Flash Flood Guidance
Issued by NWS

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AWUS01 KWNH 090309
FFGMPD
FLZ000-090910-

MESOSCALE PRECIPITATION DISCUSSION 0942
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1009 PM EST FRI DEC 08 2017

AREAS AFFECTED......PORTIONS OF CENTRAL FL...

CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE

VALID 090310Z - 090910Z

SUMMARY...CONVECTION OVER THE EASTERN GULF OF MEXICO COULD TRAIN
ACROSS PORTIONS OF CENTRAL FL...POSING A FLASH FLOOD THREAT INTO
THE EARLY MORNING HOURS.

DISCUSSION...REGIONAL RADARS CONTINUED TO SHOW SCATTERED
CONVECTION DEVELOPING AHEAD OF A SHORT WAVE OVER THE EASTERN GULF
OF MEXICO. THE MOST RECENT IR LOOP INDICATED SLOWLY COOLING TOPS
WITH THE CONVECTION... AS IT FORMS ALONG AN AXIS OF 1500-2500 J/KG
EXTENDING ACROSS CENTRAL AND SOUTHWEST FL (THE 00Z KTBW SOUNDING
SHOWED 1900+ J/KG OF SBCAPE). A 30 TO 40 KNOT LOW LEVEL FLOW (PER
RECENT REGIONAL VWP) CONTINUES TO TRANSPORT 2.00 INCH PRECIPITABLE
WATER AIR (WHICH IS ABOUT TWO STANDARD DEVIATIONS ABOVE THE MEAN)
AHEAD OF THE DEVELOPING CONVECTION.

THE KTBW RADAR SHOWED HOURLY RAINFALL RATES NEAR AN INCH WITH THE
ACTIVITY FROM PINELLAS SOUTH THROUGH MANATEE COUNTIES.
TO THIS POINT...THE CONVECTION HAS REMAINED SCATTERED...BUT THIS
IS EXPECTED TO CHANGE AS LOW PRESSURE FORMS ON A STATIONARY FRONT
EAST OF THE SC COAST...DRAGGING A COLD FRONT ACROSS CENTRAL AND
SOUTH FL BETWEEN 05Z AND 09Z.

DIVERGENCE INCREASES ACROSS CENTRAL AND SOUTH FL IN THE RIGHT REAR
QUADRANT OF A 130 KNOT JET STREAK CROSSING THE SOUTHEAST STATES
INTO THE MID ATLANTIC. THIS SHOULD SUPPORT MORE ORGANIZED LINES OF
CONVECTION MOVING ASHORE BETWEEN KTPA AND KFMY. THERE IS A MULTI
HIGH RESOLUTION MODEL SIGNAL (LED BY THE MOST RECENT HRRR) FOR
LOCAL 2.00 TO 4.00 INCH RAINFALL AMOUNTS BETWEEN THE
ABOVEMENTIONED LOCATIONS. EACH MODEL INDICATES THAT TRAINING
BECOMES MORE OF A CONCERN AS PROPAGATION VECTORS SLOW AHEAD OF THE
FRONT.

THREE HOUR FLASH FLOOD GUIDANCE VALUES ARE FAIRLY HIGH (GENERALLY
ABOVE 3.50 INCHES)  SO TRAINING WOULD BE NECESSARY TO SUPPORT
FLASH FLOODING CONCERNS. GIVEN THE DEEP MOISTURE IN PLACE...AND
THE POTENTIAL FOR TRAINING...LOCAL FLASH FLOODING IS POSSIBLE
THROUGH ABOUT 09/09Z.

HAYES

...PLEASE SEE WWW.WPC.NCEP.NOAA.GOV FOR GRAPHIC PRODUCT...

ATTN...WFO...MFL...MLB...TBW...

ATTN...RFC...SERFC...

LAT...LON   28628112 28318075 28288072 27878047 27468042
            27068070 26678122 26428189 26518230 27188280
            27598296 27978278 28608182



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