Quantitative Precipitation Forecast
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FOUS30 KWBC 152128
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
528 PM EDT TUE AUG 15 2017

...VALID 2128Z 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
10 WSW PIR 35 E K7L2 10 NE KBAC 20 NW DTL 10 WSW SAZ 15 ESE 2P3
MKT 15 ESE CAV 20 NNW TNU FFL 10 NNW EOK 25 SW EOK 25 SE IRK
10 SE CDJ 40 SW LWD 10 NW STJ 25 SE LXT 20 NNW SGF 35 WNW RUE
35 ENE MLC 30 E SNL IAB GBD 45 SW HLC 15 E AKO 25 NE CYS TOR
40 SE IEN 10 WSW PIR.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
20 NNE MRH 10 SSW ILM 10 SE CPC 10 SSE LBT 10 NNE LBT
15 WNW JNX 10 SE AVC 30 ENE FYJ 10 NNW WAL 15 SE OXB 35 ESE WAL
15 E 9W7 30 WNW HSE 20 NNE MRH.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
20 ESE MDD 15 E SWW 15 WNW 7F9 35 W 6R9 40 NW DRT 55 SSE E38
20 NNE MRF 15 N FST 20 ESE MDD.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
20 WNW SHL 20 NNW CIN 15 NE ADU 10 WSW ICL 20 N MHK 20 S SLN
30 ESE RSL 15 N RSL 15 WNW HLC 30 SSW MCK 35 SE IML 15 E IML
25 W BBW ODX 25 SSE ONL 25 NNW ONL 30 SE 9V9 30 ENE 9V9
10 SSE HON 30 SW BKX FSD 20 WNW SHL.


2100 UTC UPDATE

EXTENDED THE MARGINAL RISK FURTHER SOUTH INTO THE EASTERN ARKANSAS
BASIN WHERE DEEPENING MOISTURE (PWS INCREASING TO AT OR ABOVE 2
INCHES) ALONG AN OLD FRONTAL BOUNDARY IS EXPECTED TO SUPPORT
DEVELOPING SHOWERS AND THUNDERSTORMS ACROSS THE REGION LATE THIS
AFTERNOON INTO THE EVENING...WITH LOCALLY HEAVY AMOUNTS POSSIBLE.

ALSO ADDED A MARGINAL RISK TO PORTIONS OF THE WEST-CENTRAL TX
WHERE INCREASING MOISTURE ALONG AN OLD OUTFLOW BOUNDARY IS
SUPPORTING INCREASING SHOWER AND THUNDERSTORM COVERAGE.  THE
EXPECTATION IS THAT COVERAGE WILL CONTINUE TO INCREASE DURING THE
NEXT FEW HOURS...WITH SOME CELL TRAINING CONTRIBUTING TO LOCALLY
HEAVY AMOUNTS.  REFER TO WPC MESOSCALE PRECIPITATION DISCUSSION
#698 FOR FURTHER DETAILS.

PEREIRA

1900 UTC UPDATE

THE MARGINAL AND SLIGHT RISK AREAS WERE REMOVED FROM WESTERN
TN---ACROSS AR INTO PORTIONS OF THE SOUTHERN PLAINS GIVEN TRENDS
WITH CURRENT CONVECTION.  ONLY SOME MINOR CHANGES MADE OVER THE
CENTRAL PLAINS TO THE MARGINAL AND SLIGHT RISK AREAS.


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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