Quantitative Precipitation Forecast
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FOUS30 KWBC 260057
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
855 PM EDT MON MAY 25 2015

...VALID 01Z TUE MAY 26 2015 - 12Z TUE MAY 26 2015...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
30 SW 3T5 20 WSW UTS 10 W OCH 20 NE GGG TXK 20 SW MWT
20 NNW MWT 35 W RUE 35 WNW RUE 35 SSW HRO 25 S HRO 25 SSE HRO
25 SSE FLP BVX 25 WNW M97 25 NNW GWO 20 N JAN 25 ENE BTR
15 ESE KVNP 35 NNW KHQI 20 ESE KBBF 20 WSW KMZG NGP RBO 15 N ALI
40 N ALI 50 SSE SSF 40 SE RND 30 SW 3T5.

MODERATE RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
20 NNE KXIH 15 N KBQX 30 S PSX 20 N KRP 35 NNW RKP 40 WSW VCT
40 WNW VCT 40 NW VCT 25 S 11R 20 ENE UTS 30 NE OCH 10 NW SHV
30 SSE TXK 35 ENE TXK 20 SSW M89 15 SSE M89 30 ESE M89 25 SW PBF
15 WSW LLQ 20 NNW BQP 30 SW MLU 10 N DRI 20 NNE KXIH.


0100 UTC UPDATE...

HAVE REMOVED A LARGE PART OF THE PREVIOUS AREA ON ITS WESTERN
SIDE..WHERE RAINS HAVE ENDED..AND TRIMMED EASTERN PORTIONS OF THE
PREVIOUS AREA..WHERE RAINS WILL NOT REACH BEFORE THE END OF THE
PERIOD.  OTHERWISE..STILL MAINTAINED THE SLIGHT AND MODERATE RISKS
FROM EASTERN TX INTO LA..MUCH OF AR AND WESTERN MS..AND ESPECIALLY
SO FROM PARTS OF EASTERN TX INTO WESTERN LA AND SOUTHERN AR.  THE
EAST-CENTRAL AND SOUTHEASTERN TX REGION INTO WESTERN LA IS
PARTICULARLY WORRISOME..WITH THE NORTHEAST-SOUTHWEST CONVECTIVE
LINE SLOWER TO PROGRESS SOUTH AND EAST..AND WITH A GREATER
POTENTIAL FOR CELL TRAINING WITHIN THIS LINE.  HIRES
GUIDANCE..INCLUDING RECENT HRRR RUNS..POINT TO THE HEAVIEST
RAINFALL POTENTIAL FROM EASTERN/SOUTHEASTERN TX INTO LA..AND SEE
LITTLE TO REASON TO GO AGAINST THIS IDEA..WITH CURRENT RADAR
IMAGERY/TRENDS ALSO SUPPORTING THIS.  THE CONVECTIVE LINE WILL BE
MORE PROGRESSIVE THRU AR..BUT STILL SOME INTENSE RAINFALL RATES
SUPPORT MAINTAINING AT LEAST A SLIGHT RISK THIS AREA.  PREVIOUS
DISCUSSION FOLLOWS...

TERRY

1500 UTC UPDATE

CHANGES TO THE PREVIOUS DAY 1 EXCESSIVE RAINFALL POTENTIAL OUTLOOK
WERE TO EXPAND THE MODERATE RISK AREA BACK TO THE NORTH AND
NORTHWEST ACROSS NORTHEAST TEXAS INTO FAR SOUTHEAST OK AND
SOUTHWEST AR.  THIS WAS FOR CURRENT RADAR TRENDS THAT DO SHOW
ORGANIZED CONVECTION FORMING AHEAD OF THE WELL DEFINED VORT
FORECAST TO LIFT NORTHEASTWARD FROM WEST TX INTO CENTRAL OK
MONDAY---AND FOR THE IN SITU LOWER FFG VALUES ACROSS THESE AREAS.
AS MENTIONED IN THE PREVIOUS DISCUSSION---THERE ARE DIFFERENCES IN
THE CURRENT MODELS WITH RESPECT TO WHETHER THERE WILL BE ONE---OR
TWO PRECIPITATION MAXIMUM OVER THE SOUTHERN PLAINS.  THE HI RES
ARW AND NSSL WRF---WHICH WERE EMPHASIZING MORE THE SOUTHERN
MAXIMA---DO NOT APPEAR TO BE HANDLING THE CURRENT CONVECTION
MOVING OUT OF SOUTHWEST TO WEST TX.  THE CMC GEM---NAM CONEST DO
SEEM TO HANDLE THE CURRENT NORTHERN MAX WELL---GIVING MORE
CONFIDENCE THAT THERE MAY BE HEAVIER TOTALS IN THE NORTHERN MAX
AND A GREATER RISK OF PRECIP TOTALS EXCEEDING FFG VALUES.  THIS
DOES NOT PRECLUDE THAT A SOUTHERN MAX WILL DEVELOP---WHICH DOES
HAVE SUPPORT IN THE HI RES NMMB AND MANY OF THE HI RES ENSEMBLE
MEANS AND THE HI RES ARW AND NSSL WRF.

OTHER CHANGES TO THE PREVIOUS OUTLOOK WERE TO EXPAND THE EASTERN
EDGE OF THE SLIGHT RISK AREA INTO MOST OF EASTERN MS AND WESTERN
AL. SLOW MOVING AREAS OF CONVECTION OR CONVECTION TRAINING IN A
GENERAL SOUTH TO NORTHERLY DIRECTION MAY PRODUCE ISOLATED RUNOFF
ISSUES DESPITE RELATIVELY HIGH FFG VALUES.

ORAVEC


...SOUTHERN PLAINS EAST INTO THE LOWER MS VALLEY AND SOUTH TOWARD
THE WESTERN AND CENTRAL GULF COAST...

THE NEXT UPPER LEVEL JET STREAK AND ASSOCIATED SHORTWAVE ROUNDING
THE BASE OF THE BROAD TROUGH IS CURRENTLY DIVING ESE TOWARD THE TX
BIG BEND. IN RESPONSE TO THE APPROACHING WAVE...LOW-MID LEVEL
WARM/MOISTURE ADVECTION DEVELOPS IN WEST TEXAS AND INCREASES
HEADING INTO CENTRAL TEXAS THIS AFTERNOON.  RAINFALL AMOUNTS AND
COVERAGE INCREASE AS THE AFTERNOON PROGRESSES...WITH AN AREA OF
MODERATE TO HEAVY RAIN EXPECTED TO DEVELOP.

THE MODEL GUIDANCE IS SPLIT IN TERMS OF WHERE THE AXIS OF HEAVIEST
RAIN WILL FALL. THE GLOBAL GUIDANCE CONTINUES TO BE FARTHER NORTH
ACROSS THE ARKLATEX NORTHEAST TOWARD THE THE MO/AR BORDER. MUCH OF
THE MESOSCALE GUIDANCE IS FARTHER SOUTH TOWARD THE GULF COAST...IN
LIGHT OF THE INCREASING LLJ OVERNIGHT AND (THUS) MORE UPWIND
PROPAGATION (S-SW) TOWARD THE GULF COAST WHERE THE GREATER
DEEP-LAYER INSTABILITY WILL RESIDE (MODEL MUCAPES BECOME 2X AS
HIGH NEAR THE GULF COAST COMPARED TO AREAS FARTHER NORTH). PRIOR
TO THE UPTICK IN LOW-LEVEL FLOW (NOCTURNALLY-ENHANCED OVERNIGHT).
PER THE NSSL-WRF AND WRF-ARW SIMULATED REFLECTIVITY GUIDANCE...
CELL MOTION FARTHER NORTH (ARKLATEX NORTHWARD) WILL BE MORE
NORTHEAST OR DOWNWIND PROPAGATING...MORE IN LINE WITH THE MEAN
850-300FF MB FLOW...GIVEN THE NOT-AS-ROBUST LOW-LEVEL INFLOW.

THE MODELS DO SHOW ENHANCED QG FORCING OVER THE AFOREMENTIONED
NORTHERN AREA...I.E. ENHANCED UPPER DIVERGENCE AND ASSOCIATED
LOW-MID LEVEL FRONTOGENESIS WITHIN THE RRQ OF A DEVELOPING (ALBEIT
SUBTLE) UPPER LEVEL JET STREAK ACROSS THE MIDWEST. FOR THIS
REASON...COULD CERTAINLY SEE AREAL-AVERAGE AMOUNTS WITHIN THE
0.50-1.5+ INCH RANGE ALONG THE ARKLATEX NORTHEAST TOWARD THE MO/AR
BORDER...HOWEVER...GIVEN THE TRENDS (GROWING CONSENSUS) AMONG THE
MULTIPLE HIGH RESOLUTION MODELS...HAVE NOTED A BROADER HIGHER
MAXIMA (1.5-2.5+ INCHES) FROM EASTERN TX ALONG THE GULF COAST INTO
WESTERN LA.

BECAUSE OF THE SPREAD IN THE GUIDANCE...WPC WILL MAINTAIN A BROAD
"SLIGHT RISK" REGION FOR EXCESSIVE RAINFALL ACROSS EASTERN
PORTIONS OF THE SOUTHERN PLAINS INTO THE LOWER MS VALLEY FOR THE
NEW DAY 1 EXCESSIVE RAINFALL OUTLOOK (12Z MON - 12Z TUE).
HOWEVER...HAVE DROPPED THE NORTHERN EDGE OF THE MODERATE RISK AREA
A BIT SOUTH FROM THE PREVIOUS (DAY 2) OUTLOOK...AGAIN BASED ON THE
SIGNAL OF WHERE THE BULK OF THE HEAVIEST RAINFALL RATES AND CELL
TRAINING WILL OCCUR WITH THE ANTICIPATED MCS LATER THIS AFTERNOON
INTO EARLY TUE.

HURLEY
$$





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