center for the latest guidance regarding the forecast track of Hurricane Dorian. ..Smith.. 09/01/2019 Read more

SPC Day 2 Fire Weather Outlook
Day 2 Fire Weather Outlook NWS Storm Prediction Center Norman OK 0125 AM CDT Sun Sep 01 2019 Valid 021200Z - 031200Z ...CRITICAL FIRE WEATHER AREA FOR PARTS OF EASTERN IDAHO... ...Synopsis... A mature embedded impulse will traverse the northern Rockies along the crest of a fortified upper-level ridge on Day 2/Monday. Stronger flow aloft will glance the central/northern Rockies and northern Great Basin areas, inducing a surface mass response which will promote very breezy and dry conditions favorable for wildfire spread. ...Northern Great Basin into the central/northern Rockies... Widespread 15-20 mph sustained west-southwesterly winds, coincident with 10-20% RH, are expected to occur by afternoon across much of Wyoming, westward into Idaho and far southern Montana, and continue past sunset, where an elevated delineation was added. An additional downslope component of surface flow along the lee of the Bitterroot Range will also encourage sustained westerly winds of at least 20-25 mph (perhaps with higher gusts) across parts of the Snake River Plain, atop critically dry fuels, where a critical area was added. At least locally critical conditions may also be observed in terrain favoring locations east of the Snake River Plain into the Great Divide basin. However, the lack of widespread stronger flow across these areas lends too low of confidence to expand the critical area eastward at this time, though conditions will be monitored for a possible upgrade in later outlooks. ..Squitieri.. 09/01/2019 ...Please see www.spc.noaa.gov/fire for graphic product... Read more