MESOSCALE PRECIPITATION DISCUSSION 0293
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
518 PM EST SAT DEC 21 2013
 
AREAS AFFECTED...SRN IL...NRN KY...IN...OH 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 212217Z - 220317Z
 
SUMMARY...BROAD SCALE MODERATE RAINS AND SOME EMBEDDED HEAVIER
DOWNPOURS...WILL INCREASE TOWARD PEAK COVERAGE AND INTENSITY THIS
EVENING. MANY AREAS HAD ALREADY RECEIVED 1.5 TO 2.5 INCHES OF RAIN
TODAY. THESE AMOUNTS MAY BE DOUBLED BY LATE EVENING...WITH
INSTANCES OF FLASH FLOODING BECOMING MORE COMMON.

DISCUSSION...A LARGE SCALE HEAVY RAIN EVENT WAS UNDERWAY. GIVEN
THE NATURE OF THE FORCING MECHANISMS...AND MINIMAL INFLUENCE OF
DEEP CONVECTION OR COLD POOLS AT THIS LATITUDE...THE QPFS FROM
MOST GLOBAL AND HIGH RESOLUTION MODELS WERE IN STRONG AGREEMENT. A
CORRIDOR OF MAXIMUM ASCENT WILL OCCUR NEAR THE SURFACE FRONT AND
AHEAD OF LOW PRESSURE MOVING UP FROM ARKANSAS. WPC IS FORECASTING
AREAL AVERAGE RAINFALL OF 1 TO 1.5 INCHES BETWEEN 00Z AND 06Z FROM
WRN KY ACROSS SRN IN INTO NW OH.

NEAR THE FRONT...CAPE VALUES...EVEN FOR MOST UNSTABLE
PARCELS...WILL BE LIMITED TO A FEW HUNDRED J/KG AT BEST.
STRATIFORM MODERATE RAIN WITH SOME EMBEDDED THUNDER WILL LIKELY
YIELD ENOUGH RAIN TO MEET FLASH FLOOD GUIDANCE ON THE LONGER TIME
SCALES...3 TO 6 HOURS...FOR WHICH GUIDANCE VALUES HAD FALLEN TO
AROUND 1 INCH OR LESS IN PARTS OF IL/IN/OH. THUS...INSTANCES OF
FLASH FLOODING MAY BECOME MORE COMMON.

THE SREF FORECASTS SOMEWHAT GREATER INSTABILITY SOUTH OF THE OHIO
RIVER INTO KY...WHERE MORE ROBUST CONVECTION IS POSSIBLE.
INCREASINGLY STRONG AND VEERING WIND FIELDS SHOULD PROMOTE
EASTWARD PROPAGATION...ACTING TO LIMIT THE DURATION OF TRAINING.
BUT THIS WILL BE OFFSET BY CONVECTIVE RAIN RATES AND FLUX OF A
HIGHLY ANOMALOUS...3-4 STANDARD DEVIATIONS PW...GULF AIR MASS INTO
THE REGION. RAIN RATES MAY APPROACH 1.75 INCHES PER HOUR...WITH
LOCAL FLASH FLOODING THE RESULT. 

BURKE

ATTN...WFO...PBZ...RLX...CLE...ILN...LMK...IWX...IND...PAH...
ILX...LSX...

ATTN...RFC...LMRFC...NCRFC...OHRFC...

LAT...LON   41548413 41198536 40018753 38978880 38148926 37488897
            37118832 36768789 36728665 38048451 39928221 40908121
            41608165 41718319 41548413