Sunday, January 22, 2017

SEVERE WEATHER OUTLOOK FROM SPC

 Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1028 AM CST Sun Jan 22 2017

   Valid 221630Z - 231200Z

   ...THERE IS A HIGH RISK OF SEVERE THUNDERSTORMS OVER PARTS OF
   SOUTHERN AND CENTRAL GEORGIA...NORTHERN FL...AND EXTREME SOUTHEAST
   AL...

   ...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS OVER PARTS OF
   AL...FL...GA...AND SC...

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS OVER PARTS OF
   AL...FL...GA...SC...AND NC...

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER MUCH OF
   AL...FL...GA...SC...AND NC...

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER MUCH OF THE
   SOUTHEAST STATES...

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS PARTS OF CENTRAL
   CA...

   ...SUMMARY...
   A severe thunderstorm and tornado outbreak is expected today across
   north Florida and south Georgia, with the significant severe threat
   also expected to extend southward into central Florida and
   northeastward into South Carolina this evening.

   ...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.

   ..Hart/Leitman.. 01/22/2017

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   NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 2000Z
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