Quantitative Precipitation Forecast
Issued by NWS

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525
FOUS30 KWBC 201448
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1047 AM EDT SAT MAY 20 2017

...VALID 15Z 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
55 NNE MMAN 50 NW MMAN 35 SE MMMV 20 NNE MMMV 40 N MMMV
50 WSW MMPG 30 W UVA 20 NNW HDO 15 NNW AUS 20 S PSN 10 E GGG
30 WNW ELD 10 ESE LIT 15 NNE M19 20 NNE FAM ALN 20 NE GBG DBQ
15 NNW DEH 10 NW TOB 10 E ULM 20 SE MML 10 SW BKX 20 E HON
25 N HON 15 E 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.

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
25 W LFT EFD 20 NNE VCT 40 NNW RBO 30 SE COT 10 W COT
20 NNW COT 20 WSW SKF BAZ 10 ENE 62H 20 S LFK 35 NE OCH
35 NE BAD 20 ENE PBF 20 ESE SGT 15 N AWM 10 NW DYR 20 S CIR
10 E MVN 10 N TIP 15 ESE LOT 20 E PWK 40 E RAC 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 25 W LFT.


...15 UTC UPDATE...

SEE NO COMPELLING REASON TO SIGNIFICANTLY ADJUST THE PREVIOUSLY
ISSUED WPC MARGINAL AND SLIGHT THREAT AREAS EXCEPT TO TRIM THE WRN
PERIPHERY TO ACCOUNT FOR SYSTEM/CONVECTION PROGRESSION TRENDS FROM
RADAR THIS MORNING THROUGH 15 UTC.

SCHICHTEL


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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