The SPC is forecasting ...Outbreak of tornadoes and severe thunderstorms expected over parts of the southeast US this afternoon and tonight....   Please read the latest public statement about this event.  View What is a Watch? clip.

   SPC AC 221956

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0156 PM CST Sun Jan 22 2017

   Valid 222000Z - 231200Z

   ...THERE IS A HIGH RISK OF SEVERE THUNDERSTORMS LATE THIS AFTERNOON
   AND EVENING ACROSS SOUTHERN GEORGIA...AND NORTHERN FLORIDA INTO THE
   WEST CENTRAL FLORIDA PENINSULA...

   ...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS SURROUNDING THE
   HIGH RISK AREA...INCLUDING MUCH OF THE REMAINDER OF CENTRAL
   FLORIDA...THE REMAINDER OF CENTRAL AND SOUTHEAST GEORGIA AND MUCH OF
   THE SOUTH CAROLINA PIEDMONT AND COASTAL PLAIN...

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS SURROUNDING THE
   MODERATE RISK AREA...INCLUDING PORTIONS OF SOUTHERN NORTH
   CAROLINA...

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS SURROUNDING THE
   ENHANCED RISK AREA...INCLUDING PARTS OF NORTHEAST ALABAMA...NORTHERN
   GEORGIA...UPSTATE SOUTH CAROLINA AND MUCH OF THE REMAINDER OF
   SOUTHEASTERN NORTH CAROLINA...

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS SURROUNDING THE
   SLIGHT RISK AREA...THROUGH THE NORTH CAROLINA PIEDMONT AND PORTIONS
   OF SOUTHEAST VIRGINIA...

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS LATE THIS
   AFTERNOON AND EVENING ACROSS PARTS OF THE CENTRAL CALIFORNIA
   COAST...INCLUDING THE SAN FRANCISCO BAY REGION...

   ...SUMMARY...
   An outbreak of severe thunderstorms, including the risk for strong
   tornadoes, and very strong damaging wind gusts, appears likely late
   this afternoon through tonight across southern Georgia into the
   Carolinas, and much of Florida.

   ...20Z Outlook Update...

   ...Southeast...
   In response to large-scale forcing for ascent, vigorous thunderstorm
   development is now underway within a narrow pre-cold frontal
   corridor, from portions of eastern Alabama southward into the
   northeastern Gulf of Mexico.  Severe categorical and probabilistic
   lines remain generally unchanged outside of Florida, except to begin
   to account for the eastward progress of the front/evolving
   convective band.

   There remains some lingering uncertainty concerning the extent of
   boundary layer destabilization across parts of northern Georgia
   through the Carolinas, along/north of a northward retreating outflow
   boundary/warm front.  Otherwise, the primary lingering uncertainty
   concerns the extent to which convective cells remain discrete within
   the pre-frontal convective band.

   The continued upscale growth of convection into a solidifying squall
   line seems most probable in association with an area of stronger
   mid/upper forcing for ascent likely to overspread much of northeast
   Florida and southeastern Georgia into South Carolina through this
   evening.  If/when this occurs, severe wind potential is likely to
   increase considerably in the presence very strong low-level and deep
   layer wind fields.  Latest model guidance continues to suggest an
   intense southerly 850 mb jet streak (50-70+ kt) developing/shifting
   northeastward from the northeastern Gulf of Mexico through this
   region.  And heavy precipitation loading coupled with downward
   momentum transfer seems likely to support considerable damaging wind
   potential, including at least localized intense surface gusts in
   excess of 65 kt.

   Otherwise, strong to extreme low-level shear, with very large,
   clockwise-curved low-level hodographs will support the potential for
   long-lived/long track supercells, in the presence of weak to modest
   warm sector boundary layer instability.  This activity may impact
   the Tampa/St. Petersburg metropolitan area by early evening, and
   much of the remainder of the central and southern Florida Peninsula
   through tonight.  Severe probabilities have been increased in
   general across this region to account for this.

   ...Central California, including the San Francisco Bay area...
   No changes have been made, with models suggesting a 110-130 kt
   westerly 500 mb jet streak nosing inland across the coast late this
   afternoon and evening.  Destabilization mostly within the post-cold
   frontal environment may become sufficient to support inland
   advancing low-topped convection/convective bands accompanied by a
   risk for potentially damaging surface gusts.

   ..Kerr.. 01/22/2017

   .PREV DISCUSSION... /ISSUED 1028 AM CST Sun Jan 22 2017/

   ...AN OUTBREAK OF SEVERE STORMS AND TORNADOES IS EXPECTED THIS
   AFTERNOON AND EVENING OVER PARTS OF NORTHERN FLORIDA, AND
   CENTRAL/SOUTHERN GEORGIA...

   ...Southern AL/North FL/Southern GA...
   The late morning surface analysis shows a rapidly deepening low near
   MOB, with a convectively reinforced warm front extending eastward
   from the low along the FL/GA border.  This low is forecast to deepen
   over 12mb in the next 12 hours as it tracks northeastward.  This
   rapid cyclogenesis will be accompanied by very strong low and mid
   level wind accelerations across parts of GA/FL.  The result will be
   a zone of impressive shear profiles in the warm-sector of the low,
   along with ample low level moisture and rather steep lapse rates. 
   Forecast soundings in the HIGH risk area are characterized by
   effective helicity values of 500-700 m2/s2 overlapping MLCAPE of
   1000-1500 J/kg.  This rare parameter space will support the risk of
   long-track strong tornadoes across the HIGH risk area.  Also, very
   strong low and mid level winds and steep lapse rates suggest a
   significant risk of bowing structures capable of widespread damaging
   winds and large hail.  The line of storms will eventually sag
   southward across the entire FL Peninsula overnight with a continued
   severe risk.

   ...Northeast AL/Northern GA...
   As the rapidly deepening surface low lifts northeastward, a plume of
   rather steep mid level lapse rates and strong winds aloft will wrap
   around the low.  This may result in an arc of strong to severe
   storms affecting parts of northeast AL and northern GA later this
   afternoon and evening.  Ample low level vorticity along this arc may
   be sufficient for a few tornadoes, along with large hail and
   damaging wind gusts.

   ...Carolinas...
   The convective evolution is uncertain over parts of SC/NC later
   today due to the widespread upstream thunderstorm coverage expected,
   and the persistent thunderstorm complex now over southeast GA. 
   Given the strength of the wind fields and cyclogenesis, there
   remains a significant threat of severe storms spreading
   northeastward across much of SC and into southeast NC after dark,
   with damaging winds and a few tornadoes being the main threat.  Its
   unclear how far north and west this threat will extend, but have
   lessened severe probabilities over parts of western/central NC where
   cool air and clouds are likely to persist.

   ...Central CA Coast...
   Multiple bands of showers and thunderstorms are expected to spread
   inland and affect the central CA coast this afternoon.  Cool
   temperatures aloft and steep mid level lapse rates, combined with
   the strong west-southwesterly winds aloft, will support a risk of
   fast-moving bowing structures capable of locally damaging winds and
   hail.

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