Severe Storms

SPC Day 1 Fire Weather Outlook
Day 1 Fire Weather Outlook NWS Storm Prediction Center Norman OK 1155 AM CDT Fri Aug 09 2019 Valid 091700Z - 101200Z ...CRITICAL FIRE WEATHER AREA FOR PORTIONS OF CENTRAL INTO EASTERN OREGON... A scattered dry-thunderstorm delineation was added to portions of central and eastern Oregon. At least scattered thunderstorm development is expected, with ample buoyancy supportive of vigorous updrafts capable of producing copious amounts of lightning strikes, atop fuels that are at least modestly supportive of fire spread. While wetting rains are expected with many of the storms, a dry sfc-600 mb dry sub-cloud layer will be present, suggesting that at least a modest amount of dry strikes are possible. In addition, new lightning-induced fire starts may be exacerbated by strong to potentially severe erratic winds associated with the stronger storms. Otherwise, portions of the isolated dry thunderstorm delineation were also expanded southward into parts of northern California and central Nevada, as confidence has increased in thunderstorm development in these regions. Here, 0.50-0.75 precipitable water values, a dry sub-cloud layer, and relatively fast storms motions will all contribute to dry strike potential over fuels receptive to fire spread. In addition, the elevated delineation was adjusted in accordance to where the latest model guidance depicts 10-15% surface RH and 15+ mph sustained winds. ..Squitieri.. 08/09/2019 .PREV DISCUSSION... /ISSUED 0104 AM CDT Fri Aug 09 2019/ ...Synopsis... A longwave trough centered just west of the northern California coast will continue its slow trek eastward toward the West Coast throughout the day. As this occurs, mid-level flow will increase in a corridor from southern California northward to Idaho. The deep southerly flow will maintain moist mid-level profiles in much of the western third of the CONUS, and lift associated with the approaching trough and surface heating should foster several areas of thunderstorms. Additionally, a favorable pressure gradient and terrain-related forcing should foster areas of windy conditions across Nevada and vicinity through the evening. ...Central Nevada northward into Washington for thunderstorms... The aforementioned synoptic pattern will foster scattered areas of thunderstorms as early as mid-day while gradually increasing in coverage and intensity through the afternoon and evening hours. These storms should provide wetting rains to several areas, with isolated dry lightning strikes occurring on the periphery of wetting thunderstorm cores. Coverage will increase with northward extent into Oregon and southwestern Idaho throughout the day, with widespread areas of gusty outflow winds amidst areas of dry fuels suggestive of erratic fire behavior and complicated suppression efforts. A few of these wind gusts may exceed severe limits - refer to SPC Day 1 Convective Outlooks for more updates on this threat. At least pockets of dry fuels will exist as far east as eastern Idaho, and isolated dry thunderstorm potential has been highlighted in this area with storms expected through early evening. Storms will continue to lift northward and persist in many areas of Washington and Oregon overnight. ...Much of Nevada and far northeast California for elevated fire weather conditions... Surface troughing and vertical mixing processes will foster areas of 20-25 mph surface winds that will be strongest in a couple of corridors - one in the immediate lee of the Sierras and another along an axis from southeastern into east-central Nevada. Areas of critically low RH values will also exist for a few hours during peak heating, though clouds and areas of precipitation may hinder the degree of mixing/lowered RH in several areas as well. The overall scenario appears to be consistent with elevated fire weather thresholds, though locally critical fire weather will probably develop over southeastern Nevada for at least an hour or two. ...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 1155 AM CDT Fri Aug 09 2019 Valid 091700Z - 101200Z ...CRITICAL FIRE WEATHER AREA FOR PORTIONS OF CENTRAL INTO EASTERN OREGON... A scattered dry-thunderstorm delineation was added to portions of central and eastern Oregon. At least scattered thunderstorm development is expected, with ample buoyancy supportive of vigorous updrafts capable of producing copious amounts of lightning strikes, atop fuels that are at least modestly supportive of fire spread. While wetting rains are expected with many of the storms, a dry sfc-600 mb dry sub-cloud layer will be present, suggesting that at least a modest amount of dry strikes are possible. In addition, new lightning-induced fire starts may be exacerbated by strong to potentially severe erratic winds associated with the stronger storms. Otherwise, portions of the isolated dry thunderstorm delineation were also expanded southward into parts of northern California and central Nevada, as confidence has increased in thunderstorm development in these regions. Here, 0.50-0.75 precipitable water values, a dry sub-cloud layer, and relatively fast storms motions will all contribute to dry strike potential over fuels receptive to fire spread. In addition, the elevated delineation was adjusted in accordance to where the latest model guidance depicts 10-15% surface RH and 15+ mph sustained winds. ..Squitieri.. 08/09/2019 .PREV DISCUSSION... /ISSUED 0104 AM CDT Fri Aug 09 2019/ ...Synopsis... A longwave trough centered just west of the northern California coast will continue its slow trek eastward toward the West Coast throughout the day. As this occurs, mid-level flow will increase in a corridor from southern California northward to Idaho. The deep southerly flow will maintain moist mid-level profiles in much of the western third of the CONUS, and lift associated with the approaching trough and surface heating should foster several areas of thunderstorms. Additionally, a favorable pressure gradient and terrain-related forcing should foster areas of windy conditions across Nevada and vicinity through the evening. ...Central Nevada northward into Washington for thunderstorms... The aforementioned synoptic pattern will foster scattered areas of thunderstorms as early as mid-day while gradually increasing in coverage and intensity through the afternoon and evening hours. These storms should provide wetting rains to several areas, with isolated dry lightning strikes occurring on the periphery of wetting thunderstorm cores. Coverage will increase with northward extent into Oregon and southwestern Idaho throughout the day, with widespread areas of gusty outflow winds amidst areas of dry fuels suggestive of erratic fire behavior and complicated suppression efforts. A few of these wind gusts may exceed severe limits - refer to SPC Day 1 Convective Outlooks for more updates on this threat. At least pockets of dry fuels will exist as far east as eastern Idaho, and isolated dry thunderstorm potential has been highlighted in this area with storms expected through early evening. Storms will continue to lift northward and persist in many areas of Washington and Oregon overnight. ...Much of Nevada and far northeast California for elevated fire weather conditions... Surface troughing and vertical mixing processes will foster areas of 20-25 mph surface winds that will be strongest in a couple of corridors - one in the immediate lee of the Sierras and another along an axis from southeastern into east-central Nevada. Areas of critically low RH values will also exist for a few hours during peak heating, though clouds and areas of precipitation may hinder the degree of mixing/lowered RH in several areas as well. The overall scenario appears to be consistent with elevated fire weather thresholds, though locally critical fire weather will probably develop over southeastern Nevada for at least an hour or two. ...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 1155 AM CDT Fri Aug 09 2019 Valid 091700Z - 101200Z ...CRITICAL FIRE WEATHER AREA FOR PORTIONS OF CENTRAL INTO EASTERN OREGON... A scattered dry-thunderstorm delineation was added to portions of central and eastern Oregon. At least scattered thunderstorm development is expected, with ample buoyancy supportive of vigorous updrafts capable of producing copious amounts of lightning strikes, atop fuels that are at least modestly supportive of fire spread. While wetting rains are expected with many of the storms, a dry sfc-600 mb dry sub-cloud layer will be present, suggesting that at least a modest amount of dry strikes are possible. In addition, new lightning-induced fire starts may be exacerbated by strong to potentially severe erratic winds associated with the stronger storms. Otherwise, portions of the isolated dry thunderstorm delineation were also expanded southward into parts of northern California and central Nevada, as confidence has increased in thunderstorm development in these regions. Here, 0.50-0.75 precipitable water values, a dry sub-cloud layer, and relatively fast storms motions will all contribute to dry strike potential over fuels receptive to fire spread. In addition, the elevated delineation was adjusted in accordance to where the latest model guidance depicts 10-15% surface RH and 15+ mph sustained winds. ..Squitieri.. 08/09/2019 .PREV DISCUSSION... /ISSUED 0104 AM CDT Fri Aug 09 2019/ ...Synopsis... A longwave trough centered just west of the northern California coast will continue its slow trek eastward toward the West Coast throughout the day. As this occurs, mid-level flow will increase in a corridor from southern California northward to Idaho. The deep southerly flow will maintain moist mid-level profiles in much of the western third of the CONUS, and lift associated with the approaching trough and surface heating should foster several areas of thunderstorms. Additionally, a favorable pressure gradient and terrain-related forcing should foster areas of windy conditions across Nevada and vicinity through the evening. ...Central Nevada northward into Washington for thunderstorms... The aforementioned synoptic pattern will foster scattered areas of thunderstorms as early as mid-day while gradually increasing in coverage and intensity through the afternoon and evening hours. These storms should provide wetting rains to several areas, with isolated dry lightning strikes occurring on the periphery of wetting thunderstorm cores. Coverage will increase with northward extent into Oregon and southwestern Idaho throughout the day, with widespread areas of gusty outflow winds amidst areas of dry fuels suggestive of erratic fire behavior and complicated suppression efforts. A few of these wind gusts may exceed severe limits - refer to SPC Day 1 Convective Outlooks for more updates on this threat. At least pockets of dry fuels will exist as far east as eastern Idaho, and isolated dry thunderstorm potential has been highlighted in this area with storms expected through early evening. Storms will continue to lift northward and persist in many areas of Washington and Oregon overnight. ...Much of Nevada and far northeast California for elevated fire weather conditions... Surface troughing and vertical mixing processes will foster areas of 20-25 mph surface winds that will be strongest in a couple of corridors - one in the immediate lee of the Sierras and another along an axis from southeastern into east-central Nevada. Areas of critically low RH values will also exist for a few hours during peak heating, though clouds and areas of precipitation may hinder the degree of mixing/lowered RH in several areas as well. The overall scenario appears to be consistent with elevated fire weather thresholds, though locally critical fire weather will probably develop over southeastern Nevada for at least an hour or two. ...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 1130 AM CDT Fri Aug 09 2019 Valid 091630Z - 101200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS SD...OR...AND EASTERN VA... ...SUMMARY... Scattered severe thunderstorms are possible across parts of South Dakota, Oregon, and eastern Virginia mainly through early evening. ...SD... An embedded shortwave impulse is cresting the midlevel ridge and will move east from eastern WY across SD with an attendant surface cyclone. Elevated convection is ongoing in advance of this impulse across western/central SD and the northern extent of this activity should persist east near the SD/ND border. Surface heating on the southern-western flank of this ongoing convection, within a corridor of 65-70 F boundary-layer dewpoints, will contribute to MLCAPE from 1500-2500 J/kg between 21-00Z across west-central into south-central SD. Surface-based thunderstorm development will become more probable in the next few hours, either emanating from the southwest flank of the elevated convection and/or developing westward towards the surface cyclone. These storms should spread southeast along a pronounced differential heating corridor across central to southeast SD. Backed surface winds east of the cyclone, beneath strengthening low/mid-level flow should yield a rather enlarged hodograph towards early evening in a spatially narrow corridor from around Pierre to Mitchell. If a discrete supercell or two can be maintained through this time frame, the tornado risk may be greater than currently forecast. Otherwise, supercells may evolve into small-scale bows with a risk for significant severe wind. A cluster with severe wind as the primary hazard may progress into southeast SD/northeast NE before waning later in the evening given the dearth of instability with eastern extent in western IA. This area will be monitored for a possible upgrade in the 20Z outlook. ...Eastern VA... A subtle mid-upper speed max will progress east-southeastward from eastern WV across VA. Downstream of the Appalachians, robust diabatic heating is well underway and this will contribute to moderate buoyancy with MLCAPE of 1000-2000 J/kg. A pre-frontal surface trough may help focus storm initiation in the next few hours across central/northeast VA, with storms potentially spreading southeastward into early evening. Straight hodographs with effective bulk shear of 30-35 kt and steep low-level lapse rates will support some transient supercell structures capable of producing damaging gusts and marginally severe hail. ...Northwest... Embedded shortwave impulses will rotate northward from CA to OR around the eastern periphery of a closed low off the northern CA coast. Typically steep lapse rates over the northern Great Basin and interior Northwest, along with sufficient low-midlevel moisture, will support weak-moderate buoyancy later this afternoon across parts of OR, ID, and northern NV. Scattered thunderstorm development is expected to be focused by ascent preceding the ejecting midlevel waves and surface heating over the higher terrain. The more concentrated storms are anticipated over the OR Cascades and the higher terrain in northeastern OR, where isolated severe wind gusts and marginally severe will be possible with high-based storms in an environment supporting clusters and marginal supercells. Locally strong to severe gusts will also be possible farther east-southeast into parts of northern NV and ID. ..Grams/Bentley.. 08/09/2019 Read more

SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1130 AM CDT Fri Aug 09 2019 Valid 091630Z - 101200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS SD...OR...AND EASTERN VA... ...SUMMARY... Scattered severe thunderstorms are possible across parts of South Dakota, Oregon, and eastern Virginia mainly through early evening. ...SD... An embedded shortwave impulse is cresting the midlevel ridge and will move east from eastern WY across SD with an attendant surface cyclone. Elevated convection is ongoing in advance of this impulse across western/central SD and the northern extent of this activity should persist east near the SD/ND border. Surface heating on the southern-western flank of this ongoing convection, within a corridor of 65-70 F boundary-layer dewpoints, will contribute to MLCAPE from 1500-2500 J/kg between 21-00Z across west-central into south-central SD. Surface-based thunderstorm development will become more probable in the next few hours, either emanating from the southwest flank of the elevated convection and/or developing westward towards the surface cyclone. These storms should spread southeast along a pronounced differential heating corridor across central to southeast SD. Backed surface winds east of the cyclone, beneath strengthening low/mid-level flow should yield a rather enlarged hodograph towards early evening in a spatially narrow corridor from around Pierre to Mitchell. If a discrete supercell or two can be maintained through this time frame, the tornado risk may be greater than currently forecast. Otherwise, supercells may evolve into small-scale bows with a risk for significant severe wind. A cluster with severe wind as the primary hazard may progress into southeast SD/northeast NE before waning later in the evening given the dearth of instability with eastern extent in western IA. This area will be monitored for a possible upgrade in the 20Z outlook. ...Eastern VA... A subtle mid-upper speed max will progress east-southeastward from eastern WV across VA. Downstream of the Appalachians, robust diabatic heating is well underway and this will contribute to moderate buoyancy with MLCAPE of 1000-2000 J/kg. A pre-frontal surface trough may help focus storm initiation in the next few hours across central/northeast VA, with storms potentially spreading southeastward into early evening. Straight hodographs with effective bulk shear of 30-35 kt and steep low-level lapse rates will support some transient supercell structures capable of producing damaging gusts and marginally severe hail. ...Northwest... Embedded shortwave impulses will rotate northward from CA to OR around the eastern periphery of a closed low off the northern CA coast. Typically steep lapse rates over the northern Great Basin and interior Northwest, along with sufficient low-midlevel moisture, will support weak-moderate buoyancy later this afternoon across parts of OR, ID, and northern NV. Scattered thunderstorm development is expected to be focused by ascent preceding the ejecting midlevel waves and surface heating over the higher terrain. The more concentrated storms are anticipated over the OR Cascades and the higher terrain in northeastern OR, where isolated severe wind gusts and marginally severe will be possible with high-based storms in an environment supporting clusters and marginal supercells. Locally strong to severe gusts will also be possible farther east-southeast into parts of northern NV and ID. ..Grams/Bentley.. 08/09/2019 Read more

SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1130 AM CDT Fri Aug 09 2019 Valid 091630Z - 101200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS SD...OR...AND EASTERN VA... ...SUMMARY... Scattered severe thunderstorms are possible across parts of South Dakota, Oregon, and eastern Virginia mainly through early evening. ...SD... An embedded shortwave impulse is cresting the midlevel ridge and will move east from eastern WY across SD with an attendant surface cyclone. Elevated convection is ongoing in advance of this impulse across western/central SD and the northern extent of this activity should persist east near the SD/ND border. Surface heating on the southern-western flank of this ongoing convection, within a corridor of 65-70 F boundary-layer dewpoints, will contribute to MLCAPE from 1500-2500 J/kg between 21-00Z across west-central into south-central SD. Surface-based thunderstorm development will become more probable in the next few hours, either emanating from the southwest flank of the elevated convection and/or developing westward towards the surface cyclone. These storms should spread southeast along a pronounced differential heating corridor across central to southeast SD. Backed surface winds east of the cyclone, beneath strengthening low/mid-level flow should yield a rather enlarged hodograph towards early evening in a spatially narrow corridor from around Pierre to Mitchell. If a discrete supercell or two can be maintained through this time frame, the tornado risk may be greater than currently forecast. Otherwise, supercells may evolve into small-scale bows with a risk for significant severe wind. A cluster with severe wind as the primary hazard may progress into southeast SD/northeast NE before waning later in the evening given the dearth of instability with eastern extent in western IA. This area will be monitored for a possible upgrade in the 20Z outlook. ...Eastern VA... A subtle mid-upper speed max will progress east-southeastward from eastern WV across VA. Downstream of the Appalachians, robust diabatic heating is well underway and this will contribute to moderate buoyancy with MLCAPE of 1000-2000 J/kg. A pre-frontal surface trough may help focus storm initiation in the next few hours across central/northeast VA, with storms potentially spreading southeastward into early evening. Straight hodographs with effective bulk shear of 30-35 kt and steep low-level lapse rates will support some transient supercell structures capable of producing damaging gusts and marginally severe hail. ...Northwest... Embedded shortwave impulses will rotate northward from CA to OR around the eastern periphery of a closed low off the northern CA coast. Typically steep lapse rates over the northern Great Basin and interior Northwest, along with sufficient low-midlevel moisture, will support weak-moderate buoyancy later this afternoon across parts of OR, ID, and northern NV. Scattered thunderstorm development is expected to be focused by ascent preceding the ejecting midlevel waves and surface heating over the higher terrain. The more concentrated storms are anticipated over the OR Cascades and the higher terrain in northeastern OR, where isolated severe wind gusts and marginally severe will be possible with high-based storms in an environment supporting clusters and marginal supercells. Locally strong to severe gusts will also be possible farther east-southeast into parts of northern NV and ID. ..Grams/Bentley.. 08/09/2019 Read more

SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1130 AM CDT Fri Aug 09 2019 Valid 091630Z - 101200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS SD...OR...AND EASTERN VA... ...SUMMARY... Scattered severe thunderstorms are possible across parts of South Dakota, Oregon, and eastern Virginia mainly through early evening. ...SD... An embedded shortwave impulse is cresting the midlevel ridge and will move east from eastern WY across SD with an attendant surface cyclone. Elevated convection is ongoing in advance of this impulse across western/central SD and the northern extent of this activity should persist east near the SD/ND border. Surface heating on the southern-western flank of this ongoing convection, within a corridor of 65-70 F boundary-layer dewpoints, will contribute to MLCAPE from 1500-2500 J/kg between 21-00Z across west-central into south-central SD. Surface-based thunderstorm development will become more probable in the next few hours, either emanating from the southwest flank of the elevated convection and/or developing westward towards the surface cyclone. These storms should spread southeast along a pronounced differential heating corridor across central to southeast SD. Backed surface winds east of the cyclone, beneath strengthening low/mid-level flow should yield a rather enlarged hodograph towards early evening in a spatially narrow corridor from around Pierre to Mitchell. If a discrete supercell or two can be maintained through this time frame, the tornado risk may be greater than currently forecast. Otherwise, supercells may evolve into small-scale bows with a risk for significant severe wind. A cluster with severe wind as the primary hazard may progress into southeast SD/northeast NE before waning later in the evening given the dearth of instability with eastern extent in western IA. This area will be monitored for a possible upgrade in the 20Z outlook. ...Eastern VA... A subtle mid-upper speed max will progress east-southeastward from eastern WV across VA. Downstream of the Appalachians, robust diabatic heating is well underway and this will contribute to moderate buoyancy with MLCAPE of 1000-2000 J/kg. A pre-frontal surface trough may help focus storm initiation in the next few hours across central/northeast VA, with storms potentially spreading southeastward into early evening. Straight hodographs with effective bulk shear of 30-35 kt and steep low-level lapse rates will support some transient supercell structures capable of producing damaging gusts and marginally severe hail. ...Northwest... Embedded shortwave impulses will rotate northward from CA to OR around the eastern periphery of a closed low off the northern CA coast. Typically steep lapse rates over the northern Great Basin and interior Northwest, along with sufficient low-midlevel moisture, will support weak-moderate buoyancy later this afternoon across parts of OR, ID, and northern NV. Scattered thunderstorm development is expected to be focused by ascent preceding the ejecting midlevel waves and surface heating over the higher terrain. The more concentrated storms are anticipated over the OR Cascades and the higher terrain in northeastern OR, where isolated severe wind gusts and marginally severe will be possible with high-based storms in an environment supporting clusters and marginal supercells. Locally strong to severe gusts will also be possible farther east-southeast into parts of northern NV and ID. ..Grams/Bentley.. 08/09/2019 Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0755 AM CDT Fri Aug 09 2019 Valid 091300Z - 101200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON/EVENING FOR PARTS OF SD/NE...VA...AND OR... ...SUMMARY... Severe storms are possible across parts of South Dakota, Oregon, and eastern Virginia. ...Eastern VA area this afternoon... A subtle mid-upper speed max will progress east-southeastward from WV this morning across VA this afternoon. Surface heating in the wake of dissipating morning convection and lingering low-level moisture will contribute to moderate buoyancy (MLCAPE near 1500 J/kg) this afternoon across central/eastern VA. A pre-frontal surface trough will help focus storm initiation by early afternoon across central/northeast VA, and storms will subsequently spread southeastward through the afternoon. Straight hodographs with effective bulk shear of 30-35 kt and steep low-level lapse rates will support some organized (possible supercell) storms capable of producing damaging gusts and large hail. ...SD area this afternoon/evening... An embedded shortwave trough will crest the midlevel ridge over WY and move eastward across SD today, along with an associated weak surface low. Convection is ongoing this morning in advance of this wave across southwestern SD, and some form of this convection may persist well into the day into central SD. Surface heating on the southern-western flank of the ongoing convection, within a corridor of 65-70 F boundary-layer dewpoints, will contribute to MLCAPE near 2000 J/kg this afternoon. Surface-based thunderstorm development will become more probable by early afternoon near the weak surface low as convective inhibition diminishes. Deep-layer shear/buoyancy will support supercells capable of producing damaging winds and large hail. A tornado or two will also be possible in the narrow zone of enhanced low-level shear (0-1 km SRH near 200 m2/s2) near the surface low and the north edge of the unstable warm sector. ...Interior Northwest this afternoon/evening... Embedded shortwave troughs will rotate northward from CA to OR around the eastern periphery of a closed low off the northern CA coast. Typically steep lapse rates over the northern Great Basin and interior Northwest, along with sufficient low-midlevel moisture, will support weak-moderate buoyancy this afternoon across parts of OR, ID, and northern NV. Scattered thunderstorm development is expected this afternoon, focused by ascent preceding the ejecting midlevel waves and surface heating over the higher terrain. The more concentrated storms are expected over the OR Cascades and the higher terrain in northeastern OR, where isolated large hail and damaging gusts will be possible with high-based storms in an environment supporting clusters and marginal supercells. Gusty outflow winds will also be possible farther east-southeast into parts of northern NV and ID. ..Thompson/Kerr.. 08/09/2019 Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0755 AM CDT Fri Aug 09 2019 Valid 091300Z - 101200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON/EVENING FOR PARTS OF SD/NE...VA...AND OR... ...SUMMARY... Severe storms are possible across parts of South Dakota, Oregon, and eastern Virginia. ...Eastern VA area this afternoon... A subtle mid-upper speed max will progress east-southeastward from WV this morning across VA this afternoon. Surface heating in the wake of dissipating morning convection and lingering low-level moisture will contribute to moderate buoyancy (MLCAPE near 1500 J/kg) this afternoon across central/eastern VA. A pre-frontal surface trough will help focus storm initiation by early afternoon across central/northeast VA, and storms will subsequently spread southeastward through the afternoon. Straight hodographs with effective bulk shear of 30-35 kt and steep low-level lapse rates will support some organized (possible supercell) storms capable of producing damaging gusts and large hail. ...SD area this afternoon/evening... An embedded shortwave trough will crest the midlevel ridge over WY and move eastward across SD today, along with an associated weak surface low. Convection is ongoing this morning in advance of this wave across southwestern SD, and some form of this convection may persist well into the day into central SD. Surface heating on the southern-western flank of the ongoing convection, within a corridor of 65-70 F boundary-layer dewpoints, will contribute to MLCAPE near 2000 J/kg this afternoon. Surface-based thunderstorm development will become more probable by early afternoon near the weak surface low as convective inhibition diminishes. Deep-layer shear/buoyancy will support supercells capable of producing damaging winds and large hail. A tornado or two will also be possible in the narrow zone of enhanced low-level shear (0-1 km SRH near 200 m2/s2) near the surface low and the north edge of the unstable warm sector. ...Interior Northwest this afternoon/evening... Embedded shortwave troughs will rotate northward from CA to OR around the eastern periphery of a closed low off the northern CA coast. Typically steep lapse rates over the northern Great Basin and interior Northwest, along with sufficient low-midlevel moisture, will support weak-moderate buoyancy this afternoon across parts of OR, ID, and northern NV. Scattered thunderstorm development is expected this afternoon, focused by ascent preceding the ejecting midlevel waves and surface heating over the higher terrain. The more concentrated storms are expected over the OR Cascades and the higher terrain in northeastern OR, where isolated large hail and damaging gusts will be possible with high-based storms in an environment supporting clusters and marginal supercells. Gusty outflow winds will also be possible farther east-southeast into parts of northern NV and ID. ..Thompson/Kerr.. 08/09/2019 Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0755 AM CDT Fri Aug 09 2019 Valid 091300Z - 101200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON/EVENING FOR PARTS OF SD/NE...VA...AND OR... ...SUMMARY... Severe storms are possible across parts of South Dakota, Oregon, and eastern Virginia. ...Eastern VA area this afternoon... A subtle mid-upper speed max will progress east-southeastward from WV this morning across VA this afternoon. Surface heating in the wake of dissipating morning convection and lingering low-level moisture will contribute to moderate buoyancy (MLCAPE near 1500 J/kg) this afternoon across central/eastern VA. A pre-frontal surface trough will help focus storm initiation by early afternoon across central/northeast VA, and storms will subsequently spread southeastward through the afternoon. Straight hodographs with effective bulk shear of 30-35 kt and steep low-level lapse rates will support some organized (possible supercell) storms capable of producing damaging gusts and large hail. ...SD area this afternoon/evening... An embedded shortwave trough will crest the midlevel ridge over WY and move eastward across SD today, along with an associated weak surface low. Convection is ongoing this morning in advance of this wave across southwestern SD, and some form of this convection may persist well into the day into central SD. Surface heating on the southern-western flank of the ongoing convection, within a corridor of 65-70 F boundary-layer dewpoints, will contribute to MLCAPE near 2000 J/kg this afternoon. Surface-based thunderstorm development will become more probable by early afternoon near the weak surface low as convective inhibition diminishes. Deep-layer shear/buoyancy will support supercells capable of producing damaging winds and large hail. A tornado or two will also be possible in the narrow zone of enhanced low-level shear (0-1 km SRH near 200 m2/s2) near the surface low and the north edge of the unstable warm sector. ...Interior Northwest this afternoon/evening... Embedded shortwave troughs will rotate northward from CA to OR around the eastern periphery of a closed low off the northern CA coast. Typically steep lapse rates over the northern Great Basin and interior Northwest, along with sufficient low-midlevel moisture, will support weak-moderate buoyancy this afternoon across parts of OR, ID, and northern NV. Scattered thunderstorm development is expected this afternoon, focused by ascent preceding the ejecting midlevel waves and surface heating over the higher terrain. The more concentrated storms are expected over the OR Cascades and the higher terrain in northeastern OR, where isolated large hail and damaging gusts will be possible with high-based storms in an environment supporting clusters and marginal supercells. Gusty outflow winds will also be possible farther east-southeast into parts of northern NV and ID. ..Thompson/Kerr.. 08/09/2019 Read more

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0355 AM CDT Fri Aug 09 2019 Valid 121200Z - 171200Z ...DISCUSSION... Day 4 (Monday) Western U.S. upper trough will deamplify as it moves through the ridge position over the northern Plains. Widespread rain and thunderstorms will likely be ongoing in a warm advection regime across the central and northern Plains. While some severe threat could evolve along a cold front in wake of this activity, confidence is low regarding evolution of morning storms and its impact on subsequent destabilization potential. Days 5-8 model consensus is that upper pattern will trend to a quasi-zonal regime over the northern tier states. While there will undoubtedly be severe threats at times mainly over the northern Plains and northeast states, timing of low-amplitude shortwave troughs and uncertainty regarding where corridors of greater destabilization will be, lowers overall predictability at this range. Read more

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0355 AM CDT Fri Aug 09 2019 Valid 121200Z - 171200Z ...DISCUSSION... Day 4 (Monday) Western U.S. upper trough will deamplify as it moves through the ridge position over the northern Plains. Widespread rain and thunderstorms will likely be ongoing in a warm advection regime across the central and northern Plains. While some severe threat could evolve along a cold front in wake of this activity, confidence is low regarding evolution of morning storms and its impact on subsequent destabilization potential. Days 5-8 model consensus is that upper pattern will trend to a quasi-zonal regime over the northern tier states. While there will undoubtedly be severe threats at times mainly over the northern Plains and northeast states, timing of low-amplitude shortwave troughs and uncertainty regarding where corridors of greater destabilization will be, lowers overall predictability at this range. Read more

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0355 AM CDT Fri Aug 09 2019 Valid 121200Z - 171200Z ...DISCUSSION... Day 4 (Monday) Western U.S. upper trough will deamplify as it moves through the ridge position over the northern Plains. Widespread rain and thunderstorms will likely be ongoing in a warm advection regime across the central and northern Plains. While some severe threat could evolve along a cold front in wake of this activity, confidence is low regarding evolution of morning storms and its impact on subsequent destabilization potential. Days 5-8 model consensus is that upper pattern will trend to a quasi-zonal regime over the northern tier states. While there will undoubtedly be severe threats at times mainly over the northern Plains and northeast states, timing of low-amplitude shortwave troughs and uncertainty regarding where corridors of greater destabilization will be, lowers overall predictability at this range. Read more

SPC 0730Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0234 AM CDT Fri Aug 09 2019 Valid 111200Z - 121200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER A PORTION OF THE CENTRAL THROUGH NORTHERN HIGH PLAINS... ...SUMMARY... Isolated strong to severe storms are expected over portions of the northern through central High Plains Sunday. ...Northern through central High Plains... Upper trough now off the west U.S. coast will move east northeast through the northern Rockies and northern High Plains Sunday, cresting an upper ridge centered over the southern Plains. A plume of steeper mid-level lapse rates will overspread a moist axis that will be in place east of the higher terrain with surface dewpoints generally in the low 60s F resulting in moderate instability as the boundary layer destabilizes. Storms are expected to develop over the higher terrain and spread east into the High Plains during the afternoon and evening. A belt of stronger mid-upper flow will evolve in the gradient zone between the progressive upper trough and the ridge over the southern Plains. This will contribute to sufficient vertical shear for organized storms including supercells capable of isolated damaging wind and large hail from late afternoon into the evening. ..Dial.. 08/09/2019 Read more

SPC 0730Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0234 AM CDT Fri Aug 09 2019 Valid 111200Z - 121200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER A PORTION OF THE CENTRAL THROUGH NORTHERN HIGH PLAINS... ...SUMMARY... Isolated strong to severe storms are expected over portions of the northern through central High Plains Sunday. ...Northern through central High Plains... Upper trough now off the west U.S. coast will move east northeast through the northern Rockies and northern High Plains Sunday, cresting an upper ridge centered over the southern Plains. A plume of steeper mid-level lapse rates will overspread a moist axis that will be in place east of the higher terrain with surface dewpoints generally in the low 60s F resulting in moderate instability as the boundary layer destabilizes. Storms are expected to develop over the higher terrain and spread east into the High Plains during the afternoon and evening. A belt of stronger mid-upper flow will evolve in the gradient zone between the progressive upper trough and the ridge over the southern Plains. This will contribute to sufficient vertical shear for organized storms including supercells capable of isolated damaging wind and large hail from late afternoon into the evening. ..Dial.. 08/09/2019 Read more

SPC 0730Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0234 AM CDT Fri Aug 09 2019 Valid 111200Z - 121200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER A PORTION OF THE CENTRAL THROUGH NORTHERN HIGH PLAINS... ...SUMMARY... Isolated strong to severe storms are expected over portions of the northern through central High Plains Sunday. ...Northern through central High Plains... Upper trough now off the west U.S. coast will move east northeast through the northern Rockies and northern High Plains Sunday, cresting an upper ridge centered over the southern Plains. A plume of steeper mid-level lapse rates will overspread a moist axis that will be in place east of the higher terrain with surface dewpoints generally in the low 60s F resulting in moderate instability as the boundary layer destabilizes. Storms are expected to develop over the higher terrain and spread east into the High Plains during the afternoon and evening. A belt of stronger mid-upper flow will evolve in the gradient zone between the progressive upper trough and the ridge over the southern Plains. This will contribute to sufficient vertical shear for organized storms including supercells capable of isolated damaging wind and large hail from late afternoon into the evening. ..Dial.. 08/09/2019 Read more

SPC Day 2 Fire Weather Outlook
Day 2 Fire Weather Outlook NWS Storm Prediction Center Norman OK 0126 AM CDT Fri Aug 09 2019 Valid 101200Z - 111200Z ...Synopsis... The mid-level trough responsible for D1 fire weather concerns in the West will take on a negative tilt while slowly migrating northeastward over Oregon and vicinity. As this occurs, a belt of enhanced mid-level flow will shift eastward toward eastern Nevada and eastern Idaho. Meanwhile, areas of scattered to widespread thunderstorm activity will once again migrate over inland portions of the Pacific Northwest and northern California. ...Eastern Nevada, far western Utah, and eastern Idaho... Vertical mixing processes beneath the mid-level jet core will encourage development of a belt of relatively strong (15-25 mph) south-southwesterly surface winds during peak heating periods across the region. This region also resides on the western fringe of much of the rainfall over the past month or so, with dry fuels supporting ongoing fires across the region. One lingering uncertainty with regard to the extent of the fire-weather threat in this area will be potential for wetting rainfall over the region on D1/Fri, which may temper fuels in a few areas. However, elevated to locally critical fire weather will likely exist given near-critical RH values expected during the afternoon. Some portions of this region may need a critical upgrade in later outlook updates. ...Washington, Oregon, and northern California for thunderstorms... The continued presence of mid-level moisture and a nearby trough will again foster areas of northeastward-moving clusters of storms across the region. However, the extent of dry thunder potential is a bit less clear compared to prior days due to 1) expected areas of wetting rainfall on D1/Fri, which should temper fuel states on at least a localized basis and 2) the coverage of wetting rainfall during the afternoon and evening, which should further temper fuel states over a much broader area especially in Oregon. CAMS/high-res guidance even depicts upscale growth into linear complex(es) during peak heating hours. Nevertheless, areas that can remain dry will be susceptible to isolated dry lightning strikes outside of heavier thunderstorm cores, and gusty/erratic winds near downdrafts are expected. ..Cook.. 08/09/2019 ...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 0126 AM CDT Fri Aug 09 2019 Valid 101200Z - 111200Z ...Synopsis... The mid-level trough responsible for D1 fire weather concerns in the West will take on a negative tilt while slowly migrating northeastward over Oregon and vicinity. As this occurs, a belt of enhanced mid-level flow will shift eastward toward eastern Nevada and eastern Idaho. Meanwhile, areas of scattered to widespread thunderstorm activity will once again migrate over inland portions of the Pacific Northwest and northern California. ...Eastern Nevada, far western Utah, and eastern Idaho... Vertical mixing processes beneath the mid-level jet core will encourage development of a belt of relatively strong (15-25 mph) south-southwesterly surface winds during peak heating periods across the region. This region also resides on the western fringe of much of the rainfall over the past month or so, with dry fuels supporting ongoing fires across the region. One lingering uncertainty with regard to the extent of the fire-weather threat in this area will be potential for wetting rainfall over the region on D1/Fri, which may temper fuels in a few areas. However, elevated to locally critical fire weather will likely exist given near-critical RH values expected during the afternoon. Some portions of this region may need a critical upgrade in later outlook updates. ...Washington, Oregon, and northern California for thunderstorms... The continued presence of mid-level moisture and a nearby trough will again foster areas of northeastward-moving clusters of storms across the region. However, the extent of dry thunder potential is a bit less clear compared to prior days due to 1) expected areas of wetting rainfall on D1/Fri, which should temper fuel states on at least a localized basis and 2) the coverage of wetting rainfall during the afternoon and evening, which should further temper fuel states over a much broader area especially in Oregon. CAMS/high-res guidance even depicts upscale growth into linear complex(es) during peak heating hours. Nevertheless, areas that can remain dry will be susceptible to isolated dry lightning strikes outside of heavier thunderstorm cores, and gusty/erratic winds near downdrafts are expected. ..Cook.. 08/09/2019 ...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 0126 AM CDT Fri Aug 09 2019 Valid 101200Z - 111200Z ...Synopsis... The mid-level trough responsible for D1 fire weather concerns in the West will take on a negative tilt while slowly migrating northeastward over Oregon and vicinity. As this occurs, a belt of enhanced mid-level flow will shift eastward toward eastern Nevada and eastern Idaho. Meanwhile, areas of scattered to widespread thunderstorm activity will once again migrate over inland portions of the Pacific Northwest and northern California. ...Eastern Nevada, far western Utah, and eastern Idaho... Vertical mixing processes beneath the mid-level jet core will encourage development of a belt of relatively strong (15-25 mph) south-southwesterly surface winds during peak heating periods across the region. This region also resides on the western fringe of much of the rainfall over the past month or so, with dry fuels supporting ongoing fires across the region. One lingering uncertainty with regard to the extent of the fire-weather threat in this area will be potential for wetting rainfall over the region on D1/Fri, which may temper fuels in a few areas. However, elevated to locally critical fire weather will likely exist given near-critical RH values expected during the afternoon. Some portions of this region may need a critical upgrade in later outlook updates. ...Washington, Oregon, and northern California for thunderstorms... The continued presence of mid-level moisture and a nearby trough will again foster areas of northeastward-moving clusters of storms across the region. However, the extent of dry thunder potential is a bit less clear compared to prior days due to 1) expected areas of wetting rainfall on D1/Fri, which should temper fuel states on at least a localized basis and 2) the coverage of wetting rainfall during the afternoon and evening, which should further temper fuel states over a much broader area especially in Oregon. CAMS/high-res guidance even depicts upscale growth into linear complex(es) during peak heating hours. Nevertheless, areas that can remain dry will be susceptible to isolated dry lightning strikes outside of heavier thunderstorm cores, and gusty/erratic winds near downdrafts are expected. ..Cook.. 08/09/2019 ...Please see www.spc.noaa.gov/fire for graphic product... Read more

SPC Day 1 Fire Weather Outlook
Day 1 Fire Weather Outlook NWS Storm Prediction Center Norman OK 0104 AM CDT Fri Aug 09 2019 Valid 091200Z - 101200Z ...Synopsis... A longwave trough centered just west of the northern California coast will continue its slow trek eastward toward the West Coast throughout the day. As this occurs, mid-level flow will increase in a corridor from southern California northward to Idaho. The deep southerly flow will maintain moist mid-level profiles in much of the western third of the CONUS, and lift associated with the approaching trough and surface heating should foster several areas of thunderstorms. Additionally, a favorable pressure gradient and terrain-related forcing should foster areas of windy conditions across Nevada and vicinity through the evening. ...Central Nevada northward into Washington for thunderstorms... The aforementioned synoptic pattern will foster scattered areas of thunderstorms as early as mid-day while gradually increasing in coverage and intensity through the afternoon and evening hours. These storms should provide wetting rains to several areas, with isolated dry lightning strikes occurring on the periphery of wetting thunderstorm cores. Coverage will increase with northward extent into Oregon and southwestern Idaho throughout the day, with widespread areas of gusty outflow winds amidst areas of dry fuels suggestive of erratic fire behavior and complicated suppression efforts. A few of these wind gusts may exceed severe limits - refer to SPC Day 1 Convective Outlooks for more updates on this threat. At least pockets of dry fuels will exist as far east as eastern Idaho, and isolated dry thunderstorm potential has been highlighted in this area with storms expected through early evening. Storms will continue to lift northward and persist in many areas of Washington and Oregon overnight. ...Much of Nevada and far northeast California for elevated fire weather conditions... Surface troughing and vertical mixing processes will foster areas of 20-25 mph surface winds that will be strongest in a couple of corridors - one in the immediate lee of the Sierras and another along an axis from southeastern into east-central Nevada. Areas of critically low RH values will also exist for a few hours during peak heating, though clouds and areas of precipitation may hinder the degree of mixing/lowered RH in several areas as well. The overall scenario appears to be consistent with elevated fire weather thresholds, though locally critical fire weather will probably develop over southeastern Nevada for at least an hour or two. ..Cook.. 08/09/2019 ...Please see www.spc.noaa.gov/fire for graphic product... Read more