Quantitative Precipitation Forecast
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FOUS30 KWBC 130830
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
429 AM EDT SUN AUG 13 2017

...VALID 12Z SUN AUG 13 2017 - 12Z MON AUG 14 2017...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
45 S OLS 65 W OLS 50 SSW CGZ 10 WSW CHD 35 SSW PRC 20 W PRC
40 NNW PRC 20 SSE 40G 15 W INW 35 N SOW 25 SSE GUP 10 E GNT
45 S ABQ 25 NNW 4CR 40 SSE LVS 15 SSW RTN 20 ENE VTP LIC
15 WSW GLD 45 NNW GCK 30 S DDC 35 NW JWG OKC 10 ENE ADH
25 NNE MLC 15 ESE FYV 30 W BVX 10 S NQA 30 W TUP 20 ENE GWO
15 NW HKS 25 NNW MCB 10 S HDC 15 NE BVE 25 SSW KMIS 20 NNW KMDJ
30 WSW 9F2 15 W P92 15 NW LFT 15 WSW DRI 20 WSW JAS 35 NE CLL
10 SW GDJ 20 N DYS 10 W SWW 40 S BPG 40 N 6R6 50 SE E38 40 S E38
100 N MMCU 105 SW MMCS 75 S DUG 45 S OLS.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
15 N RWI 15 ESE NTU 45 ENE 9W7 30 E FFA 30 NE HSE HSE 20 E MRH
SUT 20 SW MYR 40 SW MYR 25 NNW CHS OGB CAE 30 N CUB 15 S VUJ
20 NNW SOP LHZ 15 N RWI.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
20 NW PRX 20 NW MWT 10 NNW LZK 15 SSW UTA 20 SSE GLH 30 SSW MLU
30 NNE OCH 20 WSW TYR 10 SW TRL 10 NE TKI 20 NW PRX.


...01 UTC UPDATE...

MAIN ADJUSTMENT APPLIED WAS TO SHIFT THE PREVIOUSLY ISSUED
MODERATE EXCESSIVE THREAT AREA ESEWD MORE INTO SERN OK/NERN TX AT
THE EXPENSE OF W-CENTRAL OK AHEAD OF THE MAIN APPROACHING WAVE.
WPC MESOSCALE PRECIPITATION DISCUSSION #675 IS NOW ALSO BEING SENT
TO ADDRESS THE SHORT TERM CONVECTIVE ENVIRONMENT DETAILS AND
POTENTIAL. OTHERWISE...ONLY MODIFIED THE MARGINAL AND SLIGHT AREAS
OVER THE PLAINS AS WELL AS OVER THE NORTHEAST TO ACCOUNT FOR
LATEST TRENDS FROM STLT/RADAR AND THE HRRR...MOSTLY FROM
CONVECTIVE CELL PROPAGATIONS SINCE THE LAST ERO/ERD UPDATE BACK AT
15 UTC. DID NOT ADJUST THE MARGINAL AREA OVER THE SWRN US
MUCH...BUT CONVECTION ALONG/JUST SOUTH OF THE MOGGOLON RIM HAS
BEEN MORE ORGANIZED/OFFERED SOME TRAINING AND CONTINUED RUNOFF
POTENTIAL LOCALLY AS PER OUTFLOW INTERACTION...SO ADDED A SLENDER
SLIGHT RISK AREA TO ADDRESS ONGOING ACTIVITY.

SCHICHTEL


12Z RAOBS SHOWED A MOISTURE RICH ATMOSPHERE ALREADY IN PLACE OVER
MUCH OF THE EASTERN AND SOUTHERN U.S. WITH PRECIPITABLE WATER
VALUES GENERALLY RUNNING AT OR ABOVE 1.8 INCHES FROM THE MID
ATLANTIC ACROSS THE SOUTHEAST AND SOUTHERN STATES AS FAR WEST AS W
TX.

...TX AND OK TO GULF COAST...

MADE NO CHANGES TO THE PREVIOUSLY ISSUED MODERATE RISK AREA OVER
OK GIVEN THE APPROACH OF A WAVE SEEN ON WATER VAPOR AND THE LOW
LEVEL BOUNDARY OVER NORTH TX.  THERE WAS A STRONG THETAE GRADIENT
AT H85...AND WHILE THE ADVECTION WAS NOT PARTICULARLY STRONG DUE
TO THE WEAK H85 WINDS...THE APPROACH OF THE WAVE SHOULD HELP
STRENGTHEN THE LOWER FLOW AND INCREASE ADVECTION/MOISTURE
TRANSPORT INTO THE FRONT.  PRECIPITABLE WATER VALUES WERE ALREADY
CLOSE TO 2 INCHES AND THE SOUNDINGS IN THE REGION WHERE
CHARACTERIZED BY TALL...SKINNY CAPE.    SO CELLS SHOULD PROVE TO
BE EFFICIENT RAIN MAKERS. WE SAW LITTLE REASON TO CHANGE THE
MARGINAL RISK AREA THAT EXTENDED SOUTHEAST TOWARDS THE GULF OF
MEXICO.  LOW LEVEL BOUNDARIES/FORCING WILL NOT BE AS STRONG BUT IT
WOULD NOT TAKE MUCH TO INITIATE LOCALLY HEAVY RAINFALL PRODUCING
CELLS HERE.

...PA/NY AND MID ATLANTIC REGION...


WE INCLUDED A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PARTS OF PA
AND NY.  THE HIGH RES MODELS WERE IN PRETTY GOOD AGREEMENT THAT
ANOTHER ROUND OF SHOWERS AND THUNDERSTORMS WILL DEVELOP
ALONG/AHEAD OF A WAVE ROTATING AROUND A CLOSED CIRCULATION JUST
NORTH OF THE INTERNATIONAL BORDER.  CAPE VALUES AROUND 1000 J PER
KG WILL BE IN PLACE AT THAT TIME OF THE DAY...SO AM EXPECTING
SCATTERED AFTERNOON/EVENING CONVECTION.  SOME PLACES UP IN CENTRAL
PA RECEIVED HEAVY RAINFALL ON FRIDAY NIGHT...SO THE POTENTIAL
EXISTS FOR FLOODING PROBLEMS AGAIN.  OPTED TO CONNECT THIS AREA
WITH A PRE EXISTING RISK AREA OVER SE VA AND PARTS OF THE
DELMARVA.

...WESTERN U.S...

GIVEN UNCERTAINTY IN HOW MUCH MOISTURE HAS BEEN SCOURED OUT OVER
PARTS OF THE DESERT SOUTHWEST...PULLED A MARGINAL RISK OF
EXCESSIVE RAINFALL AS FAR WEST AS SOUTHERN CLARK COUNTY NV AND FAR
EASTERN SAN BERNARDINO COUNTY CA.  THE SOUNDING AT KVEF STILL
SHOWED PRECIPITABLE VALUE AMOUNTS IN EXCESS OF 1.3 INCHES WITH K
VALUES OVER 40.  THE SOUNDING IN THE SUB CLOUD LAYER LOOKED
SIMILAR TO THE 12Z SOUNDING ON FRIDAY...WHICH SUGGESTS THAT THERE
COULD STILL BE SOME LATE DAY CONVECTION CAPABLE OF PRODUCING
LOCALLY HEAVY RAINFALL.  IN ADDITION...A MECHANISM THAT WOULD
SCOUR OUT THAT KIND OF MOISTURE WAS NOT TERRIBLY EVIDENT ON
SATELLITE IMAGERY. WILL RE EVALUATE LATER.

...NORTHERN PLAINS...

IMPULSES DIGGING THROUGH A MEAN NRN STREAM UPPER LEVEL TROUGH
POSITION OVER THE N-CENTRAL PLAINS AND UPPER JET SUPPORT WILL
PRODUCE ASCENT. LOWER LEVEL SOUTHERLY RETURN FLOW WILL ADVECT
MOISTURE NORTH INTO THE REGION WITH PW VALUES INCREASING TO AOA
1.25 INCHES OVER NEB/SD BY LATER THIS AFTERNOON.  DESTABILIZATION
AND LOW LEVEL CONVERGENCE SHOULD FAVOR INCREASING CONVECTION.
EXPANDED THE NORTHWARD EXTENT A BIT GIVEN DEGREE OF INSTABILITY
AND THE PRESENCE OF SOME HEAVY RAIN PRODUCING CELLS GENERATED BY
THE HIGH RES CONVECTIVE ALLOWING MODELS.  CONFIDENCE WAS NOT
ENOUGH TO INTRODUCE A SLIGHT RISK.

GRAPHICS AVAILABLE ON THE WEB AT WWW.WPC.NCEP.NOAA.GOV

BANN

$$





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