Quantitative Precipitation Forecast
Issued by NWS

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FOUS30 KWBC 200829
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
428 AM EDT SAT MAY 20 2017

...VALID 12Z SAT MAY 20 2017 - 12Z SUN MAY 21 2017...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
75 N MMMV 20 W ECU 25 ENE OSA 10 WNW LRF 15 N M19 45 WNW POF
20 SE GBG 20 SE CWI 15 NNE MXO DEH AUM 20 E FRM 20 E PQN
15 E HON 15 SSE ABR 10 SSW FAR FSE 15 SSE VWU 10 ESE EVM IWD
25 SE EGV 20 E SUE 20 NE CAD 15 WSW OSC 20 WSW CWGD HZY CKB
25 N AVC 10 SE EDE HSE 50 ESE MRH 20 SSE MRH 25 SW MRH CTZ
20 NNW SOP 20 NNE SVH 15 WNW TNB 20 SSW TRI 15 NW FQD 20 ESE GSP
DNL EZM 20 E 11J 35 NNE 1B7 25 WNW KCRH 15 SSW PSX 15 NE HBV
55 NNE MMAN 40 ESE MMMV 75 N MMMV.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
15 WSW MKJ 10 NNE LNP 35 ENE JKL 30 SE HTS 15 S CRW 20 W LWB
20 NNW ROA 25 SW LYH 15 NNE BUY 15 WSW MKJ.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
20 NNE LHB 25 WSW ELD 20 N DYR 20 N TIP 25 E UGN 25 ENE MKG
10 ESE OZW 15 SSE AOH 35 NNW FFT 10 ENE GLW 25 SW CSV 35 W RHP
25 SW AVL GYH 25 ENE IIY MLJ 30 WNW OZR 30 NNE MOB BTR 20 NE VCT
35 NNW RBO 25 SE COT 35 WNW COT 20 NW HDO 20 NNE LHB.


EAST TX---LOWER MS VALLEY---TN VALLEY---SOUTHEAST---OH
VALLEY---LOWER LAKES INTO THE UPPER MS VALLEY

VERY BROAD MARGINAL AND SLIGHT RISK AREAS WERE MAINTAINED FROM THE
PREVIOUS OUTLOOK FOR WHAT WILL LIKELY BE ANOTHER ROUND OF
WIDESPREAD HEAVY PRECIPITATION AHEAD OF THE STRONG CLOSED LOW
MOVING NORTHEASTWARD THIS PERIOD FROM THE CENTRAL PLAINS AT THE
BEGINNING OF THE PERIOD INTO THE NORTHERN PLAINS/UPPER MS VALLEY
REGION BY EARLY SUNDAY.  THE RECENT VERY FAVORABLE HEAVY RAIN
PATTERN WILL PERSIST INTO THE NEW DAY 1 PERIOD WITH STRONG LIFT
EXPECTED AHEAD OF THE CLOSED LOW IN AN AXIS OF PW ANOMALIES 1-2+
STANDARD DEVIATIONS ABOVE THE MEAN.  THIS WILL SUPPORT THE VERY
BROAD RISK AREAS EXTENDING FROM EAST TX INTO THE LOWER MS
VALLEY---TN VALLEY/SOUTHEAST--NORTHWARD INTO THE LOWER OH
VALLEY--LOWER LAKES AND UPPER MS VALLEY. CHANGES TO THE PREVIOUS
OUTLOOK AREA WERE TO PUSH THE SLIGHT RISK AREA FARTHER EASTWARD
INTO THE SOUTHEAST/SOUTHERN APPALACHIANS. THIS WAS TO COVER THE
GENERAL MODEL CONSENSUS THAT HEAVY RAINS COULD DEVELOP FARTHER
EAST THAN IN PREVIOUS FORECASTS--ALTHOUGH THE TIMING OF THIS
POTENTIALLY HEAVY RAINS IS VERY DIFFERENT IN THE LATEST GUIDANCE.
A SLIGHT RISK AREA WAS ALSO INTRODUCED ACROSS PORTIONS OF THE
CENTRAL APPALACHIANS FROM IN THE VICINITY OF THE KY/WV/VA
BORDER---SOUTHEAST INTO SW VA.  LOW FFG VALUES HERE AND MODEL
CONSENSUS FOR HEAVY RAINFALL POTENTIAL WARRANTED THE SLIGHT RISK
INTRODUCTION.  RECENT VERIFICATION HAS SHOWN VERY POOR SHORT TERM
MODEL SKILL---WITH THIS LIKELY TO CONTINUE DURING THE UPCOMING DAY
1 PERIOD GIVEN THE LARGE SPREAD IN QPF DETAILS.  THIS IS LEADING
TO LOW CONFIDENCE IN THE DETAILS---BUT AGAIN HIGHER CONFIDENCE
THAT ADDITIONAL VERY HEAVY TO EXCESSIVE RAINFALL AMOUNTS ARE
POSSIBLE GIVEN THE OVERALL FAVORABLE PATTERN.   WHILE THERE MAY
LIKELY BE A WEAKENING TO THE CURRENT ORGANIZED CONVECTION PRIOR TO
OR SHORTLY AFTER 1200 UTC---RE-INVIGORATION OF WIDESPREAD
CONVECTION LIKELY IN THE VERY MOIST AND UNSTABLE AIRMASS AHEAD OF
THE CLOSED LOW.  A PERIOD OF TRAINING OR SLOW CELL MOVEMENT
POSSIBLE THROUGH THE RISK AREAS---ESPECIALLY IN THE 0000 TO 1200
UTC SUNDAY TIME FRAME WHEN CONVECTION WILL LIKELY PEAK. CONFIDENCE
IN WHERE THIS WILL OCCUR IS LOW AND HAS KEPT US FROM ANY DECREASE
IN THE VERY BROAD RISK AREAS.

ORAVEC
$$





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