Quantitative Precipitation Forecast
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FOUS30 KWBC 261439
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1038 AM EDT WED APR 26 2017

...VALID 15Z WED APR 26 2017 - 12Z THU APR 27 2017...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
50 NE PVC SFM AUG 25 WNW CWSS 25 NE CWSS 15 ENE CWPE CWVU.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
GWO 40 WSW MLU 35 SE GGG 20 E CRS LNC GVT 20 SW RKR FYV
35 ENE SGF 30 SW PPQ 10 NW PPQ 30 NE GBG 15 E DLL 25 WNW MKG
15 E LWA 15 NNE HUF 20 ENE M30 10 SSE CKV 40 NNE TUP 30 WSW TUP
GWO.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
15 SSE IGQ 25 S VPZ 15 E DNV 20 NW RSV 20 NNE CIR 30 N DYR
10 E MKL 30 ESE OLV 45 SE UTA 15 NE BQP 35 E BAD 10 W GGG
10 NE TYR 3T1 10 S SLR 25 N DEQ HRO 40 SE VIH 10 SSW STL STL
20 WSW TAZ PNT C09 15 ESE JOT 15 SSE IGQ.


1500 UTC UPDATE

CHANGES TO THE PREVIOUS EXCESSIVE RAINFALL POTENTIAL OUTLOOK WERE
TO EXTEND THE MARGINAL AND SLIGHT RISK AREAS APPROXIMATELY 100 NM
FARTHER TO THE SOUTHWEST INTO FAR SOUTHERN ARKANSAS...FAR
NORTHEAST TX AND FAR NORTHERN LOUISIANA.  THIS IS TO COVER SOME OF
THE FARTHER SOUTH QPF SOLUTIONS...ESPECIALLY THE NAM CONEST WHICH
SEEMS TO BE VERIFYING WELL SO FAR WITH THE CURRENT ORGANIZED
CONVECTION OVER THE SOUTHERN PLAINS.  THE LATEST 1200 UTC NAM
CONEST HAS TRENDED SLIGHTLY FARTHER SOUTH WITH THE HEAVY RAINFALL
FROM ITS 0600 UTC RUN---SHOWING HEAVY TOTALS INTO NORTHERN LA.
ELSEWHERE---NO CHANGES WERE MADE TO THE REMAINDER OF THE RISK
AREAS.  PLEASE SEE WPC`S MESOSCALE PRECIPITATION DISCUSSION #0148
VALID UNTIL 1820 UTC FOR ADDITIONAL INFORMATION.

ORAVEC


INITIAL DISCUSSION

...EASTERN OK INTO THE LOWER/MID MS VALLEY AND PORTIONS OF THE
OH/TN VALLEY...

AS OF 08Z CONVECTION IS ONGOING ALONG A NORTHEAST TO SOUTHWEST
ORIENTED LINE ACROSS PORTIONS OF MO...EASTERN OK AND NORTHWEST AR.
THE APPROACH OF ADDITIONAL SHORTWAVE ENERGY AND INCREASED UPPER
LEVEL DIFFERENCE SHOULD LEAD TO ADDITIONAL CONVECTIVE DEVELOPMENT
INTO EARLY MORNING ACROSS PORTIONS OF EASTERN OK INTO WESTERN AR
AND SOUTHERN MO. EXPECT THAT THERE COULD BE A PERIOD OF TRAINING
CONVECTION THIS MORNING INTO EARLY AFTERNOON ACROSS PORTIONS OF
FAR EASTERN OK INTO CENTRAL AND NORTHERN AR. IT IS HERE WHERE
THERE IS A PERIOD LATER TONIGHT INTO WEDNESDAY MORNING WHERE WE
SEE AN INCREASE IN 850 MB MOISTURE TRANSPORT CONVERGENCE...WITH
CORFIDI VECTORS GENERALLY PARALLEL TO THE ORIENTATION OF THE
CONVERGENCE AXIS. THIS SUGGEST WE COULD SEE SOME WEST TO EAST
TRAINING FOR A PERIOD INTO EARLY WEDNESDAY AFTERNOON. EXPECTING
AREAL AVERAGED RAINFALL OF 1-3" ACROSS THIS AREA...WITH LOCALIZED
3-5" AMOUNTS PROBABLE. BY EARLY TO MID AFTERNOON THE WAVE AND
FRONT BECOME MORE PROGRESSIVE ACROSS THIS REGION AND THE
ORIENTATION OF THE FRONT AND LOW LEVEL MOISTURE TRANSPORT BECOME
MORE SUGGESTIVE OF A PROGRESSIVE EASTWARD MOVING CONVECTIVE LINE.
THIS SHOULD HELP KEEP AMOUNTS FROM GETTING TOO EXTREME ACROSS
OK/AR. THIS LINE WILL MOVE INTO WESTERN TN BY THIS EVENING. THE
LINE SHOULD BE PROGRESSIVE BY THIS TIME...BUT HEAVY RAINFALL RATES
ARE STILL LIKELY WHICH COULD RESULT IN SOME LOCALIZED FLASH FLOOD
ISSUES IN MORE SUSCEPTIBLE AREAS. HAVE A SLIGHT RISK FOR LOCATIONS
THAT SHOULD SEE THE HIGHEST RAINFALL TOTALS FROM EASTERN OK INTO
CENTRAL/NORTHERN AR AND FAR WESTERN TN.


ALSO COULD SEE SOME TRAINING FROM SOUTHEAST MO INTO SOUTHERN
IL...AS THIS AREA CURRENTLY APPEARS TO BE NEAR THE PIVOT POINT OF
CONVECTION AS THE SYSTEM BECOMES MORE NEUTRAL TO NEGATIVELY TILTED
THIS AFTERNOON. THUS WOULD EXPECT A LONGER DURATION OF CONVECTIVE
ACTIVITY ACROSS THIS AREA...ALTHOUGH THE PROGRESSIVENESS OF THE
WAVE WILL EVENTUALLY PUSH THE FRONT EASTWARD AND END THE
CONVECTIVE THREAT EARLY TONIGHT. A PRETTY STRONG HIGH RES MODEL
SIGNAL FOR LOCALIZED 3-5" AMOUNTS IN THIS AREA TODAY..AND THUS
WILL EXTEND THE SLIGHT RISK TO INCLUDE THIS REGION. WILL CARRY A
MARGINAL RISK FURTHER NORTH ACROSS NORTHERN IL INTO SOUTHERN WI.
THINK THE HEAVIEST CONVECTIVE ACTIVITY WILL REMAIN SOUTHEAST OF
THIS AREA AS SUGGESTED BY ALL THE HIGH RES CAM GUIDANCE. THINK
MOST OF THE GLOBAL MODELS ARE A BIT TOO HEAVY WITH QPF AMOUNTS
ACROSS THIS AREA...LIKELY NOT PROPAGATING CONVECTION CORRECTLY OFF
TO THE EAST WITH TIME...AND THUS MOVING THE HEAVIER AMOUNTS MORE
DUE NORTH. PREFER TO LEAN OUR FORECAST MORE IN THE DIRECTION OF
THE MORE PROGRESSIVE 12Z ECMWF...0Z WRF ARW...NSSL WRF AND THE
PARALLEL NMMB (WHICH IS MORE PROGRESSIVE THAN THE OPERATIONAL
NMMB).

...SOUTHERN MAINE...

THE SLOW MOVING CLOSED LOW WILL MOVE OFF OF SOUTHERN NEW ENGLAND
TODAY. STRONG SOUTHERLY FLOW AND ANOMALOUS PRECIPITABLE WATER
VALUES APPROACHING 3 STANDARD DEVIATIONS ABOVE THE CLIMATOLOGICAL
MEAN WILL RESULT IN CONTINUED SHOWERY CONDITIONS INTO MAINE TODAY.
A LACK OF INSTABILITY WILL KEEP RAIN RATES IN CHECK (GENERALLY
BELOW 0.25" IN AN HOUR)...AND GENERALLY LOOKING AT AREAL AVERAGED
AMOUNTS AROUND 1" ALONG THE MAINE COASTLINE...WITH ISOLATED
AMOUNTS UP TO 2" POSSIBLE. NOT EXPECTING SIGNIFICANT ISSUES FROM
THIS RAINFALL...BUT COULD SEE SOME PONDING OF WATER AND OTHER
MINOR ISSUES. THUS WILL CONTINUE TO CARRY THE MARGINAL RISK OVER
FROM THE PREVIOUS DAY 2 OUTLOOK.

CHENARD

$$




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