Quantitative Precipitation Forecast
Issued by NWS

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FOUS30 KWBC 150100
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
900 PM EDT MON AUG 14 2017

...VALID 01Z TUE AUG 15 2017 - 12Z TUE AUG 15 2017...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
90 W MRF 55 WNW MRF 25 SW PEQ 20 N FST 45 E FST 55 NE 6R6
30 E 6R6 40 S 6R6 85 SSW 6R6.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
20 NE LNK 20 S CSQ 25 NNE CDJ 35 SSW CDJ LWC 30 NNW MHK
15 S EAR 10 WNW GRI 20 NE LNK.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
25 WSW MKL 15 SW MSL 15 SSE GTR 35 NNW TVR 20 N DTN 20 ENE LNC
15 NNW DUA 15 S OKM XNA 15 NE BVX 25 WSW MKL.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
25 NNE 1A5 10 N CHA 35 NW MDQ 25 SW MQY 10 NW 1A6 25 NNW DAN
10 S ECG 15 ESE OCW 15 SSW DPL 10 NE SOP 10 SE HKY 25 NNE 1A5.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
10 ESE SRC 25 SSW OLV 10 N GWO 20 NE ELD 15 SW DEQ 25 ESE MLC
10 NNW JSV 35 SSW HRO 10 ESE SRC.


...LOWER MISSISSIPPI VALLEY / OK/TX/AR/MS/TN/LA...

THE PRIMARY CONCERN HERE IS TRANSPORT AND CONVERGENCE OF
MODERATELY UNSTABLE AIR IN TOWARD AN MCV THAT WAS MOVING DUE EAST
OUT OF EASTERN OKLAHOMA AS OF MID EVENING. MOST UNSTABLE CAPE
VALUES OF AT LEAST 1000 J/KG ARE EXPECTED...COUPLED WITH
ANOMALOUSLY RICH MOISTURE AT OR ABOVE 2 INCHES. THE ENVIRONMENT
ALONE SHOULD YIELD EXTREME SHORT TERM RAIN RATES AND LOCAL 2-PLUS
INCH TOTALS OVER A SHORT TIME. IN AREAS WHERE CONVECTION ALIGNS
WEST TO EAST...HOWEVER...AT THE NOSE OF THE LOW LEVEL
FLOW...TRAINING COULD LEAD TO MORE GREATLY EXCESSIVE TOTALS...SUCH
AS IN THE NSSL WRF AND 18Z NAM CONUS NEST SOLUTIONS WHICH SIGNAL
MORE THAN SEVEN INCHES IN SPOTS. FLASH FLOOD GUIDANCE WAS ALREADY
LOWERED IN THIS REGION BY EARLIER RAINFALL...MAKING FLASH FLOODING
SOMEWHAT LIKELY...ALTHOUGH RELATIVELY SPARSE COVERAGE OF HEAVY
RAINFALL AND LACK OF CONFIDENCE IN ITS PLACEMENT HAVE SWAYED WPC
TO MAINTAIN SLIGHT RISK PROBABILITIES.


...EASTERN TENNESSEE INTO NORTH CAROLINA...

WEST TO EAST ORIENTED THUNDERSTORMS WERE LIFTING NORTHWARD THROUGH
AREAS EAST OF RALEIGH. THE SYNOPTIC ENVIRONMENT WAS BROADLY
FAVORABLE...WITH SOME WARM ADVECTION AND A SLOWLY STRENGTHENING
UPPER JET CIRCULATION. THE SLOW MOVING CONVECTION HAD PROMPTED ONE
FLASH FLOOD WARNING AS OF LATE EVENING. BACK WEST...ATTENTION IS
ON THE LOW AMPLITUDE SHORTWAVE TROUGH MOVING THROUGH EASTERN
TENNESSEE. THIS SHOULD SUPPORT POCKETS OF STRONG CONVECTION AND
CONVECTIVE RAIN RATES FROM EASTERN TN INTO NC THROUGH THE LATE
NIGHT HOURS...PER MOST OF THE MODEL GUIDANCE AND RECENT RAP RUNS.
DEEP LAYER FLOW IS DECIDEDLY WESTERLY WHICH SHOULD PROMOTE FORWARD
MOTION AND NOT TOO MUCH OF A TRAINING CONCERN...ALTHOUGH THE VERY
MOIST AND MODERATELY UNSTABLE ENVIRONMENT COULD SUPPORT RAINFALL
PRODUCING FLASH FLOODING IN ANY SUSCEPTIBLE LOCATIONS.


...TEXAS PANHANDLE...

THUNDERSTORMS WERE AGAIN MOVING OFF THE HIGH TERRAIN AND TRACKING
THROUGH AN AREA CHARACTERIZED BY A PERSISTENT SURFACE FRONTAL ZONE
AND ENOUGH ANTECEDENT WET GROUND TO BOOST LOW LEVEL MOISTURE /
INSTABILITY. AN ORGANIZED MCS HAD FORMED...AND ALTHOUGH IT WAS A
SMALL MCS AT 01Z...IT WILL TRACK OVER RECENTLY SATURATED
SOILS...WHICH ENHANCES THE POTENTIAL FOR RAPID RUNOFF. WPC
INTRODUCED A MARGINAL RISK AREA FOR MUCH OF THE TEXAS PANHANDLE.


...SOUTHWEST SOUTH DAKOTA...

A VERY SMALL SCALE THREAT OF FLASH FLOODING HAD FORMED BY MID
EVENING NEAR AND SOUTH OF RAPID CITY. ORGANIZED VIGOROUS
CELLS...SOME ATTEMPTING TO TAKE ON UPDRAFT ROTATION...WERE
ANCHORED ALONG A WARM FRONT. LOW LEVEL INFLOW OF 20 TO 30 KNOTS
WILL SUSTAIN THIS ACTIVITY...WHICH MAY BE VERY SLOW MOVING AND
FEATURE A FEW CELL MERGERS UNTIL SUCH TIME AS DEEP LAYER FORCING
AND MORE OUTFLOW DOMINATED CONVECTION OVERTAKES THE REGION FROM
THE WEST. ISOLATED 3-PLUS INCH RAINFALL IS POSSIBLE...MAINLY EAST
THROUGH SOUTHEAST OF RAPID CITY.

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

BURKE
$$





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