Quantitative Precipitation Forecast
Issued by NWS

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FOUS30 KWBC 121451
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1050 AM EDT SAT AUG 12 2017

...VALID 15Z SAT AUG 12 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 25 NNE CQC 20 ENE SKX 25 SSE ALS 10 S CPW
30 ESE TEX 30 SSE GUC 35 SE MYP 20 NE TAD 20 WSW SPD 50 W GCK
25 ESE GLD 15 E IEN 20 NNW D07 25 E DIK 15 ESE N60 15 SSE K5H4
10 NW KBAC 25 ESE KGWR 8D3 20 NNW FSD 35 NNW OFK 10 S AUH
25 SW CNK 10 SSW IAB 25 WSW BVO 30 ESE FSM 30 WNW ELD 30 N ESF
20 W MCB 15 SSW HBG GPT 10 S BIX 15 E S58 10 W KCMB 35 ENE CXO
25 SSE CRS 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 NNE MRH 20 ESE SUT 10 ESE MYR 25 WSW CPC
10 S AVC AVC 15 E LKU 25 E W99 10 SSW JST 15 ENE UNV 20 N IPT
25 SSW UCA 15 NW GFL 20 W EEN 15 WSW DXR NXX 50 ESE WWD.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
25 NNW GAG 20 WSW END 10 NNW GOK 15 SSW OKM 35 SW RKR 15 S DEQ
35 ENE 4F4 15 SSE 4F4 15 NE TRL 35 SW SPS 45 WNW CDS AMA
20 NW BGD 20 W PYX 25 NNW GAG.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
HLC 15 E MCK 25 NNE LBF 20 NW ODX 20 NW GRI 40 S HSI 50 N RSL
HLC.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
FFA 35 NE NKT 10 SSE NCA ISO 15 WSW PGV AKQ 15 SE NHK
35 ENE OXB.

MODERATE RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
20 WSW JWG 10 WSW PWA 10 SE SNL 25 SSE MLC 25 NNE PRX 10 SE PRX
15 NE GVT 15 SSW GYI 30 E SPS 15 WNW FDR 30 NE CDS 40 ESE PPA
20 SSE HHF 35 ESE HHF 35 NNW CSM 20 WSW JWG.


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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