MESOSCALE PRECIPITATION DISCUSSION 0925
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
313 PM EST SUN NOV 05 2017

AREAS AFFECTED...FAR EC MO...CTRL/SRN IL...CTRL/SRN IN

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

VALID 052006Z - 060200Z

SUMMARY...LOCALIZED FLASH FLOODING WILL BECOME POSSIBLE ALONG AND
NEAR A SURFACE FRONT THIS AFTERNOON. RAIN RATES MAY REACH UP TO
1-2 IN/HR...WHICH SHOULD BE SUFFICIENT TO PRODUCE FLASH FLOODING
IF STORMS CAN TRAIN (REPEATEDLY AFFECT) A GIVEN LOCATION FOR OVER
AN HOUR.

DISCUSSION...CONVECTION HAS INCREASED IN BOTH EXTENT AND VIGOR
OVER THE PAST FEW HOURS SOUTHWESTWARD ALONG THE SURFACE FRONT
THROUGH CENTRAL ILLINOIS AND INTO THE ST. LOUIS METRO AREA.
VISIBLE SATELLITE IMAGERY SHOWED MORE BREAKS IN THE LOW CLOUD
COVER SOUTH OF THE FRONT...AND THUS THE STRONGEST SBCAPE IN THE
REGION WAS LOCATED OVER PORTIONS OF IL/MO (CONFIRMED BY RAP
ANALYSIS). LATEST CIRA BLENDED TPW AND GPS PWAT OBSERVATIONS
SUGGEST THAT PRECIPITABLE WATER VALUES HAVE CLIMBED TO NEAR 1.5
INCHES NEAR AND SOUTH OF THE FRONT...WHICH IS NEAR THE
CLIMATOLOGICAL MAXIMUM FOR THIS TIME OF YEAR FOR THE REGION. THE
COMBINATION OF STRONG INSTABILITY AND ANOMALOUSLY HIGH ATMOSPHERIC
MOISTURE WILL ALLOW STORMS TO PRODUCE HEAVY RAINFALL ALONG AND
AHEAD OF THE FRONT.

AS THE LINE OF STORMS CONTINUES TO DEVELOP AND BECOME ORGANIZED
(WITH 50-60 KT OF EFFECTIVE DEEP LAYER SHEAR) IT MAY BEGIN TO
PROPAGATE OFF THE FRONT...WHICH COULD ULTIMATELY REDUCE THE
RESIDENCE TIME OF HEAVY RAIN IN ANY GIVEN LOCATION. THE LACK OF A
PROTRACTED PERIOD OF HEAVY RAINFALL WILL BE ONE OF THE MAIN
LIMITING FACTORS...AS WILL THE NARROW WIDTH OF THE CONVECTIVE BAND
AT THE CURRENT TIME. HOWEVER...GIVEN THE ENVIRONMENT AND THE
CLOUD-BEARING LAYER MEAN WIND ROUGHLY ALIGNED PARALLEL TO THE
SURFACE FRONT...SOME LOCALIZED FLASH FLOODING CANNOT BE RULED
OUT...PARTICULARLY IF CONVECTIVE CLUSTERS MANAGE TO ORIENT
FAVORABLY NEAR URBANIZED AREAS.

THE GREATEST THREAT OF FLASH FLOODING BY LATE AFTERNOON OR EARLY
EVENING IN THE OUTLINED AREA WILL LIKELY BE IN PORTIONS OF
INDIANA. SOME OF CENTRAL AND SOUTHERN INDIANA HAS ALREADY RECEIVED
HEAVY RAINFALL EARLIER TODAY...AND HI-RES MODEL QPF IS HIGHER
FURTHER TO THE EAST. IN GENERAL...CONVECTION SHOULD BE MORE
SCATTERED IN NATURE FURTHER SW ALONG THE FRONT AS IT WILL BE
INCREASINGLY DISPLACED FROM THE MORE FAVORABLE LARGE-SCALE
FORCING. ONE AREA THAT HAS RECEIVED SOME OF THE HEAVIEST RAINFALL
THUS FAR IS FROM NEAR COVINGTON IN TO NEAR MUNCIE IN...AND THIS
COULD BE A FAVORED AREA FOR FLASH FLOODING GIVEN ANTECEDENT
CONDITIONS.

LAMERS

ATTN...WFO...ILX...IND...IWX...LMK...LOT...LSX...PAH...

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

LAT...LON   40578612 40278556 39658542 39058568 38798597
            38458690 38148808 37838889 37648980 37659056
            38169120 38939110 39539044 40098913 40388783
            40558680