Quantitative Precipitation Forecast
Issued by NWS

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FOUS30 KWBC 231318
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
917 AM EDT SAT MAY 23 2015

...VALID 15Z SAT MAY 23 2015 - 12Z SUN MAY 24 2015...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
35 ENE FST 30 ESE LBB 15 E BGD 20 SSW PTT 30 SSW FNB 20 NE MCI
40 SW SZL SLG 30 NNE PRX 25 ESE ACT 15 S BYY 25 SE BKS
45 SW MMNL 45 NNE MMMV 65 WSW MMPG 25 ESE 6R6 35 ENE FST.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
30 SSW CDR 25 S AIA 45 SSE SNY 10 NE ITR 35 SE LIC 25 ENE COS
DEN 15 SSE PUM 25 WSW ARL 25 SSW PAT 10 SW TMH 45 NE DGW
30 SSW CDR.

MODERATE RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
10 ESE UKL 20 ENE CNU 20 SE CFV 30 NNW MLC 30 E AQR 15 ESE GLE
15 E SEP 20 E AUS 40 NNW VCT 15 N RBO 10 SSW MMNL 60 W MMNL MMPG
25 N DRT 20 NNW E29 30 WSW SJT 25 SW SWW 50 SSE CDS 35 SSE HHF
25 SSE WWR 30 NNW WDG 30 SSW EMP 10 ESE UKL.

HIGH RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
45 SE MMPG 25 WSW ERV 10 W T82 20 E T82 10 N SAT 35 SSW SSF
15 NE LRD 20 WNW MMNL 45 SE MMPG.



...HEAVY RAINFALL EVENT ACROSS MUCH OF THE SOUTHERN TO SOUTH
CENTRAL PLAINS...

I UPGRADED THE EXCESSIVE RAINFALL RISK TO HIGH OVER PARTS OF SOUTH
TEXAS BASED ON INCREASING AGREEMENT AMONG THE HIGH RESOLUTION
MODELS OF HEAVY RAIN THERE WITH FAVORABLE AVAILABLE INSTABILITY
AND ANOMALOUSLY HIGH AVAILABLE MOISTURE/HIGH FORECAST MOISTURE
FLUXES...AND ANOTHER RECENT ROUND OF SHOWERS/STORMS TO LOWER THE
RAINFALL NEEDED TO CAUSE FLOODING.
MULTIPLE HIGH RESOLUTION MODELS INCLUDING THE NAM
CONEST...WRF-ARW...WRF-NMMB...NSSL-WRF BRING HEAVIER RAINFALL
AMOUNTS ACROSS SOUTH TEXAS AND HAVE BEEN JOINED BY THE 10-11Z HIGH
RES RAPID REFRESH RUNS.  THE HIGH RES MODELS FORECAST THE HIGHEST
TOTALS IN SOUTH TEXAS OF 3-6 INCHES...WITH LOCALLY HIGHER TOTALS.

THE INITIAL CLUSTER OF SHOWERS AND STORMS MOVES OUT ACROSS OK THIS
AFTERNOON AND TONIGHT. THEN THERE IS EXPECTED TO BE A LARGE
SCALE...SLOW MOVING BAND OF HEAVY SHOWERS AND THUNDERSTORMS THIS
EVENING AND OVERNIGHT IN CENTRAL TO SOUTHERN TX. CONSIDERING THE
ANTECEDENT SATURATED SOILS AND LOW FFG ON BOTH SIDES OF THE RED
RIVER ACROSS SOUTHERN-CENTRAL OK AND NORTHERN TX AND ALSO IN
SOUTHERN TEXAS...THE POTENTIAL FOR ADDITIONAL FLASH FLOODING OVER
THESE AREAS WILL BE ENHANCED.

INCREASED S-N UPPER CONFLUENCE EAST OF THE UPPER TROUGH WILL
INDUCE AN ANOMALOUS 90-100 KT SOUTHERLY 250 MB JET STREAK ACROSS
THE SOUTHERN-CENTRAL HIGH PLAINS...ONE WHICH BY LATE IN THE PERIOD
WOULD PROVIDE AN ADDITIONAL BOOST TO THE ALREADY ROBUST UPPER
LEVEL DIVERGENCE AND DEEP-LAYER ASCENT WITHIN ITS RIGHT ENTRANCE
REGION ACROSS THE SOUTHERN PLAINS.

THE MESOSCALE GUIDANCE SUGGESTS MULTIPLE ROUNDS OF CLUSTERED
CONVECTION. THE STRENGTHENING LOW LEVEL INFLOW (45-50 KT SOUTHERLY
LLJ ~850 MB) AND ANOMALOUS 850-700 MB MOISTURE TRANSPORT FROM THE
WESTERN GULF WILL BOOST PW VALUES BETWEEN 1.75-2.00+ INCHES...OR
2-2.5 STANDARD DEVIATIONS ABOVE THE NORM PER THE SREF/GEFS
ENSEMBLES. MODERATE DEEP-LAYER INSTABILITY (MUCAPES 1000-2000
J/KG) WILL BE IN PLACE THIS EVENING AND OVERNIGHT ACROSS THE
SOUTHERN PLAINS...SO CELLS DEVELOPING IN THE REGION WILL HAVE
POTENTIAL TO PRODUCE RAINFALL RATES TO 2 INCHES PER HOUR.


...HIGH PLAINS OF NORTHEAST CO/WESTERN NEBRASKA/SOUTHEAST WY...

I EXPANDED THE SLIGHT RISK AREA SOUTH IN NORTHEAST CO AS THE FRI
NIGHT CLUSTER OF HEAVY SHOWERS/STORMS MAKE THE AREA MORE
VULNERABLE TO FLOODING TODAY AND TONIGHT...WITH THE MODELS
FORECASTING ADDITIONAL ROUND OF SHOWERS/POSSIBLE STORMS THIS
AFTERNOON AND EVENING.

AMPLIFYING UPPER TROUGH INCREASES THE UPPER DIFFLUENCE. THE
DEVELOPING S-N UPPER LEVEL JET STREAK ACROSS THE SOUTHERN-CENTRAL
HIGH PLAINS ON THE EASTERN EDGE OF THE TROUGH WILL ENHANCE THE
UPPER DIVERGENCE AND DEEP-LAYER ASCENT ACROSS THE OUTLOOK AREA IN
THE LEFT EXIT REGION. THE FAVORABLE DYNAMICAL PROFILE ALONG WITH
THE 20-30 KT SOUTHEASTERLY (UPSLOPE) LOW-LEVEL INFLOW...ANOMALOUS
MOISTURE FLUX/PW VALUES...AND AVAILABLE DEEP-LAYER INSTABILITY
(MUCAPES 500-1500 J/KG) WILL LEAD TO AREAS OF HEAVY TO POTENTIALLY
EXCESSIVE RAINFALL.  ADDITIONAL SHOWERS/STORMS ARE EXPECTED THIS
AFTERNOON AS 700 MB CONVERGENCE MAXIMA MOVE THROUGH THE AREA.
AREAL-AVERAGE AMOUNTS ARE EXPECTED TO RANGE AROUND 1-1.25 INCH.
PER THE HIGHER RESOLUTION GUIDANCE...ISOLATED HIGHER AMOUNTS OF
2-3+ INCHES WITHIN A 6-12 HOUR PERIOD WOULD LEAD TO LOCALIZED
RUNOFF ISSUES CONSIDERING THE RELATIVELY LOW FFG VALUES IN THE
AREA.

PETERSEN/HURLEY
$$





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