MESO: Nws Weather Prediction Center College Park Md

AWUS01 KWNH 162129
FFGMPD
SCZ000-GAZ000-FLZ000-ALZ000-170312-

MESOSCALE PRECIPITATION DISCUSSION 0217
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
528 PM EDT FRI AUG 16 2013

AREAS AFFECTED...NORTHERN FL AND SOUTHERN GA

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

VALID 162127Z - 170312Z

SUMMARY...A THIN BAND OF THUNDERSTORMS HAS FORMED NEAR A SHARP
FRONTAL ZONE FROM NORTHERNMOST FL ACROSS SOUTHERN GA. SLOW-MOVING
THUNDERSTORMS WITH RAINFALL RATES OF 2"+ PER HOUR COULD CAUSE
REGIONAL FLASH FLOODING.

DISCUSSION...A STRONG STATIONARY FRONT FOR MID-AUGUST WITH A
COUPLE EMBEDDED WEAK AREAS OF LOW PRESSURE IS ACTING AS A FOCUS
FOR A SOLIDIFYING LINE OF CONVECTION FROM THE NORTHERN FL
PANHANDLE ACROSS SOUTHERN GA. RAINFALL RATES OF 2"+ PER HOUR HAVE
ESTIMATED BY DOPPLER RADAR WITHIN THE STRONGER THUNDERSTORMS
EMBEDDED IN THE NARROW BAND. DIVERGENCE ALOFT OVER THE FRONT IS
BEING AIDED BY A SHORTWAVE ACROSS AL AND NORTHERN GA.
PRECIPITABLE WATER VALUES OF 2-2.25 INCHES ARE POOLING NEAR THE
BOUNDARY WHICH IS AIDING PRECIPITATION EFFICIENCY. CAPE VALUES
REMAIN IN THE NEIGHBORHOOD OF 1000 J/KG AND LOW-LEVEL INFLOW --
SIMILAR TO THE MAGNITUDE OF THE 0-3 KM VERTICAL WIND SHEAR -- OF
20-25 KNOTS IS CONVERGING INTO THE BOUNDARY AND A NARROW ANGLE.
THE CAPE AND LOW-LEVEL SHEAR VALUES SEEN IN THIS REGION ARE
NORMALLY NOT SUFFICIENT FOR ORGANIZED CONVECTION, WHICH COULD
EXPLAIN ITS THIN LINEAR APPEARANCE ON RADAR IMAGERY. PROPAGATION
VECTORS ARE WEAK AND ALIGNED ALONG THE FRONTAL BOUNDARY, WHICH
INCREASES THE FLASH FLOOD RISK.

THE 15Z AND 18Z HRRR RUNS HAVE DONE A VERY GOOD JOB DEPICTING THIS
FORMING LINE OF THUNDERSTORMS, AND FORECAST THE NARROW BAND TO
CONTINUE TO EXIST UNTIL 03Z BEFORE DISSIPATING. THEREFORE, THIS
MPD IS VALID UNTIL JUST AFTER 03Z. USED POSSIBLE OVER LIKELY AS
THE FLASH FLOOD GUIDANCE VALUES IN THIS REGION REMAIN MODERATELY
HIGH, ON THE ORDER OF 2.5 INCHES IN ONE HOUR AND 3-4 INCHES IN
THREE HOURS, WHICH COULD BE EXCEEDED ON A REGIONAL BASIS --
CONFIDENCE IN A MAJOR REGIONAL FLASH FLOOD EVENT IS BELOW AVERAGE.
HOWEVER, LOCALIZED RAINFALL AMOUNTS OF 4-6 INCHES ARE POSSIBLE
WITHIN THE DEFINED AREA OVER A SHORT PERIOD OF TIME.

ROTH

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

ATTN...WFO...CHS...JAX...FFC...TAE...MOB...

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

LAT...LON 31328110 30738330 30228660 30558677 31118545 31828338
32388129 32488004 31898014 31328110

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