Quantitative Precipitation Forecast
Issued by NWS

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000
FOUS30 KWBC 020108
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
907 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 HAD BECOME MORE NUMEROUS LATE IN THE
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 (18Z) 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...

0100 UTC UPDATE...

THE EXCESSIVE RAINFALL THREAT CONTINUES THROUGH THE OVERNIGHT
ALONG AND NEAR THE GULF COAST FROM THE UPPER TX COAST---ACROSS
CENTRAL TO SOUTHERN LA AND INTO SOUTHERN MS. 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 CONTINUES TO BE A MODEL SIGNAL FOR HEAVY TO EXCESSIVE
RAINFALL AMOUNTS ACROSS THESE AREAS...WITH BETTER HIGH-RES CAM
CONSENSUS FOR A POCKET OF 3-6+ INCHES ACROSS THE UPPER TX COAST
(TO INCLUDE THE HOUSTON/GALVESTON AREA) PER RECENT
HRRR...EXPERIMENTAL HRRR...AND NAM CONEST RUNS.

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.
THE LATEST (18Z) SSEO GUIDANCE SHOWS PROBABILITIES OF 3 HOURLY QPF
EXCEEDING 3 HOURLY FFG CLIMBING BETWEEN 60-80% WITHIN THE MODERATE
RISK AREA AFTER 09Z.

HURLEY
$$




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