Quantitative Precipitation Forecast
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000
FOUS30 KWBC 151417
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1017 AM EDT TUE AUG 15 2017

...VALID 15Z TUE AUG 15 2017 - 12Z WED AUG 16 2017...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
15 W STJ 30 E CNU 20 SW JLN 15 NW XNA 15 NW HRO 25 WNW ARG
25 NNE BYH 40 NE MKL 50 N MSL 10 WNW MSL 30 ESE TUP 25 SSW TUP
10 NNE GLH 30 ESE M89 25 WSW M89 20 SSW RKR 10 SE MKO 30 SW BVO
20 NNW WDG 15 W JWG 25 E HBR 15 WNW SPS 55 SSW F05 45 NNE SWW
40 NNW SNK 10 E PVW 10 WNW PPA 30 NE PYX 10 SW DDC 55 SW HLC
40 E GLD 15 NNE AKO 25 NE CYS TOR 40 SE IEN 20 S PIR 25 ESE MBG
10 NE K7L2 45 W JMS 10 SSW JMS K2D5 30 S KGWR 10 W 8D3 1G2
15 S OTG 10 N DNS 15 SW ICL 15 W STJ.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
20 NNE MRH 10 SSW ILM 10 WNW CPC 10 SW POB RDU 15 WSW DAN
20 S ROA 25 NNW LYH 10 ESE LKU 25 WNW MFV 25 ENE NTU 30 WNW HSE
20 NNE MRH.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
35 E CNK 25 WSW MHK 20 SSW SLN 30 ESE RSL 35 N RSL 40 NE HLC
25 ESE MCK 30 NW MCK 30 SSW TIF 15 SW ANW 15 SSE 9V9 20 SW HON
30 SW BKX 25 WNW ORC SUX 15 NW FET 20 ENE JYR 10 NNE HJH
35 E CNK.


1500 UTC UPDATE

NORTHERN AR INTO FAR WESTERN TN

CHANGES TO THE PREVIOUS EXCESSIVE RAINFALL POTENTIAL OUTLOOK WERE
TO ADD A SLIGHT RISK AREA ACROSS REGIONS OF NORTHERN AR THAT HAVE
RECEIVED VERY HEAVY RAINFALL OVER THE PAST SEVERAL HOURS AND HAVE
SEEN FFG VALUES LOWERED SIGNIFICANTLY.  LATEST IR IMAGERY IS
SHOWING WARMING OF TOPS---SUGGESTING THE GREATEST THREAT FOR
ADDITIONAL HEAVY TO LOCALLY EXCESSIVE AMOUNTS WILL BE IN THE SHORT
TERM AND MOST LIKELY IF ANY ADDITIONAL CONVECTION FORMS ACROSS
REGIONS THAT HAVE RECEIVED VERY HEAVY AMOUNTS.  THE ONLY REGION
WITH ANY HINT OF COOLING CLOUD TOPS IS ON THE LEADING EDGE OF THE
CONVECTION OVER NORTHEAST AR.  THE SLIGHT RISK WAS EXTENDED
EASTWARD INTO FAR NORTHEAST AR AND FAR WESTERN TN WHERE FFG VALUES
ARE AROUND 1.5 FOR AN HOUR AND DUAL POL IS SHOWING INCREASING
HOURLY AMOUNTS IN THE VICINITY OF THIS CLOUD TOP COOLING.
ELSEWHERE---DUAL POL IS SHOWING A DECREASE IN HOURLY AMOUNTS
ACROSS THE REMAINDER OF AR WHERE THE HEAVIEST AMOUNTS HAVE
OCCURRED BUT THE AFOREMENTIONED WARMING CLOUD TOPS ARE OCCURRING.
 THE LATEST HRRR SUPPORTS THE DECREASING PRECIP THREAT OVER
WESTERN TO CENTRAL AR WITH QPF AMOUNT DECREASING WITH TIME LATE
MORNING.   PLEASE SEE WPC`S MESOSCALE PRECIPITATION DISCUSSION
#0696 VALID UNTIL APPROXIMATELY 1700 UTC FOR ADDITIONAL
INFORMATION ACROSS THIS AREA.

FAR EASTERN NE INTO WESTERN IA

THE PREVIOUS SLIGHT RISK AREA WAS EXPANDED EASTWARD INTO FAR
WESTERN IA AS PER LATEST RADAR TRENDS. WHILE CLOUD TOPS ARE
SHOWING SOME SIGNS OF A WARMING TREND---VERY HEAVY HOURLY RATES OF
1.5"+ ARE PUSHING INTO WESTERN IA IN THE VICINITY OF I-80---WITH
THIS THREAT EXPECTED TO PERSIST FOR THE NEXT FEW HOURS.

ORAVEC


INITIAL DISCUSSION

...USED A COMPOSITE BLEND OF REASONABLY CLUSTERED NBM/NMMB/NAM
CONEST AND WPC CONTINUITY/BIASED CORRECTED QPF AS A STARTING POINT
IN THIS COMPLEX PATTERN AND THEN APPLIED MANUAL MODIFICATIONS AS
PER STLT/RADAR/HRRR TRENDS...


....MID-MS/TN VALLEYS TO S-CENTRAL APPALACHIANS/MID ATLANTIC...

A WAVY MOISTURE-LADEN FRONTAL BOUNDARY EXTENDING FROM THE
CAROLINAS BACK INTO OK IS EXPECTED TO REMAIN A FOCUS FOR SHOWERS
AND THUNDERSTORMS CAPABLE OF PRODUCING MODERATE TO HEAVY
RAINS/RUNOFF ISSUES AS A SERIES OF MID LEVEL SHORTWAVES INTERACT
WITH THE CORRESPONDING AXIS OF DEEP MOISTURE. PWS OF 1.75 TO 2.25
INCHES INTERACTING WITH A STRING OF SHORTWAVES WILL CONTINUE TO
SUPPORT CLUSTERS OF SHOWERS AND THUNDERSTORMS. DEEP MOISTURE IS
EXPECTED TO SUPPORT EFFICIENT RAINFALL PROCESSES...WHILE DEEP
WESTERLY FLOW PARALLEL TO THE BOUNDARY MAY ENCOURAGE CELL
TRAINING. PERHAPS THE BEST POTENTIAL IN THIS ACTIVE WAVY FLOW MAY
BE OVER THE AR AND THE TN VALLEY AS INFLOW REBOUNDS AHEAD OF
APPROACHING SRN PLAINS MCVS AND WELL DOWNSTREAM OVER THE S-CENTRAL
MID-ATLC IN A REGION OF FAVORABLE RIGHT ENTRANCE REGION UPPER JET
SUPPORT. THEREFORE...ISSUED A WPC MARGINAL EXCESSIVE RAINFALL
THREAT AREA FOR THESE TWO AREAS. WPC MESOSCALE PRECIPITATION
DISCUSSION #693 HAS ALSO BEEN ISSUED FOR SHORT TERM DETAILS
CENTERED OVER AR.

...PLAINS...

A WPC SLIGHT AND MARGINAL EXCESSIVE RAINFALL THREAT AREA HAS BEEN
ISSUED FOR MUCH OF THE N-CENTRAL TO S-CENTRAL PLAINS...WITH THE
SLIGHT AREA CENTERED OVER THE CONVECTIVE APPEX/REPEAT CELL REGION
INVOF SE SD AND NEBRASKA INTO KS.

CONVECTION SHOULD INCREASINGLY FLOURISH AS HEIGHT FALLS/EMBEDDED
VORT ENERGY WITH APPROACH OF WRN US MID-UPPER LEVEL TROUGH/JET
ENERGIES INTO THE PLAINS. SURFACE CYCLOGENESIS AND NORTHWARD
TRANSPORT OF MOISTURE UP THROUGH THE SRN PLAINS AND INTO/OVER A
WAVY N-CENTRAL US FRONTAL SYSTEM SHOULD FURTHER INCREASE
INSTABILITY AND LOWER ATMOSPHERIC CONVERGENCE/LLJ INFLOW. WITH PWS
INCREASING TO AOA 2 INCHES UP THROUGH THE PLAINS...SUSPECT HEAVY
CONVECTIVE RAINS WILL OFFER POTENTIAL FOR LOCAL RUNOFF ISSUES AND
QPF PROGS FOCUS QUITE A BIT OF ORGANIZED AFTERNOON/OVER NIGHT
ACTIVITY OVER THE N-CENTRAL PLAINS THAT SHOULD GRADUALLY WORK
LATER PERIOD INTO THE MID-UPPER MS VALLEY. MEANWHILE EXPECT
IMPULSES/UPPER DIFFLUENCE ALSO FAVORS CLUSTERS OF SRN PLAINS HEAVY
CONVECTION/MCVS IN SEPARATE ACTIVE FLOW.

...CENTRAL AND ERN GULF COAST...

DEEP MOISTURE AND WEAK FLOW ALOFT IS EXPECTED TO SUPPORT SCATTERED
SLOW MOVING AFTERNOON CONVECTION ALONG THE CENTRAL AND ERN GULF
COAST. WHILE WEAK RIDGING ALOFT MAY HAMPER DEVELOPMENT...STORMS
THAT DO FORM WILL LIKELY BE SLOW MOVING GIVEN WEAK FLOW ALOFT AND
GIVEN THE AMPLE MOISTURE...THEY ARE EXPECTED TO BE EFFICIENT BUT
SPOTTY RAINFALL PRODUCERS.

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

SCHICHTEL
$$





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