Quantitative Precipitation Forecast
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FOUS30 KWBC 260046
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
845 PM EDT TUE APR 25 2017

...VALID 01Z WED APR 26 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 SSW ADH 10 SSE GOK 15 NNW SWO 25 E WLD 25 SSW IXD 45 NNW COU
30 NNE COU 25 NNE SGF 25 ENE ROG 25 NE FSM RKR 25 ESE MLC
10 SSW ADH.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
10 WNW RVS 25 WNW GMJ 15 SW JLN 20 ESE JLN 15 N ROG 15 NE JSV
25 SW JSV 20 NE MLC 25 WNW MLC 20 NNW ADH CQB 10 WNW RVS.


0100 UTC UPDATE

REMOVED THE MARGINAL RISK AREA ACROSS NE NC/SE VA WAS UPPER LOW
CONTINUES TO LIFT OFF TO THE NORTHEAST ALONG THE NC/VA COAST WHICH
SHOULD CONTINUE TO ALLOW LOSS OF ANY RESIDUAL DAYTIME INSTABILITY.


ACROSS ERN OK INTO SW MO/NW AR...ADDED A SLIGHT RISK AREA WITH
ANTICIPATION OF RAPID EXPANSION OF CONVECTION ALONG COLD FRONT
DROPPING SLOWLY SEWD ACROSS THE REGION TONIGHT..SUPPORTED BY
STRONGER AREA OF HEIGHT FALLS DROPPING SEWD TOWARD THE TX
PANHANDLE REGION AFTER MIDNIGHT.  MAIN CONCERN WILL BE ALONG SRN
OR FLANKING LINE OF DEVELOPING CONVECTION WHERE 85H SLY OR SSWLY
FLOW REMAINS FAIRLY FOCUSED SUGGESTING A PERIOD OF VERY SLOW
MOVING OR CERTAINLY REPEATING CONVECTION ACROSS THE SAME AREA..AS
MID/UPR FLOW WILL BE NEARLY PARALLEL TO THE FRONT.  LAST SEVERAL
HRRR RUNS KEEP HEAVIEST RAINS SOUTH OF 12Z NSSL WRF..WRF ARW AND
WRF NMM BUT CLOSER IN AXIS TO THE 12Z ECMWF AND 18Z HI RES NAM.
SLIGHT RISK AREA ENCOMPASSES MUCH OF THE RECENT HRRR FOCUS FOR
HEAVIER RAINS..BUT DID BROADEN AREA SLIGHT TO THE NORTH TO ACCOUNT
FOR EARLIER MODEL SPREAD.  RECENT HRRR RUNS ALSO SUGGEST LOCALIZED
STORM TOTAL AMOUNTS IN EXCESS OF 4 INCHES WILL BE POSSIBLE WITH
MUCH OF THAT OCCURRING IN 3 HOURS OR LESS. GIVEN THE HEAVIER RAINS
THAT HAVE FALLEN ACROSS PARTS OF NE OK INTO SW MO OVER THE PAST
WEEK..FEEL UPGRADING TO SLIGHT RISK IS WARRANTED.

SULLIVAN

...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.



...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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