Flash Flood Guidance
Issued by NWS

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567
AWUS01 KWNH 251616
FFGMPD
NYZ000-PAZ000-252210-

MESOSCALE PRECIPITATION DISCUSSION 0063
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1115 AM EST SAT FEB 25 2017

AREAS AFFECTED...PORTIONS OF CNTRL NY

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

VALID 251614Z - 252210Z

SUMMARY...RAINFALL RATES OF 0.5 TO 1.0 IN/HR OVER A 1-2 HR PERIOD
ARE EXPECTED TO MOVE THROUGH PORTIONS OF CNTRL NY EARLY THIS
AFTERNOON. DUE TO LOW FLASH FLOOD GUIDANCE AND HIGH STREAM
LEVELS...FLASH FLOODING WILL BE POSSIBLE ON A LOCALIZED BASIS.

DISCUSSION...AT 16Z...REGIONAL RADAR IMAGERY AND LIGHTNING
DETECTION SHOWED A NNE-SSW ORIENTED AXIS OF LIGHT TO MODERATE
RAINFALL WITH EMBEDDED HEAVY RAINFALL FROM THUNDERSTORMS TRACKING
RAPIDLY THROUGH WRN NY. KCCX RADAR ALSO SHOWED AN INCREASE IN
REFLECTIVITY VALUES OVER THE PAST 30 MINUTES OVER CLINTON AND
LYCOMING COUNTIES IN N-CNTRL PA. THE ACTIVITY IS OCCURRING AHEAD
OF A COLD FRONT MOVING STEADILY EWD THROUGH WRN NY AND PA. GOES
EAST WATER VAPOR IMAGERY SHOWED THAT A POTENT SHORTWAVE TROUGH
AXIS MOVING THROUGH THE OHIO VALLEY WAS ACQUIRING A NEGATIVE TILT
AS OF 1545Z. 12Z RAOBS ALSO SHOWED A 100 TO 110 KT JET STREAK AT
500 MB BETWEEN DTX AND ILN WHICH IS FORECAST TO TRANSLATE TO THE
SRN ONTARIO/QUEBEC BORDER BETWEEN 18Z AND 21Z...LEAVING THE RIGHT
ENTRANCE REGION OF THE JET STREAK OVER CNTRL NY ALONG WITH
INCREASING MID-UPPER DIFFLUENCE.

WHILE INSTABILITY IS WEAK...AT OR ABOUT 500 J/KG...AND NEARLY
MAXED OUT OVER MUCH OF NY DUE TO CLOUD COVER...INCREASING
DYNAMICAL SUPPORT ALOFT SHOULD HELP TO INCREASE RAINFALL INTENSITY
INTO THE 0.5 TO 1.0 IN/HR RANGE OVER THE NEXT 2-3 HOURS. WHILE THE
AXIS OF RAINFALL WILL BE PROGRESSIVE AHEAD OF THE COLD FRONT...A
PERIOD OF 1-2 HOURS OF THESE RAINFALL RATES IS LIKELY TO ECLIPSE
FLASH FLOOD GUIDANCE IN A FEW AREAS. WHILE FLASH FLOOD GUIDANCE IS
UNUSUALLY LOW...0.25 TO 0.75 IN/HR IN A FEW LOCATIONS ACROSS
S-CNTRL NY AND 1 INCH IN 3 HOURS FOR LOCATIONS EAST OF LAKE
ONTARIO INTO THE MOHAWK VALLEY...NATIONAL WATER MODEL ANALYSES
INDICATE STREAMFLOWS ACROSS THE REGION ARE RUNNING MUCH ABOVE
NORMAL LIKELY TO DUE RECENT SNOW MELT. WHILE THE SITUATION DOES
NOT REPRESENT A TYPICAL FLASH FLOOD SETUP...THERE ARE SIGNALS
POINTING TO A FEW LOCALIZED RUNOFF ISSUES ACROSS PORTIONS OF
UPSTATE NY THROUGH THE EARLY AFTERNOON.

OTTO

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

ATTN...WFO...ALY...BGM...BTV...BUF...

ATTN...RFC...MARFC...NERFC...

LAT...LON   44227458 43837419 43067402 42657424 41987449
            41737487 41707585 41937653 42677618 43567623
            44077570



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