Severe Storms

SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1124 AM CDT Tue Sep 10 2019 Valid 101630Z - 111200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON AND EVENING OVER PARTS OF SOUTHERN SOUTH DAKOTA AND NORTHERN NEBRASKA... ...SUMMARY... An enhanced threat for severe hail and wind should develop this afternoon and evening across parts of the north-central Plains, mostly near the Nebraska/South Dakota line. A tornado threat exists in that area as well. ...Central/Northern High Plains... A shortwave trough currently moving across UT will track into the central and northern High Plains this evening. Model guidance suggests that midlevel height falls and lift will overspread parts of western WY and the NE Panhandle after 18z, with convective initiation occurring a few hours afterward. Storms will be focused along a surface baroclinic zone that extends from northeast WY southeastward into the NE Panhandle - then eastward across NE. Forecast soundings in vicinity of the boundary show MLCAPE values around 3000 J/kg and a weak cap. Initial storm structures will likely be supercellular, with a risk of very large hail and isolated tornadoes. A consensus of CAM solutions agree that storms will congeal and grow upscale through the evening as they track eastward along the boundary across NE, with a focused area of enhanced damaging wind threat. ...ID/UT/WY/MT... Scattered thunderstorms are expected to intensify early this afternoon beneath the core of the midlevel shortwave trough over northern UT and southeast ID. These storms will be relatively fast-moving and in a steep lapse rate environment. The strongest cells in this region will pose a risk of hail and damaging wind gusts. Some activity may remain strong as it moves across northern/western WY into southern MT this evening. ...Western KS into northeast NM... Full sunshine will lead to an axis of moderate CAPE values this afternoon along the dryline from western KS into northeast NM. All model guidance shows the development of isolated thunderstorms in a deeply mixed but weakly sheared environment. A few of the storms will be capable of strong downburst winds for a few hours this afternoon and evening. ...Lower MI... A weak convectively-enhanced upper trough is moving across WI. This feature will move eastward into Lower MI this afternoon, with scattered thunderstorms likely to form. Rather strong winds aloft and sufficient CAPE suggest a risk of gusty/damaging winds in the strongest cells. ..Hart/Wendt.. 09/10/2019 Read more

SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1124 AM CDT Tue Sep 10 2019 Valid 101630Z - 111200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON AND EVENING OVER PARTS OF SOUTHERN SOUTH DAKOTA AND NORTHERN NEBRASKA... ...SUMMARY... An enhanced threat for severe hail and wind should develop this afternoon and evening across parts of the north-central Plains, mostly near the Nebraska/South Dakota line. A tornado threat exists in that area as well. ...Central/Northern High Plains... A shortwave trough currently moving across UT will track into the central and northern High Plains this evening. Model guidance suggests that midlevel height falls and lift will overspread parts of western WY and the NE Panhandle after 18z, with convective initiation occurring a few hours afterward. Storms will be focused along a surface baroclinic zone that extends from northeast WY southeastward into the NE Panhandle - then eastward across NE. Forecast soundings in vicinity of the boundary show MLCAPE values around 3000 J/kg and a weak cap. Initial storm structures will likely be supercellular, with a risk of very large hail and isolated tornadoes. A consensus of CAM solutions agree that storms will congeal and grow upscale through the evening as they track eastward along the boundary across NE, with a focused area of enhanced damaging wind threat. ...ID/UT/WY/MT... Scattered thunderstorms are expected to intensify early this afternoon beneath the core of the midlevel shortwave trough over northern UT and southeast ID. These storms will be relatively fast-moving and in a steep lapse rate environment. The strongest cells in this region will pose a risk of hail and damaging wind gusts. Some activity may remain strong as it moves across northern/western WY into southern MT this evening. ...Western KS into northeast NM... Full sunshine will lead to an axis of moderate CAPE values this afternoon along the dryline from western KS into northeast NM. All model guidance shows the development of isolated thunderstorms in a deeply mixed but weakly sheared environment. A few of the storms will be capable of strong downburst winds for a few hours this afternoon and evening. ...Lower MI... A weak convectively-enhanced upper trough is moving across WI. This feature will move eastward into Lower MI this afternoon, with scattered thunderstorms likely to form. Rather strong winds aloft and sufficient CAPE suggest a risk of gusty/damaging winds in the strongest cells. ..Hart/Wendt.. 09/10/2019 Read more

SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1124 AM CDT Tue Sep 10 2019 Valid 101630Z - 111200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON AND EVENING OVER PARTS OF SOUTHERN SOUTH DAKOTA AND NORTHERN NEBRASKA... ...SUMMARY... An enhanced threat for severe hail and wind should develop this afternoon and evening across parts of the north-central Plains, mostly near the Nebraska/South Dakota line. A tornado threat exists in that area as well. ...Central/Northern High Plains... A shortwave trough currently moving across UT will track into the central and northern High Plains this evening. Model guidance suggests that midlevel height falls and lift will overspread parts of western WY and the NE Panhandle after 18z, with convective initiation occurring a few hours afterward. Storms will be focused along a surface baroclinic zone that extends from northeast WY southeastward into the NE Panhandle - then eastward across NE. Forecast soundings in vicinity of the boundary show MLCAPE values around 3000 J/kg and a weak cap. Initial storm structures will likely be supercellular, with a risk of very large hail and isolated tornadoes. A consensus of CAM solutions agree that storms will congeal and grow upscale through the evening as they track eastward along the boundary across NE, with a focused area of enhanced damaging wind threat. ...ID/UT/WY/MT... Scattered thunderstorms are expected to intensify early this afternoon beneath the core of the midlevel shortwave trough over northern UT and southeast ID. These storms will be relatively fast-moving and in a steep lapse rate environment. The strongest cells in this region will pose a risk of hail and damaging wind gusts. Some activity may remain strong as it moves across northern/western WY into southern MT this evening. ...Western KS into northeast NM... Full sunshine will lead to an axis of moderate CAPE values this afternoon along the dryline from western KS into northeast NM. All model guidance shows the development of isolated thunderstorms in a deeply mixed but weakly sheared environment. A few of the storms will be capable of strong downburst winds for a few hours this afternoon and evening. ...Lower MI... A weak convectively-enhanced upper trough is moving across WI. This feature will move eastward into Lower MI this afternoon, with scattered thunderstorms likely to form. Rather strong winds aloft and sufficient CAPE suggest a risk of gusty/damaging winds in the strongest cells. ..Hart/Wendt.. 09/10/2019 Read more

SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1124 AM CDT Tue Sep 10 2019 Valid 101630Z - 111200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON AND EVENING OVER PARTS OF SOUTHERN SOUTH DAKOTA AND NORTHERN NEBRASKA... ...SUMMARY... An enhanced threat for severe hail and wind should develop this afternoon and evening across parts of the north-central Plains, mostly near the Nebraska/South Dakota line. A tornado threat exists in that area as well. ...Central/Northern High Plains... A shortwave trough currently moving across UT will track into the central and northern High Plains this evening. Model guidance suggests that midlevel height falls and lift will overspread parts of western WY and the NE Panhandle after 18z, with convective initiation occurring a few hours afterward. Storms will be focused along a surface baroclinic zone that extends from northeast WY southeastward into the NE Panhandle - then eastward across NE. Forecast soundings in vicinity of the boundary show MLCAPE values around 3000 J/kg and a weak cap. Initial storm structures will likely be supercellular, with a risk of very large hail and isolated tornadoes. A consensus of CAM solutions agree that storms will congeal and grow upscale through the evening as they track eastward along the boundary across NE, with a focused area of enhanced damaging wind threat. ...ID/UT/WY/MT... Scattered thunderstorms are expected to intensify early this afternoon beneath the core of the midlevel shortwave trough over northern UT and southeast ID. These storms will be relatively fast-moving and in a steep lapse rate environment. The strongest cells in this region will pose a risk of hail and damaging wind gusts. Some activity may remain strong as it moves across northern/western WY into southern MT this evening. ...Western KS into northeast NM... Full sunshine will lead to an axis of moderate CAPE values this afternoon along the dryline from western KS into northeast NM. All model guidance shows the development of isolated thunderstorms in a deeply mixed but weakly sheared environment. A few of the storms will be capable of strong downburst winds for a few hours this afternoon and evening. ...Lower MI... A weak convectively-enhanced upper trough is moving across WI. This feature will move eastward into Lower MI this afternoon, with scattered thunderstorms likely to form. Rather strong winds aloft and sufficient CAPE suggest a risk of gusty/damaging winds in the strongest cells. ..Hart/Wendt.. 09/10/2019 Read more

SPC Day 1 Fire Weather Outlook
Day 1 Fire Weather Outlook NWS Storm Prediction Center Norman OK 1038 AM CDT Tue Sep 10 2019 Valid 101700Z - 111200Z The ongoing forecast is on track and no changes are needed. See the previous discussion below for more details. ..Cook.. 09/10/2019 .PREV DISCUSSION... /ISSUED 0134 AM CDT Tue Sep 10 2019/ ...Synopsis... Broad cyclonic flow, associated with a deepening mid-level shortwave trough, will prevail across the western CONUS during the period. Breezy conditions, with patchy areas of drier air, will result from a low-level mass response to the impinging mid-level trough, promoting very modest wildfire-spread potential across parts of the Great Basin. In addition, widespread deep-layer ascent ahead of the trough will promote isolated to scattered thunderstorms across eastern portions of the Great Basin, into the Four Corners, central/northern Rockies, northwestward into parts of the Pacific Northwest. On the backside of the trough, surface to mid-level flow will be predominantly northerly/offshore, encouraging a modest Sundowner event across parts of Coastal Southern California towards the end of the period. ...Parts of the Great Basin... While elevated conditions will be mostly localized in nature in advance of the mid-level trough, some widespread 15-20 mph sustained south-southwesterly surface winds coinciding with 15-20% RH may occur across parts of central, eastern, and southern Nevada. The most likely timing of these conditions would be after peak heating of the afternoon. Farther east into Utah, surface southwesterly winds may easily exceed 20 mph, particularly in terrain-favoring locations, but surface RH above 20% depicted by the latest model guidance suggests that elevated fire concerns will be mainly localized in nature, with an elevated delineation withheld for this outlook. ...Eastern Great Basin into the central/northern Rockies... At least isolated to scattered thunderstorms will develop during the afternoon hours, aided by afternoon peak heating/boundary-layer mixing, and by deep-layer ascent provided by the mid-level shortwave trough. These storms are expected to be relatively fast-moving in nature, with precipitable water values under 0.75 inches and dry sub-cloud layers extending well above 700 mb in most locales. Still, fuels across these area are expected to be marginally to modestly receptive to new ignitions and subsequent fire spread on the large scale. As such, the localized threat for new dry-lightning induced fire starts precludes an isolated dry thunderstorm delineation. ...Parts of Coastal Southern California... Towards the end of the period, northerly sustained surface winds within the 15-25 mph range are expected along with 20-25% RH. Given dry fuels receptive to fire spread, elevated fire weather conditions are expected across portions of Ventura and Santa Barbara Counties, particularly in the higher terrain of the Santa Ynez Mountains, where winds will be strongest, with the poorest RH recovery. ...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 1038 AM CDT Tue Sep 10 2019 Valid 101700Z - 111200Z The ongoing forecast is on track and no changes are needed. See the previous discussion below for more details. ..Cook.. 09/10/2019 .PREV DISCUSSION... /ISSUED 0134 AM CDT Tue Sep 10 2019/ ...Synopsis... Broad cyclonic flow, associated with a deepening mid-level shortwave trough, will prevail across the western CONUS during the period. Breezy conditions, with patchy areas of drier air, will result from a low-level mass response to the impinging mid-level trough, promoting very modest wildfire-spread potential across parts of the Great Basin. In addition, widespread deep-layer ascent ahead of the trough will promote isolated to scattered thunderstorms across eastern portions of the Great Basin, into the Four Corners, central/northern Rockies, northwestward into parts of the Pacific Northwest. On the backside of the trough, surface to mid-level flow will be predominantly northerly/offshore, encouraging a modest Sundowner event across parts of Coastal Southern California towards the end of the period. ...Parts of the Great Basin... While elevated conditions will be mostly localized in nature in advance of the mid-level trough, some widespread 15-20 mph sustained south-southwesterly surface winds coinciding with 15-20% RH may occur across parts of central, eastern, and southern Nevada. The most likely timing of these conditions would be after peak heating of the afternoon. Farther east into Utah, surface southwesterly winds may easily exceed 20 mph, particularly in terrain-favoring locations, but surface RH above 20% depicted by the latest model guidance suggests that elevated fire concerns will be mainly localized in nature, with an elevated delineation withheld for this outlook. ...Eastern Great Basin into the central/northern Rockies... At least isolated to scattered thunderstorms will develop during the afternoon hours, aided by afternoon peak heating/boundary-layer mixing, and by deep-layer ascent provided by the mid-level shortwave trough. These storms are expected to be relatively fast-moving in nature, with precipitable water values under 0.75 inches and dry sub-cloud layers extending well above 700 mb in most locales. Still, fuels across these area are expected to be marginally to modestly receptive to new ignitions and subsequent fire spread on the large scale. As such, the localized threat for new dry-lightning induced fire starts precludes an isolated dry thunderstorm delineation. ...Parts of Coastal Southern California... Towards the end of the period, northerly sustained surface winds within the 15-25 mph range are expected along with 20-25% RH. Given dry fuels receptive to fire spread, elevated fire weather conditions are expected across portions of Ventura and Santa Barbara Counties, particularly in the higher terrain of the Santa Ynez Mountains, where winds will be strongest, with the poorest RH recovery. ...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 1038 AM CDT Tue Sep 10 2019 Valid 101700Z - 111200Z The ongoing forecast is on track and no changes are needed. See the previous discussion below for more details. ..Cook.. 09/10/2019 .PREV DISCUSSION... /ISSUED 0134 AM CDT Tue Sep 10 2019/ ...Synopsis... Broad cyclonic flow, associated with a deepening mid-level shortwave trough, will prevail across the western CONUS during the period. Breezy conditions, with patchy areas of drier air, will result from a low-level mass response to the impinging mid-level trough, promoting very modest wildfire-spread potential across parts of the Great Basin. In addition, widespread deep-layer ascent ahead of the trough will promote isolated to scattered thunderstorms across eastern portions of the Great Basin, into the Four Corners, central/northern Rockies, northwestward into parts of the Pacific Northwest. On the backside of the trough, surface to mid-level flow will be predominantly northerly/offshore, encouraging a modest Sundowner event across parts of Coastal Southern California towards the end of the period. ...Parts of the Great Basin... While elevated conditions will be mostly localized in nature in advance of the mid-level trough, some widespread 15-20 mph sustained south-southwesterly surface winds coinciding with 15-20% RH may occur across parts of central, eastern, and southern Nevada. The most likely timing of these conditions would be after peak heating of the afternoon. Farther east into Utah, surface southwesterly winds may easily exceed 20 mph, particularly in terrain-favoring locations, but surface RH above 20% depicted by the latest model guidance suggests that elevated fire concerns will be mainly localized in nature, with an elevated delineation withheld for this outlook. ...Eastern Great Basin into the central/northern Rockies... At least isolated to scattered thunderstorms will develop during the afternoon hours, aided by afternoon peak heating/boundary-layer mixing, and by deep-layer ascent provided by the mid-level shortwave trough. These storms are expected to be relatively fast-moving in nature, with precipitable water values under 0.75 inches and dry sub-cloud layers extending well above 700 mb in most locales. Still, fuels across these area are expected to be marginally to modestly receptive to new ignitions and subsequent fire spread on the large scale. As such, the localized threat for new dry-lightning induced fire starts precludes an isolated dry thunderstorm delineation. ...Parts of Coastal Southern California... Towards the end of the period, northerly sustained surface winds within the 15-25 mph range are expected along with 20-25% RH. Given dry fuels receptive to fire spread, elevated fire weather conditions are expected across portions of Ventura and Santa Barbara Counties, particularly in the higher terrain of the Santa Ynez Mountains, where winds will be strongest, with the poorest RH recovery. ...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 1038 AM CDT Tue Sep 10 2019 Valid 101700Z - 111200Z The ongoing forecast is on track and no changes are needed. See the previous discussion below for more details. ..Cook.. 09/10/2019 .PREV DISCUSSION... /ISSUED 0134 AM CDT Tue Sep 10 2019/ ...Synopsis... Broad cyclonic flow, associated with a deepening mid-level shortwave trough, will prevail across the western CONUS during the period. Breezy conditions, with patchy areas of drier air, will result from a low-level mass response to the impinging mid-level trough, promoting very modest wildfire-spread potential across parts of the Great Basin. In addition, widespread deep-layer ascent ahead of the trough will promote isolated to scattered thunderstorms across eastern portions of the Great Basin, into the Four Corners, central/northern Rockies, northwestward into parts of the Pacific Northwest. On the backside of the trough, surface to mid-level flow will be predominantly northerly/offshore, encouraging a modest Sundowner event across parts of Coastal Southern California towards the end of the period. ...Parts of the Great Basin... While elevated conditions will be mostly localized in nature in advance of the mid-level trough, some widespread 15-20 mph sustained south-southwesterly surface winds coinciding with 15-20% RH may occur across parts of central, eastern, and southern Nevada. The most likely timing of these conditions would be after peak heating of the afternoon. Farther east into Utah, surface southwesterly winds may easily exceed 20 mph, particularly in terrain-favoring locations, but surface RH above 20% depicted by the latest model guidance suggests that elevated fire concerns will be mainly localized in nature, with an elevated delineation withheld for this outlook. ...Eastern Great Basin into the central/northern Rockies... At least isolated to scattered thunderstorms will develop during the afternoon hours, aided by afternoon peak heating/boundary-layer mixing, and by deep-layer ascent provided by the mid-level shortwave trough. These storms are expected to be relatively fast-moving in nature, with precipitable water values under 0.75 inches and dry sub-cloud layers extending well above 700 mb in most locales. Still, fuels across these area are expected to be marginally to modestly receptive to new ignitions and subsequent fire spread on the large scale. As such, the localized threat for new dry-lightning induced fire starts precludes an isolated dry thunderstorm delineation. ...Parts of Coastal Southern California... Towards the end of the period, northerly sustained surface winds within the 15-25 mph range are expected along with 20-25% RH. Given dry fuels receptive to fire spread, elevated fire weather conditions are expected across portions of Ventura and Santa Barbara Counties, particularly in the higher terrain of the Santa Ynez Mountains, where winds will be strongest, with the poorest RH recovery. ...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 1038 AM CDT Tue Sep 10 2019 Valid 101700Z - 111200Z The ongoing forecast is on track and no changes are needed. See the previous discussion below for more details. ..Cook.. 09/10/2019 .PREV DISCUSSION... /ISSUED 0134 AM CDT Tue Sep 10 2019/ ...Synopsis... Broad cyclonic flow, associated with a deepening mid-level shortwave trough, will prevail across the western CONUS during the period. Breezy conditions, with patchy areas of drier air, will result from a low-level mass response to the impinging mid-level trough, promoting very modest wildfire-spread potential across parts of the Great Basin. In addition, widespread deep-layer ascent ahead of the trough will promote isolated to scattered thunderstorms across eastern portions of the Great Basin, into the Four Corners, central/northern Rockies, northwestward into parts of the Pacific Northwest. On the backside of the trough, surface to mid-level flow will be predominantly northerly/offshore, encouraging a modest Sundowner event across parts of Coastal Southern California towards the end of the period. ...Parts of the Great Basin... While elevated conditions will be mostly localized in nature in advance of the mid-level trough, some widespread 15-20 mph sustained south-southwesterly surface winds coinciding with 15-20% RH may occur across parts of central, eastern, and southern Nevada. The most likely timing of these conditions would be after peak heating of the afternoon. Farther east into Utah, surface southwesterly winds may easily exceed 20 mph, particularly in terrain-favoring locations, but surface RH above 20% depicted by the latest model guidance suggests that elevated fire concerns will be mainly localized in nature, with an elevated delineation withheld for this outlook. ...Eastern Great Basin into the central/northern Rockies... At least isolated to scattered thunderstorms will develop during the afternoon hours, aided by afternoon peak heating/boundary-layer mixing, and by deep-layer ascent provided by the mid-level shortwave trough. These storms are expected to be relatively fast-moving in nature, with precipitable water values under 0.75 inches and dry sub-cloud layers extending well above 700 mb in most locales. Still, fuels across these area are expected to be marginally to modestly receptive to new ignitions and subsequent fire spread on the large scale. As such, the localized threat for new dry-lightning induced fire starts precludes an isolated dry thunderstorm delineation. ...Parts of Coastal Southern California... Towards the end of the period, northerly sustained surface winds within the 15-25 mph range are expected along with 20-25% RH. Given dry fuels receptive to fire spread, elevated fire weather conditions are expected across portions of Ventura and Santa Barbara Counties, particularly in the higher terrain of the Santa Ynez Mountains, where winds will be strongest, with the poorest RH recovery. ...Please see www.spc.noaa.gov/fire for graphic product... Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0757 AM CDT Tue Sep 10 2019 Valid 101300Z - 111200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ASTRIDE MUCH OF THE NEBRASKA/SOUTH DAKOTA STATE LINE AND INTO ADJOINING PARTS OF EACH STATE... ...SUMMARY... An enhanced threat for severe hail and wind should develop this afternoon and evening across parts of the north-central Plains, mostly near the Nebraska/South Dakota line. A tornado threat exists in that area as well. ...Synopsis... A strong shortwave trough located about 1000 nm west of Vancouver Island is forecast to deepen into an expansive, progressive 500-mb cyclone today. As this occurs, downstream ridging across eastern Canada and a closed cyclone over the Pacific Northwest each will begin to break down somewhat, thereby eroding the Rex configuration now in place over northwestern North America. A substantial synoptic-scale trough extends from the Pacific Northwest cyclone south-southeastward across coastal southern CA. As the cyclone weakens/opens slightly, the trough will move eastward, reaching to near an axis from MSO-TWF-LAS-YUM by 12Z. Associated height falls will spread across the central Rockies and High Plains during the latter half of the period, supporting a broad, hybrid frontal-wave/ lee cyclone at the surface over the central High Plains. A weak mid/upper-level shortwave trough -- now evident in moisture- channel imagery from the southern MB/ON border across northwestern MN -- will move eastward across the width of northern ON, reaching western QC by 12Z. As this occurs, the associated surface frontal- wave cyclone -- analyzed at 11Z over northern MN -- should ripple eastward across the length of Lake Superior and much of adjoining northeastern ON toward QC this evening. The trailing cold front was drawn initially from the MN low to north-central NE, becoming nearly stationary from north-central NE west-southwestward across northern CO. A trough was drawn from a weak low over east- central CO north-northeastward to the front in western NE. By 00Z, the cold front should reach eastern Upper MI and south-central WI, becoming quasistationary from there across extreme northern IA, then a warm front across northern NE near the SD line and into east-central/ southeastern WY. By 12Z, the front should extend across central Lower MI, south-central WI, north-central/northwestern IA and northern NE near SD, with much of the NE part likely having been altered by convective outflow. ...North-central Plains... Thunderstorms are expected to develop this afternoon in two principal regimes: convergence along/near the surface front over northwestern NE and perhaps nearby southwestern SD, and upslope postfrontal lift across parts of eastern WY into the Black Hills region. During the first few hours of both regimes, supercells will be possible with all severe hazards (tornado, wind, hail), with some significant/damaging hail supported by forecast soundings. The most unstable air mass will exist along and south of the warm front, where surface dew points in the 60s F and steep low/middle- level lapse rates will contribute to peak preconvective MLCAPE commonly reaching the 3000-3500 J/kg range, transitioning to 1500- 2500 J/kg westward across eastern WY in the upslope regime. Northwest and south of the front, long low-level hodographs and favorable deep shear will prevail, while backed flow along and just north of the front will enlarge low-level shear and storm-relative boundary-layer winds. Deep shear should increase area-wide from late afternoon through evening, with forecast soundings reasonably depicting 45-55-kt effective-shear vectors. Between the latter factor and focused convergence, the frontal zone should serve as the focus for upscale convective growth through evening. One or two clusters of convection should evolve from the supercellular activity and shift eastward across the outlook area, offering a growing threat for severe gusts -- some of which also may reach significant levels (hurricane force) on a localized basis. A roughly eastward forward-propagational MCS appears possible astride the NE/SD line through the evening and into parts of the overnight hours, with a continuing wind-damage threat toward the Siouxland area of northwestern IA and southeastern SD before the activity wanes tonight. ...Southern Lower MI... Scattered thunderstorms are ongoing over eastern WI and portions of Lake Michigan, in a regime of strong low-level warm advection and moisture transport. While expected to remain below severe limits, the downshear spread of clouds and precip across Lower MI should foster a prefrontal outflow/differential-heating boundary with relatively maximized low-level lift, over portions of southern Lower MI. While the specific location of the boundary remains somewhat uncertain, confidence in its development and in some related afternoon genesis of at least isolated strong/severe convection has increased enough to warrant introducing marginal unconditional probabilities. The main concerns with any sustained convection near the boundary will be damaging gusts and marginally severe hail. Forecast soundings in the nearby warm sector suggest that strong surface heating and dew points generally in the 60s F will support peak mid/late-afternoon MLCAPE near 2000 J/kg. A well-mixed/ inverted-v thermodynamic profile should develop in the boundary layer, amidst minimal MLCINH. Very little directional shear is expected, limiting hodograph sizes, though deep/cloud-layer shear may be sufficient to support organized multicells. Convective potential also exists farther north nearer to the cold front, but this is very conditional on destabilization within/behind the morning clouds/convection, and too conditional for any probabilities at this time. ...Portions of Intermountain/northern Great Basin... Widely scattered to scattered thunderstorms should form through much of the afternoon and into the early evening over an irregularly shaped swath from northeastern NV to extreme southern MT, northern UT, western WY and northwestern CO. Isolated severe gusts/hail will be possible. Cooling aloft related to the approaching mid/upper- level trough, overlying diurnal surface heating, will result in minimal MLCINH and steep deep-layer lapse rates (e.g, near 8 deg c/km from surface-300 mb in some forecast soundings), amidst sufficient low-level moisture to support sustained/deep convection. Cooling aloft will offset diabatic low-level cooling enough to maintain an isolated strong-severe threat a few more hours into the evening/nighttime hours than less synoptically forced scenarios. ..Edwards/Dial.. 09/10/2019 Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0757 AM CDT Tue Sep 10 2019 Valid 101300Z - 111200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ASTRIDE MUCH OF THE NEBRASKA/SOUTH DAKOTA STATE LINE AND INTO ADJOINING PARTS OF EACH STATE... ...SUMMARY... An enhanced threat for severe hail and wind should develop this afternoon and evening across parts of the north-central Plains, mostly near the Nebraska/South Dakota line. A tornado threat exists in that area as well. ...Synopsis... A strong shortwave trough located about 1000 nm west of Vancouver Island is forecast to deepen into an expansive, progressive 500-mb cyclone today. As this occurs, downstream ridging across eastern Canada and a closed cyclone over the Pacific Northwest each will begin to break down somewhat, thereby eroding the Rex configuration now in place over northwestern North America. A substantial synoptic-scale trough extends from the Pacific Northwest cyclone south-southeastward across coastal southern CA. As the cyclone weakens/opens slightly, the trough will move eastward, reaching to near an axis from MSO-TWF-LAS-YUM by 12Z. Associated height falls will spread across the central Rockies and High Plains during the latter half of the period, supporting a broad, hybrid frontal-wave/ lee cyclone at the surface over the central High Plains. A weak mid/upper-level shortwave trough -- now evident in moisture- channel imagery from the southern MB/ON border across northwestern MN -- will move eastward across the width of northern ON, reaching western QC by 12Z. As this occurs, the associated surface frontal- wave cyclone -- analyzed at 11Z over northern MN -- should ripple eastward across the length of Lake Superior and much of adjoining northeastern ON toward QC this evening. The trailing cold front was drawn initially from the MN low to north-central NE, becoming nearly stationary from north-central NE west-southwestward across northern CO. A trough was drawn from a weak low over east- central CO north-northeastward to the front in western NE. By 00Z, the cold front should reach eastern Upper MI and south-central WI, becoming quasistationary from there across extreme northern IA, then a warm front across northern NE near the SD line and into east-central/ southeastern WY. By 12Z, the front should extend across central Lower MI, south-central WI, north-central/northwestern IA and northern NE near SD, with much of the NE part likely having been altered by convective outflow. ...North-central Plains... Thunderstorms are expected to develop this afternoon in two principal regimes: convergence along/near the surface front over northwestern NE and perhaps nearby southwestern SD, and upslope postfrontal lift across parts of eastern WY into the Black Hills region. During the first few hours of both regimes, supercells will be possible with all severe hazards (tornado, wind, hail), with some significant/damaging hail supported by forecast soundings. The most unstable air mass will exist along and south of the warm front, where surface dew points in the 60s F and steep low/middle- level lapse rates will contribute to peak preconvective MLCAPE commonly reaching the 3000-3500 J/kg range, transitioning to 1500- 2500 J/kg westward across eastern WY in the upslope regime. Northwest and south of the front, long low-level hodographs and favorable deep shear will prevail, while backed flow along and just north of the front will enlarge low-level shear and storm-relative boundary-layer winds. Deep shear should increase area-wide from late afternoon through evening, with forecast soundings reasonably depicting 45-55-kt effective-shear vectors. Between the latter factor and focused convergence, the frontal zone should serve as the focus for upscale convective growth through evening. One or two clusters of convection should evolve from the supercellular activity and shift eastward across the outlook area, offering a growing threat for severe gusts -- some of which also may reach significant levels (hurricane force) on a localized basis. A roughly eastward forward-propagational MCS appears possible astride the NE/SD line through the evening and into parts of the overnight hours, with a continuing wind-damage threat toward the Siouxland area of northwestern IA and southeastern SD before the activity wanes tonight. ...Southern Lower MI... Scattered thunderstorms are ongoing over eastern WI and portions of Lake Michigan, in a regime of strong low-level warm advection and moisture transport. While expected to remain below severe limits, the downshear spread of clouds and precip across Lower MI should foster a prefrontal outflow/differential-heating boundary with relatively maximized low-level lift, over portions of southern Lower MI. While the specific location of the boundary remains somewhat uncertain, confidence in its development and in some related afternoon genesis of at least isolated strong/severe convection has increased enough to warrant introducing marginal unconditional probabilities. The main concerns with any sustained convection near the boundary will be damaging gusts and marginally severe hail. Forecast soundings in the nearby warm sector suggest that strong surface heating and dew points generally in the 60s F will support peak mid/late-afternoon MLCAPE near 2000 J/kg. A well-mixed/ inverted-v thermodynamic profile should develop in the boundary layer, amidst minimal MLCINH. Very little directional shear is expected, limiting hodograph sizes, though deep/cloud-layer shear may be sufficient to support organized multicells. Convective potential also exists farther north nearer to the cold front, but this is very conditional on destabilization within/behind the morning clouds/convection, and too conditional for any probabilities at this time. ...Portions of Intermountain/northern Great Basin... Widely scattered to scattered thunderstorms should form through much of the afternoon and into the early evening over an irregularly shaped swath from northeastern NV to extreme southern MT, northern UT, western WY and northwestern CO. Isolated severe gusts/hail will be possible. Cooling aloft related to the approaching mid/upper- level trough, overlying diurnal surface heating, will result in minimal MLCINH and steep deep-layer lapse rates (e.g, near 8 deg c/km from surface-300 mb in some forecast soundings), amidst sufficient low-level moisture to support sustained/deep convection. Cooling aloft will offset diabatic low-level cooling enough to maintain an isolated strong-severe threat a few more hours into the evening/nighttime hours than less synoptically forced scenarios. ..Edwards/Dial.. 09/10/2019 Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0757 AM CDT Tue Sep 10 2019 Valid 101300Z - 111200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ASTRIDE MUCH OF THE NEBRASKA/SOUTH DAKOTA STATE LINE AND INTO ADJOINING PARTS OF EACH STATE... ...SUMMARY... An enhanced threat for severe hail and wind should develop this afternoon and evening across parts of the north-central Plains, mostly near the Nebraska/South Dakota line. A tornado threat exists in that area as well. ...Synopsis... A strong shortwave trough located about 1000 nm west of Vancouver Island is forecast to deepen into an expansive, progressive 500-mb cyclone today. As this occurs, downstream ridging across eastern Canada and a closed cyclone over the Pacific Northwest each will begin to break down somewhat, thereby eroding the Rex configuration now in place over northwestern North America. A substantial synoptic-scale trough extends from the Pacific Northwest cyclone south-southeastward across coastal southern CA. As the cyclone weakens/opens slightly, the trough will move eastward, reaching to near an axis from MSO-TWF-LAS-YUM by 12Z. Associated height falls will spread across the central Rockies and High Plains during the latter half of the period, supporting a broad, hybrid frontal-wave/ lee cyclone at the surface over the central High Plains. A weak mid/upper-level shortwave trough -- now evident in moisture- channel imagery from the southern MB/ON border across northwestern MN -- will move eastward across the width of northern ON, reaching western QC by 12Z. As this occurs, the associated surface frontal- wave cyclone -- analyzed at 11Z over northern MN -- should ripple eastward across the length of Lake Superior and much of adjoining northeastern ON toward QC this evening. The trailing cold front was drawn initially from the MN low to north-central NE, becoming nearly stationary from north-central NE west-southwestward across northern CO. A trough was drawn from a weak low over east- central CO north-northeastward to the front in western NE. By 00Z, the cold front should reach eastern Upper MI and south-central WI, becoming quasistationary from there across extreme northern IA, then a warm front across northern NE near the SD line and into east-central/ southeastern WY. By 12Z, the front should extend across central Lower MI, south-central WI, north-central/northwestern IA and northern NE near SD, with much of the NE part likely having been altered by convective outflow. ...North-central Plains... Thunderstorms are expected to develop this afternoon in two principal regimes: convergence along/near the surface front over northwestern NE and perhaps nearby southwestern SD, and upslope postfrontal lift across parts of eastern WY into the Black Hills region. During the first few hours of both regimes, supercells will be possible with all severe hazards (tornado, wind, hail), with some significant/damaging hail supported by forecast soundings. The most unstable air mass will exist along and south of the warm front, where surface dew points in the 60s F and steep low/middle- level lapse rates will contribute to peak preconvective MLCAPE commonly reaching the 3000-3500 J/kg range, transitioning to 1500- 2500 J/kg westward across eastern WY in the upslope regime. Northwest and south of the front, long low-level hodographs and favorable deep shear will prevail, while backed flow along and just north of the front will enlarge low-level shear and storm-relative boundary-layer winds. Deep shear should increase area-wide from late afternoon through evening, with forecast soundings reasonably depicting 45-55-kt effective-shear vectors. Between the latter factor and focused convergence, the frontal zone should serve as the focus for upscale convective growth through evening. One or two clusters of convection should evolve from the supercellular activity and shift eastward across the outlook area, offering a growing threat for severe gusts -- some of which also may reach significant levels (hurricane force) on a localized basis. A roughly eastward forward-propagational MCS appears possible astride the NE/SD line through the evening and into parts of the overnight hours, with a continuing wind-damage threat toward the Siouxland area of northwestern IA and southeastern SD before the activity wanes tonight. ...Southern Lower MI... Scattered thunderstorms are ongoing over eastern WI and portions of Lake Michigan, in a regime of strong low-level warm advection and moisture transport. While expected to remain below severe limits, the downshear spread of clouds and precip across Lower MI should foster a prefrontal outflow/differential-heating boundary with relatively maximized low-level lift, over portions of southern Lower MI. While the specific location of the boundary remains somewhat uncertain, confidence in its development and in some related afternoon genesis of at least isolated strong/severe convection has increased enough to warrant introducing marginal unconditional probabilities. The main concerns with any sustained convection near the boundary will be damaging gusts and marginally severe hail. Forecast soundings in the nearby warm sector suggest that strong surface heating and dew points generally in the 60s F will support peak mid/late-afternoon MLCAPE near 2000 J/kg. A well-mixed/ inverted-v thermodynamic profile should develop in the boundary layer, amidst minimal MLCINH. Very little directional shear is expected, limiting hodograph sizes, though deep/cloud-layer shear may be sufficient to support organized multicells. Convective potential also exists farther north nearer to the cold front, but this is very conditional on destabilization within/behind the morning clouds/convection, and too conditional for any probabilities at this time. ...Portions of Intermountain/northern Great Basin... Widely scattered to scattered thunderstorms should form through much of the afternoon and into the early evening over an irregularly shaped swath from northeastern NV to extreme southern MT, northern UT, western WY and northwestern CO. Isolated severe gusts/hail will be possible. Cooling aloft related to the approaching mid/upper- level trough, overlying diurnal surface heating, will result in minimal MLCINH and steep deep-layer lapse rates (e.g, near 8 deg c/km from surface-300 mb in some forecast soundings), amidst sufficient low-level moisture to support sustained/deep convection. Cooling aloft will offset diabatic low-level cooling enough to maintain an isolated strong-severe threat a few more hours into the evening/nighttime hours than less synoptically forced scenarios. ..Edwards/Dial.. 09/10/2019 Read more

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0247 AM CDT Tue Sep 10 2019 Valid 131200Z - 181200Z ...DISCUSSION... ...Friday/Day 4 to Saturday/Day 5... On Friday, the medium-range models are in good agreement. The models have an upper-level trough in the Upper Mississippi Valley with a cold front from the Great Lakes to the mid Mississippi Valley. Thunderstorm development will be possible along parts of the front Friday afternoon and evening. On Saturday, the models move a shortwave trough and associated cold front across the north-central U.S. Thunderstorm development, with some possibly severe, will be possible along the front during the afternoon and evening. The models vary somewhat on the quick eastward progression of the shortwave trough. This introduces considerable uncertainty. Where the instability axis ends up near peak heating will help determine the corridor with the greatest severe threat. ...Sunday/Day 6 to Tuesday/Day 8... From Sunday through Tuesday, the models develop an upper-level ridge from the northern Plains into the Great Lakes but show significant differences in its character. Although moderate instability will be possible beneath the ridge each afternoon, convective coverage would remain very isolated. Even so, an isolated severe threat can not be ruled out across parts of the north-central states each afternoon. Spatial uncertainty is substantial during this time in the forecast. Read more

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0247 AM CDT Tue Sep 10 2019 Valid 131200Z - 181200Z ...DISCUSSION... ...Friday/Day 4 to Saturday/Day 5... On Friday, the medium-range models are in good agreement. The models have an upper-level trough in the Upper Mississippi Valley with a cold front from the Great Lakes to the mid Mississippi Valley. Thunderstorm development will be possible along parts of the front Friday afternoon and evening. On Saturday, the models move a shortwave trough and associated cold front across the north-central U.S. Thunderstorm development, with some possibly severe, will be possible along the front during the afternoon and evening. The models vary somewhat on the quick eastward progression of the shortwave trough. This introduces considerable uncertainty. Where the instability axis ends up near peak heating will help determine the corridor with the greatest severe threat. ...Sunday/Day 6 to Tuesday/Day 8... From Sunday through Tuesday, the models develop an upper-level ridge from the northern Plains into the Great Lakes but show significant differences in its character. Although moderate instability will be possible beneath the ridge each afternoon, convective coverage would remain very isolated. Even so, an isolated severe threat can not be ruled out across parts of the north-central states each afternoon. Spatial uncertainty is substantial during this time in the forecast. Read more

SPC 0730Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0215 AM CDT Tue Sep 10 2019 Valid 121200Z - 131200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE SOUTHERN AND CENTRAL PLAINS...LOWER TO MID MISSOURI VALLEY AND UPPER MIDWEST... ...SUMMARY... Thunderstorms associated with wind damage and isolated large hail will be possible on Thursday from eastern Kansas into northwest Missouri and Iowa. ...Southern and Central Plains/Lower to Mid Missouri Valley/Upper Midwest... An upper-level low is forecast to move northeastward across the northern Plains on Thursday. At the surface, a low is forecast to move into the Upper Mississippi Valley as a cold front advances eastward across Iowa, northwest Missouri and central Kansas. Ahead of the front, surface dewpoints should be in the upper 60s to near 70 F, helping moderate instability to develop around midday. Model consensus suggests that convective coverage should gradually increase along the front from Thursday morning into afternoon until a line is established. This convective line is forecast to move eastward across Iowa, northern Missouri and eastern Kansas from late afternoon to mid evening. Veered winds to the south-southwest ahead of the front along with 0-6 km shear values in the 30 to 40 kt range would be favorable for organized multicell bowing segments. The bowing segments would be capable of damaging wind gusts and hail. If cell rotation can develop along the stronger portions of the convective line, then isolated large hail would also be possible. The severe threat should taper off with south-southwestward extent into southern Kansas and northwestern Oklahoma, where deep-layer shear is forecast to be much weaker. ..Broyles.. 09/10/2019 Read more

SPC 0730Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0215 AM CDT Tue Sep 10 2019 Valid 121200Z - 131200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE SOUTHERN AND CENTRAL PLAINS...LOWER TO MID MISSOURI VALLEY AND UPPER MIDWEST... ...SUMMARY... Thunderstorms associated with wind damage and isolated large hail will be possible on Thursday from eastern Kansas into northwest Missouri and Iowa. ...Southern and Central Plains/Lower to Mid Missouri Valley/Upper Midwest... An upper-level low is forecast to move northeastward across the northern Plains on Thursday. At the surface, a low is forecast to move into the Upper Mississippi Valley as a cold front advances eastward across Iowa, northwest Missouri and central Kansas. Ahead of the front, surface dewpoints should be in the upper 60s to near 70 F, helping moderate instability to develop around midday. Model consensus suggests that convective coverage should gradually increase along the front from Thursday morning into afternoon until a line is established. This convective line is forecast to move eastward across Iowa, northern Missouri and eastern Kansas from late afternoon to mid evening. Veered winds to the south-southwest ahead of the front along with 0-6 km shear values in the 30 to 40 kt range would be favorable for organized multicell bowing segments. The bowing segments would be capable of damaging wind gusts and hail. If cell rotation can develop along the stronger portions of the convective line, then isolated large hail would also be possible. The severe threat should taper off with south-southwestward extent into southern Kansas and northwestern Oklahoma, where deep-layer shear is forecast to be much weaker. ..Broyles.. 09/10/2019 Read more

SPC Day 2 Fire Weather Outlook
Day 2 Fire Weather Outlook NWS Storm Prediction Center Norman OK 0204 AM CDT Tue Sep 10 2019 Valid 111200Z - 121200Z ...Synopsis... A pronounced mid-level shortwave trough will move across the western CONUS during the Day 2/Wednesday period. Stronger flow aloft will accompany the through, with a belt of 50+ knot 500 mb flow expected to traverse the Four Corners region by late afternoon. At the same time, deep boundary layer mixing may occur across parts of the Four Corners, promoting modest potential for wildfire spread. ...Parts of the Four Corners area... By afternoon peak heating, 15-25 mph sustained westerly winds and 15-20% RH will become commonplace across portions of the northern Colorado Plateau, to the windward side of the central Rockies. Given modestly dry fuels in place, an elevated area was delineated to account for marginal wildfire-spread potential in this area. ..Squitieri.. 09/10/2019 ...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 0204 AM CDT Tue Sep 10 2019 Valid 111200Z - 121200Z ...Synopsis... A pronounced mid-level shortwave trough will move across the western CONUS during the Day 2/Wednesday period. Stronger flow aloft will accompany the through, with a belt of 50+ knot 500 mb flow expected to traverse the Four Corners region by late afternoon. At the same time, deep boundary layer mixing may occur across parts of the Four Corners, promoting modest potential for wildfire spread. ...Parts of the Four Corners area... By afternoon peak heating, 15-25 mph sustained westerly winds and 15-20% RH will become commonplace across portions of the northern Colorado Plateau, to the windward side of the central Rockies. Given modestly dry fuels in place, an elevated area was delineated to account for marginal wildfire-spread potential in this area. ..Squitieri.. 09/10/2019 ...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 0134 AM CDT Tue Sep 10 2019 Valid 101200Z - 111200Z ...Synopsis... Broad cyclonic flow, associated with a deepening mid-level shortwave trough, will prevail across the western CONUS during the period. Breezy conditions, with patchy areas of drier air, will result from a low-level mass response to the impinging mid-level trough, promoting very modest wildfire-spread potential across parts of the Great Basin. In addition, widespread deep-layer ascent ahead of the trough will promote isolated to scattered thunderstorms across eastern portions of the Great Basin, into the Four Corners, central/northern Rockies, northwestward into parts of the Pacific Northwest. On the backside of the trough, surface to mid-level flow will be predominantly northerly/offshore, encouraging a modest Sundowner event across parts of Coastal Southern California towards the end of the period. ...Parts of the Great Basin... While elevated conditions will be mostly localized in nature in advance of the mid-level trough, some widespread 15-20 mph sustained south-southwesterly surface winds coinciding with 15-20% RH may occur across parts of central, eastern, and southern Nevada. The most likely timing of these conditions would be after peak heating of the afternoon. Farther east into Utah, surface southwesterly winds may easily exceed 20 mph, particularly in terrain-favoring locations, but surface RH above 20% depicted by the latest model guidance suggests that elevated fire concerns will be mainly localized in nature, with an elevated delineation withheld for this outlook. ...Eastern Great Basin into the central/northern Rockies... At least isolated to scattered thunderstorms will develop during the afternoon hours, aided by afternoon peak heating/boundary-layer mixing, and by deep-layer ascent provided by the mid-level shortwave trough. These storms are expected to be relatively fast-moving in nature, with precipitable water values under 0.75 inches and dry sub-cloud layers extending well above 700 mb in most locales. Still, fuels across these area are expected to be marginally to modestly receptive to new ignitions and subsequent fire spread on the large scale. As such, the localized threat for new dry-lightning induced fire starts precludes an isolated dry thunderstorm delineation. ...Parts of Coastal Southern California... Towards the end of the period, northerly sustained surface winds within the 15-25 mph range are expected along with 20-25% RH. Given dry fuels receptive to fire spread, elevated fire weather conditions are expected across portions of Ventura and Santa Barbara Counties, particularly in the higher terrain of the Santa Ynez Mountains, where winds will be strongest, with the poorest RH recovery. ..Squitieri.. 09/10/2019 ...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 0134 AM CDT Tue Sep 10 2019 Valid 101200Z - 111200Z ...Synopsis... Broad cyclonic flow, associated with a deepening mid-level shortwave trough, will prevail across the western CONUS during the period. Breezy conditions, with patchy areas of drier air, will result from a low-level mass response to the impinging mid-level trough, promoting very modest wildfire-spread potential across parts of the Great Basin. In addition, widespread deep-layer ascent ahead of the trough will promote isolated to scattered thunderstorms across eastern portions of the Great Basin, into the Four Corners, central/northern Rockies, northwestward into parts of the Pacific Northwest. On the backside of the trough, surface to mid-level flow will be predominantly northerly/offshore, encouraging a modest Sundowner event across parts of Coastal Southern California towards the end of the period. ...Parts of the Great Basin... While elevated conditions will be mostly localized in nature in advance of the mid-level trough, some widespread 15-20 mph sustained south-southwesterly surface winds coinciding with 15-20% RH may occur across parts of central, eastern, and southern Nevada. The most likely timing of these conditions would be after peak heating of the afternoon. Farther east into Utah, surface southwesterly winds may easily exceed 20 mph, particularly in terrain-favoring locations, but surface RH above 20% depicted by the latest model guidance suggests that elevated fire concerns will be mainly localized in nature, with an elevated delineation withheld for this outlook. ...Eastern Great Basin into the central/northern Rockies... At least isolated to scattered thunderstorms will develop during the afternoon hours, aided by afternoon peak heating/boundary-layer mixing, and by deep-layer ascent provided by the mid-level shortwave trough. These storms are expected to be relatively fast-moving in nature, with precipitable water values under 0.75 inches and dry sub-cloud layers extending well above 700 mb in most locales. Still, fuels across these area are expected to be marginally to modestly receptive to new ignitions and subsequent fire spread on the large scale. As such, the localized threat for new dry-lightning induced fire starts precludes an isolated dry thunderstorm delineation. ...Parts of Coastal Southern California... Towards the end of the period, northerly sustained surface winds within the 15-25 mph range are expected along with 20-25% RH. Given dry fuels receptive to fire spread, elevated fire weather conditions are expected across portions of Ventura and Santa Barbara Counties, particularly in the higher terrain of the Santa Ynez Mountains, where winds will be strongest, with the poorest RH recovery. ..Squitieri.. 09/10/2019 ...Please see www.spc.noaa.gov/fire for graphic product... Read more