Severe Storms

SPC Day 1 Fire Weather Outlook
Day 1 Fire Weather Outlook NWS Storm Prediction Center Norman OK 1033 AM CST Fri Feb 23 2024 Valid 231700Z - 241200Z ...NO CRITICAL AREAS... No changes to the ongoing forecast. ..Wendt.. 02/23/2024 .PREV DISCUSSION... /ISSUED 0151 AM CST Fri Feb 23 2024/ ...Synopsis... In the mid levels, troughing is forecast to intensify over the eastern US as ridging builds over the West Coast. Strong mid-level flow will shift over the east as high pressure begins to move into the central US. At the surface, a weak cold front will move offshore with north/northwesterly winds likely behind it. While weaker winds are expected over much of the CONUS, somewhat stronger flow is possible in the lee of the Rockies over parts of the High Plains this afternoon. Localized dry and breezy conditions may emerge across portions of NE, CO, and KS. However, stronger winds will be limited in overlap with dry fuels suggesting fire-weather concerns will be limited for much of the country. ...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 1033 AM CST Fri Feb 23 2024 Valid 231700Z - 241200Z ...NO CRITICAL AREAS... No changes to the ongoing forecast. ..Wendt.. 02/23/2024 .PREV DISCUSSION... /ISSUED 0151 AM CST Fri Feb 23 2024/ ...Synopsis... In the mid levels, troughing is forecast to intensify over the eastern US as ridging builds over the West Coast. Strong mid-level flow will shift over the east as high pressure begins to move into the central US. At the surface, a weak cold front will move offshore with north/northwesterly winds likely behind it. While weaker winds are expected over much of the CONUS, somewhat stronger flow is possible in the lee of the Rockies over parts of the High Plains this afternoon. Localized dry and breezy conditions may emerge across portions of NE, CO, and KS. However, stronger winds will be limited in overlap with dry fuels suggesting fire-weather concerns will be limited for much of the country. ...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 1033 AM CST Fri Feb 23 2024 Valid 231700Z - 241200Z ...NO CRITICAL AREAS... No changes to the ongoing forecast. ..Wendt.. 02/23/2024 .PREV DISCUSSION... /ISSUED 0151 AM CST Fri Feb 23 2024/ ...Synopsis... In the mid levels, troughing is forecast to intensify over the eastern US as ridging builds over the West Coast. Strong mid-level flow will shift over the east as high pressure begins to move into the central US. At the surface, a weak cold front will move offshore with north/northwesterly winds likely behind it. While weaker winds are expected over much of the CONUS, somewhat stronger flow is possible in the lee of the Rockies over parts of the High Plains this afternoon. Localized dry and breezy conditions may emerge across portions of NE, CO, and KS. However, stronger winds will be limited in overlap with dry fuels suggesting fire-weather concerns will be limited for much of the country. ...Please see www.spc.noaa.gov/fire for graphic product... Read more

SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1003 AM CST Fri Feb 23 2024 Valid 231630Z - 241200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... No organized severe storms are expected today. ...Carolinas... Morning surface analysis shows a low over VA with a trailing cold front extending southwestward into the Gulf Coast states. This front will sweep southeastward today across the Carolinas. Cloud cover is diminishing across SC ahead of the front, which should result in some heating/destabilization. However, this heating will be behind a pre-frontal trough, where veering surface winds are weakening low-level convergence and shear. Cold temperatures aloft and steep lapse rates may still result in a few afternoon thunderstorms, with small hail possible in the stronger cells. However, guidance appears less favorable for severe storms than earlier anticipated. ..Hart/Bentley.. 02/23/2024 Read more

SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1003 AM CST Fri Feb 23 2024 Valid 231630Z - 241200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... No organized severe storms are expected today. ...Carolinas... Morning surface analysis shows a low over VA with a trailing cold front extending southwestward into the Gulf Coast states. This front will sweep southeastward today across the Carolinas. Cloud cover is diminishing across SC ahead of the front, which should result in some heating/destabilization. However, this heating will be behind a pre-frontal trough, where veering surface winds are weakening low-level convergence and shear. Cold temperatures aloft and steep lapse rates may still result in a few afternoon thunderstorms, with small hail possible in the stronger cells. However, guidance appears less favorable for severe storms than earlier anticipated. ..Hart/Bentley.. 02/23/2024 Read more

SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1003 AM CST Fri Feb 23 2024 Valid 231630Z - 241200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... No organized severe storms are expected today. ...Carolinas... Morning surface analysis shows a low over VA with a trailing cold front extending southwestward into the Gulf Coast states. This front will sweep southeastward today across the Carolinas. Cloud cover is diminishing across SC ahead of the front, which should result in some heating/destabilization. However, this heating will be behind a pre-frontal trough, where veering surface winds are weakening low-level convergence and shear. Cold temperatures aloft and steep lapse rates may still result in a few afternoon thunderstorms, with small hail possible in the stronger cells. However, guidance appears less favorable for severe storms than earlier anticipated. ..Hart/Bentley.. 02/23/2024 Read more

SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1003 AM CST Fri Feb 23 2024 Valid 231630Z - 241200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... No organized severe storms are expected today. ...Carolinas... Morning surface analysis shows a low over VA with a trailing cold front extending southwestward into the Gulf Coast states. This front will sweep southeastward today across the Carolinas. Cloud cover is diminishing across SC ahead of the front, which should result in some heating/destabilization. However, this heating will be behind a pre-frontal trough, where veering surface winds are weakening low-level convergence and shear. Cold temperatures aloft and steep lapse rates may still result in a few afternoon thunderstorms, with small hail possible in the stronger cells. However, guidance appears less favorable for severe storms than earlier anticipated. ..Hart/Bentley.. 02/23/2024 Read more

SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1003 AM CST Fri Feb 23 2024 Valid 231630Z - 241200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... No organized severe storms are expected today. ...Carolinas... Morning surface analysis shows a low over VA with a trailing cold front extending southwestward into the Gulf Coast states. This front will sweep southeastward today across the Carolinas. Cloud cover is diminishing across SC ahead of the front, which should result in some heating/destabilization. However, this heating will be behind a pre-frontal trough, where veering surface winds are weakening low-level convergence and shear. Cold temperatures aloft and steep lapse rates may still result in a few afternoon thunderstorms, with small hail possible in the stronger cells. However, guidance appears less favorable for severe storms than earlier anticipated. ..Hart/Bentley.. 02/23/2024 Read more

SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1003 AM CST Fri Feb 23 2024 Valid 231630Z - 241200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... No organized severe storms are expected today. ...Carolinas... Morning surface analysis shows a low over VA with a trailing cold front extending southwestward into the Gulf Coast states. This front will sweep southeastward today across the Carolinas. Cloud cover is diminishing across SC ahead of the front, which should result in some heating/destabilization. However, this heating will be behind a pre-frontal trough, where veering surface winds are weakening low-level convergence and shear. Cold temperatures aloft and steep lapse rates may still result in a few afternoon thunderstorms, with small hail possible in the stronger cells. However, guidance appears less favorable for severe storms than earlier anticipated. ..Hart/Bentley.. 02/23/2024 Read more

SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1003 AM CST Fri Feb 23 2024 Valid 231630Z - 241200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... No organized severe storms are expected today. ...Carolinas... Morning surface analysis shows a low over VA with a trailing cold front extending southwestward into the Gulf Coast states. This front will sweep southeastward today across the Carolinas. Cloud cover is diminishing across SC ahead of the front, which should result in some heating/destabilization. However, this heating will be behind a pre-frontal trough, where veering surface winds are weakening low-level convergence and shear. Cold temperatures aloft and steep lapse rates may still result in a few afternoon thunderstorms, with small hail possible in the stronger cells. However, guidance appears less favorable for severe storms than earlier anticipated. ..Hart/Bentley.. 02/23/2024 Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0633 AM CST Fri Feb 23 2024 Valid 231300Z - 241200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF SOUTH CAROLINA AND SOUTHEASTERN NORTH CAROLINA... ...SUMMARY... A few strong to severe storms are possible during the afternoon and early evening over parts of South Carolina into southeast North Carolina. ...Synopsis... While ridging will persist across the western U.S., a broad area of cyclonic flow will remain over the central and eastern portions of the country through the period. Within the cyclonic flow field, a short-wave trough will continue moving eastward across the Southeast through this evening. In tandem with this short-wave trough, a cold front now crossing the southern Appalachians will continue advancing across the East Coast States today. The front is expected to clear the Mid- and Southern Atlantic Coasts this evening, while continuing southeastward across the Florida Peninsula tonight. ...South Carolina vicinity... Bands of weak, pre-frontal convection are moving eastward across the southern Appalachians/Southeast early this morning. Clouds and ongoing precipitation will hinder heating this morning, though by afternoon some clearing ahead of the front may occur, which -- combined with relatively steep lapse rates aloft -- should permit modest destabilization to occur. As the front shifts across Georgia and the Carolinas this afternoon, an additional, low-topped band or two of convection should develop. Given relatively strong southwesterly flow aloft, a few stronger thunderstorms may evolve, potentially capable of producing locally strong/gusty winds and marginally severe hail, before storms weaken/move offshore during the evening. ..Goss.. 02/23/2024 Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0633 AM CST Fri Feb 23 2024 Valid 231300Z - 241200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF SOUTH CAROLINA AND SOUTHEASTERN NORTH CAROLINA... ...SUMMARY... A few strong to severe storms are possible during the afternoon and early evening over parts of South Carolina into southeast North Carolina. ...Synopsis... While ridging will persist across the western U.S., a broad area of cyclonic flow will remain over the central and eastern portions of the country through the period. Within the cyclonic flow field, a short-wave trough will continue moving eastward across the Southeast through this evening. In tandem with this short-wave trough, a cold front now crossing the southern Appalachians will continue advancing across the East Coast States today. The front is expected to clear the Mid- and Southern Atlantic Coasts this evening, while continuing southeastward across the Florida Peninsula tonight. ...South Carolina vicinity... Bands of weak, pre-frontal convection are moving eastward across the southern Appalachians/Southeast early this morning. Clouds and ongoing precipitation will hinder heating this morning, though by afternoon some clearing ahead of the front may occur, which -- combined with relatively steep lapse rates aloft -- should permit modest destabilization to occur. As the front shifts across Georgia and the Carolinas this afternoon, an additional, low-topped band or two of convection should develop. Given relatively strong southwesterly flow aloft, a few stronger thunderstorms may evolve, potentially capable of producing locally strong/gusty winds and marginally severe hail, before storms weaken/move offshore during the evening. ..Goss.. 02/23/2024 Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0633 AM CST Fri Feb 23 2024 Valid 231300Z - 241200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF SOUTH CAROLINA AND SOUTHEASTERN NORTH CAROLINA... ...SUMMARY... A few strong to severe storms are possible during the afternoon and early evening over parts of South Carolina into southeast North Carolina. ...Synopsis... While ridging will persist across the western U.S., a broad area of cyclonic flow will remain over the central and eastern portions of the country through the period. Within the cyclonic flow field, a short-wave trough will continue moving eastward across the Southeast through this evening. In tandem with this short-wave trough, a cold front now crossing the southern Appalachians will continue advancing across the East Coast States today. The front is expected to clear the Mid- and Southern Atlantic Coasts this evening, while continuing southeastward across the Florida Peninsula tonight. ...South Carolina vicinity... Bands of weak, pre-frontal convection are moving eastward across the southern Appalachians/Southeast early this morning. Clouds and ongoing precipitation will hinder heating this morning, though by afternoon some clearing ahead of the front may occur, which -- combined with relatively steep lapse rates aloft -- should permit modest destabilization to occur. As the front shifts across Georgia and the Carolinas this afternoon, an additional, low-topped band or two of convection should develop. Given relatively strong southwesterly flow aloft, a few stronger thunderstorms may evolve, potentially capable of producing locally strong/gusty winds and marginally severe hail, before storms weaken/move offshore during the evening. ..Goss.. 02/23/2024 Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0633 AM CST Fri Feb 23 2024 Valid 231300Z - 241200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF SOUTH CAROLINA AND SOUTHEASTERN NORTH CAROLINA... ...SUMMARY... A few strong to severe storms are possible during the afternoon and early evening over parts of South Carolina into southeast North Carolina. ...Synopsis... While ridging will persist across the western U.S., a broad area of cyclonic flow will remain over the central and eastern portions of the country through the period. Within the cyclonic flow field, a short-wave trough will continue moving eastward across the Southeast through this evening. In tandem with this short-wave trough, a cold front now crossing the southern Appalachians will continue advancing across the East Coast States today. The front is expected to clear the Mid- and Southern Atlantic Coasts this evening, while continuing southeastward across the Florida Peninsula tonight. ...South Carolina vicinity... Bands of weak, pre-frontal convection are moving eastward across the southern Appalachians/Southeast early this morning. Clouds and ongoing precipitation will hinder heating this morning, though by afternoon some clearing ahead of the front may occur, which -- combined with relatively steep lapse rates aloft -- should permit modest destabilization to occur. As the front shifts across Georgia and the Carolinas this afternoon, an additional, low-topped band or two of convection should develop. Given relatively strong southwesterly flow aloft, a few stronger thunderstorms may evolve, potentially capable of producing locally strong/gusty winds and marginally severe hail, before storms weaken/move offshore during the evening. ..Goss.. 02/23/2024 Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0633 AM CST Fri Feb 23 2024 Valid 231300Z - 241200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF SOUTH CAROLINA AND SOUTHEASTERN NORTH CAROLINA... ...SUMMARY... A few strong to severe storms are possible during the afternoon and early evening over parts of South Carolina into southeast North Carolina. ...Synopsis... While ridging will persist across the western U.S., a broad area of cyclonic flow will remain over the central and eastern portions of the country through the period. Within the cyclonic flow field, a short-wave trough will continue moving eastward across the Southeast through this evening. In tandem with this short-wave trough, a cold front now crossing the southern Appalachians will continue advancing across the East Coast States today. The front is expected to clear the Mid- and Southern Atlantic Coasts this evening, while continuing southeastward across the Florida Peninsula tonight. ...South Carolina vicinity... Bands of weak, pre-frontal convection are moving eastward across the southern Appalachians/Southeast early this morning. Clouds and ongoing precipitation will hinder heating this morning, though by afternoon some clearing ahead of the front may occur, which -- combined with relatively steep lapse rates aloft -- should permit modest destabilization to occur. As the front shifts across Georgia and the Carolinas this afternoon, an additional, low-topped band or two of convection should develop. Given relatively strong southwesterly flow aloft, a few stronger thunderstorms may evolve, potentially capable of producing locally strong/gusty winds and marginally severe hail, before storms weaken/move offshore during the evening. ..Goss.. 02/23/2024 Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0633 AM CST Fri Feb 23 2024 Valid 231300Z - 241200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF SOUTH CAROLINA AND SOUTHEASTERN NORTH CAROLINA... ...SUMMARY... A few strong to severe storms are possible during the afternoon and early evening over parts of South Carolina into southeast North Carolina. ...Synopsis... While ridging will persist across the western U.S., a broad area of cyclonic flow will remain over the central and eastern portions of the country through the period. Within the cyclonic flow field, a short-wave trough will continue moving eastward across the Southeast through this evening. In tandem with this short-wave trough, a cold front now crossing the southern Appalachians will continue advancing across the East Coast States today. The front is expected to clear the Mid- and Southern Atlantic Coasts this evening, while continuing southeastward across the Florida Peninsula tonight. ...South Carolina vicinity... Bands of weak, pre-frontal convection are moving eastward across the southern Appalachians/Southeast early this morning. Clouds and ongoing precipitation will hinder heating this morning, though by afternoon some clearing ahead of the front may occur, which -- combined with relatively steep lapse rates aloft -- should permit modest destabilization to occur. As the front shifts across Georgia and the Carolinas this afternoon, an additional, low-topped band or two of convection should develop. Given relatively strong southwesterly flow aloft, a few stronger thunderstorms may evolve, potentially capable of producing locally strong/gusty winds and marginally severe hail, before storms weaken/move offshore during the evening. ..Goss.. 02/23/2024 Read more

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0224 AM CST Fri Feb 23 2024 Valid 261200Z - 021200Z ...DISCUSSION... Strong southern stream westerly upper-level flow will extend from northwest Mexico through the southern half of the U.S. on Day 4/Mon. In northern stream flow, a strong upper trough will develop east/southeast from the Pacific Northwest toward the northern/central High Plains. Deepening surface low pressure over the northern Plains, with a surface trough extending southward through the southern Plains, will result in increasing southerly low-level flow across the Gulf of Mexico northward to the Mid-MS Valley. This will allow for substantial airmass modification ahead of the western upper trough and southeastward-advancing surface cold front through Day 6/Wed. By Day 5/Tue afternoon, improved boundary-layer moisture (50s to low 60s F dewpoints) is forecast to arrive across the Ozark Plateau and the Mid-MS and Lower OH Valley vicinity. At the same time, an EML with a plume of steep midlevel lapse rates shifting east from the Plains will overspread the central U.S. vicinity. This should allow for at least modest destabilization, though quality of surface-based instability remains in question given marginal low-level moisture. Nevertheless, favorable vertical shear and strong forcing associated with a surging cold front will support organized thunderstorms with an attendant severe risk across a broad region of the central U.S. Uncertainty has increased heading into Day 6/Wed as this system shifts east across OH/TN Valley toward the Appalachians. The last couple of cycles from the ECMWF have the surface cold front surging east much faster than the GFS. While the operational GFS remains much slower, the GEFS ensemble guidance overall has trended faster. Given the combination of uncertainty and overall trends, severe probabilities will be maintained for Day 6/Wed, but trimmed. It is likely this delineated area will continue to change in the coming days given higher uncertainty. Beyond Day 6/Wed, spread in forecast guidance continues to increase and predictability is low. Read more

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0224 AM CST Fri Feb 23 2024 Valid 261200Z - 021200Z ...DISCUSSION... Strong southern stream westerly upper-level flow will extend from northwest Mexico through the southern half of the U.S. on Day 4/Mon. In northern stream flow, a strong upper trough will develop east/southeast from the Pacific Northwest toward the northern/central High Plains. Deepening surface low pressure over the northern Plains, with a surface trough extending southward through the southern Plains, will result in increasing southerly low-level flow across the Gulf of Mexico northward to the Mid-MS Valley. This will allow for substantial airmass modification ahead of the western upper trough and southeastward-advancing surface cold front through Day 6/Wed. By Day 5/Tue afternoon, improved boundary-layer moisture (50s to low 60s F dewpoints) is forecast to arrive across the Ozark Plateau and the Mid-MS and Lower OH Valley vicinity. At the same time, an EML with a plume of steep midlevel lapse rates shifting east from the Plains will overspread the central U.S. vicinity. This should allow for at least modest destabilization, though quality of surface-based instability remains in question given marginal low-level moisture. Nevertheless, favorable vertical shear and strong forcing associated with a surging cold front will support organized thunderstorms with an attendant severe risk across a broad region of the central U.S. Uncertainty has increased heading into Day 6/Wed as this system shifts east across OH/TN Valley toward the Appalachians. The last couple of cycles from the ECMWF have the surface cold front surging east much faster than the GFS. While the operational GFS remains much slower, the GEFS ensemble guidance overall has trended faster. Given the combination of uncertainty and overall trends, severe probabilities will be maintained for Day 6/Wed, but trimmed. It is likely this delineated area will continue to change in the coming days given higher uncertainty. Beyond Day 6/Wed, spread in forecast guidance continues to increase and predictability is low. Read more

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0224 AM CST Fri Feb 23 2024 Valid 261200Z - 021200Z ...DISCUSSION... Strong southern stream westerly upper-level flow will extend from northwest Mexico through the southern half of the U.S. on Day 4/Mon. In northern stream flow, a strong upper trough will develop east/southeast from the Pacific Northwest toward the northern/central High Plains. Deepening surface low pressure over the northern Plains, with a surface trough extending southward through the southern Plains, will result in increasing southerly low-level flow across the Gulf of Mexico northward to the Mid-MS Valley. This will allow for substantial airmass modification ahead of the western upper trough and southeastward-advancing surface cold front through Day 6/Wed. By Day 5/Tue afternoon, improved boundary-layer moisture (50s to low 60s F dewpoints) is forecast to arrive across the Ozark Plateau and the Mid-MS and Lower OH Valley vicinity. At the same time, an EML with a plume of steep midlevel lapse rates shifting east from the Plains will overspread the central U.S. vicinity. This should allow for at least modest destabilization, though quality of surface-based instability remains in question given marginal low-level moisture. Nevertheless, favorable vertical shear and strong forcing associated with a surging cold front will support organized thunderstorms with an attendant severe risk across a broad region of the central U.S. Uncertainty has increased heading into Day 6/Wed as this system shifts east across OH/TN Valley toward the Appalachians. The last couple of cycles from the ECMWF have the surface cold front surging east much faster than the GFS. While the operational GFS remains much slower, the GEFS ensemble guidance overall has trended faster. Given the combination of uncertainty and overall trends, severe probabilities will be maintained for Day 6/Wed, but trimmed. It is likely this delineated area will continue to change in the coming days given higher uncertainty. Beyond Day 6/Wed, spread in forecast guidance continues to increase and predictability is low. Read more

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0224 AM CST Fri Feb 23 2024 Valid 261200Z - 021200Z ...DISCUSSION... Strong southern stream westerly upper-level flow will extend from northwest Mexico through the southern half of the U.S. on Day 4/Mon. In northern stream flow, a strong upper trough will develop east/southeast from the Pacific Northwest toward the northern/central High Plains. Deepening surface low pressure over the northern Plains, with a surface trough extending southward through the southern Plains, will result in increasing southerly low-level flow across the Gulf of Mexico northward to the Mid-MS Valley. This will allow for substantial airmass modification ahead of the western upper trough and southeastward-advancing surface cold front through Day 6/Wed. By Day 5/Tue afternoon, improved boundary-layer moisture (50s to low 60s F dewpoints) is forecast to arrive across the Ozark Plateau and the Mid-MS and Lower OH Valley vicinity. At the same time, an EML with a plume of steep midlevel lapse rates shifting east from the Plains will overspread the central U.S. vicinity. This should allow for at least modest destabilization, though quality of surface-based instability remains in question given marginal low-level moisture. Nevertheless, favorable vertical shear and strong forcing associated with a surging cold front will support organized thunderstorms with an attendant severe risk across a broad region of the central U.S. Uncertainty has increased heading into Day 6/Wed as this system shifts east across OH/TN Valley toward the Appalachians. The last couple of cycles from the ECMWF have the surface cold front surging east much faster than the GFS. While the operational GFS remains much slower, the GEFS ensemble guidance overall has trended faster. Given the combination of uncertainty and overall trends, severe probabilities will be maintained for Day 6/Wed, but trimmed. It is likely this delineated area will continue to change in the coming days given higher uncertainty. Beyond Day 6/Wed, spread in forecast guidance continues to increase and predictability is low. Read more