Quantitative Precipitation Forecast
Issued by NWS

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FOUS30 KWBC 210854
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
454 AM EDT FRI APR 21 2017

...VALID 12Z FRI APR 21 2017 - 12Z SAT APR 22 2017...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
10 SSW I16 15 WSW HLX 15 N AVL 25 NW MDQ 25 WSW PBF 20 WSW PRX
30 WNW CHK 15 N AVK 10 ENE EWK 10 SSE DMO 15 NNW BLV 10 NE HNB
30 NNW LOZ 10 SSW I16.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
15 NNE WLD 40 SSW DMO 20 NNW HSB 15 W OWB 25 N HOP 15 E DYR
20 E HOT 20 WNW DEQ 10 NNE AQR PWA 15 NNE WLD.


...SOUTHERN-CENTRAL PLAINS EASTWARD THROUGH THE TENNESSEE
VALLEY...LOWER OHIO VALLEY...AND MID ATLANTIC...

A SLOWLY EVOLVING UPPER TROUGH...ONE THAT WILL ELONGATE WITH TIME
AS IT BECOMES INCREASINGLY CONSTRICTED BY THE RIDGES NORTH AND
SOUTH...WILL COMBINE WITH FAVORABLE UPPER JET DYNAMICS (COUPLED
JET STREAKS) IN GENERATING ADDITIONAL HEAVY RAINFALL NORTH OF THE
SURFACE STATIONARY FRONT. WHILE NOT CORRELATED WITH THE STRONGEST
DEEP-LAYER INSTABILITY SOUTH OF THE SURFACE BOUNDARY...THE MODEL
CONSENSUS (BOTH GLOBAL AND HIGH-RES CAMS) IS FOR AN EXPANSIVE
SWATH OF 1+ INCH 24 HOUR AMOUNTS FROM EASTERN OK-SOUTHEAST KS
EASTWARD THROUGH SOUTHERN MO/IL...NORTHERN AR...AND WESTERN KY/TN.
GIVEN THE CLOSER PROXIMITY TO THE HIGHER FORECAST CAPES AND PW
VALUES...ALONG WITH THE DYNAMICALLY-FAVORABLE COUPLED UPPER LEVEL
JET STREAKS AND STRENGTHENING LOW-LEVEL MOISTURE FLUX (~2 STANDARD
DEVIATIONS ABOVE THE NORM)...THE MODELS APPEAR TO BE CONVERGING ON
THE HEAVIEST RAINFALL OVER THE AFOREMENTIONED AREAS WEST OF THE
MISSISSIPPI...PARTICULARLY OVER THE OZARKS IN NORTHWEST
AR-SOUTHEAST MO GIVEN THE UPSLOPE ENHANCEMENT. WPC UTILIZED A
NON-NAM/NON-SREF MUTLI-MODEL BLEND WITH THE QPF...LEAD BY THE
MEANS (INCLUDING HIGH-RES ENSEMBLE)...WHICH COMPARES FAVORABLY TO
THE PARALLEL NBM. THE NAM AND SREF MEAN WERE A BIT TOO FAR NORTH
WITH THE HEAVIEST QPF...FARTHER REMOVED FROM THE BEST INSTABILITY
AND PW...AND THUS WERE NOT UTILIZED.

BASED FROM SOME OF THE HIGH-RES CAMS...AREAS WITH HIGHER AMOUNTS
OF 3-5+" ARE ANTICIPATED WITHIN THE STRONGEST ELEVATED
CONVECTION...ESPECIALLY OVER THE SOUTHERN OZARKS. WHILE SHORT TERM
RAINFALL RATES (1-3 HR) WILL BE SOMEWHAT CONSTRAINED BY THE
ABSENCE OF MORE ROBUST INSTABILITY...THE SLOWLY-EVOLVING SYNOPTIC
PATTERN AND RESULTANT MULTIPLE ROUNDS OF CONVECTION OVER THE SAME
AREAS WILL INCREASE SOIL MOISTURE/LOWER FFGS WITH TIME. THIS
IN-TURN WOULD RAISE THE EXCESSIVE RAINFALL POTENTIAL...ESPECIALLY
OVER THE SOUTHERN OZARKS THIS EVENING AS THE SOUTHERLY LOW-LEVEL
INFLOW INCREASES TO 50+ KTS AHEAD OF THE APPROACHING SURFACE LOW.

HURLEY

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