Flash Flood Guidance
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091
AWUS01 KWNH 181731
FFGMPD
PAZ000-OHZ000-INZ000-182345-

MESOSCALE PRECIPITATION DISCUSSION 0936
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1231 PM EST SAT NOV 18 2017

AREAS AFFECTED...NORTHERN OH...EAST CENTRAL IND...FAR NORTHWEST PA

CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY

VALID 181745Z - 182345Z

SUMMARY...CONTINUED TRAINING/REPEAT SHOWERS WITH CONVECTIVE
ELEMENTS OVER ALREADY SATURATED SOILS LIKELY TO SUPPORT FLASH
FLOODING CONDITIONS THROUGH AFTERNOON/EARLY EVENING.

DISCUSSION...EARLY MORNING SHOWERS WITH EMBEDDED CONVECTIVE
ELEMENTS PER MRMS/MESONET OBSERVATION HAVE PRODUCED A SWATH OF
1.5-2.5" TOTALS ACROSS N CENTRAL IND/OH FROM KOKOMO THROUGH
MARION/MANSFIELD OH THIS MORNING SATURATING THE SOILS AND REDUCING
FFG VALUES IN THE REGION AND SETTING THE STAGE FOR ADDITIONAL
FLOODING CONCERNS THIS AFTERNOON.  17Z MESO ANALYSIS DEPICTS A
COOLED POOL OF AIR ACROSS THIS REGION AS THE WARM FRONT IS TRYING
TO SURGE NORTHWARD ACROSS SW OH EFFECTIVELY REINFORCING THE FRONT.
 STRONG 50-60KT 850MB LLJ AND SFC 20-30KT FLOW WILL USE THIS
REINFORCED BOUNDARY AS UPGLIDE/ISENTROPIC ASCENT.  WARM SECTOR IS
ALSO CHARACTERIZED BY SFC T REACHING THE UPPER 50S TO MID 60S WITH
ABOUT 5-7 DEGREE DEWPOINT DEPRESSIONS.  THIS SUPPORTS AN
INCREASINGLY UNSTABLE ENVIRONMENT AND ALLOWS FOR 500-750 J/KG
MUCAPES CURRENTLY PERHAPS REACHING NEAR 1000 J/KG VERY CLOSE TO
THE SURFACE INFLECTION.

STRONG 120+KT 3H JET STREAK ACROSS THE CENTRAL MO VALLEY IS NOSING
TOWARD SW IND ALLOWING LEFT EXIT DYNAMICS COUPLED WITH A RIGHT
ENTRANCE TO A SMALL 80KT ANTICYCLONICALLY CURVED OUTFLOW CHANNEL
OVER MI (SUPPORTING EXPANDING BAROCLINIC LEAF IN GOES-16 WV
CHANNELS). THIS ORIENTATION SHOULD ALLOW FOR THE SURFACE WAVE TO
AMPLIFY AND LIFT NORTHWARD...REDUCING THE EARLIER FAVORED
UNIDIRECTIONAL STEERING FLOW THAT SUPPORTED TRAINING THIS MORNING.
 HOWEVER...STRONGER CONVECTION ENHANCED BY THE REINFORCED COLD
POOL IN E CENTRAL IND AND N CENTRAL OH...SHOULD ALLOW FOR A
STRONGER CORRIDOR TO TRACK THROUGH THE SATURATED SOIL AND WITH
HOURLY RAIN RATES UP TO 1.5"/HR AND TOTALS OF 1.25" ARE LIKELY TO
SUPPORT CONTINUED FLOODING CONCERNS WITH SOME LOCALIZED FLASH
FLOODING CONCERNS LIKELY THROUGH 21-22Z.

WITH TIME THE STRONGER WAA JUST AHEAD OF THE COLD FRONT AND
FURTHER NORTHEAST TRACK/AMPLIFICATION OF THE SURFACE CYCLONE WILL
INCREASE HEAVY RAINFALL/REPEAT TRACKS THROUGH THE LOWER FFG VALUES
OVER NERN OH/FAR NW PA WHERE DORMANT GROUND CONDITIONS SHOULD
ALLOW FOR INCREASED RUNOFF AND LESS ABSORPTION.  AS SUCH HAVE
INCORPORATED NE OH IN THE MPD AREA OF CONCERN WITH 1.5-2" TOTALS
LIKELY AND AT LEAST A  POSSIBLE FLOODING/ISOLATED FLASH FLOODING
THREAT THROUGH 00Z.  THIS IS SUPPORTED BY RECENT RAPID REFRESH
GUIDANCE OF THE RAP/HRRR AND THE 12Z ARW.

GALLINA

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

ATTN...WFO...CLE...ILN...IND...IWX...PBZ...

ATTN...RFC...OHRFC...

LAT...LON   42088007 41557969 41158004 40688103 40028195
            39758457 39608634 40188666 40468645 40978532
            41198438 41388286 41458243 41588204 41548178
            41848124 42038047



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