Quantitative Precipitation Forecast
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FOUS30 KWBC 251411
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1010 AM EDT TUE APR 25 2017

...VALID 15Z TUE APR 25 2017 - 12Z WED APR 26 2017...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
15 SW ALB 25 NE POU 20 W ORE 10 WSW AFN 10 WNW DAW 10 W NHZ
25 ESE PWM 20 E BVY PYM 10 ENE BID 15 SE FOK 10 ENE BLM TTN MPO
15 SW ALB.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
10 NNW AKQ 10 S CPK 15 SSE ECG 20 ENE EWN 15 W EWN 10 NNE JNX
20 ESE HNZ 15 NNE AVC 10 NNW AKQ.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
30 ESE SNL 10 SSE GOK 15 NNW SWO 25 E WLD 10 SW LWC 30 S IRK
30 NNE COU 15 SW SGF 10 SE ROG 15 W JSV 30 ESE SNL.


1500 UTC UPDATE

NO CHANGES MADE TO THE PREVIOUS EXCESSIVE RAINFALL POTENTIAL
OUTLOOK.  WHILE THE VERY HEAVY AND EXCESSIVE RAINS HAVE DIMINISHED
OVER CENTRAL NC THE MARGINAL RISK AREA WAS MAINTAINED FOR ANY
ADDITIONAL CONVECTION THAT MIGHT FLARE NEAR OR TO THE NORTH AND
NORTHEAST OF THE UPPER CENTER FORECAST TO LIFT THROUGH EASTERN NC
INTO FAR SOUTHEAST VA...AS PER THE PREVIOUS THINKING BELOW.

ORAVEC

...NORTHEAST...

THE CLOSED LOW ALONG THE CAROLINA COAST WILL MOVE NORTHEAST TODAY
OFF THE MID ATLANTIC AND SOUTHERN NEW ENGLAND COASTS. AN ANOMALOUS
PLUME OF MOISTURE (2-3 STANDARD DEVIATIONS ABOVE THE
CLIMATOLOGICAL MEAN) AHEAD AND EAST OF THIS FEATURE...COMBINED
WITH STRONG ONSHORE FLOW AND SOME DIFFLUENCE ALOFT WILL RESULT IN
A STREAM OF SHOWERS MOVING NORTHWARD WITH TIME. THE EXPECTATION IS
THAT THE HEAVY RAINFALL CURRENTLY OVER PORTIONS OF NC/VA WILL
DECREASE IN INTENSITY THIS MORNING AS SOME DRY AIR IS ENTRAINED
INTO THE SYSTEM...AND THE CLOSED LOW BEGINS PICKING UP FORWARD
SPEED OFF TO THE NORTHEAST. HEAVIEST RAINFALL AMOUNTS DURING THE
DAY 1 PERIOD (12Z TUE-12Z WED) WILL LIKELY END UP FOCUSED FROM NJ
INTO SOUTHERN NEW ENGLAND...WHERE ONSHORE MOIST FLOW WILL PERSIST
THE LONGEST TO THE EAST OF THE CLOSED LOW. WHILE MOST OF THE
PRECIPITATION WILL BE SHOWERY WITH RAINFALL RATES NOT ALL THAT
IMPRESSIVE...THERE ARE SIGNS THAT SOME WEAK ELEVATED INSTABILITY
WILL TRY TO MOVE INLAND ACROSS PORTIONS OF NJ INTO SOUTHERN NEW
ENGLAND. THIS SHOULD ALLOW FOR SOME EMBEDDED CONVECTIVE ELEMENTS
LEADING TO LOCALLY HIGHER RAINFALL RATES AROUND 0.5"-0.75" IN AN
HOUR. EXPECTING AREAL AVERAGED RAINFALL AMOUNTS TO GENERALLY BE IN
THE 1-2" RANGE FROM NJ INTO SOUTHERN NEW ENGLAND. HOWEVER HIGH RES
GUIDANCE SUGGESTS LOCALIZED 2-4" AMOUNTS ARE PROBABLE...WITH THE
BEST CHANCE FROM NORTHERN NJ TOWARDS NYC INTO SOUTHERN CT. THESE
TOTALS MAY BE ENOUGH TO BEGIN SATURATING SOILS AND RESULT IN SOME
MARGINAL FLOODING CONCERNS TODAY.

...NORTHEAST NC INTO SOUTHEAST VA...

LOCALLY HEAVY RAINFALL IS MOVING ACROSS NORTH CAROLINA THIS
MORNING. EXPECT THIS ACTIVITY TO GENERALLY DECREASE IN INTENSITY
AFTER 12Z. HOWEVER DO THINK WE COULD SEE ADDITIONAL CONVECTION
DEVELOP THIS AFTERNOON UNDERNEATH THE CLOSED LOW. CONVECTION
BECAME PRETTY ACTIVE TODAY UNDERNEATH THIS FEATURE OVER SC...WHICH
RESULTED IN SOME SLOW MOVING CONVECTION DROPPING SOME PRETTY HEFTY
TOTALS. SOME SIGNS WITHIN MOST OF THE HIGH RES GUIDANCE THAT THIS
COULD HAPPEN AGAIN THIS AFTERNOON AS WE DESTABILIZE UNDERNEATH THE
CLOSED LOW. THUS COULD END UP WITH SOME LOCALIZED 1-4" AMOUNTS
ACROSS PORTIONS OF NORTHEAST NC INTO SOUTHEAST VA ASSUMING WE CAN
DESTABILIZE ENOUGH THIS AFTERNOON.

...PORTIONS OF KS/OK/MO/AR...

CONVECTION IS EXPECTED TO BREAK OUT ACROSS PORTIONS OF EASTERN
OK/KS INTO WESTERN MO LATER THIS AFTERNOON INTO THIS EVENING. AT
THE SURFACE WILL HAVE A SLOW EASTWARD MOVING NORTHEAST TO
SOUTHWEST ORIENTED BOUNDARY STRETCHING ACROSS THE AREA. EXPECT THE
AREA TO REMAIN CAPPED FOR MOST OF THE DAY...WITH THE APPROACH OF A
SHORTWAVE AND INCREASED DIFFLUENCE ALOFT HELPING BREAK THE CAP
AFTER 0Z. 850 MB MOISTURE TRANSPORT AND CONVERGENCE REALLY PICKS
UP ACROSS THE AREA AFTER 0Z AS WELL...WITH A SEVERAL HOUR PERIOD
WHEN THIS 850MB MOISTURE CONVERGENCE AXIS DOES NOT MOVE ALL THAT
MUCH. THIS SUGGESTS THAT THERE COULD BE A PERIOD OF BACK-BUILDING
AND/OR REPEAT CONVECTION. STORM MOTIONS OFF TO THE NORTHEAST ARE
ALSO GENERALLY PARALLEL TO THE BOUNDARY...SUGGESTIVE OF SOME
TRAINING POTENTIAL. HOWEVER THE FRONT DOES EVENTUALLY PROGRESS OFF
TO THE EAST...SO THE WINDOW FOR TRAINING IS NOT ALL THAT
LONG...WHICH SHOULD KEEP RAINFALL AMOUNTS FROM GETTING TOO
EXTREME. HREF V2 PROBABILITIES SHOW A HIGH THREAT OF ISOLATED TO
SCATTERED 2" AMOUNTS WITH THIS CONVECTION...BUT PROBABILITIES OF
3"+ ARE PRETTY LOW. THUS CURRENTLY SEEMS LIKE THIS WILL END UP
BEING A PRETTY MARGINAL EVENT...AND THUS WILL NOT ADD ANY SLIGHT
RISK AT THIS TIME. WILL HAVE TO CONTINUE TO MONITOR THOUGH...AS
THE EVOLUTION OF THE 850 MB MOISTURE TRANSPORT MENTIONED ABOVE
DOES INTRODUCE SOME CONCERN THAT TRAINING/BACK-BUILDING COULD
RESULT IN LOCALLY HIGHER TOTALS THAN FORECAST. THUS WILL FOLLOW
TRENDS AND DECIDE IF A SLIGHT RISK IS WARRANTED OR NOT AS WE HEAD
THROUGH THE DAY.

CHENARD


$$





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