Flash Flood Guidance
Issued by NWS

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000
AWUS01 KWNH 232346
FFGMPD
PAZ000-MDZ000-VAZ000-WVZ000-240400-

MESOSCALE PRECIPITATION DISCUSSION 0910
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
745 PM EDT MON OCT 23 2017

AREAS AFFECTED...EASTERN/NORTHERN WV...SOUTHWEST PA...NORTHWEST
VA...FAR WESTERN MD

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

VALID 232345Z - 240400Z

SUMMARY...LINGERING FLASH FLOOD RISK WITHIN TERRAIN OF CENTRAL
APPALACHIANS.

DISCUSSION...VERY STRONG SYNOPTIC CYCLONE DOMINATES THE OHIO
VALLEY WITH HIGHLY ANOMALOUS MOIST WARM CONVEYOR BELT ACROSS
EASTERN US PUMPING MOISTURE AND SOME MODEST ELEVATED INSTABILITY
INTO TERRAIN OF VA/WV. OVERALL THE PICTURE APPEARS TO BE IMPROVING
AS LARGE CONVECTIVE SHIELD CONTINUES TO ERODE AND WARM ACROSS
SOUTH CENTRAL VA.  A SURFACE LOW IN FAR NW NC WITH SOUTHWARD
EXTENDING COLD FRONT THROUGH THE CENTRAL CAROLINAS. EAST OF WHICH
VERY STRONG (30-40KT) SOUTHERLY AND SOUTHEASTERLY LOW LEVEL FLOW
(925-850MB) IS ADVECTED OVER WEAK EFFECTIVE WARM FRONT DENOTED BY
UPPER 60S/LOW 70S TDS SOUTH ACROSS NC/SC BORDER SEPARATING MT
GULF/CARIBBEAN AIR FROM ATLANTIC MT AIR INTO A FAIRLY NARROW
TROWAL ACROSS THE CENTRAL APPALACHIANS AT THIS TIME.  NEAR THE
FRONT INSTABILITY OF 250-500 J/KG MUCAPE STILL EXISTS AN AT LEAST
100 J/KG AS FAR NORTH AS THE EASTERN WV PANHANDLE ALONG WITH TOTAL
PWATS UP TO 1.5".  THESE PARAMETERS/FLUX INTO TERRAIN WILL
CONTINUE TO SUPPORT 1-1.25"/HR RAIN RATES WITH 2-3 HR DURATION
ALLOWING FOR 2-3" TOTALS (POSSIBILY HIGHER FURTHER SOUTH ACROSS
THE WESTERN VA)...LESSER FURTHER NORTH BUT GIVEN LOWER FFG ACROSS
WV/SW PA THERE REMAINS SOME MINOR FF THREAT THERE AS WELL EVEN
WITH 1-2" TOTALS.

HOWEVER...LIMITING FACTORS TOWARD EXCEEDING FLASH FLOOD GUIDANCE
CONTINUE TO GROW.  FOREMOST BEING INCREASED CAPPING/FURTHER
DISTANCE FROM WARM SECTOR AS WELL AS STEADILY INCREASING FFG
VALUES OVER EASTERN WV/NW VA.  ADDITIONALLY...WARM CONVEYOR BELT
WILL START TO REDUCE OPTIMAL ANGLE OF TERRAIN FOR OROGRAPHIC
ASCENT.  ALL CONSIDERED THE THREAT OF FLASH FLOODING REMAINS BUT
THE OVERALL MAGNITUDE IS REDUCING IN AREAL COVERAGE/RISK COMPARED
TO FURTHER SW EARLIER TODAY.

GALLINA

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

ATTN...WFO...CTP...LWX...PBZ...RLX...RNK...

ATTN...RFC...MARFC...OHRFC...SERFC...

LAT...LON   40418013 40287918 39567881 39177811 38467838
            37737893 37407948 37598040 38948072 40018041




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