Quantitative Precipitation Forecast
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FOUS30 KWBC 020057
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
857 PM EDT SUN MAY 01 2016

...VALID 01Z MON MAY 02 2016 - 12Z MON MAY 02 2016...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
20 NNW ACP 15 SW BTR 20 WSW MSY 10 WNW KXPY 15 NNE KSPR
15 NNE KCRH 15 NNW KGVX 10 S SGR 15 SE UTS 35 NNE JAS 20 NNW ACP.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
20 S PKB CKB 20 ESE EKN 10 SE HSP 20 ENE MKJ 20 NNE LNP
20 SSE HTS 20 S PKB.

MODERATE RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
15 WNW KCMB 10 SSW GLS 15 NNE EFD 25 NNW BPT 25 S ACP
15 NNW PTN 25 ENE SRN 15 WNW KCMB.




...SOUTHERN PORTIONS OF THE OHIO VALLEY INTO THE CENTRAL
APPALACHIANS...

SHOWERS AND THUNDERSTORMS HAVE BECOME MORE NUMEROUS LATE THIS
AFTERNOON ACROSS NORTHERN KY AND WESTERN WV... WITHIN AN
INCREASINGLY DIFFLUENT PATTERN ALOFT AHEAD OF A SHORTWAVE IN IOWA
AND SOUTH OF A SHORTWAVE
ACROSS SOUTHEAST ONTARIO. PRECIPITABLE WATER VALUES ARE RELATIVELY
LOW...GENERALLY BETWEEN 1.00-1.25" PER THE LATEST GPS VALUES.
DAYTIME RANGE PER GPS VALUES. QUITE A FEW BREAKS IN THE CLOUD
COVER EARLIER IN THE AFTERNOON HAS ALLOWED FOR INCREASED
DESTABILIZATION AS SURFACE-BASED CAPES HAVE CLIMBED BETWEEN
1000-2000 J/KG PER THE SPC MESOANALYSIS. SOUTHWESTERLY LOW-LEVEL
INFLOW INTO A QUASI-STATIONARY LOW LEVEL BOUNDARY HAS INCREASED TO
AROUND 20 KTS PER VAD WIND PROFILES...WITH SUFFICIENT DIRECTIONAL
AND SPEED SHEAR ALOFT TO FAVOR CONTINUED FORWARD (DOWNWIND)
PROPAGATION. HOWEVER...WITH THE SLOW MOVING SURFACE
BOUNDARY...CELL MERGERS AND AND VERY SHORT PERIODS OF TRAINING
HAVE RESULTED IN 1-1.5" AN HOUR RAIN RATES PER RADAR IMAGERY.
GIVEN THE TOPOGRAPHY...ANTECEDENT SATURATED SOILS...AND THUS VERY
LOW FFG (1" OR LESS WITHIN 3 HOURS)...SOME EXCESSIVE RUNOFF IS
ANTICIPATED WHERE THE CELLS MERGE/TRAIN. THE LATEST SSEO GUIDANCE
IN FACT SHOWS AN UPTICK IN PROBABILITIES OF 3 HOURLY QPF EXCEEDING
3 HOURLY FFG WITHIN THE OUTLOOK AREA (BETWEEN 30-60%) THROUGH
02-04Z...OR PRIOR TO THE LOSS OF FAVORABLE DEEP-LAYER INSTABILITY.


...UPPER TX COAST---CENTRAL TO SOUTHERN LA INTO SOUTHWEST MS...

THE EXCESSIVE RAINFALL THREAT CONTINUES THROUGH THIS AFTERNOON
ALONG AND NEAR THE GULF COAST FROM THE UPPER TX COAST---ACROSS
CENTRAL TO SOUTHERN LA AND INTO SOUTHERN MS.  THE FORECAST BACKING
OF THE LOW LEVEL FLOW TO A MORE SOUTHERLY DIRECTION OFF THE GULF
OF MEXICO IS ALREADY FIRING CONVECTION ACROSS THE UPPER TX COAST
INTO SOUTHERN LA.  CONVECTION LIKELY TO REMAIN ACTIVE ALONG AND TO
THE SOUTHEAST OF THE SLOW MOVING FRONTAL BOUNDARY STRETCHING FROM
SOUTHEAST TX INTO THE LOWER MS VALLEY THIS PERIOD AS THIS MOIST
ONSHORE FLOW PERSISTS ALONG WITH FAVORABLE UPPER DIFFLUENCE AND
UPPER DIVERGENCE/LOW LEVEL MOISTURE CONVERGENCE MAXIMA CROSSING
THE REGION...AS SHOWN IN THE SPC MESOSCALE ANALYSIS.

THERE IS A MODEL SIGNAL FOR HEAVY TO EXCESSIVE RAINFALL AMOUNTS
ACROSS THESE AREAS.  THE 08-12Z RUNS OF THE HIGH RES RAPID REFRESH
AND EXPERIMENTAL RUNS...ALONG WITH WITH THE 00Z RUN OF THE SPC WRF
TO SHOW 2-4 INCHES OF RAIN WITH ISOLATED TOTALS OF 6 INCHES.  THE
0000 HI RES NSSL WRF DEVELOPED THE ACTIVITY FURTHER SOUTH IN THE
GULF SO WITH ACTIVITY ALREADY HAVING DEVELOPED INLAND LOOKS TO BE
THE LEAST RELIABLE OF THE GUIDANCE SUITE.

WITH THE RECENT VERY HEAVY RAINFALL EVENT OVER PORTIONS OF
SOUTHEAST TX INTO SOUTHERN LA HAVING LOWERED FFG VALUES---FLOODING
SHOULD OCCUR WHERE SLOW MOVING CELLS PRODUCE 2" PER HOUR RATES.
SOUTHEAST PROPAGATION SHOULD BRING THE CELLS INTO THE COASTAL
WATERS LATER THIS AFTERNOON AND EVENING...SO THE EXCESSIVE RAIN
THREAT SHOULD WIND DOWN THEN.

PETERSEN/HURLEY
$$





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