Severe Storms

SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0142 PM CST Sat Dec 16 2023 Valid 162000Z - 171200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS MUCH OF THE FLORIDA PENINSULA... ...SUMMARY... The threat for a few damaging gusts and tornadoes will increase by tonight into Sunday morning across the Florida peninsula and Keys. ...20z Update... The previous outlook remains on track, and no changes have been made to severe probabilities across FL and far southeast GA. Overall severe risk will remain conditional through the period given limited thermodynamic environment hindered by weak diurnal heating and poor low-level lapse rates. However, given increasing vertical shear, particularly in the low-levels later this evening/overnight, some risk for locally strong/damaging gusts and a tornado or two remains possible. ..Leitman.. 12/16/2023 .PREV DISCUSSION... /ISSUED 1031 AM CST Sat Dec 16 2023/ ...Florida... A weak surface low residing over the central Gulf of Mexico will move slowly northeastward, strengthening as mid-level troughing now moving southeastward into the western Gulf advances. Warm advection ahead of this system is yielding widespread clouds/precipitation across the eastern Gulf and much of Florida and the Keys late this morning. Though lightning has remained offshore, shallow convection near the Keys has exhibited transient rotation, aided by enhanced easterly low-level flow which veers weakly with height. While a waterspout or brief tornado cannot be ruled out with this activity, weak lapse rates/meager instability should preclude appreciable tornado threat through the day. Later this evening/overnight, as the upper system advances across the Gulf and the surface low nears -- and eventually reaches -- Florida, stronger deep-layer flow gradually overspreading the Peninsula will allow some increase in conditional tornado potential. However, with inland instability forecast to remain weak, will maintain 5% tornado probability, along with potential for locally gusty/damaging winds. Read more

SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0142 PM CST Sat Dec 16 2023 Valid 162000Z - 171200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS MUCH OF THE FLORIDA PENINSULA... ...SUMMARY... The threat for a few damaging gusts and tornadoes will increase by tonight into Sunday morning across the Florida peninsula and Keys. ...20z Update... The previous outlook remains on track, and no changes have been made to severe probabilities across FL and far southeast GA. Overall severe risk will remain conditional through the period given limited thermodynamic environment hindered by weak diurnal heating and poor low-level lapse rates. However, given increasing vertical shear, particularly in the low-levels later this evening/overnight, some risk for locally strong/damaging gusts and a tornado or two remains possible. ..Leitman.. 12/16/2023 .PREV DISCUSSION... /ISSUED 1031 AM CST Sat Dec 16 2023/ ...Florida... A weak surface low residing over the central Gulf of Mexico will move slowly northeastward, strengthening as mid-level troughing now moving southeastward into the western Gulf advances. Warm advection ahead of this system is yielding widespread clouds/precipitation across the eastern Gulf and much of Florida and the Keys late this morning. Though lightning has remained offshore, shallow convection near the Keys has exhibited transient rotation, aided by enhanced easterly low-level flow which veers weakly with height. While a waterspout or brief tornado cannot be ruled out with this activity, weak lapse rates/meager instability should preclude appreciable tornado threat through the day. Later this evening/overnight, as the upper system advances across the Gulf and the surface low nears -- and eventually reaches -- Florida, stronger deep-layer flow gradually overspreading the Peninsula will allow some increase in conditional tornado potential. However, with inland instability forecast to remain weak, will maintain 5% tornado probability, along with potential for locally gusty/damaging winds. Read more

SPC 1730Z Day 2 Outlook
Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1129 AM CST Sat Dec 16 2023 Valid 171200Z - 181200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS NORTHEAST SOUTH CAROLINA INTO EASTERN NORTH CAROLINA AND THE OUTER BANKS... ...SUMMARY... Severe thunderstorms are possible Sunday from northeast South Carolina into eastern North Carolina and the Outer Banks. Primary severe hazard is damaging wind gusts. ...Southeast and Mid-Atlantic Coastal Vicinity... Overall forecast philosophy remains similar to the previous outlook, and only minor changes have been made based on latest forecast guidance. A rapidly deepening surface low is forecast to be near the northeast FL/GA coastal vicinity Sunday morning. This low will quickly lift north/northeast across the Carolinas through Sunday evening, and the Mid-Atlantic overnight. Strong east/southeasterly low-level flow will allow for mid to upper 60s F dewpoints along the SC/NC coast, with low to mid 60s F dewpoints a bit further inland along the coastal plain. However, destabilization will be muted due to widespread cloud cover, ongoing showers ahead of the surface low, and poor low-level lapse rates. In fact, low-level instability will remain quite poor, with forecast soundings indicating much of the instability focused above the 850-700 mb layer, near the top of the deep moist layer. Low-level shear will be quite impressive, with forecast hodographs being rather large and curved. This may result in some rotation of convective elements. However, given expected poor low-level thermodynamics, tornado potential should remain low/brief. Strongly forced convection within this strongly sheared environment also will pose a risk for isolated strong/damaging gusts. Further south along the GA coast into portions of the FL Peninsula, a low severe risk may persist for a few hours during the morning along the primary surface trough before convection moves offshore. ..Leitman.. 12/16/2023 Read more

SPC 1730Z Day 2 Outlook
Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1129 AM CST Sat Dec 16 2023 Valid 171200Z - 181200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS NORTHEAST SOUTH CAROLINA INTO EASTERN NORTH CAROLINA AND THE OUTER BANKS... ...SUMMARY... Severe thunderstorms are possible Sunday from northeast South Carolina into eastern North Carolina and the Outer Banks. Primary severe hazard is damaging wind gusts. ...Southeast and Mid-Atlantic Coastal Vicinity... Overall forecast philosophy remains similar to the previous outlook, and only minor changes have been made based on latest forecast guidance. A rapidly deepening surface low is forecast to be near the northeast FL/GA coastal vicinity Sunday morning. This low will quickly lift north/northeast across the Carolinas through Sunday evening, and the Mid-Atlantic overnight. Strong east/southeasterly low-level flow will allow for mid to upper 60s F dewpoints along the SC/NC coast, with low to mid 60s F dewpoints a bit further inland along the coastal plain. However, destabilization will be muted due to widespread cloud cover, ongoing showers ahead of the surface low, and poor low-level lapse rates. In fact, low-level instability will remain quite poor, with forecast soundings indicating much of the instability focused above the 850-700 mb layer, near the top of the deep moist layer. Low-level shear will be quite impressive, with forecast hodographs being rather large and curved. This may result in some rotation of convective elements. However, given expected poor low-level thermodynamics, tornado potential should remain low/brief. Strongly forced convection within this strongly sheared environment also will pose a risk for isolated strong/damaging gusts. Further south along the GA coast into portions of the FL Peninsula, a low severe risk may persist for a few hours during the morning along the primary surface trough before convection moves offshore. ..Leitman.. 12/16/2023 Read more

SPC 1730Z Day 2 Outlook
Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1129 AM CST Sat Dec 16 2023 Valid 171200Z - 181200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS NORTHEAST SOUTH CAROLINA INTO EASTERN NORTH CAROLINA AND THE OUTER BANKS... ...SUMMARY... Severe thunderstorms are possible Sunday from northeast South Carolina into eastern North Carolina and the Outer Banks. Primary severe hazard is damaging wind gusts. ...Southeast and Mid-Atlantic Coastal Vicinity... Overall forecast philosophy remains similar to the previous outlook, and only minor changes have been made based on latest forecast guidance. A rapidly deepening surface low is forecast to be near the northeast FL/GA coastal vicinity Sunday morning. This low will quickly lift north/northeast across the Carolinas through Sunday evening, and the Mid-Atlantic overnight. Strong east/southeasterly low-level flow will allow for mid to upper 60s F dewpoints along the SC/NC coast, with low to mid 60s F dewpoints a bit further inland along the coastal plain. However, destabilization will be muted due to widespread cloud cover, ongoing showers ahead of the surface low, and poor low-level lapse rates. In fact, low-level instability will remain quite poor, with forecast soundings indicating much of the instability focused above the 850-700 mb layer, near the top of the deep moist layer. Low-level shear will be quite impressive, with forecast hodographs being rather large and curved. This may result in some rotation of convective elements. However, given expected poor low-level thermodynamics, tornado potential should remain low/brief. Strongly forced convection within this strongly sheared environment also will pose a risk for isolated strong/damaging gusts. Further south along the GA coast into portions of the FL Peninsula, a low severe risk may persist for a few hours during the morning along the primary surface trough before convection moves offshore. ..Leitman.. 12/16/2023 Read more

SPC 1730Z Day 2 Outlook
Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1129 AM CST Sat Dec 16 2023 Valid 171200Z - 181200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS NORTHEAST SOUTH CAROLINA INTO EASTERN NORTH CAROLINA AND THE OUTER BANKS... ...SUMMARY... Severe thunderstorms are possible Sunday from northeast South Carolina into eastern North Carolina and the Outer Banks. Primary severe hazard is damaging wind gusts. ...Southeast and Mid-Atlantic Coastal Vicinity... Overall forecast philosophy remains similar to the previous outlook, and only minor changes have been made based on latest forecast guidance. A rapidly deepening surface low is forecast to be near the northeast FL/GA coastal vicinity Sunday morning. This low will quickly lift north/northeast across the Carolinas through Sunday evening, and the Mid-Atlantic overnight. Strong east/southeasterly low-level flow will allow for mid to upper 60s F dewpoints along the SC/NC coast, with low to mid 60s F dewpoints a bit further inland along the coastal plain. However, destabilization will be muted due to widespread cloud cover, ongoing showers ahead of the surface low, and poor low-level lapse rates. In fact, low-level instability will remain quite poor, with forecast soundings indicating much of the instability focused above the 850-700 mb layer, near the top of the deep moist layer. Low-level shear will be quite impressive, with forecast hodographs being rather large and curved. This may result in some rotation of convective elements. However, given expected poor low-level thermodynamics, tornado potential should remain low/brief. Strongly forced convection within this strongly sheared environment also will pose a risk for isolated strong/damaging gusts. Further south along the GA coast into portions of the FL Peninsula, a low severe risk may persist for a few hours during the morning along the primary surface trough before convection moves offshore. ..Leitman.. 12/16/2023 Read more

SPC Day 1 Fire Weather Outlook
Day 1 Fire Weather Outlook NWS Storm Prediction Center Norman OK 1043 AM CST Sat Dec 16 2023 Valid 161700Z - 171200Z ...NO CRITICAL AREAS... Widespread precipitation and cooler temperatures will keep Fire-weather concerns low across the CONUS. See the previous discussion. ..Lyons.. 12/16/2023 .PREV DISCUSSION... /ISSUED 1227 AM CST Sat Dec 16 2023/ ...Synopsis... An amplifying mid-level trough across the eastern CONUS will encourage rapid surface cyclone development over the Florida Peninsula as surface high pressure becomes established across much of the rest of the U.S. today. Cooler and moister surface conditions atop poorly receptive fuels suggest that significant wildfire-spread potential should be limited over most areas of the CONUS. A weak surface pressure gradient will support some offshore flow across southern California, but the wildfire-spread threat in this region should be tempered by overall weaker surface wind fields. ...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 1043 AM CST Sat Dec 16 2023 Valid 161700Z - 171200Z ...NO CRITICAL AREAS... Widespread precipitation and cooler temperatures will keep Fire-weather concerns low across the CONUS. See the previous discussion. ..Lyons.. 12/16/2023 .PREV DISCUSSION... /ISSUED 1227 AM CST Sat Dec 16 2023/ ...Synopsis... An amplifying mid-level trough across the eastern CONUS will encourage rapid surface cyclone development over the Florida Peninsula as surface high pressure becomes established across much of the rest of the U.S. today. Cooler and moister surface conditions atop poorly receptive fuels suggest that significant wildfire-spread potential should be limited over most areas of the CONUS. A weak surface pressure gradient will support some offshore flow across southern California, but the wildfire-spread threat in this region should be tempered by overall weaker surface wind fields. ...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 1043 AM CST Sat Dec 16 2023 Valid 161700Z - 171200Z ...NO CRITICAL AREAS... Widespread precipitation and cooler temperatures will keep Fire-weather concerns low across the CONUS. See the previous discussion. ..Lyons.. 12/16/2023 .PREV DISCUSSION... /ISSUED 1227 AM CST Sat Dec 16 2023/ ...Synopsis... An amplifying mid-level trough across the eastern CONUS will encourage rapid surface cyclone development over the Florida Peninsula as surface high pressure becomes established across much of the rest of the U.S. today. Cooler and moister surface conditions atop poorly receptive fuels suggest that significant wildfire-spread potential should be limited over most areas of the CONUS. A weak surface pressure gradient will support some offshore flow across southern California, but the wildfire-spread threat in this region should be tempered by overall weaker surface wind fields. ...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 1043 AM CST Sat Dec 16 2023 Valid 161700Z - 171200Z ...NO CRITICAL AREAS... Widespread precipitation and cooler temperatures will keep Fire-weather concerns low across the CONUS. See the previous discussion. ..Lyons.. 12/16/2023 .PREV DISCUSSION... /ISSUED 1227 AM CST Sat Dec 16 2023/ ...Synopsis... An amplifying mid-level trough across the eastern CONUS will encourage rapid surface cyclone development over the Florida Peninsula as surface high pressure becomes established across much of the rest of the U.S. today. Cooler and moister surface conditions atop poorly receptive fuels suggest that significant wildfire-spread potential should be limited over most areas of the CONUS. A weak surface pressure gradient will support some offshore flow across southern California, but the wildfire-spread threat in this region should be tempered by overall weaker surface wind fields. ...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 1031 AM CST Sat Dec 16 2023 Valid 161630Z - 171200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS MUCH OF THE FLORIDA PENINSULA... ...SUMMARY... The threat for a few damaging gusts and tornadoes will increase by tonight into Sunday morning across the Florida peninsula and Keys. ...Florida... A weak surface low residing over the central Gulf of Mexico will move slowly northeastward, strengthening as mid-level troughing now moving southeastward into the western Gulf advances. Warm advection ahead of this system is yielding widespread clouds/precipitation across the eastern Gulf and much of Florida and the Keys late this morning. Though lightning has remained offshore, shallow convection near the Keys has exhibited transient rotation, aided by enhanced easterly low-level flow which veers weakly with height. While a waterspout or brief tornado cannot be ruled out with this activity, weak lapse rates/meager instability should preclude appreciable tornado threat through the day. Later this evening/overnight, as the upper system advances across the Gulf and the surface low nears -- and eventually reaches -- Florida, stronger deep-layer flow gradually overspreading the Peninsula will allow some increase in conditional tornado potential. However, with inland instability forecast to remain weak, will maintain 5% tornado probability, along with potential for locally gusty/damaging winds. ..Goss/Thornton.. 12/16/2023 Read more

SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1031 AM CST Sat Dec 16 2023 Valid 161630Z - 171200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS MUCH OF THE FLORIDA PENINSULA... ...SUMMARY... The threat for a few damaging gusts and tornadoes will increase by tonight into Sunday morning across the Florida peninsula and Keys. ...Florida... A weak surface low residing over the central Gulf of Mexico will move slowly northeastward, strengthening as mid-level troughing now moving southeastward into the western Gulf advances. Warm advection ahead of this system is yielding widespread clouds/precipitation across the eastern Gulf and much of Florida and the Keys late this morning. Though lightning has remained offshore, shallow convection near the Keys has exhibited transient rotation, aided by enhanced easterly low-level flow which veers weakly with height. While a waterspout or brief tornado cannot be ruled out with this activity, weak lapse rates/meager instability should preclude appreciable tornado threat through the day. Later this evening/overnight, as the upper system advances across the Gulf and the surface low nears -- and eventually reaches -- Florida, stronger deep-layer flow gradually overspreading the Peninsula will allow some increase in conditional tornado potential. However, with inland instability forecast to remain weak, will maintain 5% tornado probability, along with potential for locally gusty/damaging winds. ..Goss/Thornton.. 12/16/2023 Read more

SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1031 AM CST Sat Dec 16 2023 Valid 161630Z - 171200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS MUCH OF THE FLORIDA PENINSULA... ...SUMMARY... The threat for a few damaging gusts and tornadoes will increase by tonight into Sunday morning across the Florida peninsula and Keys. ...Florida... A weak surface low residing over the central Gulf of Mexico will move slowly northeastward, strengthening as mid-level troughing now moving southeastward into the western Gulf advances. Warm advection ahead of this system is yielding widespread clouds/precipitation across the eastern Gulf and much of Florida and the Keys late this morning. Though lightning has remained offshore, shallow convection near the Keys has exhibited transient rotation, aided by enhanced easterly low-level flow which veers weakly with height. While a waterspout or brief tornado cannot be ruled out with this activity, weak lapse rates/meager instability should preclude appreciable tornado threat through the day. Later this evening/overnight, as the upper system advances across the Gulf and the surface low nears -- and eventually reaches -- Florida, stronger deep-layer flow gradually overspreading the Peninsula will allow some increase in conditional tornado potential. However, with inland instability forecast to remain weak, will maintain 5% tornado probability, along with potential for locally gusty/damaging winds. ..Goss/Thornton.. 12/16/2023 Read more

SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1031 AM CST Sat Dec 16 2023 Valid 161630Z - 171200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS MUCH OF THE FLORIDA PENINSULA... ...SUMMARY... The threat for a few damaging gusts and tornadoes will increase by tonight into Sunday morning across the Florida peninsula and Keys. ...Florida... A weak surface low residing over the central Gulf of Mexico will move slowly northeastward, strengthening as mid-level troughing now moving southeastward into the western Gulf advances. Warm advection ahead of this system is yielding widespread clouds/precipitation across the eastern Gulf and much of Florida and the Keys late this morning. Though lightning has remained offshore, shallow convection near the Keys has exhibited transient rotation, aided by enhanced easterly low-level flow which veers weakly with height. While a waterspout or brief tornado cannot be ruled out with this activity, weak lapse rates/meager instability should preclude appreciable tornado threat through the day. Later this evening/overnight, as the upper system advances across the Gulf and the surface low nears -- and eventually reaches -- Florida, stronger deep-layer flow gradually overspreading the Peninsula will allow some increase in conditional tornado potential. However, with inland instability forecast to remain weak, will maintain 5% tornado probability, along with potential for locally gusty/damaging winds. ..Goss/Thornton.. 12/16/2023 Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0638 AM CST Sat Dec 16 2023 Valid 161300Z - 171200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE FL PENINSULA AND KEYS... ...SUMMARY... The threat for a few damaging gusts and tornadoes will increase by tonight into Sunday morning across the Florida peninsula and Keys. ...FL through Sunday morning... No changes to previous outlook area. Cyclogenesis is underway across the central Gulf of Mexico in association with a southern stream shortwave trough. The cyclone is expected to consolidate/deepen and move toward central/north FL by the end of the period, as a result of phasing with an upstream trough now near the TX coast, and due to convective feedback. These processes will result in strengthening wind fields and northward moisture transport across the FL peninsula, especially tonight into Sunday morning. As boundary-layer dewpoints of 68-72 F spread northward, destabilization should be sufficient for surface-based storms later today through Sunday morning. Isolated, weakly rotating storms will be possible today in the warm advection zone, starting late this morning across the Keys and spreading northward along the Atlantic coast this afternoon. The primary ascent band/convection and associated wind shift are expected to approach the FL Gulf coast near or after 03z and continue eastward across the peninsula through 09-12z Sunday. A somewhat broken band of storms is expected just ahead of the wind shift in an environment of 500-1000 J/kg MLCAPE, modest lapse rates aloft and strengthening vertical shear. Forecast profiles show large, curved hodographs in the low levels and sufficient hodograph length/deep-layer vertical shear for supercells. Assuming moisture advection and overnight mechanical mixing are strong enough inland, the potential for damaging gusts and a few tornadoes will spread inland from the Gulf coast. Other supercells with the potential for damaging gusts and tornadoes could also form in the convergence zone and somewhat richer low-level moisture along the east-central and southeast FL coasts overnight. The main uncertainties in this forecast will be the magnitude of the mass response/vertical shear, and the degree of low-level warming/moistening inland overnight. Both will be a function of how quickly the Gulf cyclone consolidates and deepens in a data sparse area. Given the modest lapse rates aloft, maintenance of surface-based convection will be sensitive to a few degrees of temperature/dewpoint up to the cyclone track. ..Thompson/Broyles.. 12/16/2023 Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0638 AM CST Sat Dec 16 2023 Valid 161300Z - 171200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE FL PENINSULA AND KEYS... ...SUMMARY... The threat for a few damaging gusts and tornadoes will increase by tonight into Sunday morning across the Florida peninsula and Keys. ...FL through Sunday morning... No changes to previous outlook area. Cyclogenesis is underway across the central Gulf of Mexico in association with a southern stream shortwave trough. The cyclone is expected to consolidate/deepen and move toward central/north FL by the end of the period, as a result of phasing with an upstream trough now near the TX coast, and due to convective feedback. These processes will result in strengthening wind fields and northward moisture transport across the FL peninsula, especially tonight into Sunday morning. As boundary-layer dewpoints of 68-72 F spread northward, destabilization should be sufficient for surface-based storms later today through Sunday morning. Isolated, weakly rotating storms will be possible today in the warm advection zone, starting late this morning across the Keys and spreading northward along the Atlantic coast this afternoon. The primary ascent band/convection and associated wind shift are expected to approach the FL Gulf coast near or after 03z and continue eastward across the peninsula through 09-12z Sunday. A somewhat broken band of storms is expected just ahead of the wind shift in an environment of 500-1000 J/kg MLCAPE, modest lapse rates aloft and strengthening vertical shear. Forecast profiles show large, curved hodographs in the low levels and sufficient hodograph length/deep-layer vertical shear for supercells. Assuming moisture advection and overnight mechanical mixing are strong enough inland, the potential for damaging gusts and a few tornadoes will spread inland from the Gulf coast. Other supercells with the potential for damaging gusts and tornadoes could also form in the convergence zone and somewhat richer low-level moisture along the east-central and southeast FL coasts overnight. The main uncertainties in this forecast will be the magnitude of the mass response/vertical shear, and the degree of low-level warming/moistening inland overnight. Both will be a function of how quickly the Gulf cyclone consolidates and deepens in a data sparse area. Given the modest lapse rates aloft, maintenance of surface-based convection will be sensitive to a few degrees of temperature/dewpoint up to the cyclone track. ..Thompson/Broyles.. 12/16/2023 Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0638 AM CST Sat Dec 16 2023 Valid 161300Z - 171200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE FL PENINSULA AND KEYS... ...SUMMARY... The threat for a few damaging gusts and tornadoes will increase by tonight into Sunday morning across the Florida peninsula and Keys. ...FL through Sunday morning... No changes to previous outlook area. Cyclogenesis is underway across the central Gulf of Mexico in association with a southern stream shortwave trough. The cyclone is expected to consolidate/deepen and move toward central/north FL by the end of the period, as a result of phasing with an upstream trough now near the TX coast, and due to convective feedback. These processes will result in strengthening wind fields and northward moisture transport across the FL peninsula, especially tonight into Sunday morning. As boundary-layer dewpoints of 68-72 F spread northward, destabilization should be sufficient for surface-based storms later today through Sunday morning. Isolated, weakly rotating storms will be possible today in the warm advection zone, starting late this morning across the Keys and spreading northward along the Atlantic coast this afternoon. The primary ascent band/convection and associated wind shift are expected to approach the FL Gulf coast near or after 03z and continue eastward across the peninsula through 09-12z Sunday. A somewhat broken band of storms is expected just ahead of the wind shift in an environment of 500-1000 J/kg MLCAPE, modest lapse rates aloft and strengthening vertical shear. Forecast profiles show large, curved hodographs in the low levels and sufficient hodograph length/deep-layer vertical shear for supercells. Assuming moisture advection and overnight mechanical mixing are strong enough inland, the potential for damaging gusts and a few tornadoes will spread inland from the Gulf coast. Other supercells with the potential for damaging gusts and tornadoes could also form in the convergence zone and somewhat richer low-level moisture along the east-central and southeast FL coasts overnight. The main uncertainties in this forecast will be the magnitude of the mass response/vertical shear, and the degree of low-level warming/moistening inland overnight. Both will be a function of how quickly the Gulf cyclone consolidates and deepens in a data sparse area. Given the modest lapse rates aloft, maintenance of surface-based convection will be sensitive to a few degrees of temperature/dewpoint up to the cyclone track. ..Thompson/Broyles.. 12/16/2023 Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0638 AM CST Sat Dec 16 2023 Valid 161300Z - 171200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE FL PENINSULA AND KEYS... ...SUMMARY... The threat for a few damaging gusts and tornadoes will increase by tonight into Sunday morning across the Florida peninsula and Keys. ...FL through Sunday morning... No changes to previous outlook area. Cyclogenesis is underway across the central Gulf of Mexico in association with a southern stream shortwave trough. The cyclone is expected to consolidate/deepen and move toward central/north FL by the end of the period, as a result of phasing with an upstream trough now near the TX coast, and due to convective feedback. These processes will result in strengthening wind fields and northward moisture transport across the FL peninsula, especially tonight into Sunday morning. As boundary-layer dewpoints of 68-72 F spread northward, destabilization should be sufficient for surface-based storms later today through Sunday morning. Isolated, weakly rotating storms will be possible today in the warm advection zone, starting late this morning across the Keys and spreading northward along the Atlantic coast this afternoon. The primary ascent band/convection and associated wind shift are expected to approach the FL Gulf coast near or after 03z and continue eastward across the peninsula through 09-12z Sunday. A somewhat broken band of storms is expected just ahead of the wind shift in an environment of 500-1000 J/kg MLCAPE, modest lapse rates aloft and strengthening vertical shear. Forecast profiles show large, curved hodographs in the low levels and sufficient hodograph length/deep-layer vertical shear for supercells. Assuming moisture advection and overnight mechanical mixing are strong enough inland, the potential for damaging gusts and a few tornadoes will spread inland from the Gulf coast. Other supercells with the potential for damaging gusts and tornadoes could also form in the convergence zone and somewhat richer low-level moisture along the east-central and southeast FL coasts overnight. The main uncertainties in this forecast will be the magnitude of the mass response/vertical shear, and the degree of low-level warming/moistening inland overnight. Both will be a function of how quickly the Gulf cyclone consolidates and deepens in a data sparse area. Given the modest lapse rates aloft, maintenance of surface-based convection will be sensitive to a few degrees of temperature/dewpoint up to the cyclone track. ..Thompson/Broyles.. 12/16/2023 Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0638 AM CST Sat Dec 16 2023 Valid 161300Z - 171200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE FL PENINSULA AND KEYS... ...SUMMARY... The threat for a few damaging gusts and tornadoes will increase by tonight into Sunday morning across the Florida peninsula and Keys. ...FL through Sunday morning... No changes to previous outlook area. Cyclogenesis is underway across the central Gulf of Mexico in association with a southern stream shortwave trough. The cyclone is expected to consolidate/deepen and move toward central/north FL by the end of the period, as a result of phasing with an upstream trough now near the TX coast, and due to convective feedback. These processes will result in strengthening wind fields and northward moisture transport across the FL peninsula, especially tonight into Sunday morning. As boundary-layer dewpoints of 68-72 F spread northward, destabilization should be sufficient for surface-based storms later today through Sunday morning. Isolated, weakly rotating storms will be possible today in the warm advection zone, starting late this morning across the Keys and spreading northward along the Atlantic coast this afternoon. The primary ascent band/convection and associated wind shift are expected to approach the FL Gulf coast near or after 03z and continue eastward across the peninsula through 09-12z Sunday. A somewhat broken band of storms is expected just ahead of the wind shift in an environment of 500-1000 J/kg MLCAPE, modest lapse rates aloft and strengthening vertical shear. Forecast profiles show large, curved hodographs in the low levels and sufficient hodograph length/deep-layer vertical shear for supercells. Assuming moisture advection and overnight mechanical mixing are strong enough inland, the potential for damaging gusts and a few tornadoes will spread inland from the Gulf coast. Other supercells with the potential for damaging gusts and tornadoes could also form in the convergence zone and somewhat richer low-level moisture along the east-central and southeast FL coasts overnight. The main uncertainties in this forecast will be the magnitude of the mass response/vertical shear, and the degree of low-level warming/moistening inland overnight. Both will be a function of how quickly the Gulf cyclone consolidates and deepens in a data sparse area. Given the modest lapse rates aloft, maintenance of surface-based convection will be sensitive to a few degrees of temperature/dewpoint up to the cyclone track. ..Thompson/Broyles.. 12/16/2023 Read more

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0314 AM CST Sat Dec 16 2023 Valid 191200Z - 241200Z ...DISCUSSION... An upper trough will likely extend from southwest Quebec into the Mid-Atlantic early D4/Tuesday, before then progressing eastward throughout the day. Zonal flow is expected across much of the CONUS in its wake on D5/Wednesday, before a slow-moving upper low initially off the southern CA coast introduces some amplitude into the southern stream. This upper low will likely remain off the southern CA coast through the period, but a preceding low-amplitude shortwave may move through the Southwest on D5/Wednesday and into Plains on D6/Thursday. Modest low-level moisture return should precede this shortwave, and some interaction between this shortwave (and attendant cold front) with this buoyancy is possible on D7/Friday. However, weak buoyancy is currently expected to limit the overall severe potential. Read more