Quantitative Precipitation Forecast
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000
FOUS30 KWBC 160056
QPFERD

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

...VALID 01Z WED AUG 16 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
35 ESE OCW 20 SSE CTZ 10 WSW HRJ 15 S AVC RIC 10 S FYJ CPK
15 S ECG 35 ESE OCW.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
15 NNW SDA 50 ENE HLC 25 N GLD 35 ESE LIC 25 SW LIC DEN
20 ENE BRX 55 SSW CUT IEN 30 NW VTN 9V9 15 WNW FSD 20 ENE PQN
20 SSW MKT FOD 15 NNW SDA.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
30 SE MDD 25 SW DYS 40 S ABI 20 E E29 40 NW DRT 50 SW 6R6
45 SE E38 20 ENE FST 30 SE MDD.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
20 ENE JLN 40 SW TBN 20 SW UNO 10 SW HRO 20 S SLG 10 SW AQR
10 NNW ADM SNL 20 NNW TUL 20 SSE CFV 20 ENE JLN.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
10 SW LBF 30 N BBW 20 WNW OFK 20 NW ORC 15 W EST 20 SSE SLB
10 W HNR 15 W MLE 10 SSW JYR 15 SSW HSI 25 S HDE 15 SE MCK
30 E IML 10 SW LBF.


0100 UTC UPDATE

ACROSS THE CENTRAL PLAINS AND MID MO VALLEY...MADE FURTHER
MODIFICATIONS TO THE PREVIOUS OUTLOOK BASED UPON CURRENT RADAR
SATELLITE TRENDS...AS WELL AS RECENT RUNS OF THE HRRR.  THIS
INCLUDED NARROWING THE SLIGHT RISK TO CENTRAL/EASTERN NEB AND
NORTHWESTERN IA.  ONGOING BACKBUILDING CONVECTION ALONG AND NORTH
OF A WARM FRONT IS EXPECTED TO CONTINUE THROUGH THE REMAINDER OF
THE EVENING INTO THE OVERNIGHT HOURS.  LATEST RUNS OF THE HRRR
SHOWS WIDESPREAD ADDITIONAL ACCUMULATIONS OF THE 1-3 INCHES...WITH
LOCALLY HEAVIER AMOUNTS THROUGH 12 UTC.  REFER TO WPC MESOSCALE
PRECIPITATION DISCUSSION #700 (VALID THROUGH 0500 UTC) FOR DETAILS
ON THE SHORT-TERM THREAT.

ACROSS THE ARKANSAS BASIN/MID MS VALLEY...REMOVED MUCH OF
SOUTHEASTERN KS FROM THE MARGINAL RISK...BUT EXPANDED IT SOME
ACROSS EASTERN OK INTO SOUTHERN MO AND NORTHERN AR.  RADAR
INDICATES RAINFALL RATES IN MOST STORMS IN NORTHEASTERN OK ARE
STARTING TO DECREASE.  HOWEVER...ONGOING SLOW MOVING/BACKBUILDING
CONVECTION IS EXPECTED TO CONTINUE FOR A FEW MORE HOURS AND MAY
CONTINUE TO PRODUCE SOME LOCALLY HEAVY AMOUNTS.  SOME OF THESE
STORMS MAY PROPAGATE FURTHER EAST ALONG THE OLD FRONTAL BOUNDARY
NEAR THE MO/AR BORDER.  HOWEVER...DECREASING INSTABILITY IS
EXPECTED TO LIMIT THE POTENTIAL FOR WIDESPREAD HEAVY AMOUNTS VERY
FAR EAST INTO SOUTHERN MO/NORTHERN AR.

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.

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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