Quantitative Precipitation Forecast
Issued by NWS

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FOUS30 KWBC 100831
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
430 AM EDT THU AUG 10 2017

...VALID 12Z THU AUG 10 2017 - 12Z FRI AUG 11 2017...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
15 S ELD 30 NW GLH 35 W TUP 10 ESE MSL 35 NE MDQ 30 NE CSV
20 NW LOZ 40 NNW JKL 15 SW HTS 35 WNW I16 15 WSW 6V3 20 SSW AVL
10 NW MLJ 20 SW LSF 10 SW OZR 20 ENE BFM NBG 10 SW LFT 20 N POE
15 S ELD.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
20 NNW AAT 50 S AAT 45 ENE RDD 25 SW SIY 25 NE MFR 20 NE LMT
20 NNW AAT.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
20 SSE 9BB 35 S EKO 10 N B23 45 SW AWH 20 NE AWH 20 SSE TWF
25 NNW MLD 30 N U78 20 S WEY 10 NNE P60 15 WSW COD 40 N RIW
25 NW LND 10 WSW BPI 40 N FIR 10 SSE FIR 25 SE FIR 35 NNE VEL
10 S VEL 45 N PUC 35 E SLC 15 W EVW 20 ESE LGU 15 SW MLD
55 NNE ENV 20 SSE 9BB.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
55 ENE CWCJ 50 N CYLD 40 E CYLD 50 N CYZE 10 N CWNL 10 NNE CAD
25 ESE RAC 15 W UGN 15 ESE MSN CWA 30 N PBH TWM 30 NNE ELO
20 E CWDV.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
35 SSW ARL 20 NE ARL 30 NNE CYS 40 NW AKO 20 NNW AKO 30 SE IML
25 S HLC 20 S SLN 20 NE UKL 40 N SGF 25 NNE HRO FSM 15 NNW ADM
10 N LTS AMA 30 ENE RTN 20 NNE CCU 35 SSW ARL.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
15 NE HST 25 S HST 20 W HST 20 WNW HWO FXE 15 NE HST.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
20 NW LAA LIC 30 ENE LIC 20 NW ITR 45 NW GCK 20 N PTT 40 S EMP
15 WNW JLN 20 NNW TQH 15 SW MKO 15 N PVJ 25 W CHK CSM 25 W HHF
25 SSW EHA 20 N SPD 20 NW LAA.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
30 E JAN 35 ESE JAN 25 W PIB 20 N MCB 15 NNE HEZ 25 NNE ESF
30 ENE IER 30 W MLU 25 SW GLH 35 N HKS 30 E JAN.


OVERALL MANUALLY ADJUSTED A BLEND OF A THIRD WPC CONTINUITY WITH
TWO-THIRDS 04 UTC NBM THAT SEEMS TO BEST SHOW PCPN TRENDS.

...UPPER MS VALLEY/GREAT LAKES...

GUIDANCE REMAINS FAIRLY WELL CLUSTERED WITH DEPICTION OF WELL
DEFINED HEIGHT FALLS FROM THE NRN PLAINS TO THE UPPER MS
VALLEY/GREAT LAKES DAY 1. WHILE THERE ARE A LOT DETAIL QPF DETAIL
DIFFERENCES AMONG THE MODELS...CONSENSUS IS FOR THE POTENTIAL FOR
MODERATE TO LOCALLY HEAVY PRECIP TOTALS IN THE REGION OF UPPER
DIFFLUENCE AHEAD OF THESE HEIGHT FALLS FROM THE UPPER MS VALLEY
INTO THE LAKES AND SOUTHWARD INTO THE MID MS VALLEY WITH APPROACH
OF A WAVY FRONTAL SYSTEM. WHILE PRECIPITATION AREAS SHOULD BE
GENERALLY PROGRESSIVE AHEAD OF THESE HEIGHT FALLS...THERE MAY BE
ENHANCED TOTALS IN THE COMMA HEAD DEFORMATION BAND PIVOTING OVER
THE UPPER LAKES. PRECIP MAY ALSO HAVE UVV ENHANCEMENT FROM
NORTHEAST FLOW OFF OF LAKE SUPERIOR AND FAVORABLE RIGHT ENTRANCE
REGION UPPER JET LIFT. THIS WARRANTS A MARGINAL EXCESSIVE RAINFALL
THREAT FOR ASSOCIATED RUNOFF ISSUE POTENTIAL.

...NRN CA TO THE CENTRAL GREAT BASIN AND UNDERNEATH OVER THE
SOUTHWEST...

A REX BLOCK THAT HAS BEEN OFF THE PAC NW/NRN CA THE PAST FEW DAYS
WILL BEGIN TO BREAK DOWN AS NE PAC HEIGHT FALLS APPROACH THE
COAST. SCATTERED DIURNAL CONVECTION REMAINS LIKELY THIS PERIOD IN
THE VICINITY OF AN UPPER LOW EASTWARD FROM NRN CA INTO THE GREAT
BASIN. PW VALUES REMAIN ABOVE AVERAGE ACROSS THESE
REGIONS...SUPPORTING POTENTIAL FOR ISOLATED MODERATE TO HEAVY
TOTALS. GUIDANCE HAS BEEN GENERALLY UNDER FORECASTING PCPN
COVERAGE AND LOCAL POTENTIAL. THIS WARRANTS A MARGINAL EXCESSIVE
RAINFALL THREAT FOR ASSOCIATED RUNOFF ISSUE POTENTIAL. INCLUDED
PORTIONS OF AZ/WRN NM UNDERNEATH WITH CONTINUED THREAT FOR
CONVECTION.

...LEE OF THE CENTRAL ROCKIES TO THE S-CENTRAL PLAINS...

A SERIES OF IMPULSES MOVING ALONG THE SRN EDGE OF THE WESTERLIES
OUT FROM THE WEST TO THE CENTRAL ROCKIES AND S-CENTRAL PLAINS
SHOULD SUPPORT A PRECIP MAX FROM THE VICINITY OF SOUTHEAST WY/ERN
CO SOUTHEASTWARD TOWARD THE TX/OK PANHANDLE AND ACROSS SRN KS/SW
MO AND OK. CONVECTION WILL BE SUPPORTED BY FAVORABLE UPPER
DIFFLUENCE NEAR A FRONTAL ZONE THAT WILL ACT TO POOL MOIST INFLOW.
THE 04 UTC NBM AND 00 UTC NAM CONEST ALLOW MODERATE TO HEAVY
PRECIP WORK MORE IN ERNEST INTO OK THAN MOST OTHER/PRIOR GUIDANCE
AND THIS MAY BE REASONABLE GIVEN INSTABILITY AND TROUGH
AMPLIFICATION. THIS WARRANTS A SLIGHT EXCESSIVE RAINFALL THREAT
FOR ASSOCIATED RUNOFF ISSUE POTENTIAL GIVEN MODEL SUPPORT
INCLUDING SOME LOCALLY HIGH RAINFALL POTENTIAL.

...CENTRAL GULF COAST...SOUTHEAST/FL...TN VALLEY INTO THE UPPER OH
VALLEY...

A WAVY SURFACE FRONTAL BOUNDARY STRETCHING FROM TX AND THE GULF
COAST TO OFF THE SOUTHEAST COAST HAS BEGIN TO PUSH NORTH. PW
VALUES WILL REMAIN ABOVE AVERAGE ALONG/SOUTH OF THIS BOUNDARY TO
SUPPORT ADDITIONAL WIDESPREAD CONVECTION. MESO CIRCULATIONS OUT
FROM THE GULF OF MEXICO AND NOW OVER LA ADD CONVECTIVE FOCUS ALONG
WITH DEEPENED SRN/SERN FL MOISTURE AXIS/WEAKNESS ALOFT. STLT
ALREADY SHOWS ACTIVE CONVECTION ALONG/OFF SE FL SO A MARGINAL
EXCESSIVE THREAT AREA WAS ADDED.

WPC HAS RECENTLY ISSUED MESOSCALE PRECIPITATION DISCUSSION #662
FOR A LEAD-IN SHORT TERM THREAT OVER LA WHERE SLOW MOVING
CONVECTION HAS FIRED IN THE DEEPLY MOIST AIRMASS...PROMPTING A
SLIGHT EXCESSIVE RAINFALL RISK AREA. IN RESPONSE TO THE AMPLIFYING
AREA OF HEIGHT FALLS OVER THE UPPER MS VALLEY/UPPER LAKES
REGION...ABOVE AVERAGE PW VALUES WILL ALSO BEGIN TO PUSH
NORTHEASTWARD TO THE WEST OF THE APPALACHIANS THROUGH ERN TN/KY TO
THE UPPER OH VALLEY REGION...SUPPORTING INCREASING POTENTIAL FOR
MODERATE TO LOCALLY HEAVY PRECIP ACROSS THESE AREAS. THIS WARRANTS
A MARGINAL EXCESSIVE RAINFALL THREAT FOR ASSOCIATED RUNOFF ISSUE
POTENTIAL FOR A GOOD PORTION OF THE REST OF THIS REGION GIVEN
AVAILABLE MOISTURE.

SCHICHTEL
$$





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