Quantitative Precipitation Forecast
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000
FOUS30 KWBC 170101
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
900 PM EDT SUN APR 16 2017

...VALID 01Z MON APR 17 2017 - 12Z MON APR 17 2017...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
20 S EKN 20 SW I16 15 WNW 1A6 BNA 15 E MKL 15 NNW SGT
30 SSW M89 15 ENE GGG 15 NNW LHB 20 W 3T5 RBO 20 WSW BKS
45 SSW HBV 30 S MMNL 45 WNW LRD 10 SSE MMPG 20 WSW DRT 45 S 6R6
10 NNW 6R6 60 NNE 6R6 35 S BPG 20 ENE SNK 40 E PVW 40 ESE PPA
25 NNW WWR 15 SW HUT 35 SSW IXD 15 ENE AIZ 30 ESE FAM 10 SW EHR
25 ENE LOU 20 SSE LHQ 15 WSW AFJ 20 SE LBE 20 SSE 2G4 20 S EKN.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
20 SSW CYCX 10 N CWSS 40 W CWSS 20 SE GNR 25 E CWHV 30 SE CWIG
35 W FVE 20 NE CYSL.


...01Z UPDATE...

THE LATEST EXCESSIVE RAINFALL OUTLOOK CONTINUES TO MAINTAIN AN
EXPANSIVE MARGINAL RISK AREA GIVEN SCATTERED TO NUMEROUS CLUSTERS
OF THUNDERSTORMS EXTENDING FROM THE OH VALLEY SOUTHWEST INTO THE
MID MS VALLEY AND SOUTHERN PLAINS. THE RISK AREA HAS BEEN ADJUSTED
FARTHER WEST ACROSS TX GIVEN THE WESTWARD EXTENT OF LOW LEVEL
MOISTURE THIS EVENING AND A VERY STRONG INSTABILITY GRADIENT WHERE
CONVECTION HAS BEEN FOCUSING OVER THE LAST COUPLE OF HOURS. THE
CONVECTION OVER THE OH VALLEY SHOULD TEND TO RELATIVELY
PROGRESSIVE AND SHOULD WEAKEN OVERNIGHT GIVEN A LOSS OF DAYTIME
HEATING...BUT STILL MAY RESULT IN SOME ISOLATED RUNOFF/FLASH FLOOD
CONCERNS OVER THE NEXT COUPLE OF HOURS. HOWEVER...DOWN ACROSS
AREAS OF THE TX HILL COUNTRY AND TOWARD THE RIO GRANDE VALLEY NEAR
AND EAST OF THE BIG BEND AREA...CONVECTION IS EXPECTED TO BECOME
MORE ORGANIZED AS AN ELONGATED AXIS OF SHORTWAVE ENERGY EJECTS
EAST FROM EASTERN NM/WEST TX AND FAR NORTHERN MX. RECENT HRRR
GUIDANCE CONTINUES TO ADVERTISE HEAVY RAINFALL HERE OVERNIGHT.

ORRISON

PREVIOUS DISCUSSION...

OH VALLEY---MID MS VALLEY INTO PORTIONS OF THE SOUTHERN PLAINS

A VERY LARGE MARGINAL RISK AREA WAS MAINTAINED FOR THE UPCOMING
DAY 1 FORECAST PERIOD STRETCHING FROM THE OH VALLEY---INTO THE
MID MS VALLEY AND SOUTHWESTWARD ACROSS SOUTHERN MO---SOUTHEAST
KS---NORTHERN AR---EASTERN OK AND STRETCHING FROM NORTHEAST TO
SOUTH CENTRAL TX.   AN AXIS OF ABOVE AVERAGE PW VALUES...1-2+
STANDARD DEVIATIONS ABOVE THE MEAN WILL CONTINUE TO STRETCH ALONG
AND AHEAD OF THE FRONTAL ZONE FORECAST TO BE SETTLING SLOWLY
SOUTHWARD THROUGH PORTIONS OF THE CENTRAL TO SOUTHERN
PLAINS---LOWER MO VALLEY--MID MS VALLEY AND OH VALLEY.  IN
GENERAL---MODELS AGREE ON THE POTENTIAL FOR ACTIVE CONVECTION IN
THE VICINITY OF THIS FRONT GIVEN FAVORABLE UPPER
DYNAMICS---ABUNDANT MOISTURE AND STRONG FRONTAL CONVERGENCE AND
THE POTENTIAL FOR WIDESPREAD MODERATE TO HEAVY RAINFALL TOTALS
ACROSS THESE AREAS.  STILL A LOT OF UNCERTAINTIES EVEN IN A
PATTERN SUPPORTING ACTIVE FAIRLY LARGE SCALE CONVECTION---LEADING
TO OVERALL LOW CONFIDENCE WITH SOME OF THE SHORTER TERM DETAILS.
THE WPC QPF LEANED MORE TOWARD THE IN HOUSE ENSEMBLE MEANS TO
MITIGATE THE WIDE SPREAD IN DETAILS AT THE SHORTER TIME PERIODS.
THIS RESULTED IN A FAIRLY LARGE REGIONS OF .50-1"+ QPF AMOUNTS
STRETCHING ALONG THE OH RIVER---INTO THE MID MS VALLEY---SOUTHERN
MO---FAR SOUTHEAST KS INTO EASTERN OK.  TRAINING OF CELLS PARALLEL
TO THIS SLOW MOVING FRONTAL ZONE WILL CONTINUE TO BE A THREAT FOR
THE UPCOMING DAY 1 TIME PERIOD.

TO THE SOUTH OF THE SLOW MOVING FRONTAL ZONE---THERE IS A LOT OF
QPF DIFFERENCES STRETCHING FROM SOUTH CENTRAL TX INTO NORTHEAST
TX.  THIS REGION WILL BE ALONG THE SOUTHERN EDGE OF THE WESTERLIES
WHERE THERE IS CONSENSUS IN THE MODELS FOR SHORTWAVE ENERGY MOVING
EAST NORTHEASTWARD.  THERE WILL LIKELY BE THE POTENTIAL FOR
ORGANIZED CONVECTIVE COMPLEXES BOTH ACROSS NORTHEAST TX AND SOUTH
CENTRAL TX ALONG PORTIONS OF THE CENTRAL RIO GRANDE OF TX.
HOWEVER---CONFIDENCE IN WHERE THEY WILL OCCUR ARE EXTREMELY LOW
GIVEN LARGE RUN TO RUN VARIABILITY AMONG THE HI RES GUIDANCE AND
LARGE DIFFERENCES BETWEEN THE LATEST MODELS.  ADDING TO THE
UNCERTAINTIES IS DIFFERENT HANDLING OF THE EVOLUTION OF FRONTAL
CONVECTION FARTHER TO THE NORTH AND WHETHER ANY ORGANIZED ACTIVITY
SINKS FASTER TO THE SOUTH OF STAYS CLOSER TO THE FRONT---WITH A
VARIETY OF SOLUTIONS AVAILABLE IN THE LATEST SUITE OF GUIDANCE.
WPC QPF AMOUNTS WERE FAIRLY CONSERVATIVE GIVEN THE WIDE SPREAD IN
SOLUTIONS.  HOWEVER---THERE WILL BE THE POTENTIAL FOR HEAVY TOTALS
AND LOCAL RUNOFF ISSUES WHERE THE CONVECTIVE COMPLEXES MAXIMIZE.

NORTHERN MAINE

A SMALL MARGINAL RISK AREA WAS CONTINUED AS PER THE 15 UTC WPC
UPDATE ACROSS NORTHERN MAINE FOR THE UPCOMING DAY 1 PERIOD.
MODELS SHOW GOOD AGREEMENT IN PUSHING SURFACE LOW PRESSURE
EASTWARD FROM THE EASTERN GREAT LAKES---ACROSS NORTHERN  NY STATE
AND INTO NORTHERN NEW ENGLAND SUNDAY AND OFFSHORE INTO THE
CANADIAN MARITIMES SUNDAY NIGHT INTO EARLY MONDAY.  THERE IS
FAIRLY GOOD AGREEMENT ON THE MODERATE TO HEAVY PRECIPITATION
POTENTIAL IN THE STRONG ISENTROPIC LIFT AREA AHEAD OF THIS SURFACE
WAVE.  ISOLATED 3 HOURLY RATES OF .75-1" POSSIBLE FROM SUNDAY
AFTERNOON INTO SUNDAY EVENING ACROSS NORTHERN MAINE.  THESE
AMOUNTS WILL BE CLOSE TO THE FFG VALUES---WITH ISOLATED RUNOFF
ISSUES POSSIBLE.

ORAVEC
$$





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