Quantitative Precipitation Forecast
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FOUS30 KWBC 180007
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
805 PM EDT WED AUG 17 2016

...VALID 01Z THU AUG 18 2016 - 12Z THU AUG 18 2016...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
10 SSE KMIU 20 W EBG 45 N MMAN 10 NNE MMMV 110 SSW 6R6
45 SE E38 30 NE FST 10 NNW ABI 15 WSW GYI 10 NW M89 35 NE LLQ
15 ENE GLH 25 SE GLH 25 SSW HKS 20 NNW MCB 25 SE BTR SRN.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
75 E MQI 10 E FVX 15 NNE ROA 15 NW BCB 25 NW LWB 20 S MGW AOO
15 ENE THV 15 E ACY 120 ESE ACY.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
10 ESE CGE 25 WSW MFV FYJ 15 SE LKU 10 SW OMH 25 WNW CJR
15 SSE MRB 10 SSE FDK MTN 10 S RJD 10 ESE CGE.


...TEXAS/LA/AR...

FOR THE REMAINDER OF THE OVERNIGHT...NOCTURNAL CONVECTION WITHIN
AXIS OF UNSEASONABLY HIGH PWS WITH ANOMALIES OF 2-3 STD DEVIATIONS
ABOVE NORMAL IN THE RIO GRANDE VALLEY OF CENTRAL TEXAS...IS
EXPECTED TO BE RATHER DISORGANIZED OWING TO LACK OF WELL DEFINED
MID/UPR FORCING OR LOW LEVEL FOCUS.  THAT SAID..WITH RATHER LIGHT
DEEP LAYERED FLOW ANY STORMS THAT DVLP OVERNIGHT WITHIN AXIS OF 2
TO 2.25+" PWS WILL BE CAPABLE OF PRODUCING SOME LOCALIZED HEAVY
RAIN RATES WITH HI RES MODEL GUIDANCE INDICATING SOME VERY ISOLD
AREAS OF 2`+ RAINS ACRS PORTIONS OF CNTL TX INTO THE THE ARKLATEX
REGION OVERNIGHT.  GIVEN THE LARGER SEPARATION OF EXPECTED HEAVIER
RAIN AREAS OVERNIGHT WITH LOSS OF DAYTIME HEATING...HAVE LOWERED
EXCESSIVE THREAT TO MARGINAL FOR THE REMAINDER OF THE OVERNIGHT
PD.


...MID ATLANTIC AND CENTRAL APPALACHIANS...

0100 UTC UPDATE...HAVE SHORTENED WRN EXTENT OF MARGINAL AREA WEST
OF THE APLCNS WITH CONTINUED PROGRESSION OF ORGANIZED CONVECTIVE
AREA ACRS THE MID ATLC REGION WITH SLIGHT RISK REMAINING FOR A FEW
HOURS THIS EVENING THROUGH PARTS OF CNTL MD INTO NRN VA AND THE
WRN DELMARVA AS STORMS ROLLING EAST OF THE BLUE RIDGE TAP RESIDUAL
AFTN CAPE ENERGY STRADDLING WEAK E/W FRONTAL BNDRY THRU THE REGION
AIDED BY WEAK S/WV ENERGY DROPPING SEWD FROM THE OH VALLEY.  SEE
MPD#573 IN EFFECT UNTIL 04Z FOR FURTHER INFORMATION ACRS THIS
AREA. PREVIOUS DISCUSSION FOLLOWS...

AT 15Z WE INTRODUCED A SLIGHT RISK OVER THE MID ATLANTIC AFTER
MAKING SOME ADJUSTMENTS TO THE EXPECTED QPF AND THROUGH
COORDINATION WITH LOCAL OFFICES. IN THE 18Z QPF RELEASE WE WILL BE
NUDGING THE AXIS OF HEAVIEST RAIN NORTHWARD WHERE THE MAJORITY OF
HI-RES GUIDANCE HAS IT FROM NOVA THROUGH THE DC AREA AND ANAPOLIS
TO THE EASTERN SHORT OF MD. A SECONDARY MAXIMUM...HOWEVER...IS
EXPECTED DOWN TOWARD RICHMOND...WHILE A THIRD LOCAL MAXIMUM IS
EXPECTED OVER WEST VIRGINIA. THE STRONG WAVE EXITING NEW ENGLAND
HAD VEERED WINDS SUCH THAT A TROUGH AXIS AND CAPE AXIS WILL BECOME
ORIENTED FROM CENTRAL VA UP THROUGH EASTERN MD TODAY. SUFFICIENT
MOISTURE AND INSTABILITY EXISTS BACK WEST OF THE TROUGH
AXIS...HOWEVER...FOR THUNDERSTORMS TO ROLL OFF THE HIGHER TERRAIN
AND MERGE WITH ANY ACTIVITY OCCURRING DOWN IN THE COASTAL PLAIN.
DEEP WESTERLY FLOW SHOULD YIELD FAIRLY QUICK INDIVIDUAL STORM
MOTIONS...BUT THE PROSPECT FOR CELL MERGERS IN A VERY MOIST
ENVIRONMENT RAISES THE POSSIBILITY OF ISOLATED INTENSE SHORT TERM
RAIN RATES. WHAT PUSHES THIS BEYOND MARGINAL AND INTO THE SLIGHT
RISK CATEGORY IS THE PERSISTENT SYNOPTIC LIFT THAT WILL ACCOMPANY
A SHORTWAVE ARRIVING THIS EVENING...SUCH THAT MULTIPLE ROUNDS OF
STORMS MAY AFFECT SOME AREAS...AS INDICATED BY ENSEMBLE
PROBABILISTIC QPF OUTPUT WHICH SHOWS SOME NON-DIURNAL
TRENDS...PEAKING AROUND 3-6Z. FLASH FLOOD GUIDANCE VALUES ARE ALSO
RELATIVELY LOWER WITHIN THE SLIGHT RISK AREA...AND ALSO BACK
ACROSS WEST VIRGINIA...ALTHOUGH RESIDENCE TIME OF CONVECTION
SHOULD BE LESS THERE.




SULLIVAN/BURKE/PETERSEN
$$





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