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000
FOUS30 KWBC 211348
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
948 AM EDT TUE MAY 21 2013

...VALID 15Z TUE MAY 21 2013 - 12Z 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
DTN 10 ESE TRL DFW 20 ENE RPH 20 NNW RPH 35 S F05 25 S F05
15 NNW SPS 20 S LAW 20 WNW MLC 10 NE MLC 30 NNW RUE 15 W BVX
10 SW JBR 20 ESE JBR 20 SSE HKA 20 WNW MKL MKL 30 SSE MKL
45 SSE MKL 30 N TUP 30 WNW TUP 50 SE UTA 40 NNE GLH 30 S LLQ DTN.


UPDATE

SOUTHERN PLAINS INTO THE LOWER MS VALLEY

CHANGES TO THE PREVIOUS EXCESSIVE RAINFALL POTENTIAL OUTLOOK WERE
TO ELONGATE THE RISK AREA IN A MORE WEST TO EAST
DIRECTION---EXTENDING IT WESTWARD ALONG THE TX/OK BORDER TO JUST
EAST OF 100 W AND TO SUPPRESS THE EASTERN END OF THE PREVIOUS AREA
SOUTHWARD INTO FAR NORTHERN MS AND FAR SOUTHWESTERN TN TO COVER
THE HI RES ARW AND HI RES NMM QPF AXES.  UNCERTAINTIES ON WHETHER
THE WELL DEFINED WEST TO EAST ORIENTED CONVECTIVE LINE CURRENTLY
STRETCHING ACROSS SOUTHEAST OK INTO NORTHWEST AR WILL BLOCK ANY
APPRECIABLE CONVECTION FROM MOVING FARTHER TO THE NORTH AND EAST
LATER TONIGHT INTO THE EARLY MORNING HOURS OF WED.  FOR THE
SHORTER TERM---TRAINING OF CELLS IN A WEST TO EAST DIRECTION TO
THE NORTH OF THE OUTFLOW BOUNDARY WHICH HAS SUNK SOUTHWARD INTO
NORTHEAST TX AND SOUTHERN AR WILL CONTINUE AS MOIST SOUTHWESTERLY
LOW LEVEL FLOW CONTINUES TO OVERRUN THE OUTFLOW BOUNDARY.  VERY
FAVORABLE COUPLET JET EXIT/ENTRANCE REGION DYNAMICS WILL CONTINUE
TO ENHANCE LARGE SCALE LIFT OVER THE SOUTHERN PLAINS TODAY WITH
HEAVY RAINS LIKELY TO CONTINUE AS THEY WHOLE CONVECTIVE AREA
SLOWLY SINKS TO THE SOUTH AND EAST.  IN AREAS OF TRAINING SHORT
TERM RAINFALL AMOUNTS OF 1-2"+ POSSIBLE.

ORAVEC

PREVIOUS DISCUSSION

...EASTERN PORTIONS OF THE SOUTHERN PLAINS (NERN TX/ERN OK)...

MULTI CELLULAR CONVECTION LATE MON NIGHT/EARLY TUE AM IS
PROGRESSING RATHER WELL...THIS ALONG THE MAINLY LINEAR ORIENTATION
WOULD LIKELY AMOUNT TO A LIMITED FLASH FLOOD THREAT WITHIN THE
CURRENT SLIGHT RISK REGION THROUGH TUE AM.  HOWEVER...BOTH THE
GLOBAL AND HIGH-RES MODEL SUITE CLUSTER FAVORABLY IN TERMS OF
DEPICTING AN ADDITIONAL ROUNDS OF HEAVY RAINFALL LATER TODAY IN
THE VICINITY OF THE THE SLOW MOVING LLVL FRONTAL BOUNDARY
STRETCHING THROUGH THE SOUTHERN PLAINS.  DURING THE DAY...THE
HIGHEST RISK FOR EXCESSIVE RAINFALL WILL BE ON EITHER SIDE OF THE
RED RIVER ACROSS ERN OK AND NERN TX...NORTHEASTWARD INTO NW ARK.
THIS AS A SHORTWAVE CURRENTLY PIVOTING ACROSS SRN NM PUSHES EAST
INTO CENTRAL OK BY 00Z WED.  THE SHORTWAVE WILL FURTHER AMPLIFY
THE LONGWAVE TROUGH...
ENHANCING THE BROAD-SCALE DYNAMICAL FORCING (UPPER DIVERGENCE/LLVL
MOISTURE CONVERGENCE) ACROSS THE AFOREMENTIONED AREAS LATER
TODAY...PARTICULARLY BY LATE AFTN AND EVENING AS THE NAM/GFS/ECMWF
ALL SHOW ENHANCED RIGHT ENTRANCE REGION (FRONTOGENETIC) FORCING
FROM THE UPPER JET GRADIENT ACROSS THE CENTRAL PLAINS TO MID MS
VLY.  AMPLE LLVL INFLOW AND CONVERGENCE ALONG THE FRONTAL ZONE
WITH A MOISTURE RICH ENVIRONMENT IN PLACE (PW`S PEAKING ~1.75" OR
CLOSE TO 2 STD DEVIATIONS ABOVE NORMAL...WHILE K INDICES IN THE
MID-UPPER 30S)...WILL SUPPORT THE POTENTIAL FOR COPIOUS RAINFALL
WITH THE DEVELOPING CONVECTION LATER TODAY.  FOR NOW...CONTINUED
WITH A SLIGHT RISK OVER THIS REGION...
GIVEN THE STRONG (DEEP) INSTABILITY AND WITH THE DRY MID-LEVEL AIR
NOT FAR UPSTREAM...THUS THE
LIKELIHOOD THAT AS EXPERIENCED ON MON CELLS WILL BE MOVING AT A
FAIRLY PROGRESSIVE CLIP AND AS SUCH POSE A MORE LIMITED FLASH
FLOOD THREAT.  AT THE SAME TIME...THE MORE ORGANIZED CONVECTIVE
CLUSTERS...ESPECIALLY SUPER CELLS...WILL HAVE A MUCH GREATER RISK
FOR AT LEAST LOCALIZED FLASH FLOODING.

...PORTIONS OF THE LOWER-MID MISSISSIPPI VALLEY...

TUE NIGHT INTO WED MORNING...THE EXCESSIVE RAINFALL RISK SHIFTS
INTO THE LOWER-MID MS VLY...GENERALLY N OF THE LA/AR BORDER UP TO
THE SATL AREA.  MODEST SWRLY NOCTURNAL LLJ (35-45 MPH) ALONG WITH
THE PW`S BTWN 1.5 AND 1.75" AHEAD OF THE AFOREMENTIONED SHORTWAVE
TROUGH AND SW-NE ORIENTED SFC COLD FRONT WILL GENERATE ADDITIONAL
AREAS OF HEAVY RAINFALL.  THE RISK IS HEIGHTENED GIVEN THE
NEGATIVE TILT OF THE TROUGH AXIS AND (THUS) SOME BACKING OF THE
FLOW ALOFT...MORE PARALLEL TO THE LLVL BNDRY THAN OTHERWISE...
WHICH WILL LEAD TO A SLOWER W-E PROGRESSION OF THE CONVECTION.
ISOLATED 2-4+ INCH RAINFALL AMOUNTS WILL BE POSSIBLE IN A FEW
HOURS ACROSS THE THREAT AREA.

HURLEY
$$