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FOUS30 KWBC 210137
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
935 PM EDT MON MAY 20 2013

...VALID 03Z TUE MAY 21 2013 - 00Z WED MAY 22 2013...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
20 NE LBR 25 W PRX 15 S GYI 10 S GLE 25 NNW LUD 35 ESE SPS
30 ESE SPS 35 S DUC 25 WSW 1F0 15 WNW 1F0 10 SE PVJ 10 NE PVJ
15 S SNL 25 WNW OKM 20 NW GMJ 25 NE JLN 45 N SGF 15 WNW AIZ
10 NE AIZ TBN 40 SSW TBN 20 NW BPK 20 W FLP 15 SSW FLP
25 NNW BVX 30 W ARG 15 W ARG 20 NNE M19 10 SSW M19 LRF
20 SSW MWT 20 NE LBR.

MADE ONLY VERY MINOR CHANGES TO THE PREVIOUS ISSUANCE..WITH STILL
A VERY GOOD CHANCE OF HEAVY RAINFALL REMAINDER OF THIS PERIOD IN
THE VICINITY OF THE THE SURFACE FRONTAL BOUNDARY CURRENTLY
STRETCHING THROUGH THE SOUTHERN PLAINS WHICH WILL BE VERY SLOW
MOVING INTO LATER TUESDAY AFTERNOON. STRENGTHENING SOUTHERLY TO
SOUTHWESTERLY LOW LEVEL INFLOW INTO AND AHEAD OF THIS BOUNDARY
WILL RAISE PW VALUES TO 1.5-2 STANDARD DEVIATIONS ABOVE THE MEAN.
THE STRONG FRONTAL CONVERGENCE AND VERY FAVORABLE UPPER DIFFLUENCE
IN THE COUPLED JET EXIT/ENTRANCE REGION OVR THE SOUTHERN PLAINS
WILL SUPPORT VERY ACTIVE CONVECTION PRETTY MUCH THE ENTIRE
PERIOD...ALTHOUGH THERE MAY BE A BREAK IN ACTIVITY BETWEEN
CONVECTION LATER MONDAY NIGHT INTO TUE MORNING AND A SECOND ROUND
LATER TUESDAY AFTERNOON---BUT OVERALL A VERY ACTIVE PRECIPITATION
PERIOD LIKELY ACROSS PORTIONS OF THE SOUTHERN PLAINS INTO THE MID
MS VALLEY REGION.  THERE MAY ALSO BE A PERIOD OF TRAINING OR BACK
BUILDING OF CELLS IN THE SOUTHWESTERLY FLOW ALONG THIS FRONT
TONIGHT INTO EARLY TUESDAY.  IN AREAS OF TRAINING/BACK
BUILDING---ISOLATED 2-3+ INCH RAINFALL AMOUNTS POSSIBLE IN A FEW
HOURS.  WHILE THERE CONTINUES TO BE RATHER NUMEROUS DIFFERENCES IN
QPF DETAILS ON THE SHORTER FORECAST TIME SCALE AMONG THE LATEST
MODELS---THERE IS BETTER AGREEMENT OVERALL FOR THIS FORECAST
PERIOD FOR HEAVY RAINFALL POTENTIAL FROM NORTHEASTERN TX---ACROSS
EASTERN TO SOUTHEASTERN OK---CENTRAL TO NORTHERN AR AND INTO
CENTRAL TO SOUTHERN MO.


...NORTHERN PLAINS/UPPER MS VALLEY...

NO CHANGE TO EARLIER THINKING HERE.  THERE IS GOOD AGREEMENT IN
THE LATEST MODEL GUIDANCE WITH THE VERY SLOW EASTWARD PUSH OF THE
STRONG CLOSED LOW INITIALLY OVER THE EASTERN PORTION OF THE
NORTHERN PLAINS.  A PERSISTENT COMMA HEAD/DEFORMATION RAINFALL
BAND WILL AFFECT THE NORTHERN PLAINS INTO THE FAR NORTHERN UPPER
MS VALLEY WITH A DURATION MODERATE TO ISOLATED HEAVY RAINFALL
EVENT.  GIVEN THE EXPECTED LONG DURATION OF MODERATE PRECIPITATION
AMOUNTS---DO NOT BELIEVE THERE WILL BE A SIGNIFICANT RISK OF
RUNOFF ISSUES FROM 6 HOURLY AMOUNTS OF .25-.50+ INCH AND ISOLATED
TOTALS OF 1-1.5+ INCHES FOR THE FORECAST PERIOD.

TERRY
$$