Severe Storms

SPC Day 1 Fire Weather Outlook
Day 1 Fire Weather Outlook NWS Storm Prediction Center Norman OK 1152 AM CDT Tue Sep 03 2019 Valid 031700Z - 041200Z Changes have been made to the ISODRYT area across portions of the northern/central Great Basin. Water vapor satellite imagery indicates that a weak shortwave trough was located in the vicinity of the northern NV/UT border. The 12Z LKN soundings shows subsidence occurring in the wake of this feature. Given no appreciable mid-level cooling expected, convection occurring in northeastern Nevada is questionable this afternoon. Farther to the south and east, GPS PWAT observations show a plume of monsoonal moisture moving northward. A steady increase in PWAT values through the afternoon/evening lends doubt to how dry storms will be, particularly across central/western Utah. Lastly, mean flow within the cloud-bearing layer on forecast soundings is around 10-15 mph which would suggest at least a mixed-mode of wet/dry storms with a relatively quick transition to wet in some locations. For these reasons, the ISODRYT area has been relegated to east-central Nevada on the edge of moisture plume. While uncertainty still remains, this area appears to have the greatest probability of a few dry lighting strikes. ..Wendt.. 09/03/2019 .PREV DISCUSSION... /ISSUED 0112 AM CDT Tue Sep 03 2019/ ...Synopsis... A mid-level ridge will remain in place across the western CONUS, with an embedded shortwave trough propagating around the ridge across the Pacific Northwest. Mildly dry and breezy conditions may occur east of the Cascades as the stronger flow aloft attempts to mix downward to the surface. Mid-level monsoonal moisture will also be present across parts of the Great Basin, fueling isolated thunderstorms, with a few dry strikes possible. ...Pacific Northwest... By afternoon peak heating, boundary layer mixing, in conjunction with downslope flow along the lee of the Cascades, will contribute to westerly winds reaching 15 mph at times, particularly in the Harney Basin area, with RH dropping into the 15-25% range. As winds exceeding 15 mph will be brief and confined to mainly terrain favoring locations, an elevated delineation has been withheld at this time. ...Portions of the Great Basin... Mid-level moisture will meander northwestward into central parts of the Great Basin (including parts of Nevada into western Utah), where afternoon heating will provide enough buoyancy and lift to induce isolated thunderstorms. Though these storms will be slow moving, cells are expected to be high based in nature (i.e. rooted atop a sfc-500 mb dry sub-cloud layer), and are expected to occur over fuels that are near-critical to critically receptive to fire spread, warranting the addition of an isolated dry thunderstorm delineation. ...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 1152 AM CDT Tue Sep 03 2019 Valid 031700Z - 041200Z Changes have been made to the ISODRYT area across portions of the northern/central Great Basin. Water vapor satellite imagery indicates that a weak shortwave trough was located in the vicinity of the northern NV/UT border. The 12Z LKN soundings shows subsidence occurring in the wake of this feature. Given no appreciable mid-level cooling expected, convection occurring in northeastern Nevada is questionable this afternoon. Farther to the south and east, GPS PWAT observations show a plume of monsoonal moisture moving northward. A steady increase in PWAT values through the afternoon/evening lends doubt to how dry storms will be, particularly across central/western Utah. Lastly, mean flow within the cloud-bearing layer on forecast soundings is around 10-15 mph which would suggest at least a mixed-mode of wet/dry storms with a relatively quick transition to wet in some locations. For these reasons, the ISODRYT area has been relegated to east-central Nevada on the edge of moisture plume. While uncertainty still remains, this area appears to have the greatest probability of a few dry lighting strikes. ..Wendt.. 09/03/2019 .PREV DISCUSSION... /ISSUED 0112 AM CDT Tue Sep 03 2019/ ...Synopsis... A mid-level ridge will remain in place across the western CONUS, with an embedded shortwave trough propagating around the ridge across the Pacific Northwest. Mildly dry and breezy conditions may occur east of the Cascades as the stronger flow aloft attempts to mix downward to the surface. Mid-level monsoonal moisture will also be present across parts of the Great Basin, fueling isolated thunderstorms, with a few dry strikes possible. ...Pacific Northwest... By afternoon peak heating, boundary layer mixing, in conjunction with downslope flow along the lee of the Cascades, will contribute to westerly winds reaching 15 mph at times, particularly in the Harney Basin area, with RH dropping into the 15-25% range. As winds exceeding 15 mph will be brief and confined to mainly terrain favoring locations, an elevated delineation has been withheld at this time. ...Portions of the Great Basin... Mid-level moisture will meander northwestward into central parts of the Great Basin (including parts of Nevada into western Utah), where afternoon heating will provide enough buoyancy and lift to induce isolated thunderstorms. Though these storms will be slow moving, cells are expected to be high based in nature (i.e. rooted atop a sfc-500 mb dry sub-cloud layer), and are expected to occur over fuels that are near-critical to critically receptive to fire spread, warranting the addition of an isolated dry thunderstorm delineation. ...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 1152 AM CDT Tue Sep 03 2019 Valid 031700Z - 041200Z Changes have been made to the ISODRYT area across portions of the northern/central Great Basin. Water vapor satellite imagery indicates that a weak shortwave trough was located in the vicinity of the northern NV/UT border. The 12Z LKN soundings shows subsidence occurring in the wake of this feature. Given no appreciable mid-level cooling expected, convection occurring in northeastern Nevada is questionable this afternoon. Farther to the south and east, GPS PWAT observations show a plume of monsoonal moisture moving northward. A steady increase in PWAT values through the afternoon/evening lends doubt to how dry storms will be, particularly across central/western Utah. Lastly, mean flow within the cloud-bearing layer on forecast soundings is around 10-15 mph which would suggest at least a mixed-mode of wet/dry storms with a relatively quick transition to wet in some locations. For these reasons, the ISODRYT area has been relegated to east-central Nevada on the edge of moisture plume. While uncertainty still remains, this area appears to have the greatest probability of a few dry lighting strikes. ..Wendt.. 09/03/2019 .PREV DISCUSSION... /ISSUED 0112 AM CDT Tue Sep 03 2019/ ...Synopsis... A mid-level ridge will remain in place across the western CONUS, with an embedded shortwave trough propagating around the ridge across the Pacific Northwest. Mildly dry and breezy conditions may occur east of the Cascades as the stronger flow aloft attempts to mix downward to the surface. Mid-level monsoonal moisture will also be present across parts of the Great Basin, fueling isolated thunderstorms, with a few dry strikes possible. ...Pacific Northwest... By afternoon peak heating, boundary layer mixing, in conjunction with downslope flow along the lee of the Cascades, will contribute to westerly winds reaching 15 mph at times, particularly in the Harney Basin area, with RH dropping into the 15-25% range. As winds exceeding 15 mph will be brief and confined to mainly terrain favoring locations, an elevated delineation has been withheld at this time. ...Portions of the Great Basin... Mid-level moisture will meander northwestward into central parts of the Great Basin (including parts of Nevada into western Utah), where afternoon heating will provide enough buoyancy and lift to induce isolated thunderstorms. Though these storms will be slow moving, cells are expected to be high based in nature (i.e. rooted atop a sfc-500 mb dry sub-cloud layer), and are expected to occur over fuels that are near-critical to critically receptive to fire spread, warranting the addition of an isolated dry thunderstorm delineation. ...Please see www.spc.noaa.gov/fire for graphic product... Read more

SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1139 AM CDT Tue Sep 03 2019 Valid 031630Z - 041200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE MIDWEST AND GREAT LAKES... ...SUMMARY... Scattered severe thunderstorms are expected mainly during the late afternoon to evening hours across parts of the Great Lakes and Midwest. A few tornadoes, large hail, and damaging winds are all possible. ...Midwest/Great Lakes... An upgrade to Enhanced Risk could still be warranted for portions of the region later today pending convective/observational trends. However, as mentioned in the prior (13Z) Outlook discussion, short-term guidance continues to generally sub-optimally depict and/or remains slow to adjust to the influence of ongoing convection, which casts some uncertainty regarding the convective scenario later today. This is principally with respect to the thermodynamic environment and related likelihood and north-northeastward extent of appreciable moistening and destabilization later today, coincident with a notable deep-layer wind field. Morning observations including 12Z sounding and WSR-88D VWP data sample deep-layer winds that are very strong by late-summer standards, particularly at a latitude around southern Lake Michigan and northward including Wisconsin/Michigan. Beneath a respectable elevated mixed layer, seasonably rich low-level moisture (with around 70F surface dewpoints) is prevalent at late morning across eastern Iowa, southern Wisconsin, western Illinois near and ahead of an eastward-advancing cold front. This moisture will steadily advect eastward today, with the morning convection/residual cloud cover potentially effectively reinforcing/delaying an eastward-shifting warm front toward and across Lower Michigan and northern Indiana. Boundary-layer heating will probably be of more limited duration with north/northeast extent across Lower Michigan, but will be greater with southwest extent into Illinois. A strongly unstable air mass should develop initially near Lake Michigan southwestward across Illinois, with greater uncertainty in the degree of buoyancy farther north across Lower Michigan. At least isolated, mid-to-late afternoon deep convective redevelopment will probably occur with the approach of a cold front from western Lower Michigan into northern Illinois, with deep-layer winds well-supportive (40-50 kt effective) of initial supercells. Hail/damaging wind potential aside, low-level shear/SRH will be maximized near the effective warm front and within the increasingly narrow warm sector with northward extent across Lower Michigan. Although short-term forecast uncertainty lingers as previously discussed, on presumed/probable air mass recovery a respectable potential does exist for a couple of tornadoes, including some possibility of a strong tornado, aside from an increasing risk for damaging winds this evening. Severe risks currently appear most probable to occur across northern Indiana and southern Lower Michigan, and possibly into northern/western Ohio late tonight. The severe threat should wane overnight as the primary shortwave trough becomes increasingly separated from the lingering buoyancy plume over the Midwest. ...East-central/northeast Florida Coast... Hurricane Dorian is forecast to move northward and remain offshore; reference NHC for the latest details. This will maintain most of the Florida Atlantic Coast in the tornado-unfavorable western periphery of Dorian. Nevertheless, some enlargement to the low-level hodograph combined with weak instability might support a couple of rotating cells capable of a brief tornado through tonight. ...Deep South Texas... Reference NHC for the latest details regarding Tropical Depression Seven, which may gradually strengthen/organize over the far western Gulf of Mexico. A modest low-level strengthening of easterly winds on its northern periphery could influence low-topped supercell potential and possibly some tornado risk into Wednesday. ..Guyer/Nauslar.. 09/03/2019 Read more

SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1139 AM CDT Tue Sep 03 2019 Valid 031630Z - 041200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE MIDWEST AND GREAT LAKES... ...SUMMARY... Scattered severe thunderstorms are expected mainly during the late afternoon to evening hours across parts of the Great Lakes and Midwest. A few tornadoes, large hail, and damaging winds are all possible. ...Midwest/Great Lakes... An upgrade to Enhanced Risk could still be warranted for portions of the region later today pending convective/observational trends. However, as mentioned in the prior (13Z) Outlook discussion, short-term guidance continues to generally sub-optimally depict and/or remains slow to adjust to the influence of ongoing convection, which casts some uncertainty regarding the convective scenario later today. This is principally with respect to the thermodynamic environment and related likelihood and north-northeastward extent of appreciable moistening and destabilization later today, coincident with a notable deep-layer wind field. Morning observations including 12Z sounding and WSR-88D VWP data sample deep-layer winds that are very strong by late-summer standards, particularly at a latitude around southern Lake Michigan and northward including Wisconsin/Michigan. Beneath a respectable elevated mixed layer, seasonably rich low-level moisture (with around 70F surface dewpoints) is prevalent at late morning across eastern Iowa, southern Wisconsin, western Illinois near and ahead of an eastward-advancing cold front. This moisture will steadily advect eastward today, with the morning convection/residual cloud cover potentially effectively reinforcing/delaying an eastward-shifting warm front toward and across Lower Michigan and northern Indiana. Boundary-layer heating will probably be of more limited duration with north/northeast extent across Lower Michigan, but will be greater with southwest extent into Illinois. A strongly unstable air mass should develop initially near Lake Michigan southwestward across Illinois, with greater uncertainty in the degree of buoyancy farther north across Lower Michigan. At least isolated, mid-to-late afternoon deep convective redevelopment will probably occur with the approach of a cold front from western Lower Michigan into northern Illinois, with deep-layer winds well-supportive (40-50 kt effective) of initial supercells. Hail/damaging wind potential aside, low-level shear/SRH will be maximized near the effective warm front and within the increasingly narrow warm sector with northward extent across Lower Michigan. Although short-term forecast uncertainty lingers as previously discussed, on presumed/probable air mass recovery a respectable potential does exist for a couple of tornadoes, including some possibility of a strong tornado, aside from an increasing risk for damaging winds this evening. Severe risks currently appear most probable to occur across northern Indiana and southern Lower Michigan, and possibly into northern/western Ohio late tonight. The severe threat should wane overnight as the primary shortwave trough becomes increasingly separated from the lingering buoyancy plume over the Midwest. ...East-central/northeast Florida Coast... Hurricane Dorian is forecast to move northward and remain offshore; reference NHC for the latest details. This will maintain most of the Florida Atlantic Coast in the tornado-unfavorable western periphery of Dorian. Nevertheless, some enlargement to the low-level hodograph combined with weak instability might support a couple of rotating cells capable of a brief tornado through tonight. ...Deep South Texas... Reference NHC for the latest details regarding Tropical Depression Seven, which may gradually strengthen/organize over the far western Gulf of Mexico. A modest low-level strengthening of easterly winds on its northern periphery could influence low-topped supercell potential and possibly some tornado risk into Wednesday. ..Guyer/Nauslar.. 09/03/2019 Read more

SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1139 AM CDT Tue Sep 03 2019 Valid 031630Z - 041200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE MIDWEST AND GREAT LAKES... ...SUMMARY... Scattered severe thunderstorms are expected mainly during the late afternoon to evening hours across parts of the Great Lakes and Midwest. A few tornadoes, large hail, and damaging winds are all possible. ...Midwest/Great Lakes... An upgrade to Enhanced Risk could still be warranted for portions of the region later today pending convective/observational trends. However, as mentioned in the prior (13Z) Outlook discussion, short-term guidance continues to generally sub-optimally depict and/or remains slow to adjust to the influence of ongoing convection, which casts some uncertainty regarding the convective scenario later today. This is principally with respect to the thermodynamic environment and related likelihood and north-northeastward extent of appreciable moistening and destabilization later today, coincident with a notable deep-layer wind field. Morning observations including 12Z sounding and WSR-88D VWP data sample deep-layer winds that are very strong by late-summer standards, particularly at a latitude around southern Lake Michigan and northward including Wisconsin/Michigan. Beneath a respectable elevated mixed layer, seasonably rich low-level moisture (with around 70F surface dewpoints) is prevalent at late morning across eastern Iowa, southern Wisconsin, western Illinois near and ahead of an eastward-advancing cold front. This moisture will steadily advect eastward today, with the morning convection/residual cloud cover potentially effectively reinforcing/delaying an eastward-shifting warm front toward and across Lower Michigan and northern Indiana. Boundary-layer heating will probably be of more limited duration with north/northeast extent across Lower Michigan, but will be greater with southwest extent into Illinois. A strongly unstable air mass should develop initially near Lake Michigan southwestward across Illinois, with greater uncertainty in the degree of buoyancy farther north across Lower Michigan. At least isolated, mid-to-late afternoon deep convective redevelopment will probably occur with the approach of a cold front from western Lower Michigan into northern Illinois, with deep-layer winds well-supportive (40-50 kt effective) of initial supercells. Hail/damaging wind potential aside, low-level shear/SRH will be maximized near the effective warm front and within the increasingly narrow warm sector with northward extent across Lower Michigan. Although short-term forecast uncertainty lingers as previously discussed, on presumed/probable air mass recovery a respectable potential does exist for a couple of tornadoes, including some possibility of a strong tornado, aside from an increasing risk for damaging winds this evening. Severe risks currently appear most probable to occur across northern Indiana and southern Lower Michigan, and possibly into northern/western Ohio late tonight. The severe threat should wane overnight as the primary shortwave trough becomes increasingly separated from the lingering buoyancy plume over the Midwest. ...East-central/northeast Florida Coast... Hurricane Dorian is forecast to move northward and remain offshore; reference NHC for the latest details. This will maintain most of the Florida Atlantic Coast in the tornado-unfavorable western periphery of Dorian. Nevertheless, some enlargement to the low-level hodograph combined with weak instability might support a couple of rotating cells capable of a brief tornado through tonight. ...Deep South Texas... Reference NHC for the latest details regarding Tropical Depression Seven, which may gradually strengthen/organize over the far western Gulf of Mexico. A modest low-level strengthening of easterly winds on its northern periphery could influence low-topped supercell potential and possibly some tornado risk into Wednesday. ..Guyer/Nauslar.. 09/03/2019 Read more

SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1139 AM CDT Tue Sep 03 2019 Valid 031630Z - 041200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE MIDWEST AND GREAT LAKES... ...SUMMARY... Scattered severe thunderstorms are expected mainly during the late afternoon to evening hours across parts of the Great Lakes and Midwest. A few tornadoes, large hail, and damaging winds are all possible. ...Midwest/Great Lakes... An upgrade to Enhanced Risk could still be warranted for portions of the region later today pending convective/observational trends. However, as mentioned in the prior (13Z) Outlook discussion, short-term guidance continues to generally sub-optimally depict and/or remains slow to adjust to the influence of ongoing convection, which casts some uncertainty regarding the convective scenario later today. This is principally with respect to the thermodynamic environment and related likelihood and north-northeastward extent of appreciable moistening and destabilization later today, coincident with a notable deep-layer wind field. Morning observations including 12Z sounding and WSR-88D VWP data sample deep-layer winds that are very strong by late-summer standards, particularly at a latitude around southern Lake Michigan and northward including Wisconsin/Michigan. Beneath a respectable elevated mixed layer, seasonably rich low-level moisture (with around 70F surface dewpoints) is prevalent at late morning across eastern Iowa, southern Wisconsin, western Illinois near and ahead of an eastward-advancing cold front. This moisture will steadily advect eastward today, with the morning convection/residual cloud cover potentially effectively reinforcing/delaying an eastward-shifting warm front toward and across Lower Michigan and northern Indiana. Boundary-layer heating will probably be of more limited duration with north/northeast extent across Lower Michigan, but will be greater with southwest extent into Illinois. A strongly unstable air mass should develop initially near Lake Michigan southwestward across Illinois, with greater uncertainty in the degree of buoyancy farther north across Lower Michigan. At least isolated, mid-to-late afternoon deep convective redevelopment will probably occur with the approach of a cold front from western Lower Michigan into northern Illinois, with deep-layer winds well-supportive (40-50 kt effective) of initial supercells. Hail/damaging wind potential aside, low-level shear/SRH will be maximized near the effective warm front and within the increasingly narrow warm sector with northward extent across Lower Michigan. Although short-term forecast uncertainty lingers as previously discussed, on presumed/probable air mass recovery a respectable potential does exist for a couple of tornadoes, including some possibility of a strong tornado, aside from an increasing risk for damaging winds this evening. Severe risks currently appear most probable to occur across northern Indiana and southern Lower Michigan, and possibly into northern/western Ohio late tonight. The severe threat should wane overnight as the primary shortwave trough becomes increasingly separated from the lingering buoyancy plume over the Midwest. ...East-central/northeast Florida Coast... Hurricane Dorian is forecast to move northward and remain offshore; reference NHC for the latest details. This will maintain most of the Florida Atlantic Coast in the tornado-unfavorable western periphery of Dorian. Nevertheless, some enlargement to the low-level hodograph combined with weak instability might support a couple of rotating cells capable of a brief tornado through tonight. ...Deep South Texas... Reference NHC for the latest details regarding Tropical Depression Seven, which may gradually strengthen/organize over the far western Gulf of Mexico. A modest low-level strengthening of easterly winds on its northern periphery could influence low-topped supercell potential and possibly some tornado risk into Wednesday. ..Guyer/Nauslar.. 09/03/2019 Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0738 AM CDT Tue Sep 03 2019 Valid 031300Z - 041200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS PARTS OF THE GREAT LAKES AND MIDWEST... ...SUMMARY... Scattered severe thunderstorms are expected mainly during the late afternoon to mid-evening across parts of the Great Lakes and Midwest regions. A few tornadoes, large hail, and damaging winds are all possible. ...Great Lakes and Midwest... Expansive stratiform and convective swaths are ongoing from northern Lower MI to eastern WI and northern IL. The leading convection is associated with an eastward-moving MCV, while upstream activity is being forced by robust low-level warm advection ahead of a vigorous shortwave trough over northern MN. The cluster over far northern IL may pose an isolated severe threat through midday as it spreads towards northern IN. Latest guidance is largely underestimating the extent of ongoing convection (especially the 06Z NAM). The 06Z ESRL-HRRR and GFS appear closer to reality compared with the 00Z HREF members/ECMWF and 06Z HRRR. This yields continued uncertainty in how the convective scenario will play out later this afternoon and evening. As such, while potential exists for a significant tornado, an upgrade to a category 3-Enhanced Slight Risk has been deferred. Seasonably rich low-level moisture is prevalent upstream of the warm-advection driven convection across IA/southern MN/southwest WI, characterized by near 70 surface dew points. This rich moisture will advect eastward in the wake of this morning activity beneath an elevated mixed layer. Boundary-layer heating will probably be of more limited duration with northeast extent across Lower MI, but will be greater with southwest extent into IL. A strongly unstable air mass should develop near and southwest of Lake Michigan with greater uncertainty in the degree of buoyancy farther northeast. At least isolated, mid to late afternoon convective redevelopment will probably occur with approach of a cold front from western Lower MI into northern IL. Deep-layer shear will be strongest northeast compared to more veered flow and less enlargement to hodographs with southwest extent. With some indications of veer-back-veer wind profiles, convective mode may tend to evolve into a few clusters with embedded supercell structures. The severe threat should wane overnight as the primary shortwave trough becomes increasingly separated from the lingering buoyancy plume over the Midwest. ...East-central/northeast FL Coast... Hurricane Dorian is forecast to move northward and remain offshore. This will place most of the FL Atlantic Coast in the unfavorable northwest quadrant for tornadoes. Nevertheless, some enlargement to the low-level hodograph combined with weak instability might support a couple rotating cells capable of a brief tornado through tonight. ..Grams/Smith.. 09/03/2019 Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0738 AM CDT Tue Sep 03 2019 Valid 031300Z - 041200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS PARTS OF THE GREAT LAKES AND MIDWEST... ...SUMMARY... Scattered severe thunderstorms are expected mainly during the late afternoon to mid-evening across parts of the Great Lakes and Midwest regions. A few tornadoes, large hail, and damaging winds are all possible. ...Great Lakes and Midwest... Expansive stratiform and convective swaths are ongoing from northern Lower MI to eastern WI and northern IL. The leading convection is associated with an eastward-moving MCV, while upstream activity is being forced by robust low-level warm advection ahead of a vigorous shortwave trough over northern MN. The cluster over far northern IL may pose an isolated severe threat through midday as it spreads towards northern IN. Latest guidance is largely underestimating the extent of ongoing convection (especially the 06Z NAM). The 06Z ESRL-HRRR and GFS appear closer to reality compared with the 00Z HREF members/ECMWF and 06Z HRRR. This yields continued uncertainty in how the convective scenario will play out later this afternoon and evening. As such, while potential exists for a significant tornado, an upgrade to a category 3-Enhanced Slight Risk has been deferred. Seasonably rich low-level moisture is prevalent upstream of the warm-advection driven convection across IA/southern MN/southwest WI, characterized by near 70 surface dew points. This rich moisture will advect eastward in the wake of this morning activity beneath an elevated mixed layer. Boundary-layer heating will probably be of more limited duration with northeast extent across Lower MI, but will be greater with southwest extent into IL. A strongly unstable air mass should develop near and southwest of Lake Michigan with greater uncertainty in the degree of buoyancy farther northeast. At least isolated, mid to late afternoon convective redevelopment will probably occur with approach of a cold front from western Lower MI into northern IL. Deep-layer shear will be strongest northeast compared to more veered flow and less enlargement to hodographs with southwest extent. With some indications of veer-back-veer wind profiles, convective mode may tend to evolve into a few clusters with embedded supercell structures. The severe threat should wane overnight as the primary shortwave trough becomes increasingly separated from the lingering buoyancy plume over the Midwest. ...East-central/northeast FL Coast... Hurricane Dorian is forecast to move northward and remain offshore. This will place most of the FL Atlantic Coast in the unfavorable northwest quadrant for tornadoes. Nevertheless, some enlargement to the low-level hodograph combined with weak instability might support a couple rotating cells capable of a brief tornado through tonight. ..Grams/Smith.. 09/03/2019 Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0738 AM CDT Tue Sep 03 2019 Valid 031300Z - 041200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS PARTS OF THE GREAT LAKES AND MIDWEST... ...SUMMARY... Scattered severe thunderstorms are expected mainly during the late afternoon to mid-evening across parts of the Great Lakes and Midwest regions. A few tornadoes, large hail, and damaging winds are all possible. ...Great Lakes and Midwest... Expansive stratiform and convective swaths are ongoing from northern Lower MI to eastern WI and northern IL. The leading convection is associated with an eastward-moving MCV, while upstream activity is being forced by robust low-level warm advection ahead of a vigorous shortwave trough over northern MN. The cluster over far northern IL may pose an isolated severe threat through midday as it spreads towards northern IN. Latest guidance is largely underestimating the extent of ongoing convection (especially the 06Z NAM). The 06Z ESRL-HRRR and GFS appear closer to reality compared with the 00Z HREF members/ECMWF and 06Z HRRR. This yields continued uncertainty in how the convective scenario will play out later this afternoon and evening. As such, while potential exists for a significant tornado, an upgrade to a category 3-Enhanced Slight Risk has been deferred. Seasonably rich low-level moisture is prevalent upstream of the warm-advection driven convection across IA/southern MN/southwest WI, characterized by near 70 surface dew points. This rich moisture will advect eastward in the wake of this morning activity beneath an elevated mixed layer. Boundary-layer heating will probably be of more limited duration with northeast extent across Lower MI, but will be greater with southwest extent into IL. A strongly unstable air mass should develop near and southwest of Lake Michigan with greater uncertainty in the degree of buoyancy farther northeast. At least isolated, mid to late afternoon convective redevelopment will probably occur with approach of a cold front from western Lower MI into northern IL. Deep-layer shear will be strongest northeast compared to more veered flow and less enlargement to hodographs with southwest extent. With some indications of veer-back-veer wind profiles, convective mode may tend to evolve into a few clusters with embedded supercell structures. The severe threat should wane overnight as the primary shortwave trough becomes increasingly separated from the lingering buoyancy plume over the Midwest. ...East-central/northeast FL Coast... Hurricane Dorian is forecast to move northward and remain offshore. This will place most of the FL Atlantic Coast in the unfavorable northwest quadrant for tornadoes. Nevertheless, some enlargement to the low-level hodograph combined with weak instability might support a couple rotating cells capable of a brief tornado through tonight. ..Grams/Smith.. 09/03/2019 Read more

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0354 AM CDT Tue Sep 03 2019 Valid 061200Z - 111200Z ...DISCUSSION... Depending on the speed/timing of Hurricane Dorian, some threat for an isolated tornado or two might exist across the NC coast on day 4. Otherwise, severe potential will remain relatively low over the rest of the U.S.. Day 5 a low-amplitude shortwave trough is forecast to emerge over the northern and central Plains, but the thermodynamic environment, with limited low-level moisture, will probably remain too marginal for an organized severe threat. Day 6, overall severe potential will probably remain relatively low due primarily to richer low-level moisture having been shunted south of the stronger westerlies. Read more

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0354 AM CDT Tue Sep 03 2019 Valid 061200Z - 111200Z ...DISCUSSION... Depending on the speed/timing of Hurricane Dorian, some threat for an isolated tornado or two might exist across the NC coast on day 4. Otherwise, severe potential will remain relatively low over the rest of the U.S.. Day 5 a low-amplitude shortwave trough is forecast to emerge over the northern and central Plains, but the thermodynamic environment, with limited low-level moisture, will probably remain too marginal for an organized severe threat. Day 6, overall severe potential will probably remain relatively low due primarily to richer low-level moisture having been shunted south of the stronger westerlies. Read more

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0354 AM CDT Tue Sep 03 2019 Valid 061200Z - 111200Z ...DISCUSSION... Depending on the speed/timing of Hurricane Dorian, some threat for an isolated tornado or two might exist across the NC coast on day 4. Otherwise, severe potential will remain relatively low over the rest of the U.S.. Day 5 a low-amplitude shortwave trough is forecast to emerge over the northern and central Plains, but the thermodynamic environment, with limited low-level moisture, will probably remain too marginal for an organized severe threat. Day 6, overall severe potential will probably remain relatively low due primarily to richer low-level moisture having been shunted south of the stronger westerlies. Read more

SPC 0730Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0213 AM CDT Tue Sep 03 2019 Valid 051200Z - 061200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER A PORTION OF THE COASTAL CAROLINAS... ...SUMMARY... A marginal risk for a tornado or two might evolve across the coastal Carolinas Thursday. ...Coastal Carolinas... Hurricane Dorian is forecast by the National Hurricane Center to be located just off the southeast North Carolina coast by Thursday evening. While the more favorable quadrant for isolated tornadoes will remain offshore, scattered thunderstorms developing within the outer rain bands will spread inland where 0-2 km hodographs will be sufficient for a threat of low-level mesocyclones and a couple of tornadoes. See latest discussion from the National Hurricane Center for updates on Dorian. ..Dial.. 09/03/2019 Read more

SPC 0730Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0213 AM CDT Tue Sep 03 2019 Valid 051200Z - 061200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER A PORTION OF THE COASTAL CAROLINAS... ...SUMMARY... A marginal risk for a tornado or two might evolve across the coastal Carolinas Thursday. ...Coastal Carolinas... Hurricane Dorian is forecast by the National Hurricane Center to be located just off the southeast North Carolina coast by Thursday evening. While the more favorable quadrant for isolated tornadoes will remain offshore, scattered thunderstorms developing within the outer rain bands will spread inland where 0-2 km hodographs will be sufficient for a threat of low-level mesocyclones and a couple of tornadoes. See latest discussion from the National Hurricane Center for updates on Dorian. ..Dial.. 09/03/2019 Read more

SPC 0730Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0213 AM CDT Tue Sep 03 2019 Valid 051200Z - 061200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER A PORTION OF THE COASTAL CAROLINAS... ...SUMMARY... A marginal risk for a tornado or two might evolve across the coastal Carolinas Thursday. ...Coastal Carolinas... Hurricane Dorian is forecast by the National Hurricane Center to be located just off the southeast North Carolina coast by Thursday evening. While the more favorable quadrant for isolated tornadoes will remain offshore, scattered thunderstorms developing within the outer rain bands will spread inland where 0-2 km hodographs will be sufficient for a threat of low-level mesocyclones and a couple of tornadoes. See latest discussion from the National Hurricane Center for updates on Dorian. ..Dial.. 09/03/2019 Read more

SPC Day 2 Fire Weather Outlook
Day 2 Fire Weather Outlook NWS Storm Prediction Center Norman OK 0201 AM CDT Tue Sep 03 2019 Valid 041200Z - 051200Z ...Synopsis... An upper-level ridge will remain in place across the western CONUS for the Day 2/Wednesday period. The embedded mid-level shortwave trough moving across the Pacific Northwest on Day 1 will then traverse the northern Rockies while cresting the ridge on Day 2. With the passage of the trough, the low-level mass response will be a dry and breezy westerly wind that may foster some wildfire-spread potential. Elsewhere, from northern California into the Great Basin, adequate monsoonal moisture traversing the upper-level ridge will promote at least isolated thunderstorm potential, with a few dry strikes possible. ...Northern Rockies... With the passage of an upper-level trough and diurnal boundary layer mixing of stronger winds aloft to the surface, 15-25 mph sustained westerly surface winds are expected across parts of the northern Rockies (mainly north-central Montana) along with 15-25% RH. Finer fuels have recently begun to dry across the area, supporting the potential for grass-fire spread and as such, an elevated area has been delineated. ...Northern California into the northern Great Basin... As mid-level monsoonal moisture continues to drift northward across northern portions of the Great Basin, isolated high-based thunderstorms will become possible by afternoon peak heating. Despite slow storm motions, a dry sub-cloud layer will support at least some potential for dry strikes atop near-critical to critically dry fuels, where an isolated dry thunderstorm area was added. Isolated dry thunderstorms may also occur over northern parts of California into far southern Oregon, but low confidence in storm initiation over this area precludes a delineation at this time. ..Squitieri.. 09/03/2019 ...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 0201 AM CDT Tue Sep 03 2019 Valid 041200Z - 051200Z ...Synopsis... An upper-level ridge will remain in place across the western CONUS for the Day 2/Wednesday period. The embedded mid-level shortwave trough moving across the Pacific Northwest on Day 1 will then traverse the northern Rockies while cresting the ridge on Day 2. With the passage of the trough, the low-level mass response will be a dry and breezy westerly wind that may foster some wildfire-spread potential. Elsewhere, from northern California into the Great Basin, adequate monsoonal moisture traversing the upper-level ridge will promote at least isolated thunderstorm potential, with a few dry strikes possible. ...Northern Rockies... With the passage of an upper-level trough and diurnal boundary layer mixing of stronger winds aloft to the surface, 15-25 mph sustained westerly surface winds are expected across parts of the northern Rockies (mainly north-central Montana) along with 15-25% RH. Finer fuels have recently begun to dry across the area, supporting the potential for grass-fire spread and as such, an elevated area has been delineated. ...Northern California into the northern Great Basin... As mid-level monsoonal moisture continues to drift northward across northern portions of the Great Basin, isolated high-based thunderstorms will become possible by afternoon peak heating. Despite slow storm motions, a dry sub-cloud layer will support at least some potential for dry strikes atop near-critical to critically dry fuels, where an isolated dry thunderstorm area was added. Isolated dry thunderstorms may also occur over northern parts of California into far southern Oregon, but low confidence in storm initiation over this area precludes a delineation at this time. ..Squitieri.. 09/03/2019 ...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 0201 AM CDT Tue Sep 03 2019 Valid 041200Z - 051200Z ...Synopsis... An upper-level ridge will remain in place across the western CONUS for the Day 2/Wednesday period. The embedded mid-level shortwave trough moving across the Pacific Northwest on Day 1 will then traverse the northern Rockies while cresting the ridge on Day 2. With the passage of the trough, the low-level mass response will be a dry and breezy westerly wind that may foster some wildfire-spread potential. Elsewhere, from northern California into the Great Basin, adequate monsoonal moisture traversing the upper-level ridge will promote at least isolated thunderstorm potential, with a few dry strikes possible. ...Northern Rockies... With the passage of an upper-level trough and diurnal boundary layer mixing of stronger winds aloft to the surface, 15-25 mph sustained westerly surface winds are expected across parts of the northern Rockies (mainly north-central Montana) along with 15-25% RH. Finer fuels have recently begun to dry across the area, supporting the potential for grass-fire spread and as such, an elevated area has been delineated. ...Northern California into the northern Great Basin... As mid-level monsoonal moisture continues to drift northward across northern portions of the Great Basin, isolated high-based thunderstorms will become possible by afternoon peak heating. Despite slow storm motions, a dry sub-cloud layer will support at least some potential for dry strikes atop near-critical to critically dry fuels, where an isolated dry thunderstorm area was added. Isolated dry thunderstorms may also occur over northern parts of California into far southern Oregon, but low confidence in storm initiation over this area precludes a delineation at this time. ..Squitieri.. 09/03/2019 ...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 0201 AM CDT Tue Sep 03 2019 Valid 041200Z - 051200Z ...Synopsis... An upper-level ridge will remain in place across the western CONUS for the Day 2/Wednesday period. The embedded mid-level shortwave trough moving across the Pacific Northwest on Day 1 will then traverse the northern Rockies while cresting the ridge on Day 2. With the passage of the trough, the low-level mass response will be a dry and breezy westerly wind that may foster some wildfire-spread potential. Elsewhere, from northern California into the Great Basin, adequate monsoonal moisture traversing the upper-level ridge will promote at least isolated thunderstorm potential, with a few dry strikes possible. ...Northern Rockies... With the passage of an upper-level trough and diurnal boundary layer mixing of stronger winds aloft to the surface, 15-25 mph sustained westerly surface winds are expected across parts of the northern Rockies (mainly north-central Montana) along with 15-25% RH. Finer fuels have recently begun to dry across the area, supporting the potential for grass-fire spread and as such, an elevated area has been delineated. ...Northern California into the northern Great Basin... As mid-level monsoonal moisture continues to drift northward across northern portions of the Great Basin, isolated high-based thunderstorms will become possible by afternoon peak heating. Despite slow storm motions, a dry sub-cloud layer will support at least some potential for dry strikes atop near-critical to critically dry fuels, where an isolated dry thunderstorm area was added. Isolated dry thunderstorms may also occur over northern parts of California into far southern Oregon, but low confidence in storm initiation over this area precludes a delineation at this time. ..Squitieri.. 09/03/2019 ...Please see www.spc.noaa.gov/fire for graphic product... Read more