Severe Storms

SPC Day 1 Fire Weather Outlook
Day 1 Fire Weather Outlook NWS Storm Prediction Center Norman OK 1122 AM CDT Sat Sep 07 2019 Valid 071700Z - 081200Z Latest models are a bit stronger with surface winds in the immediate lee of the Sierras this afternoon, with localized areas of dry fuels supporting an elevated fire weather threat. A small elevated area has been added to address this fire weather scenario, with the expectation that localized areas of 20+ mph westerly surface winds will develop for a few hours late this afternoon amidst 15-25% RH. Elevated fire weather conditions remain likely this afternoon across portions of Santa Barbara County in California tonight as well. Sundowner winds with gusts to 40mph (locally higher in terrain-favored areas) will develop amidst 15-20% RH and dry fuels supporting potential fire spread. See the previous discussion below for more information. ..Cook.. 09/07/2019 .PREV DISCUSSION... /ISSUED 1147 PM CDT Fri Sep 06 2019/ ...Synopsis... A mid/upper-level shortwave trough -- located over the northern Rockies vicinity Day 1/Saturday morning -- is forecast to move eastward over the northern/central plains through the day. Meanwhile, an upstream negatively tilted mid-level trough and attendant area of enhanced mid-level flow are forecast to move onshore over portions of the western CONUS through the overnight. ...Southern California: Santa Barbara South Coast... Sundowner winds are expected to increase across portions of the Santa Barbara South Coast and adjacent foothills Day 1/Saturday afternoon/evening as northerly low-level flow is enhanced with the aforementioned trough passing over the Pacific Northwest. While sustained surface winds will generally remain around 15-20 mph, strong wind gusts of 25-40 mph are possible (locally 50+ mph in terrain favored areas). Elevated to locally critical fire weather conditions are expected as these winds overlap areas with minimum RH value around 15-20% (locally below 15%) and receptive fuels for fire spread. Poor RH recoveries may promote elevated fire weather conditions through the overnight and into Day 2/Sunday morning -- especially in areas above 1000 ft where RH values may remain below 20%. ...Pacific Northwest into Nevada... Thunderstorms are expected to increase in coverage over portions of the Cascades in Oregon/Washington (and perhaps far Northern California) during the late afternoon/evening as ascent associated with the aforementioned negatively tilted trough moves onshore. While a lightning ignition remains possible, thunderstorms should remain mostly wet precluding an isolated dry thunderstorm area. A slightly better chance for a lightning ignition exists across Nevada, where thunderstorms should develop during the afternoon. While storm motions will be relatively fast and precipitable water values generally around 0.75", recent precipitation over the past few days coupled with the expected scattered to widespread coverage precludes an isolated dry thunderstorm area at this time. ...Please see www.spc.noaa.gov/fire for graphic product... Read more

SPC Day 1 Fire Weather Outlook
Day 1 Fire Weather Outlook NWS Storm Prediction Center Norman OK 1122 AM CDT Sat Sep 07 2019 Valid 071700Z - 081200Z Latest models are a bit stronger with surface winds in the immediate lee of the Sierras this afternoon, with localized areas of dry fuels supporting an elevated fire weather threat. A small elevated area has been added to address this fire weather scenario, with the expectation that localized areas of 20+ mph westerly surface winds will develop for a few hours late this afternoon amidst 15-25% RH. Elevated fire weather conditions remain likely this afternoon across portions of Santa Barbara County in California tonight as well. Sundowner winds with gusts to 40mph (locally higher in terrain-favored areas) will develop amidst 15-20% RH and dry fuels supporting potential fire spread. See the previous discussion below for more information. ..Cook.. 09/07/2019 .PREV DISCUSSION... /ISSUED 1147 PM CDT Fri Sep 06 2019/ ...Synopsis... A mid/upper-level shortwave trough -- located over the northern Rockies vicinity Day 1/Saturday morning -- is forecast to move eastward over the northern/central plains through the day. Meanwhile, an upstream negatively tilted mid-level trough and attendant area of enhanced mid-level flow are forecast to move onshore over portions of the western CONUS through the overnight. ...Southern California: Santa Barbara South Coast... Sundowner winds are expected to increase across portions of the Santa Barbara South Coast and adjacent foothills Day 1/Saturday afternoon/evening as northerly low-level flow is enhanced with the aforementioned trough passing over the Pacific Northwest. While sustained surface winds will generally remain around 15-20 mph, strong wind gusts of 25-40 mph are possible (locally 50+ mph in terrain favored areas). Elevated to locally critical fire weather conditions are expected as these winds overlap areas with minimum RH value around 15-20% (locally below 15%) and receptive fuels for fire spread. Poor RH recoveries may promote elevated fire weather conditions through the overnight and into Day 2/Sunday morning -- especially in areas above 1000 ft where RH values may remain below 20%. ...Pacific Northwest into Nevada... Thunderstorms are expected to increase in coverage over portions of the Cascades in Oregon/Washington (and perhaps far Northern California) during the late afternoon/evening as ascent associated with the aforementioned negatively tilted trough moves onshore. While a lightning ignition remains possible, thunderstorms should remain mostly wet precluding an isolated dry thunderstorm area. A slightly better chance for a lightning ignition exists across Nevada, where thunderstorms should develop during the afternoon. While storm motions will be relatively fast and precipitable water values generally around 0.75", recent precipitation over the past few days coupled with the expected scattered to widespread coverage precludes an isolated dry thunderstorm area at this time. ...Please see www.spc.noaa.gov/fire for graphic product... Read more

SPC Day 1 Fire Weather Outlook
Day 1 Fire Weather Outlook NWS Storm Prediction Center Norman OK 1122 AM CDT Sat Sep 07 2019 Valid 071700Z - 081200Z Latest models are a bit stronger with surface winds in the immediate lee of the Sierras this afternoon, with localized areas of dry fuels supporting an elevated fire weather threat. A small elevated area has been added to address this fire weather scenario, with the expectation that localized areas of 20+ mph westerly surface winds will develop for a few hours late this afternoon amidst 15-25% RH. Elevated fire weather conditions remain likely this afternoon across portions of Santa Barbara County in California tonight as well. Sundowner winds with gusts to 40mph (locally higher in terrain-favored areas) will develop amidst 15-20% RH and dry fuels supporting potential fire spread. See the previous discussion below for more information. ..Cook.. 09/07/2019 .PREV DISCUSSION... /ISSUED 1147 PM CDT Fri Sep 06 2019/ ...Synopsis... A mid/upper-level shortwave trough -- located over the northern Rockies vicinity Day 1/Saturday morning -- is forecast to move eastward over the northern/central plains through the day. Meanwhile, an upstream negatively tilted mid-level trough and attendant area of enhanced mid-level flow are forecast to move onshore over portions of the western CONUS through the overnight. ...Southern California: Santa Barbara South Coast... Sundowner winds are expected to increase across portions of the Santa Barbara South Coast and adjacent foothills Day 1/Saturday afternoon/evening as northerly low-level flow is enhanced with the aforementioned trough passing over the Pacific Northwest. While sustained surface winds will generally remain around 15-20 mph, strong wind gusts of 25-40 mph are possible (locally 50+ mph in terrain favored areas). Elevated to locally critical fire weather conditions are expected as these winds overlap areas with minimum RH value around 15-20% (locally below 15%) and receptive fuels for fire spread. Poor RH recoveries may promote elevated fire weather conditions through the overnight and into Day 2/Sunday morning -- especially in areas above 1000 ft where RH values may remain below 20%. ...Pacific Northwest into Nevada... Thunderstorms are expected to increase in coverage over portions of the Cascades in Oregon/Washington (and perhaps far Northern California) during the late afternoon/evening as ascent associated with the aforementioned negatively tilted trough moves onshore. While a lightning ignition remains possible, thunderstorms should remain mostly wet precluding an isolated dry thunderstorm area. A slightly better chance for a lightning ignition exists across Nevada, where thunderstorms should develop during the afternoon. While storm motions will be relatively fast and precipitable water values generally around 0.75", recent precipitation over the past few days coupled with the expected scattered to widespread coverage precludes an isolated dry thunderstorm area at this time. ...Please see www.spc.noaa.gov/fire for graphic product... Read more

SPC Day 1 Fire Weather Outlook
Day 1 Fire Weather Outlook NWS Storm Prediction Center Norman OK 1122 AM CDT Sat Sep 07 2019 Valid 071700Z - 081200Z Latest models are a bit stronger with surface winds in the immediate lee of the Sierras this afternoon, with localized areas of dry fuels supporting an elevated fire weather threat. A small elevated area has been added to address this fire weather scenario, with the expectation that localized areas of 20+ mph westerly surface winds will develop for a few hours late this afternoon amidst 15-25% RH. Elevated fire weather conditions remain likely this afternoon across portions of Santa Barbara County in California tonight as well. Sundowner winds with gusts to 40mph (locally higher in terrain-favored areas) will develop amidst 15-20% RH and dry fuels supporting potential fire spread. See the previous discussion below for more information. ..Cook.. 09/07/2019 .PREV DISCUSSION... /ISSUED 1147 PM CDT Fri Sep 06 2019/ ...Synopsis... A mid/upper-level shortwave trough -- located over the northern Rockies vicinity Day 1/Saturday morning -- is forecast to move eastward over the northern/central plains through the day. Meanwhile, an upstream negatively tilted mid-level trough and attendant area of enhanced mid-level flow are forecast to move onshore over portions of the western CONUS through the overnight. ...Southern California: Santa Barbara South Coast... Sundowner winds are expected to increase across portions of the Santa Barbara South Coast and adjacent foothills Day 1/Saturday afternoon/evening as northerly low-level flow is enhanced with the aforementioned trough passing over the Pacific Northwest. While sustained surface winds will generally remain around 15-20 mph, strong wind gusts of 25-40 mph are possible (locally 50+ mph in terrain favored areas). Elevated to locally critical fire weather conditions are expected as these winds overlap areas with minimum RH value around 15-20% (locally below 15%) and receptive fuels for fire spread. Poor RH recoveries may promote elevated fire weather conditions through the overnight and into Day 2/Sunday morning -- especially in areas above 1000 ft where RH values may remain below 20%. ...Pacific Northwest into Nevada... Thunderstorms are expected to increase in coverage over portions of the Cascades in Oregon/Washington (and perhaps far Northern California) during the late afternoon/evening as ascent associated with the aforementioned negatively tilted trough moves onshore. While a lightning ignition remains possible, thunderstorms should remain mostly wet precluding an isolated dry thunderstorm area. A slightly better chance for a lightning ignition exists across Nevada, where thunderstorms should develop during the afternoon. While storm motions will be relatively fast and precipitable water values generally around 0.75", recent precipitation over the past few days coupled with the expected scattered to widespread coverage precludes an isolated dry thunderstorm area at this time. ...Please see www.spc.noaa.gov/fire for graphic product... Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0755 AM CDT Sat Sep 07 2019 Valid 071300Z - 081200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER PARTS OF THE CENTRAL PLAINS...AND NEAR THE NORTHERN CASCADES... ...SUMMARY... Isolated severe wind and hail are possible today from thunderstorms over parts of the central Plains, and near the northern Cascades. ...Synopsis... A progressive upper-air pattern will persist over the northern 1/3-1/2 of the CONUS, while continued weakening of longstanding southwestern ridging is expected. A leading shortwave trough -- now apparent in moisture-channel imagery over portions of central MT and western WY -- will shift east-southeastward over the northern High Plains to the Dakotas and northern NE through the period. Upstream ridging will shift northeastward from the Pacific Coast States to the northern/central Rockies. This will occur as a strong, negatively tilted trough -- initially located offshore from the Pacific Coast, moves inland in the 00-06Z time frame. By the end of the period, this trough at 500 mb should be located from western portions of WA/OR to near LAS then down the lower Colorado River Valley. At the surface, a quasistationary frontal zone was analyzed from a low over southeastern CO east-southeastward across northern parts of OK, to portions of the Mid-South and Tennessee Valley region. This boundary should move northward over the central Plains as a warm front, potentially merging with another baroclinic zone evident over southern SD. ...Central Plains across adjoining Missouri Valley... Isolated to widely scattered convection should form late this afternoon into this evening, within two now-conjoined corridors: from southeastern CO across northern KS to northwestern MO, and from western SD southeastward across central/southeastern NE. The northern limb will correspond to a narrow, triangular, northwest/ southeast-oriented plume of favorable moisture and antecedent destabilization, from western SD to central NE. Any sustained thunderstorms will have the potential to become supercellular, with large hail and strong-severe gusts possible. Any activity over CO, KS, NE and southern SD may be surface-based, with the northern rim of a boundary-layer moist axis impinging on relatively maximized low-level convergence near the frontal zone, low, and an inverted trough. Forecast soundings suggest 1500-2000 J/kg MLCAPE by mid/late afternoon over central NE and the eastern Sandhills, increasing to 2000-3000 J/kg toward northeastern KS (but amidst stronger capping). This will be supported by surface dew points in the 60s F and steep deep-layer lapse rates. Surface-based buoyancy will lessen in magnitude and spatial width with northward extent and in over SD and southwester extent into southeastern CO, but still may support a severe storm or two moving southeastward to eastward obliquely through the narrow favorable thermodynamic zone. Strong directional shear is expected near the warm frontal zone, though weak wind speeds will limit hodograph size in the lowest couple of km. Lack of greater coverage of both progged convection and favorable parameter space precludes more than a marginal unconditional severe risk at this time. However, the potential for convection to cross the gap between the two previous marginal risks resulted in their union. ...Interior Northwest... Widely scattered thunderstorms are expected to develop over and just east of the Cascade crest this afternoon and evening, offering isolated threats for severe hail/gusts as activity moves north- northeastward to northeastward over the outlook area. Strong heating of higher terrain will preferentially remove MLCINH conterminously with strengthening large-scale ascent related to the approaching Pacific trough. The resulting steepening of low/middle- level lapse rates, atop a corridor of at least marginally favorable low-level moisture remaining after diurnal mixing, will support pockets of 500-1000 J/kg peak preconvective MLCAPE. Just as importantly, a large-DCAPE, well-mixed boundary layer will develop over the eastern Cascades region and part of adjoining lower terrain, helping to maintain hail and accelerate downdrafts to the surface. Forecast soundings suggest 25-40 kt effective-shear vectors in support of predominantly multicellular (but potentially isolated supercellular) storm mode. ..Edwards/Smith.. 09/07/2019 Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0755 AM CDT Sat Sep 07 2019 Valid 071300Z - 081200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER PARTS OF THE CENTRAL PLAINS...AND NEAR THE NORTHERN CASCADES... ...SUMMARY... Isolated severe wind and hail are possible today from thunderstorms over parts of the central Plains, and near the northern Cascades. ...Synopsis... A progressive upper-air pattern will persist over the northern 1/3-1/2 of the CONUS, while continued weakening of longstanding southwestern ridging is expected. A leading shortwave trough -- now apparent in moisture-channel imagery over portions of central MT and western WY -- will shift east-southeastward over the northern High Plains to the Dakotas and northern NE through the period. Upstream ridging will shift northeastward from the Pacific Coast States to the northern/central Rockies. This will occur as a strong, negatively tilted trough -- initially located offshore from the Pacific Coast, moves inland in the 00-06Z time frame. By the end of the period, this trough at 500 mb should be located from western portions of WA/OR to near LAS then down the lower Colorado River Valley. At the surface, a quasistationary frontal zone was analyzed from a low over southeastern CO east-southeastward across northern parts of OK, to portions of the Mid-South and Tennessee Valley region. This boundary should move northward over the central Plains as a warm front, potentially merging with another baroclinic zone evident over southern SD. ...Central Plains across adjoining Missouri Valley... Isolated to widely scattered convection should form late this afternoon into this evening, within two now-conjoined corridors: from southeastern CO across northern KS to northwestern MO, and from western SD southeastward across central/southeastern NE. The northern limb will correspond to a narrow, triangular, northwest/ southeast-oriented plume of favorable moisture and antecedent destabilization, from western SD to central NE. Any sustained thunderstorms will have the potential to become supercellular, with large hail and strong-severe gusts possible. Any activity over CO, KS, NE and southern SD may be surface-based, with the northern rim of a boundary-layer moist axis impinging on relatively maximized low-level convergence near the frontal zone, low, and an inverted trough. Forecast soundings suggest 1500-2000 J/kg MLCAPE by mid/late afternoon over central NE and the eastern Sandhills, increasing to 2000-3000 J/kg toward northeastern KS (but amidst stronger capping). This will be supported by surface dew points in the 60s F and steep deep-layer lapse rates. Surface-based buoyancy will lessen in magnitude and spatial width with northward extent and in over SD and southwester extent into southeastern CO, but still may support a severe storm or two moving southeastward to eastward obliquely through the narrow favorable thermodynamic zone. Strong directional shear is expected near the warm frontal zone, though weak wind speeds will limit hodograph size in the lowest couple of km. Lack of greater coverage of both progged convection and favorable parameter space precludes more than a marginal unconditional severe risk at this time. However, the potential for convection to cross the gap between the two previous marginal risks resulted in their union. ...Interior Northwest... Widely scattered thunderstorms are expected to develop over and just east of the Cascade crest this afternoon and evening, offering isolated threats for severe hail/gusts as activity moves north- northeastward to northeastward over the outlook area. Strong heating of higher terrain will preferentially remove MLCINH conterminously with strengthening large-scale ascent related to the approaching Pacific trough. The resulting steepening of low/middle- level lapse rates, atop a corridor of at least marginally favorable low-level moisture remaining after diurnal mixing, will support pockets of 500-1000 J/kg peak preconvective MLCAPE. Just as importantly, a large-DCAPE, well-mixed boundary layer will develop over the eastern Cascades region and part of adjoining lower terrain, helping to maintain hail and accelerate downdrafts to the surface. Forecast soundings suggest 25-40 kt effective-shear vectors in support of predominantly multicellular (but potentially isolated supercellular) storm mode. ..Edwards/Smith.. 09/07/2019 Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0755 AM CDT Sat Sep 07 2019 Valid 071300Z - 081200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER PARTS OF THE CENTRAL PLAINS...AND NEAR THE NORTHERN CASCADES... ...SUMMARY... Isolated severe wind and hail are possible today from thunderstorms over parts of the central Plains, and near the northern Cascades. ...Synopsis... A progressive upper-air pattern will persist over the northern 1/3-1/2 of the CONUS, while continued weakening of longstanding southwestern ridging is expected. A leading shortwave trough -- now apparent in moisture-channel imagery over portions of central MT and western WY -- will shift east-southeastward over the northern High Plains to the Dakotas and northern NE through the period. Upstream ridging will shift northeastward from the Pacific Coast States to the northern/central Rockies. This will occur as a strong, negatively tilted trough -- initially located offshore from the Pacific Coast, moves inland in the 00-06Z time frame. By the end of the period, this trough at 500 mb should be located from western portions of WA/OR to near LAS then down the lower Colorado River Valley. At the surface, a quasistationary frontal zone was analyzed from a low over southeastern CO east-southeastward across northern parts of OK, to portions of the Mid-South and Tennessee Valley region. This boundary should move northward over the central Plains as a warm front, potentially merging with another baroclinic zone evident over southern SD. ...Central Plains across adjoining Missouri Valley... Isolated to widely scattered convection should form late this afternoon into this evening, within two now-conjoined corridors: from southeastern CO across northern KS to northwestern MO, and from western SD southeastward across central/southeastern NE. The northern limb will correspond to a narrow, triangular, northwest/ southeast-oriented plume of favorable moisture and antecedent destabilization, from western SD to central NE. Any sustained thunderstorms will have the potential to become supercellular, with large hail and strong-severe gusts possible. Any activity over CO, KS, NE and southern SD may be surface-based, with the northern rim of a boundary-layer moist axis impinging on relatively maximized low-level convergence near the frontal zone, low, and an inverted trough. Forecast soundings suggest 1500-2000 J/kg MLCAPE by mid/late afternoon over central NE and the eastern Sandhills, increasing to 2000-3000 J/kg toward northeastern KS (but amidst stronger capping). This will be supported by surface dew points in the 60s F and steep deep-layer lapse rates. Surface-based buoyancy will lessen in magnitude and spatial width with northward extent and in over SD and southwester extent into southeastern CO, but still may support a severe storm or two moving southeastward to eastward obliquely through the narrow favorable thermodynamic zone. Strong directional shear is expected near the warm frontal zone, though weak wind speeds will limit hodograph size in the lowest couple of km. Lack of greater coverage of both progged convection and favorable parameter space precludes more than a marginal unconditional severe risk at this time. However, the potential for convection to cross the gap between the two previous marginal risks resulted in their union. ...Interior Northwest... Widely scattered thunderstorms are expected to develop over and just east of the Cascade crest this afternoon and evening, offering isolated threats for severe hail/gusts as activity moves north- northeastward to northeastward over the outlook area. Strong heating of higher terrain will preferentially remove MLCINH conterminously with strengthening large-scale ascent related to the approaching Pacific trough. The resulting steepening of low/middle- level lapse rates, atop a corridor of at least marginally favorable low-level moisture remaining after diurnal mixing, will support pockets of 500-1000 J/kg peak preconvective MLCAPE. Just as importantly, a large-DCAPE, well-mixed boundary layer will develop over the eastern Cascades region and part of adjoining lower terrain, helping to maintain hail and accelerate downdrafts to the surface. Forecast soundings suggest 25-40 kt effective-shear vectors in support of predominantly multicellular (but potentially isolated supercellular) storm mode. ..Edwards/Smith.. 09/07/2019 Read more

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0357 AM CDT Sat Sep 07 2019 Valid 101200Z - 151200Z ...DISCUSSION... ...Tuesday/Day 4 to Thursday/Day 6... The medium-range models including the ECMWF, GFS, UKMET and Canadian are in generally good agreement at the start of the day 4 to 8 period. The models move a shortwave ridge across the northern Plains on Tuesday as an upper-level trough develops in the western U.S. At the surface, the models have a corridor of maximized low-level moisture from the central High Plains east-northeastward into the Upper Mississippi Valley. Moderate instability will be possible along parts of this corridor Tuesday afternoon. Thunderstorms that can develop along the instability gradient may have a severe threat mainly during the late afternoon and early evening. However, uncertainty remains too considerable to add a threat area. On Wednesday and Thursday, the model solutions agree that an upper-level trough along with an associated mid-level jet will move across the north-central U.S. Thunderstorms will be possible ahead of the trough on Wednesday across a moist and unstable airmass in the northern Plains and Upper Mississippi Valley. Thunderstorms will again be possible ahead of the upper-level trough on Thursday from the Upper Mississippi Valley into the Great Lakes. Some potential exists for a severe threat each day from Wednesday to Thursday. However, there is disagreement concerning how much deep-layer shear will be available across the warm sector. For this reason, will not add a threat area at this time. ...Friday/Day 7 to Saturday/Day 8... On Friday and Saturday, the models move the upper-level trough across the Great Lakes although the solutions have different timing. The GFS, ECMWF and Canadian solutions are in general agreement further west, returning low-level moisture into the north-central states from Friday night into Saturday. If this scenario pans out, an isolated severe threat would be possible in parts of the Dakotas, Nebraska and Iowa where these solutions suggest moderate instability could develop. Uncertainty is substantial at this range and will not outlook a threat area from Friday into Saturday. Read more

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0357 AM CDT Sat Sep 07 2019 Valid 101200Z - 151200Z ...DISCUSSION... ...Tuesday/Day 4 to Thursday/Day 6... The medium-range models including the ECMWF, GFS, UKMET and Canadian are in generally good agreement at the start of the day 4 to 8 period. The models move a shortwave ridge across the northern Plains on Tuesday as an upper-level trough develops in the western U.S. At the surface, the models have a corridor of maximized low-level moisture from the central High Plains east-northeastward into the Upper Mississippi Valley. Moderate instability will be possible along parts of this corridor Tuesday afternoon. Thunderstorms that can develop along the instability gradient may have a severe threat mainly during the late afternoon and early evening. However, uncertainty remains too considerable to add a threat area. On Wednesday and Thursday, the model solutions agree that an upper-level trough along with an associated mid-level jet will move across the north-central U.S. Thunderstorms will be possible ahead of the trough on Wednesday across a moist and unstable airmass in the northern Plains and Upper Mississippi Valley. Thunderstorms will again be possible ahead of the upper-level trough on Thursday from the Upper Mississippi Valley into the Great Lakes. Some potential exists for a severe threat each day from Wednesday to Thursday. However, there is disagreement concerning how much deep-layer shear will be available across the warm sector. For this reason, will not add a threat area at this time. ...Friday/Day 7 to Saturday/Day 8... On Friday and Saturday, the models move the upper-level trough across the Great Lakes although the solutions have different timing. The GFS, ECMWF and Canadian solutions are in general agreement further west, returning low-level moisture into the north-central states from Friday night into Saturday. If this scenario pans out, an isolated severe threat would be possible in parts of the Dakotas, Nebraska and Iowa where these solutions suggest moderate instability could develop. Uncertainty is substantial at this range and will not outlook a threat area from Friday into Saturday. Read more

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0357 AM CDT Sat Sep 07 2019 Valid 101200Z - 151200Z ...DISCUSSION... ...Tuesday/Day 4 to Thursday/Day 6... The medium-range models including the ECMWF, GFS, UKMET and Canadian are in generally good agreement at the start of the day 4 to 8 period. The models move a shortwave ridge across the northern Plains on Tuesday as an upper-level trough develops in the western U.S. At the surface, the models have a corridor of maximized low-level moisture from the central High Plains east-northeastward into the Upper Mississippi Valley. Moderate instability will be possible along parts of this corridor Tuesday afternoon. Thunderstorms that can develop along the instability gradient may have a severe threat mainly during the late afternoon and early evening. However, uncertainty remains too considerable to add a threat area. On Wednesday and Thursday, the model solutions agree that an upper-level trough along with an associated mid-level jet will move across the north-central U.S. Thunderstorms will be possible ahead of the trough on Wednesday across a moist and unstable airmass in the northern Plains and Upper Mississippi Valley. Thunderstorms will again be possible ahead of the upper-level trough on Thursday from the Upper Mississippi Valley into the Great Lakes. Some potential exists for a severe threat each day from Wednesday to Thursday. However, there is disagreement concerning how much deep-layer shear will be available across the warm sector. For this reason, will not add a threat area at this time. ...Friday/Day 7 to Saturday/Day 8... On Friday and Saturday, the models move the upper-level trough across the Great Lakes although the solutions have different timing. The GFS, ECMWF and Canadian solutions are in general agreement further west, returning low-level moisture into the north-central states from Friday night into Saturday. If this scenario pans out, an isolated severe threat would be possible in parts of the Dakotas, Nebraska and Iowa where these solutions suggest moderate instability could develop. Uncertainty is substantial at this range and will not outlook a threat area from Friday into Saturday. Read more

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0357 AM CDT Sat Sep 07 2019 Valid 101200Z - 151200Z ...DISCUSSION... ...Tuesday/Day 4 to Thursday/Day 6... The medium-range models including the ECMWF, GFS, UKMET and Canadian are in generally good agreement at the start of the day 4 to 8 period. The models move a shortwave ridge across the northern Plains on Tuesday as an upper-level trough develops in the western U.S. At the surface, the models have a corridor of maximized low-level moisture from the central High Plains east-northeastward into the Upper Mississippi Valley. Moderate instability will be possible along parts of this corridor Tuesday afternoon. Thunderstorms that can develop along the instability gradient may have a severe threat mainly during the late afternoon and early evening. However, uncertainty remains too considerable to add a threat area. On Wednesday and Thursday, the model solutions agree that an upper-level trough along with an associated mid-level jet will move across the north-central U.S. Thunderstorms will be possible ahead of the trough on Wednesday across a moist and unstable airmass in the northern Plains and Upper Mississippi Valley. Thunderstorms will again be possible ahead of the upper-level trough on Thursday from the Upper Mississippi Valley into the Great Lakes. Some potential exists for a severe threat each day from Wednesday to Thursday. However, there is disagreement concerning how much deep-layer shear will be available across the warm sector. For this reason, will not add a threat area at this time. ...Friday/Day 7 to Saturday/Day 8... On Friday and Saturday, the models move the upper-level trough across the Great Lakes although the solutions have different timing. The GFS, ECMWF and Canadian solutions are in general agreement further west, returning low-level moisture into the north-central states from Friday night into Saturday. If this scenario pans out, an isolated severe threat would be possible in parts of the Dakotas, Nebraska and Iowa where these solutions suggest moderate instability could develop. Uncertainty is substantial at this range and will not outlook a threat area from Friday into Saturday. Read more

SPC 0730Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0213 AM CDT Sat Sep 07 2019 Valid 091200Z - 101200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE CENTRAL AND NORTHERN PLAINS EASTWARD INTO THE UPPER MISSISSIPPI VALLEY... ...SUMMARY... Thunderstorms associated with hail and marginally severe wind gusts will be possible on Monday across parts of the central and northern Plains eastward into the upper Mississippi Valley. ...Central and Northern Plains/Upper Mississippi Valley... An upper-level ridge is forecast to move into the Great Lakes on Monday as a shortwave trough moves northeastward into the northern Plains. At the surface, a low is forecast to deepen in the northern Plains as a warm front advances northward across the upper Mississippi Valley. To the south of the warm front, a corridor of maximized low-level moisture is forecast to exist from western Illinois northwestward into southeastern South Dakota by Monday afternoon. Pockets of moderate instability may develop along this corridor. Model forecasts suggest that elevated convection will form north of the warm front from the eastern Dakotas into Minnesota Monday afternoon. Surface-based convective development will be possible mainly from the warm front southward across the moist sector during the late afternoon and early evening. The environment across the moist sector may support an isolated severe threat with forecast soundings showing MLCAPE values in the 1500 to 2500 J/kg range and 0-6 km shear of 30 to 40 kt. Mesoscale conditions will likely determine which areas have the greatest convective threat. For this reason, uncertainty is substantial concerning where the severe threat will become maximized. Have drawn a marginal threat area in eastern South Dakota, eastern Nebraska and Iowa where severe parameters show the greatest potential at this time. ..Broyles.. 09/07/2019 Read more

SPC 0730Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0213 AM CDT Sat Sep 07 2019 Valid 091200Z - 101200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE CENTRAL AND NORTHERN PLAINS EASTWARD INTO THE UPPER MISSISSIPPI VALLEY... ...SUMMARY... Thunderstorms associated with hail and marginally severe wind gusts will be possible on Monday across parts of the central and northern Plains eastward into the upper Mississippi Valley. ...Central and Northern Plains/Upper Mississippi Valley... An upper-level ridge is forecast to move into the Great Lakes on Monday as a shortwave trough moves northeastward into the northern Plains. At the surface, a low is forecast to deepen in the northern Plains as a warm front advances northward across the upper Mississippi Valley. To the south of the warm front, a corridor of maximized low-level moisture is forecast to exist from western Illinois northwestward into southeastern South Dakota by Monday afternoon. Pockets of moderate instability may develop along this corridor. Model forecasts suggest that elevated convection will form north of the warm front from the eastern Dakotas into Minnesota Monday afternoon. Surface-based convective development will be possible mainly from the warm front southward across the moist sector during the late afternoon and early evening. The environment across the moist sector may support an isolated severe threat with forecast soundings showing MLCAPE values in the 1500 to 2500 J/kg range and 0-6 km shear of 30 to 40 kt. Mesoscale conditions will likely determine which areas have the greatest convective threat. For this reason, uncertainty is substantial concerning where the severe threat will become maximized. Have drawn a marginal threat area in eastern South Dakota, eastern Nebraska and Iowa where severe parameters show the greatest potential at this time. ..Broyles.. 09/07/2019 Read more

SPC 0730Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0213 AM CDT Sat Sep 07 2019 Valid 091200Z - 101200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE CENTRAL AND NORTHERN PLAINS EASTWARD INTO THE UPPER MISSISSIPPI VALLEY... ...SUMMARY... Thunderstorms associated with hail and marginally severe wind gusts will be possible on Monday across parts of the central and northern Plains eastward into the upper Mississippi Valley. ...Central and Northern Plains/Upper Mississippi Valley... An upper-level ridge is forecast to move into the Great Lakes on Monday as a shortwave trough moves northeastward into the northern Plains. At the surface, a low is forecast to deepen in the northern Plains as a warm front advances northward across the upper Mississippi Valley. To the south of the warm front, a corridor of maximized low-level moisture is forecast to exist from western Illinois northwestward into southeastern South Dakota by Monday afternoon. Pockets of moderate instability may develop along this corridor. Model forecasts suggest that elevated convection will form north of the warm front from the eastern Dakotas into Minnesota Monday afternoon. Surface-based convective development will be possible mainly from the warm front southward across the moist sector during the late afternoon and early evening. The environment across the moist sector may support an isolated severe threat with forecast soundings showing MLCAPE values in the 1500 to 2500 J/kg range and 0-6 km shear of 30 to 40 kt. Mesoscale conditions will likely determine which areas have the greatest convective threat. For this reason, uncertainty is substantial concerning where the severe threat will become maximized. Have drawn a marginal threat area in eastern South Dakota, eastern Nebraska and Iowa where severe parameters show the greatest potential at this time. ..Broyles.. 09/07/2019 Read more

SPC 0730Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0213 AM CDT Sat Sep 07 2019 Valid 091200Z - 101200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE CENTRAL AND NORTHERN PLAINS EASTWARD INTO THE UPPER MISSISSIPPI VALLEY... ...SUMMARY... Thunderstorms associated with hail and marginally severe wind gusts will be possible on Monday across parts of the central and northern Plains eastward into the upper Mississippi Valley. ...Central and Northern Plains/Upper Mississippi Valley... An upper-level ridge is forecast to move into the Great Lakes on Monday as a shortwave trough moves northeastward into the northern Plains. At the surface, a low is forecast to deepen in the northern Plains as a warm front advances northward across the upper Mississippi Valley. To the south of the warm front, a corridor of maximized low-level moisture is forecast to exist from western Illinois northwestward into southeastern South Dakota by Monday afternoon. Pockets of moderate instability may develop along this corridor. Model forecasts suggest that elevated convection will form north of the warm front from the eastern Dakotas into Minnesota Monday afternoon. Surface-based convective development will be possible mainly from the warm front southward across the moist sector during the late afternoon and early evening. The environment across the moist sector may support an isolated severe threat with forecast soundings showing MLCAPE values in the 1500 to 2500 J/kg range and 0-6 km shear of 30 to 40 kt. Mesoscale conditions will likely determine which areas have the greatest convective threat. For this reason, uncertainty is substantial concerning where the severe threat will become maximized. Have drawn a marginal threat area in eastern South Dakota, eastern Nebraska and Iowa where severe parameters show the greatest potential at this time. ..Broyles.. 09/07/2019 Read more

SPC Day 2 Fire Weather Outlook
Day 2 Fire Weather Outlook NWS Storm Prediction Center Norman OK 1255 AM CDT Sat Sep 07 2019 Valid 081200Z - 091200Z ...Synopsis... Mid/upper-level longwave troughing is forecast to become established across the western CONUS Day 2/Sunday. As this occurs, a shortwave trough embedded near the base of the longwave trough will move from the Great Basin into the central Rockies throughout the period. ...Southwest and southern Great Basin... Elevated to locally critical conditions are possible across portions of the southwest into the southern Great Basin Day 2/Sunday afternoon/evening as enhanced mid-level flow attendant to the aforementioned shortwave trough overspreads the area and is mixed to the surface. At this time, the best potential for critical fire weather conditions appears to be across portions of southern Utah and northern Arizona, where sustained winds of around 20-25 mph are expected to overlap near critical minimum RH values. However, uncertainty regarding coverage of critical RH values and quality of fuel receptiveness due to recent precipitation precludes the introduction of a critical fire weather area at this time. ...Southern California: Santa Barbara County... Elevated fire weather conditions may already be ongoing at higher elevations (e.g., > 1 kft) of eastern Santa Barbara County at 12Z Day 2/Sunday due to poor overnight RH recoveries and persistent Sundowner winds. Elevated fire weather conditions should then increase in coverage over the Santa Barbara South Coast and adjacent foothills by afternoon/evening as gusty Sundowner winds increase and overlap areas with minimum RH values of around 15-25% and receptive fuels. ..Elliott.. 09/07/2019 ...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 1255 AM CDT Sat Sep 07 2019 Valid 081200Z - 091200Z ...Synopsis... Mid/upper-level longwave troughing is forecast to become established across the western CONUS Day 2/Sunday. As this occurs, a shortwave trough embedded near the base of the longwave trough will move from the Great Basin into the central Rockies throughout the period. ...Southwest and southern Great Basin... Elevated to locally critical conditions are possible across portions of the southwest into the southern Great Basin Day 2/Sunday afternoon/evening as enhanced mid-level flow attendant to the aforementioned shortwave trough overspreads the area and is mixed to the surface. At this time, the best potential for critical fire weather conditions appears to be across portions of southern Utah and northern Arizona, where sustained winds of around 20-25 mph are expected to overlap near critical minimum RH values. However, uncertainty regarding coverage of critical RH values and quality of fuel receptiveness due to recent precipitation precludes the introduction of a critical fire weather area at this time. ...Southern California: Santa Barbara County... Elevated fire weather conditions may already be ongoing at higher elevations (e.g., > 1 kft) of eastern Santa Barbara County at 12Z Day 2/Sunday due to poor overnight RH recoveries and persistent Sundowner winds. Elevated fire weather conditions should then increase in coverage over the Santa Barbara South Coast and adjacent foothills by afternoon/evening as gusty Sundowner winds increase and overlap areas with minimum RH values of around 15-25% and receptive fuels. ..Elliott.. 09/07/2019 ...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 1255 AM CDT Sat Sep 07 2019 Valid 081200Z - 091200Z ...Synopsis... Mid/upper-level longwave troughing is forecast to become established across the western CONUS Day 2/Sunday. As this occurs, a shortwave trough embedded near the base of the longwave trough will move from the Great Basin into the central Rockies throughout the period. ...Southwest and southern Great Basin... Elevated to locally critical conditions are possible across portions of the southwest into the southern Great Basin Day 2/Sunday afternoon/evening as enhanced mid-level flow attendant to the aforementioned shortwave trough overspreads the area and is mixed to the surface. At this time, the best potential for critical fire weather conditions appears to be across portions of southern Utah and northern Arizona, where sustained winds of around 20-25 mph are expected to overlap near critical minimum RH values. However, uncertainty regarding coverage of critical RH values and quality of fuel receptiveness due to recent precipitation precludes the introduction of a critical fire weather area at this time. ...Southern California: Santa Barbara County... Elevated fire weather conditions may already be ongoing at higher elevations (e.g., > 1 kft) of eastern Santa Barbara County at 12Z Day 2/Sunday due to poor overnight RH recoveries and persistent Sundowner winds. Elevated fire weather conditions should then increase in coverage over the Santa Barbara South Coast and adjacent foothills by afternoon/evening as gusty Sundowner winds increase and overlap areas with minimum RH values of around 15-25% and receptive fuels. ..Elliott.. 09/07/2019 ...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 1255 AM CDT Sat Sep 07 2019 Valid 081200Z - 091200Z ...Synopsis... Mid/upper-level longwave troughing is forecast to become established across the western CONUS Day 2/Sunday. As this occurs, a shortwave trough embedded near the base of the longwave trough will move from the Great Basin into the central Rockies throughout the period. ...Southwest and southern Great Basin... Elevated to locally critical conditions are possible across portions of the southwest into the southern Great Basin Day 2/Sunday afternoon/evening as enhanced mid-level flow attendant to the aforementioned shortwave trough overspreads the area and is mixed to the surface. At this time, the best potential for critical fire weather conditions appears to be across portions of southern Utah and northern Arizona, where sustained winds of around 20-25 mph are expected to overlap near critical minimum RH values. However, uncertainty regarding coverage of critical RH values and quality of fuel receptiveness due to recent precipitation precludes the introduction of a critical fire weather area at this time. ...Southern California: Santa Barbara County... Elevated fire weather conditions may already be ongoing at higher elevations (e.g., > 1 kft) of eastern Santa Barbara County at 12Z Day 2/Sunday due to poor overnight RH recoveries and persistent Sundowner winds. Elevated fire weather conditions should then increase in coverage over the Santa Barbara South Coast and adjacent foothills by afternoon/evening as gusty Sundowner winds increase and overlap areas with minimum RH values of around 15-25% and receptive fuels. ..Elliott.. 09/07/2019 ...Please see www.spc.noaa.gov/fire for graphic product... Read more

SPC 0600Z Day 2 Outlook
Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1252 AM CDT Sat Sep 07 2019 Valid 081200Z - 091200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE CENTRAL HIGH PLAINS... ...SUMMARY... Marginally severe thunderstorms with strong wind gusts and hail will be possible across parts of the central High Plains Sunday afternoon and evening. ...Central High Plains... A shortwave ridge will move across the central and northern Plains on Sunday as a shortwave trough moves into the central and northern Rockies. Ahead of the shortwave trough, a corridor of maximized low-level moisture is forecast from central Kansas west-northwestward into northeastern Colorado. Moderate instability may develop along parts of the moist corridor by Sunday afternoon. Convection appears likely to initiate in the higher terrain of the Front Range and move eastward into the High Plains during the late afternoon and early evening. NAM and GFS forecast soundings early Sunday evening across northeast Colorado and southwestern Nebraska show MUCAPE values reaching 1000 to 2000 J/kg and have 0-6 km shear in the 30 to 35 kt range. This may be enough for a marginal severe threat with the stronger multicells. Hail could be the most dominant threat early. But as cells organize and move away from the mountains, linear formation could favor a marginal wind-damage threat. ...MAXIMUM RISK BY HAZARD... Tornado: <2% - None Wind: 5% - Marginal Hail: 5% - Marginal ..Broyles.. 09/07/2019 Read more