Severe Storms

SPC Day 1 Fire Weather Outlook
Day 1 Fire Weather Outlook NWS Storm Prediction Center Norman OK 1151 AM CDT Thu Aug 22 2019 Valid 221700Z - 231200Z ...CRITICAL FIRE WEATHER AREA FOR PORTIONS OF UTAH...NORTHERN ARIZONA...SOUTHEAST NEVADA...SOUTHWEST WYOMING...AND NORTHWEST COLORADO... Only minor changes to ongoing elevated and critical areas based on the latest forecast guidance. See previous discussion below for additional details. ..Bentley.. 08/22/2019 .PREV DISCUSSION... /ISSUED 0157 AM CDT Thu Aug 22 2019/ ...Synopsis... An upper-level shortwave trough will continue moving eastward over the Pacific Northwest and northern Rockies today. An associated surface cold front will also continue pushing east and south through much of the northern Rockies and northern California and into the Great Basin. A pre-frontal surface pressure trough will run parallel to the cold front stretching southwest from north-central Montana into southern Nevada. A broad area of elevated conditions will develop stretching from northern Arizona/southern Nevada into central Wyoming, with critical conditions likely developing in far northwest Arizona/southeast Nevada through central Utah into southwest Wyoming. West-southwest sustained surface winds of 15-25 mph with RH values of 8-20% are likely to develop ahead of the cold front during the afternoon and into the evening. ERCs are mostly above the 80th percentile within the elevated/critical areas including some locations above the 95th percentile. Elevated conditions are likely across portions of the Snake River Plain and vicinity this afternoon. The cold front will likely push through the area this morning. However, daytime heating will help mix/deepen the boundary layer and increase surface temperatures with west-southwest surface winds of 15-20 mph and RH values of 15-20% developing during the afternoon. ...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 1151 AM CDT Thu Aug 22 2019 Valid 221700Z - 231200Z ...CRITICAL FIRE WEATHER AREA FOR PORTIONS OF UTAH...NORTHERN ARIZONA...SOUTHEAST NEVADA...SOUTHWEST WYOMING...AND NORTHWEST COLORADO... Only minor changes to ongoing elevated and critical areas based on the latest forecast guidance. See previous discussion below for additional details. ..Bentley.. 08/22/2019 .PREV DISCUSSION... /ISSUED 0157 AM CDT Thu Aug 22 2019/ ...Synopsis... An upper-level shortwave trough will continue moving eastward over the Pacific Northwest and northern Rockies today. An associated surface cold front will also continue pushing east and south through much of the northern Rockies and northern California and into the Great Basin. A pre-frontal surface pressure trough will run parallel to the cold front stretching southwest from north-central Montana into southern Nevada. A broad area of elevated conditions will develop stretching from northern Arizona/southern Nevada into central Wyoming, with critical conditions likely developing in far northwest Arizona/southeast Nevada through central Utah into southwest Wyoming. West-southwest sustained surface winds of 15-25 mph with RH values of 8-20% are likely to develop ahead of the cold front during the afternoon and into the evening. ERCs are mostly above the 80th percentile within the elevated/critical areas including some locations above the 95th percentile. Elevated conditions are likely across portions of the Snake River Plain and vicinity this afternoon. The cold front will likely push through the area this morning. However, daytime heating will help mix/deepen the boundary layer and increase surface temperatures with west-southwest surface winds of 15-20 mph and RH values of 15-20% developing during the afternoon. ...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 1151 AM CDT Thu Aug 22 2019 Valid 221700Z - 231200Z ...CRITICAL FIRE WEATHER AREA FOR PORTIONS OF UTAH...NORTHERN ARIZONA...SOUTHEAST NEVADA...SOUTHWEST WYOMING...AND NORTHWEST COLORADO... Only minor changes to ongoing elevated and critical areas based on the latest forecast guidance. See previous discussion below for additional details. ..Bentley.. 08/22/2019 .PREV DISCUSSION... /ISSUED 0157 AM CDT Thu Aug 22 2019/ ...Synopsis... An upper-level shortwave trough will continue moving eastward over the Pacific Northwest and northern Rockies today. An associated surface cold front will also continue pushing east and south through much of the northern Rockies and northern California and into the Great Basin. A pre-frontal surface pressure trough will run parallel to the cold front stretching southwest from north-central Montana into southern Nevada. A broad area of elevated conditions will develop stretching from northern Arizona/southern Nevada into central Wyoming, with critical conditions likely developing in far northwest Arizona/southeast Nevada through central Utah into southwest Wyoming. West-southwest sustained surface winds of 15-25 mph with RH values of 8-20% are likely to develop ahead of the cold front during the afternoon and into the evening. ERCs are mostly above the 80th percentile within the elevated/critical areas including some locations above the 95th percentile. Elevated conditions are likely across portions of the Snake River Plain and vicinity this afternoon. The cold front will likely push through the area this morning. However, daytime heating will help mix/deepen the boundary layer and increase surface temperatures with west-southwest surface winds of 15-20 mph and RH values of 15-20% developing during the afternoon. ...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 1136 AM CDT Thu Aug 22 2019 Valid 221630Z - 231200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM THE SOUTHERN PLAINS TO THE MID-ATLANTIC STATES AND THE NORTHERN/CENTRAL HIGH PLAINS... ...SUMMARY... Isolated damaging winds are possible this afternoon and evening from the southern Plains and Mid-South to the Mid-Atlantic States. Isolated severe hail and wind are also possible over the northern and central High Plains. ...Mid-Atlantic States/Carolinas... A belt of cyclonically curved/moderately strong westerlies aloft will persist over the Upper Ohio Valley and Mid-Atlantic region, with a cold front gradually progressing southeastward across these regions through tonight. Thunderstorms are expected to develop/increase over the mountains and/or in association with ongoing persistent clusters. As low-level lapse rates steepen, damaging winds will be the primary risk. A few sustained/semi-organized clusters of storms may materialize this afternoon, particularly from south-central Pennsylvania southward to near/east of the Blue Ridge in Virginia/Northern Carolina. However, current thinking is that the overall severe storm coverage/risk magnitude will be a bit lower as compared to prior days across the region. ...Southeast Wyoming/Central High Plains... To the north of an eastern Colorado-centered surface low, low-level upslope flow and differential heating in vicinity of the higher terrain is likely to contribute to isolated thunderstorm development this afternoon. Storms should intensify as they move east-southeastward within a moist/increasingly unstable environment. A few instances of isolated severe hail will initially be possible. Storms may gradually cluster with localized severe-caliber wind gust potential this evening across the southern Nebraska Panhandle/northeast Colorado vicinity, and possibly southwest Nebraska/northwest Kansas. ...Southern/eastern Montana to northern High Plains... Isolated to scattered thunderstorms are expected to develop across this area during the afternoon, and into evening with eastward extent. Isolated severe gusts/hail are the main concerns. A relative concentration of convection is possible during about 00Z-06Z across portions of eastern Montana and perhaps northeastern Wyoming. During that time frame, some of the stronger low-level mass response and convergence (related to the approaching shortwave trough), and perhaps the leading fringe of mid/upper synoptic forcing, will impinge upon a narrow plume of relatively maximized buoyancy and boundary-layer moisture. Pre-convective MLCAPE of 1000-2000 J/kg is possible this evening near an axis from RAP-GGW, amidst well-mixed subcloud layers supporting strong-severe gust potential. However, weak mid/upper-level winds suggest that severe potential should remain fairly disorganized and/or short-lived. ...Southern Plains to Mid-South/Tennessee Valley... Within a moist/unstable environment, surface-based thunderstorm development later this afternoon will be focused along zones of residual outflow/differential heating. While weak westerlies will generally prevail, ample heating/buoyancy could support localized severe-caliber downdrafts late this afternoon/early evening. ..Guyer/Bunting.. 08/22/2019 Read more

SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1136 AM CDT Thu Aug 22 2019 Valid 221630Z - 231200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM THE SOUTHERN PLAINS TO THE MID-ATLANTIC STATES AND THE NORTHERN/CENTRAL HIGH PLAINS... ...SUMMARY... Isolated damaging winds are possible this afternoon and evening from the southern Plains and Mid-South to the Mid-Atlantic States. Isolated severe hail and wind are also possible over the northern and central High Plains. ...Mid-Atlantic States/Carolinas... A belt of cyclonically curved/moderately strong westerlies aloft will persist over the Upper Ohio Valley and Mid-Atlantic region, with a cold front gradually progressing southeastward across these regions through tonight. Thunderstorms are expected to develop/increase over the mountains and/or in association with ongoing persistent clusters. As low-level lapse rates steepen, damaging winds will be the primary risk. A few sustained/semi-organized clusters of storms may materialize this afternoon, particularly from south-central Pennsylvania southward to near/east of the Blue Ridge in Virginia/Northern Carolina. However, current thinking is that the overall severe storm coverage/risk magnitude will be a bit lower as compared to prior days across the region. ...Southeast Wyoming/Central High Plains... To the north of an eastern Colorado-centered surface low, low-level upslope flow and differential heating in vicinity of the higher terrain is likely to contribute to isolated thunderstorm development this afternoon. Storms should intensify as they move east-southeastward within a moist/increasingly unstable environment. A few instances of isolated severe hail will initially be possible. Storms may gradually cluster with localized severe-caliber wind gust potential this evening across the southern Nebraska Panhandle/northeast Colorado vicinity, and possibly southwest Nebraska/northwest Kansas. ...Southern/eastern Montana to northern High Plains... Isolated to scattered thunderstorms are expected to develop across this area during the afternoon, and into evening with eastward extent. Isolated severe gusts/hail are the main concerns. A relative concentration of convection is possible during about 00Z-06Z across portions of eastern Montana and perhaps northeastern Wyoming. During that time frame, some of the stronger low-level mass response and convergence (related to the approaching shortwave trough), and perhaps the leading fringe of mid/upper synoptic forcing, will impinge upon a narrow plume of relatively maximized buoyancy and boundary-layer moisture. Pre-convective MLCAPE of 1000-2000 J/kg is possible this evening near an axis from RAP-GGW, amidst well-mixed subcloud layers supporting strong-severe gust potential. However, weak mid/upper-level winds suggest that severe potential should remain fairly disorganized and/or short-lived. ...Southern Plains to Mid-South/Tennessee Valley... Within a moist/unstable environment, surface-based thunderstorm development later this afternoon will be focused along zones of residual outflow/differential heating. While weak westerlies will generally prevail, ample heating/buoyancy could support localized severe-caliber downdrafts late this afternoon/early evening. ..Guyer/Bunting.. 08/22/2019 Read more

SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1136 AM CDT Thu Aug 22 2019 Valid 221630Z - 231200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM THE SOUTHERN PLAINS TO THE MID-ATLANTIC STATES AND THE NORTHERN/CENTRAL HIGH PLAINS... ...SUMMARY... Isolated damaging winds are possible this afternoon and evening from the southern Plains and Mid-South to the Mid-Atlantic States. Isolated severe hail and wind are also possible over the northern and central High Plains. ...Mid-Atlantic States/Carolinas... A belt of cyclonically curved/moderately strong westerlies aloft will persist over the Upper Ohio Valley and Mid-Atlantic region, with a cold front gradually progressing southeastward across these regions through tonight. Thunderstorms are expected to develop/increase over the mountains and/or in association with ongoing persistent clusters. As low-level lapse rates steepen, damaging winds will be the primary risk. A few sustained/semi-organized clusters of storms may materialize this afternoon, particularly from south-central Pennsylvania southward to near/east of the Blue Ridge in Virginia/Northern Carolina. However, current thinking is that the overall severe storm coverage/risk magnitude will be a bit lower as compared to prior days across the region. ...Southeast Wyoming/Central High Plains... To the north of an eastern Colorado-centered surface low, low-level upslope flow and differential heating in vicinity of the higher terrain is likely to contribute to isolated thunderstorm development this afternoon. Storms should intensify as they move east-southeastward within a moist/increasingly unstable environment. A few instances of isolated severe hail will initially be possible. Storms may gradually cluster with localized severe-caliber wind gust potential this evening across the southern Nebraska Panhandle/northeast Colorado vicinity, and possibly southwest Nebraska/northwest Kansas. ...Southern/eastern Montana to northern High Plains... Isolated to scattered thunderstorms are expected to develop across this area during the afternoon, and into evening with eastward extent. Isolated severe gusts/hail are the main concerns. A relative concentration of convection is possible during about 00Z-06Z across portions of eastern Montana and perhaps northeastern Wyoming. During that time frame, some of the stronger low-level mass response and convergence (related to the approaching shortwave trough), and perhaps the leading fringe of mid/upper synoptic forcing, will impinge upon a narrow plume of relatively maximized buoyancy and boundary-layer moisture. Pre-convective MLCAPE of 1000-2000 J/kg is possible this evening near an axis from RAP-GGW, amidst well-mixed subcloud layers supporting strong-severe gust potential. However, weak mid/upper-level winds suggest that severe potential should remain fairly disorganized and/or short-lived. ...Southern Plains to Mid-South/Tennessee Valley... Within a moist/unstable environment, surface-based thunderstorm development later this afternoon will be focused along zones of residual outflow/differential heating. While weak westerlies will generally prevail, ample heating/buoyancy could support localized severe-caliber downdrafts late this afternoon/early evening. ..Guyer/Bunting.. 08/22/2019 Read more

SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1136 AM CDT Thu Aug 22 2019 Valid 221630Z - 231200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM THE SOUTHERN PLAINS TO THE MID-ATLANTIC STATES AND THE NORTHERN/CENTRAL HIGH PLAINS... ...SUMMARY... Isolated damaging winds are possible this afternoon and evening from the southern Plains and Mid-South to the Mid-Atlantic States. Isolated severe hail and wind are also possible over the northern and central High Plains. ...Mid-Atlantic States/Carolinas... A belt of cyclonically curved/moderately strong westerlies aloft will persist over the Upper Ohio Valley and Mid-Atlantic region, with a cold front gradually progressing southeastward across these regions through tonight. Thunderstorms are expected to develop/increase over the mountains and/or in association with ongoing persistent clusters. As low-level lapse rates steepen, damaging winds will be the primary risk. A few sustained/semi-organized clusters of storms may materialize this afternoon, particularly from south-central Pennsylvania southward to near/east of the Blue Ridge in Virginia/Northern Carolina. However, current thinking is that the overall severe storm coverage/risk magnitude will be a bit lower as compared to prior days across the region. ...Southeast Wyoming/Central High Plains... To the north of an eastern Colorado-centered surface low, low-level upslope flow and differential heating in vicinity of the higher terrain is likely to contribute to isolated thunderstorm development this afternoon. Storms should intensify as they move east-southeastward within a moist/increasingly unstable environment. A few instances of isolated severe hail will initially be possible. Storms may gradually cluster with localized severe-caliber wind gust potential this evening across the southern Nebraska Panhandle/northeast Colorado vicinity, and possibly southwest Nebraska/northwest Kansas. ...Southern/eastern Montana to northern High Plains... Isolated to scattered thunderstorms are expected to develop across this area during the afternoon, and into evening with eastward extent. Isolated severe gusts/hail are the main concerns. A relative concentration of convection is possible during about 00Z-06Z across portions of eastern Montana and perhaps northeastern Wyoming. During that time frame, some of the stronger low-level mass response and convergence (related to the approaching shortwave trough), and perhaps the leading fringe of mid/upper synoptic forcing, will impinge upon a narrow plume of relatively maximized buoyancy and boundary-layer moisture. Pre-convective MLCAPE of 1000-2000 J/kg is possible this evening near an axis from RAP-GGW, amidst well-mixed subcloud layers supporting strong-severe gust potential. However, weak mid/upper-level winds suggest that severe potential should remain fairly disorganized and/or short-lived. ...Southern Plains to Mid-South/Tennessee Valley... Within a moist/unstable environment, surface-based thunderstorm development later this afternoon will be focused along zones of residual outflow/differential heating. While weak westerlies will generally prevail, ample heating/buoyancy could support localized severe-caliber downdrafts late this afternoon/early evening. ..Guyer/Bunting.. 08/22/2019 Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0759 AM CDT Thu Aug 22 2019 Valid 221300Z - 231200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM OKLAHOMA TO PARTS OF THE OHIO VALLEY...MID-ATLANTIC AND NEW ENGLAND...AND OVER PORTIONS OF THE CENTRAL AND NORTHERN HIGH PLAINS... ...SUMMARY... Damaging gusts, with a few severe, are possible this afternoon and evening from Oklahoma to parts of the Ohio Valley, Mid-Atlantic and New England. Isolated severe hail and wind will also be possible over the central and northern High Plains. ...Synopsis... An amplified and progressive northern stream will characterize the mid/upper-level pattern trough the period, with sharply defined, synoptic-scale ridging moving eastward across the northern Plains, Upper Midwest and areas of Canada near western Hudson Bay. To the east, a well-defined cyclone near the James Bay coast of QC will progress eastward toward the northern Gulf of St. Lawrence. A trailing, positively tilted shortwave trough will deamplify as it moves eastward from the upper Great Lakes to New England, amidst broadly confluent flow. Upstream of the synoptic ridge, another substantial shortwave trough was readily apparent in moisture-channel imagery over the interior Pacific Northwest. This perturbation will decouple from an initially phased but more progressive vorticity banner over western Canada, then move slowly eastward across the northern Rockies. By the end of the period, the 500-mb trough should extend from north-central MT to northwestern UT. To its southeast, and south of the synoptic ridge, a weak shortwave trough is located over the central/southern High Plains, and should move slowly eastward across OK and northwest TX through the period. ...Northeastern CONUS to southern Plains... Isolated to scattered thunderstorms are expected to develop episodically throughout the period -- but maximized from afternoon into early evening -- offering sporadic damaging winds, isolated severe gusts, and in the western parts of the outlook area, isolated severe hail. Mid/upper winds will be maximized over the Northeast, while moisture is greatest across the South, and midlevel lapse rates maximized from the southern Plains to the Mid-South. A few loosely organized bands of convection may develop under the southern rim of somewhat stronger flow aloft, across the north-central Appalachians into the Mid-Atlantic coastal plain, as well as portions of southern/eastern New England where favorable low-level moisture will remain. One of those convective bands may involve an eastward shift of an area of strong thunderstorms ongoing over portions of OH/WV, later impinging upon areas of diabatically driven surface destabilization. Such potential will depend on the structure/survival of the related cold pool across the Appalachians. A limiting factor will be weak deep-layer lapse rates, keeping MLCAPE below 1000 J/kg in most areas from central VA northward/northeastward, with pockets below 500 J/kg. Buoyancy will increase southward over the Carolinas and southwestward across the southern Appalachians region, where heating and low-level lapse rates will be stronger. From this region westward to the southern Plains, prefrontal outflow/differential- heating boundaries will be the main foci for convective development and localized intensification. Although flow aloft and deep shear will be weak, limiting overall organization of the severe potential, relative maxima in convective coverage may occur over portions of OK and the Ozarks region. Subtle large-scale lift ahead of the southern High Plains shortwave trough will augment already steep midlevel lapse rates, while intense surface heating occurs ahead of the front and away from areas of persistent/antecedent cloud cover, weakening MLCINH to negligible levels. Well-mixed subcloud layers will support maintenance of hail and downdrafts to the surface. Localized concentrations of severe potential probably will develop within this lengthy outlook area, and a 15%/slight risk may be added as mesoscale trends warrant. However, uncertainties on that and smaller scales preclude greater than marginal unconditional severe probabilities being assigned at this time. ...Northern Rockies/Plains to central High Plains... Isolated to scattered thunderstorms are expected to develop across this area during the afternoon, and into evening with eastward extent. Isolated severe gusts/hail are the main concerns. Primary sources for lift will include the Pacific cold front and lee troughing over MT and northeastern WY, and upslope flow with heating of higher terrain along the western rim of the outlook in WY/CO. A relative concentration of convection is possible during about 00Z-06Z across portions of eastern MT and perhaps northeastern WY. During that time frame, some of the stronger low-level mass response and convergence (related to the approaching shortwave trough), and perhaps the leading fringe of mid/upper synoptic forcing, will impinge upon a narrow plume of relatively maximized buoyancy and boundary-layer moisture. Preconvective MLCAPE of 1000-2000 J/kg is possible this evening near an axis from RAP-GGW, amidst well-mixed subcloud layers supporting strong-severe gust potential. However, weak mid/upper-level winds and related minuscule values of effective shear, along with progs of quick transition to messy convective mode, suggest severe potential is fairly disorganized and/or short-lived. ..Edwards.. 08/22/2019 Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0759 AM CDT Thu Aug 22 2019 Valid 221300Z - 231200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM OKLAHOMA TO PARTS OF THE OHIO VALLEY...MID-ATLANTIC AND NEW ENGLAND...AND OVER PORTIONS OF THE CENTRAL AND NORTHERN HIGH PLAINS... ...SUMMARY... Damaging gusts, with a few severe, are possible this afternoon and evening from Oklahoma to parts of the Ohio Valley, Mid-Atlantic and New England. Isolated severe hail and wind will also be possible over the central and northern High Plains. ...Synopsis... An amplified and progressive northern stream will characterize the mid/upper-level pattern trough the period, with sharply defined, synoptic-scale ridging moving eastward across the northern Plains, Upper Midwest and areas of Canada near western Hudson Bay. To the east, a well-defined cyclone near the James Bay coast of QC will progress eastward toward the northern Gulf of St. Lawrence. A trailing, positively tilted shortwave trough will deamplify as it moves eastward from the upper Great Lakes to New England, amidst broadly confluent flow. Upstream of the synoptic ridge, another substantial shortwave trough was readily apparent in moisture-channel imagery over the interior Pacific Northwest. This perturbation will decouple from an initially phased but more progressive vorticity banner over western Canada, then move slowly eastward across the northern Rockies. By the end of the period, the 500-mb trough should extend from north-central MT to northwestern UT. To its southeast, and south of the synoptic ridge, a weak shortwave trough is located over the central/southern High Plains, and should move slowly eastward across OK and northwest TX through the period. ...Northeastern CONUS to southern Plains... Isolated to scattered thunderstorms are expected to develop episodically throughout the period -- but maximized from afternoon into early evening -- offering sporadic damaging winds, isolated severe gusts, and in the western parts of the outlook area, isolated severe hail. Mid/upper winds will be maximized over the Northeast, while moisture is greatest across the South, and midlevel lapse rates maximized from the southern Plains to the Mid-South. A few loosely organized bands of convection may develop under the southern rim of somewhat stronger flow aloft, across the north-central Appalachians into the Mid-Atlantic coastal plain, as well as portions of southern/eastern New England where favorable low-level moisture will remain. One of those convective bands may involve an eastward shift of an area of strong thunderstorms ongoing over portions of OH/WV, later impinging upon areas of diabatically driven surface destabilization. Such potential will depend on the structure/survival of the related cold pool across the Appalachians. A limiting factor will be weak deep-layer lapse rates, keeping MLCAPE below 1000 J/kg in most areas from central VA northward/northeastward, with pockets below 500 J/kg. Buoyancy will increase southward over the Carolinas and southwestward across the southern Appalachians region, where heating and low-level lapse rates will be stronger. From this region westward to the southern Plains, prefrontal outflow/differential- heating boundaries will be the main foci for convective development and localized intensification. Although flow aloft and deep shear will be weak, limiting overall organization of the severe potential, relative maxima in convective coverage may occur over portions of OK and the Ozarks region. Subtle large-scale lift ahead of the southern High Plains shortwave trough will augment already steep midlevel lapse rates, while intense surface heating occurs ahead of the front and away from areas of persistent/antecedent cloud cover, weakening MLCINH to negligible levels. Well-mixed subcloud layers will support maintenance of hail and downdrafts to the surface. Localized concentrations of severe potential probably will develop within this lengthy outlook area, and a 15%/slight risk may be added as mesoscale trends warrant. However, uncertainties on that and smaller scales preclude greater than marginal unconditional severe probabilities being assigned at this time. ...Northern Rockies/Plains to central High Plains... Isolated to scattered thunderstorms are expected to develop across this area during the afternoon, and into evening with eastward extent. Isolated severe gusts/hail are the main concerns. Primary sources for lift will include the Pacific cold front and lee troughing over MT and northeastern WY, and upslope flow with heating of higher terrain along the western rim of the outlook in WY/CO. A relative concentration of convection is possible during about 00Z-06Z across portions of eastern MT and perhaps northeastern WY. During that time frame, some of the stronger low-level mass response and convergence (related to the approaching shortwave trough), and perhaps the leading fringe of mid/upper synoptic forcing, will impinge upon a narrow plume of relatively maximized buoyancy and boundary-layer moisture. Preconvective MLCAPE of 1000-2000 J/kg is possible this evening near an axis from RAP-GGW, amidst well-mixed subcloud layers supporting strong-severe gust potential. However, weak mid/upper-level winds and related minuscule values of effective shear, along with progs of quick transition to messy convective mode, suggest severe potential is fairly disorganized and/or short-lived. ..Edwards.. 08/22/2019 Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0759 AM CDT Thu Aug 22 2019 Valid 221300Z - 231200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM OKLAHOMA TO PARTS OF THE OHIO VALLEY...MID-ATLANTIC AND NEW ENGLAND...AND OVER PORTIONS OF THE CENTRAL AND NORTHERN HIGH PLAINS... ...SUMMARY... Damaging gusts, with a few severe, are possible this afternoon and evening from Oklahoma to parts of the Ohio Valley, Mid-Atlantic and New England. Isolated severe hail and wind will also be possible over the central and northern High Plains. ...Synopsis... An amplified and progressive northern stream will characterize the mid/upper-level pattern trough the period, with sharply defined, synoptic-scale ridging moving eastward across the northern Plains, Upper Midwest and areas of Canada near western Hudson Bay. To the east, a well-defined cyclone near the James Bay coast of QC will progress eastward toward the northern Gulf of St. Lawrence. A trailing, positively tilted shortwave trough will deamplify as it moves eastward from the upper Great Lakes to New England, amidst broadly confluent flow. Upstream of the synoptic ridge, another substantial shortwave trough was readily apparent in moisture-channel imagery over the interior Pacific Northwest. This perturbation will decouple from an initially phased but more progressive vorticity banner over western Canada, then move slowly eastward across the northern Rockies. By the end of the period, the 500-mb trough should extend from north-central MT to northwestern UT. To its southeast, and south of the synoptic ridge, a weak shortwave trough is located over the central/southern High Plains, and should move slowly eastward across OK and northwest TX through the period. ...Northeastern CONUS to southern Plains... Isolated to scattered thunderstorms are expected to develop episodically throughout the period -- but maximized from afternoon into early evening -- offering sporadic damaging winds, isolated severe gusts, and in the western parts of the outlook area, isolated severe hail. Mid/upper winds will be maximized over the Northeast, while moisture is greatest across the South, and midlevel lapse rates maximized from the southern Plains to the Mid-South. A few loosely organized bands of convection may develop under the southern rim of somewhat stronger flow aloft, across the north-central Appalachians into the Mid-Atlantic coastal plain, as well as portions of southern/eastern New England where favorable low-level moisture will remain. One of those convective bands may involve an eastward shift of an area of strong thunderstorms ongoing over portions of OH/WV, later impinging upon areas of diabatically driven surface destabilization. Such potential will depend on the structure/survival of the related cold pool across the Appalachians. A limiting factor will be weak deep-layer lapse rates, keeping MLCAPE below 1000 J/kg in most areas from central VA northward/northeastward, with pockets below 500 J/kg. Buoyancy will increase southward over the Carolinas and southwestward across the southern Appalachians region, where heating and low-level lapse rates will be stronger. From this region westward to the southern Plains, prefrontal outflow/differential- heating boundaries will be the main foci for convective development and localized intensification. Although flow aloft and deep shear will be weak, limiting overall organization of the severe potential, relative maxima in convective coverage may occur over portions of OK and the Ozarks region. Subtle large-scale lift ahead of the southern High Plains shortwave trough will augment already steep midlevel lapse rates, while intense surface heating occurs ahead of the front and away from areas of persistent/antecedent cloud cover, weakening MLCINH to negligible levels. Well-mixed subcloud layers will support maintenance of hail and downdrafts to the surface. Localized concentrations of severe potential probably will develop within this lengthy outlook area, and a 15%/slight risk may be added as mesoscale trends warrant. However, uncertainties on that and smaller scales preclude greater than marginal unconditional severe probabilities being assigned at this time. ...Northern Rockies/Plains to central High Plains... Isolated to scattered thunderstorms are expected to develop across this area during the afternoon, and into evening with eastward extent. Isolated severe gusts/hail are the main concerns. Primary sources for lift will include the Pacific cold front and lee troughing over MT and northeastern WY, and upslope flow with heating of higher terrain along the western rim of the outlook in WY/CO. A relative concentration of convection is possible during about 00Z-06Z across portions of eastern MT and perhaps northeastern WY. During that time frame, some of the stronger low-level mass response and convergence (related to the approaching shortwave trough), and perhaps the leading fringe of mid/upper synoptic forcing, will impinge upon a narrow plume of relatively maximized buoyancy and boundary-layer moisture. Preconvective MLCAPE of 1000-2000 J/kg is possible this evening near an axis from RAP-GGW, amidst well-mixed subcloud layers supporting strong-severe gust potential. However, weak mid/upper-level winds and related minuscule values of effective shear, along with progs of quick transition to messy convective mode, suggest severe potential is fairly disorganized and/or short-lived. ..Edwards.. 08/22/2019 Read more

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0345 AM CDT Thu Aug 22 2019 Valid 251200Z - 301200Z ...DISCUSSION... Height falls and cooling aloft will spread southeastward across the northern Plains on Sunday/D4 and toward the upper MS Valley by Monday/D5, with a cold front affecting much of the northern and central Plains. Due to a rather large surface ridge over the Great Lakes and Northeast, the moist plume preceding this system over the Plains will remain narrow, comprised primarily of mid 60s F dewpoints. Model differences exist regarding the position (or existence) of upper disturbances preceding the main shortwave trough, such as the ECMWF depiction of a weak low over MO on Sunday/D4. Questions regarding instability also exist as early day storms are likely over parts of the northern Plains. As such, will defer severe probabilities to later outlooks. For the D6-D8 period, a deep upper low will form over northern Ontario with a broad region of strong cyclonic flow aloft enveloping much of the northern CONUS and eastern Canada. This will drive a cold front rather far south, perhaps to the northern Gulf Coast by Thursday/D8. This will reduce the potential area of thunderstorms over much of the Plains and MS Valley. Read more

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0345 AM CDT Thu Aug 22 2019 Valid 251200Z - 301200Z ...DISCUSSION... Height falls and cooling aloft will spread southeastward across the northern Plains on Sunday/D4 and toward the upper MS Valley by Monday/D5, with a cold front affecting much of the northern and central Plains. Due to a rather large surface ridge over the Great Lakes and Northeast, the moist plume preceding this system over the Plains will remain narrow, comprised primarily of mid 60s F dewpoints. Model differences exist regarding the position (or existence) of upper disturbances preceding the main shortwave trough, such as the ECMWF depiction of a weak low over MO on Sunday/D4. Questions regarding instability also exist as early day storms are likely over parts of the northern Plains. As such, will defer severe probabilities to later outlooks. For the D6-D8 period, a deep upper low will form over northern Ontario with a broad region of strong cyclonic flow aloft enveloping much of the northern CONUS and eastern Canada. This will drive a cold front rather far south, perhaps to the northern Gulf Coast by Thursday/D8. This will reduce the potential area of thunderstorms over much of the Plains and MS Valley. Read more

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0345 AM CDT Thu Aug 22 2019 Valid 251200Z - 301200Z ...DISCUSSION... Height falls and cooling aloft will spread southeastward across the northern Plains on Sunday/D4 and toward the upper MS Valley by Monday/D5, with a cold front affecting much of the northern and central Plains. Due to a rather large surface ridge over the Great Lakes and Northeast, the moist plume preceding this system over the Plains will remain narrow, comprised primarily of mid 60s F dewpoints. Model differences exist regarding the position (or existence) of upper disturbances preceding the main shortwave trough, such as the ECMWF depiction of a weak low over MO on Sunday/D4. Questions regarding instability also exist as early day storms are likely over parts of the northern Plains. As such, will defer severe probabilities to later outlooks. For the D6-D8 period, a deep upper low will form over northern Ontario with a broad region of strong cyclonic flow aloft enveloping much of the northern CONUS and eastern Canada. This will drive a cold front rather far south, perhaps to the northern Gulf Coast by Thursday/D8. This will reduce the potential area of thunderstorms over much of the Plains and MS Valley. Read more

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0345 AM CDT Thu Aug 22 2019 Valid 251200Z - 301200Z ...DISCUSSION... Height falls and cooling aloft will spread southeastward across the northern Plains on Sunday/D4 and toward the upper MS Valley by Monday/D5, with a cold front affecting much of the northern and central Plains. Due to a rather large surface ridge over the Great Lakes and Northeast, the moist plume preceding this system over the Plains will remain narrow, comprised primarily of mid 60s F dewpoints. Model differences exist regarding the position (or existence) of upper disturbances preceding the main shortwave trough, such as the ECMWF depiction of a weak low over MO on Sunday/D4. Questions regarding instability also exist as early day storms are likely over parts of the northern Plains. As such, will defer severe probabilities to later outlooks. For the D6-D8 period, a deep upper low will form over northern Ontario with a broad region of strong cyclonic flow aloft enveloping much of the northern CONUS and eastern Canada. This will drive a cold front rather far south, perhaps to the northern Gulf Coast by Thursday/D8. This will reduce the potential area of thunderstorms over much of the Plains and MS Valley. Read more

SPC Day 1 Fire Weather Outlook
Day 1 Fire Weather Outlook CORR 1 NWS Storm Prediction Center Norman OK 0157 AM CDT Thu Aug 22 2019 Valid 221200Z - 231200Z CORRECTED FOR TEXT ...CRITICAL FIRE WEATHER AREA FOR PORTIONS OF UTAH...NORTHERN ARIZONA...SOUTHEAST NEVADA...SOUTHWEST WYOMING...NORTHWEST COLORADO... ...Synopsis... An upper-level shortwave trough will continue moving eastward over the Pacific Northwest and northern Rockies today. An associated surface cold front will also continue pushing east and south through much of the northern Rockies and northern California and into the Great Basin. A pre-frontal surface pressure trough will run parallel to the cold front stretching southwest from north-central Montana into southern Nevada. A broad area of elevated conditions will develop stretching from northern Arizona/southern Nevada into central Wyoming, with critical conditions likely developing in far northwest Arizona/southeast Nevada through central Utah into southwest Wyoming. West-southwest sustained surface winds of 15-25 mph with RH values of 8-20% are likely to develop ahead of the cold front during the afternoon and into the evening. ERCs are mostly above the 80th percentile within the elevated/critical areas including some locations above the 95th percentile. Elevated conditions are likely across portions of the Snake River Plain and vicinity this afternoon. The cold front will likely push through the area this morning. However, daytime heating will help mix/deepen the boundary layer and increase surface temperatures with west-southwest surface winds of 15-20 mph and RH values of 15-20% developing during the afternoon. ..Nauslar.. 08/22/2019 ...Please see www.spc.noaa.gov/fire for graphic product... Read more

SPC Day 1 Fire Weather Outlook
Day 1 Fire Weather Outlook CORR 1 NWS Storm Prediction Center Norman OK 0157 AM CDT Thu Aug 22 2019 Valid 221200Z - 231200Z CORRECTED FOR TEXT ...CRITICAL FIRE WEATHER AREA FOR PORTIONS OF UTAH...NORTHERN ARIZONA...SOUTHEAST NEVADA...SOUTHWEST WYOMING...NORTHWEST COLORADO... ...Synopsis... An upper-level shortwave trough will continue moving eastward over the Pacific Northwest and northern Rockies today. An associated surface cold front will also continue pushing east and south through much of the northern Rockies and northern California and into the Great Basin. A pre-frontal surface pressure trough will run parallel to the cold front stretching southwest from north-central Montana into southern Nevada. A broad area of elevated conditions will develop stretching from northern Arizona/southern Nevada into central Wyoming, with critical conditions likely developing in far northwest Arizona/southeast Nevada through central Utah into southwest Wyoming. West-southwest sustained surface winds of 15-25 mph with RH values of 8-20% are likely to develop ahead of the cold front during the afternoon and into the evening. ERCs are mostly above the 80th percentile within the elevated/critical areas including some locations above the 95th percentile. Elevated conditions are likely across portions of the Snake River Plain and vicinity this afternoon. The cold front will likely push through the area this morning. However, daytime heating will help mix/deepen the boundary layer and increase surface temperatures with west-southwest surface winds of 15-20 mph and RH values of 15-20% developing during the afternoon. ..Nauslar.. 08/22/2019 ...Please see www.spc.noaa.gov/fire for graphic product... Read more

SPC Day 1 Fire Weather Outlook
Day 1 Fire Weather Outlook CORR 1 NWS Storm Prediction Center Norman OK 0157 AM CDT Thu Aug 22 2019 Valid 221200Z - 231200Z CORRECTED FOR TEXT ...CRITICAL FIRE WEATHER AREA FOR PORTIONS OF UTAH...NORTHERN ARIZONA...SOUTHEAST NEVADA...SOUTHWEST WYOMING...NORTHWEST COLORADO... ...Synopsis... An upper-level shortwave trough will continue moving eastward over the Pacific Northwest and northern Rockies today. An associated surface cold front will also continue pushing east and south through much of the northern Rockies and northern California and into the Great Basin. A pre-frontal surface pressure trough will run parallel to the cold front stretching southwest from north-central Montana into southern Nevada. A broad area of elevated conditions will develop stretching from northern Arizona/southern Nevada into central Wyoming, with critical conditions likely developing in far northwest Arizona/southeast Nevada through central Utah into southwest Wyoming. West-southwest sustained surface winds of 15-25 mph with RH values of 8-20% are likely to develop ahead of the cold front during the afternoon and into the evening. ERCs are mostly above the 80th percentile within the elevated/critical areas including some locations above the 95th percentile. Elevated conditions are likely across portions of the Snake River Plain and vicinity this afternoon. The cold front will likely push through the area this morning. However, daytime heating will help mix/deepen the boundary layer and increase surface temperatures with west-southwest surface winds of 15-20 mph and RH values of 15-20% developing during the afternoon. ..Nauslar.. 08/22/2019 ...Please see www.spc.noaa.gov/fire for graphic product... Read more

SPC 0730Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0146 AM CDT Thu Aug 22 2019 Valid 241200Z - 251200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER THE NORTHERN PLAINS... ...SUMMARY... At least isolated severe storms are possible over parts of the northern Plains Saturday. ...Synopsis... Strong cyclonic flow aloft will develop southeastward into the northern Rockies, providing increased deep-layer shear and cooling aloft to the northern High Plains. A weak shortwave trough will precede this larger-scale wave, aiding lift over the Dakotas and MN during the day. At the surface, low pressure will deepen over the northern High Plains, enhancing southerly surface winds and maintaining a plume of 60s F dewpoints from KS to southern Manitoba. Convergence along a cold front will increase overnight and into Sunday morning from eastern MT toward the Black Hills, providing lift. Elsewhere, a moist and unstable air mass will remain over the southern Plains and lower MS Valley, with various areas of storms and outflow boundaries throughout the period. Any potential marginal threat area here for wind gusts is currently unpredictable. ...Northern Plains... Storms are likely to be ongoing across the central Dakotas, and possibly into north-central NE Saturday morning, near the eastern instability gradient where southwesterly 850 mb winds of 30-40 kt will provide lift via warm advection. Marginal hail cannot be ruled out early. Later in the day, heating will remove CIN over the central and western Dakotas, and redevelopment is possible near the tail end of the departing lead wave over ND. Veering winds with height will favor a supercell or two, with severe threat dependent on how much instability can develop near an axis of 200-300 m2/s2 effective SRH. Isolated cells are also possible at peak heating over western SD. Overnight, large-scale lift will increase from MT into the western Dakotas. Steep lapse rates aloft and strengthening deep-layer shear will conditionally favor severe storms, however, it is unclear how much moisture and instability will exist overnight that far west. Parts of the area may require a categorical upgrade in future outlooks should instability increase. ..Jewell.. 08/22/2019 Read more

SPC 0730Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0146 AM CDT Thu Aug 22 2019 Valid 241200Z - 251200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER THE NORTHERN PLAINS... ...SUMMARY... At least isolated severe storms are possible over parts of the northern Plains Saturday. ...Synopsis... Strong cyclonic flow aloft will develop southeastward into the northern Rockies, providing increased deep-layer shear and cooling aloft to the northern High Plains. A weak shortwave trough will precede this larger-scale wave, aiding lift over the Dakotas and MN during the day. At the surface, low pressure will deepen over the northern High Plains, enhancing southerly surface winds and maintaining a plume of 60s F dewpoints from KS to southern Manitoba. Convergence along a cold front will increase overnight and into Sunday morning from eastern MT toward the Black Hills, providing lift. Elsewhere, a moist and unstable air mass will remain over the southern Plains and lower MS Valley, with various areas of storms and outflow boundaries throughout the period. Any potential marginal threat area here for wind gusts is currently unpredictable. ...Northern Plains... Storms are likely to be ongoing across the central Dakotas, and possibly into north-central NE Saturday morning, near the eastern instability gradient where southwesterly 850 mb winds of 30-40 kt will provide lift via warm advection. Marginal hail cannot be ruled out early. Later in the day, heating will remove CIN over the central and western Dakotas, and redevelopment is possible near the tail end of the departing lead wave over ND. Veering winds with height will favor a supercell or two, with severe threat dependent on how much instability can develop near an axis of 200-300 m2/s2 effective SRH. Isolated cells are also possible at peak heating over western SD. Overnight, large-scale lift will increase from MT into the western Dakotas. Steep lapse rates aloft and strengthening deep-layer shear will conditionally favor severe storms, however, it is unclear how much moisture and instability will exist overnight that far west. Parts of the area may require a categorical upgrade in future outlooks should instability increase. ..Jewell.. 08/22/2019 Read more

SPC 0730Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0146 AM CDT Thu Aug 22 2019 Valid 241200Z - 251200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER THE NORTHERN PLAINS... ...SUMMARY... At least isolated severe storms are possible over parts of the northern Plains Saturday. ...Synopsis... Strong cyclonic flow aloft will develop southeastward into the northern Rockies, providing increased deep-layer shear and cooling aloft to the northern High Plains. A weak shortwave trough will precede this larger-scale wave, aiding lift over the Dakotas and MN during the day. At the surface, low pressure will deepen over the northern High Plains, enhancing southerly surface winds and maintaining a plume of 60s F dewpoints from KS to southern Manitoba. Convergence along a cold front will increase overnight and into Sunday morning from eastern MT toward the Black Hills, providing lift. Elsewhere, a moist and unstable air mass will remain over the southern Plains and lower MS Valley, with various areas of storms and outflow boundaries throughout the period. Any potential marginal threat area here for wind gusts is currently unpredictable. ...Northern Plains... Storms are likely to be ongoing across the central Dakotas, and possibly into north-central NE Saturday morning, near the eastern instability gradient where southwesterly 850 mb winds of 30-40 kt will provide lift via warm advection. Marginal hail cannot be ruled out early. Later in the day, heating will remove CIN over the central and western Dakotas, and redevelopment is possible near the tail end of the departing lead wave over ND. Veering winds with height will favor a supercell or two, with severe threat dependent on how much instability can develop near an axis of 200-300 m2/s2 effective SRH. Isolated cells are also possible at peak heating over western SD. Overnight, large-scale lift will increase from MT into the western Dakotas. Steep lapse rates aloft and strengthening deep-layer shear will conditionally favor severe storms, however, it is unclear how much moisture and instability will exist overnight that far west. Parts of the area may require a categorical upgrade in future outlooks should instability increase. ..Jewell.. 08/22/2019 Read more