MESOSCALE PRECIPITATION DISCUSSION 0719
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1021 AM EST MON DEC 28 2015
 
AREAS AFFECTED...C TENNESSEE...EXT NE MISSISSIPPI...ALABAMA...NW
GEORGIA 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 281520Z - 282120Z
 
SUMMARY...SLIGHT THREAT FOR ISOLATED FLASH FLOODING AS POTENT
SQUALL LINE GIVEN ANTECEDENT CONDITIONS/FLOODING OF MAIN STEM
RIVERS.

DISCUSSION...WV SHOWS WELL DEVELOPED UPPER OVER E OK SWINGING A
VORT LOBE AROUND THE BASE TIGHTENING THE NEGATIVE TILT OF THE TROF
AND ENHANCING CONFLUENCE OF WSW POLAR STREAM AND SW SUBTROPICAL
STREAM ACROSS LA PINCHING TO AN INFLECTION POINT JUST NORTH OF MEI
BEFORE POLAR JET AXIS LIFTS NORTH  THIS CORRESPONDS WELL WITH
INCREASED DIVERGENCE SIGNAL IN RAP ANALYSIS AS WELL AS CONFLUENCE
POINT AT THE SURFACE OF WELL DEFINED SQUALL LINE AND NW-SE
ORIENTED LINE OF SEVERE CONVECTION ACROSS S AL/W FL PANHANDLE
TAKING THE APPEARANCE OF A PSEUDO-WARM FRONT STRUCTURE...THIS
ALLOWS FOR EASTWARD EXPANSION OF MODERATE SHOWERS THAT WILL EXPAND
NORTHWARD ACROSS N AL INTO S TN AHEAD OF DEEPER CONVECTION ALONG
SQUALL LINE...WITHIN THE WEDGE BETWEEN THESE TWO FEATURES IS A
VERY UNSTABLE WEDGE OF INSTABILITIES IN EXCESS OF 1500 J/KG WHICH
ASCENDED OVER THE BOUNDARY FOR MUCAPES OF 500-1000 J/KG AVAILABLE
FOR CONTINUED CONVECTIVE STRENGTH OF THE SQUALL LINE AS IT
PROGRESSES EASTWARD.  COINCIDENT TPW OF NEAR 2" AHEAD OF THE
SQUALL UP TO CENTRAL AL AND VALUES IN THE 1.5-1.7" RANGE AS FAR N
AS CENTRAL TN WILL CONTINUE TO SUPPORT RAINFALL EFFICIENCY OF
1.25"-1.5" UP TO THE TN LINE BUT LESSENING TO .5-.75" WITH REDUCED
INSTABILITY ACROSS TN.  SHIELD PRECIPITATION THAT IS EXPANDING
PRIOR TO THE SQUALL COULD SUPPORT .25-.5" ACROSS N AND CENTRAL AL.
 

NEGATIVELY THOUGH...DUE TO DEEP STRONG SWLY FLOW...SQUALL LINE
MOTION IS FAST TO NOT ALLOW FOR SIGNIFICANT TOTALS WITH 1-2"
EXPECTED WITH POSSIBLE LOCALIZED AREAS OF UP TO 2.5" ACROSS
CENTRAL AL NEAR THE INFLECTION POINT.  THESE TOTALS WOULD NOT BE
SUFFICIENT TO ECLIPSE FFG VALUES EXCEPT FOR MAYBE N AL/W AND S
CENTRAL TN WHERE VALUES ARE BELOW 2" IN 3HRS.  HOWEVER...WITH
EARLIER THIS WEEK 5-8" TOTALS ACROSS MUCH OF AL INTO NW GA...FFG
VALUES MAY HAVE REBOUNDED TOO FAST AND WINTER SOIL CONDITIONS MAY
NOT BE AS RESPONSIVE TO SUCH A QUICK BURST.  STILL THINKING
OVERALL CONDITIONS OF FLASH FLOODING WOULD BE HIGHLY LOCALIZED OR
VERY NEAR FLOODED RIVERS THAT BACK UP INTO THE FEEDING STREAMS.    

GALLINA

ATTN...WFO...BMX...FFC...HUN...MEG...MOB...MRX...OHX...

ATTN...RFC...LMRFC...OHRFC...SERFC...

LAT...LON   36548746 36448618 35918501 34598494 32818516 
            31628573 31708708 33098802 34718828 35668869 
            36168862