Quantitative Precipitation Forecast
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000
FOUS30 KWBC 120050
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
850 PM EDT WED OCT 11 2017

...VALID 01Z THU OCT 12 2017 - 12Z THU OCT 12 2017...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
70 ENE FFA 30 NE FFA 15 S SFQ LYH 30 NNE HSP CKB 15 E AFJ IDI
AOO 15 WNW JYO 20 E NYG 10 E NHK 30 E WAL 80 ESE WAL.


...MID ATLANTIC...

DEEP MOISTURE AND INSTABILITY FOCUSED ALONG A STATIONARY BOUNDARY
EXTENDING FROM SOUTHWEST PA INTO SOUTHEAST VA AND  NORTHEAST NC IS
EXPECTED TO FEED CONVECTION THAT PRODUCES HEAVY TO LOCALLY
EXCESSIVE RAINFALL INTO THE EARLY MORNING HOURS. THE MOST RECENT
BLENDED TPW PRODUCTS...AS WELL AS RAP ANALYSES...INDICATED
PRECIPITABLE WATER VALUES NEAR 2.30 INCHES (WHICH IS BETWEEN TWO
AND THREE STANDARD DEVIATIONS ABOVE THE MEAN) POOLED ALONG AND
JUST SOUTH OF THE FRONT. STORMS DEVELOPING IN THE 1000-1500 J/KG
OF MLCAPE...TAPPING THIS DEEP MOISTURE FEED...COULD PRODUCE HOURLY
RAINFALL RATES APPROACHING 2.00 INCHES AS THEY TRACK ALONG THE
FRONT...MAINLY ACROSS SOUTHEAST VA AND NORTHEAST NC.

SYNOPTIC SCALE ASCENT IN THE RIGHT REAR QUADRANT OF AN 80 KNOT JET
STREAK CROSSING PA INTO SOUTHEAST NEW ENGLAND COULD PROVIDE SOME
ORGANIZATION OF THE CONVECTION. MORE CONVECTIVE ORGANIZATION
RAISES THE POSSIBILITY OF TRAINING IN THE QUASI UNIDIRECTIONAL
FLOW (PER RECENT REGIONAL VWP). BOTH THE LATEST RAP AND HRRR
SUGGEST THERE COULD BE SUFFICIENT INSTABILITY TO SUPPLY CONVECTIVE
ELEMENTS ALONG THE FRONT THROUGH AT LEAST 12/06Z. THE MOST RECENT
SET OF HRRR SOLUTIONS INDICATED THE POTENTIAL FOR LOCAL 3.00 TO
4.00 INCH RAINFALL AMOUNTS...MAINLY OVER SOUTHEAST VA...WHERE THE
BEST CHANCE OF TRAINING IS EXPECTED.

AFTER THAT TIME...INSTABILITY COULD BECOME A LIMITING FACTOR FOR
MORE OF A FLASH FLOOD THREAT. IT IS POSSIBLE THAT THE CONVECTIVE
ORGANIZATION DOES NOT OCCUR WITH THE SYNOPTIC SCALE
LIFT...RENDERING A MORE WIDELY SCATTERED TO ISOLATED NATURE TO THE
FLASH FLOOD THREAT. BECAUSE OF THIS...THE MARGINAL RISK WAS LEFT
IN PLACE...RATHER THAN UPGRADE TO A SLIGHT RISK.

HAYES
$$





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