Quantitative Precipitation Forecast
Issued by NWS

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130
FOUS30 KWBC 130100
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
900 PM EDT SAT AUG 12 2017

...VALID 01Z SUN AUG 13 2017 - 12Z SUN AUG 13 2017...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
35 S OLS 30 S OLS 15 SSE TUS 30 E IWA 65 WSW PRC 35 SW EED
35 E DAG 30 NE LSV 20 WNW GCN 25 NNW INW 25 WNW SJN 65 S GNT
70 S ABQ 30 NW 4CR 20 E CQC 30 N LVS 10 SSE RTN 40 SE TAD
35 S LHX 30 S LHX 20 N LHX ITR 25 SE IML 25 SW LBF 25 N TIF
15 W PIR 30 WSW MBG 45 WSW K7L2 25 S BIS 45 NNE K7L2 30 WSW JMS
10 N KGWR MOX 25 WNW MML 10 SSW YKN 15 SE HSI 40 NNE DDC PYX
35 NW CSM 25 SW JWG 10 NW PWA 25 W OKM 15 SE FYV 20 ENE RUE
35 ESE M89 20 NE ELD 35 W MLU 30 N ESF 35 SW HEZ ASD 20 ESE NBG
15 N AXO 25 W 2GL 7R4 CWF 15 ENE JAS JSO 10 ESE GDJ 30 S RPH
45 N DYS 10 SE LBB 25 WSW LBB 35 E ATS 35 W GDP 35 SSE MMCS
100 SSW MMCS.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
50 E FFA 25 ESE MQI 35 W HSE 10 E NKT 30 ESE ILM 20 ESE CRE
20 NNW MYR 10 N LBT 10 SW FAY 10 NE POB 10 SE JNX 10 SSE ASJ AKQ
RIC 10 W OFP LKU 10 E OMH RMN DAA 10 WSW NAK NAK 20 ESE APG PNE
15 SW 12N 10 ENE MPO 20 NE AVP 35 WNW MSV 30 N MSV 35 SSW ALB
10 NNW PSF 20 WNW ORE 10 NW ORE 10 W BAF 10 ESE POU 15 E SMQ
15 NNE WRI 10 SSE ACY 50 ESE WWD.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
15 WNW PVJ 25 ENE ADH 25 W RKR 30 NW MWT 20 SSW MWT 35 SE TXK
30 ESE BAD 30 WNW IER 15 E TYR 15 WNW TYR RBD 15 ENE MWL
10 NNW MWL 40 WNW RPH 55 SSW F05 25 SW CDS 45 SE AMA 40 NW CDS
20 W LTS 15 WNW LAW 15 WNW PVJ.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
25 NE FFA FFA 40 WNW HSE 15 NNE NCA 20 SSW DPL 15 S DPL
10 ESE CTZ OCW 10 W ECG 15 NE ORF 20 ENE FYJ 25 N FYJ 2W6
15 E CGE 30 ESE OXB.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
30 SSW ONL 10 NNE ODX 20 NNW EAR 20 WSW HDE 20 SSE MCK
25 WSW MCK 20 NW MCK 15 NE LBF 25 NNW BBW 40 NW ODX 30 SSW ONL.

MODERATE RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
10 WNW ADM 15 W AQR 35 SE MLC 40 NW DEQ 10 NNE DEQ 15 N TXK
30 SSW TXK 15 ENE 4F4 GVT 15 NNW ADS 10 N 1F9 25 SSE SPS SPS
15 SSW DUC 10 WNW ADM.


...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...BUT
CONVECTION ALONG/JUST SOUTH OF THE MOGGOLON RIM HAS BEEN MORE
ORGANIZED/OFFERED SOME TRAINING/RUNOFF POTENTIAL LOCALLY AS PER
OUTFLOW INTERACTION.

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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