Quantitative Precipitation Forecast
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FOUS30 KWBC 200100
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
859 PM EDT FRI MAY 19 2017

...VALID 01Z SAT MAY 20 2017 - 12Z SAT MAY 20 2017...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
10 SSW CHK 25 E PPF 30 SSE OJC OJC 15 SSE FOE 30 SW EMP EWK
25 SSE CNK 30 SW HJH 25 NNE EAR 20 NW BVN 25 NE OFK 10 S DNS
20 WSW LWD FSW 10 W DEC 10 ESE OLY 35 SE BAK 40 SE ILN
25 NNE UNI 15 SSW CLE 25 WNW YNG BVI 25 WNW CKB 15 SW CRW
30 E JKL 25 SSE FTK 35 WNW HOP 15 E NQA 25 W PBF 25 SW TXK TPL
35 NE JCT 10 E SJT 50 NNE SWW 10 SSW CHK.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
BLV 15 SSW POF 15 S SRC 20 NW TXK 15 NNE 3T1 10 WNW PWG
50 SSW BWD DYS 20 SSW DUC 15 W OKM 15 SE JLN 15 S DMO 45 NNE COU
25 N SET BLV.

MODERATE RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
25 W 1F0 MKO 15 W HRO 40 NE RUE 30 W LZK 15 N DEQ 15 NNW SLR
10 SE DAL 20 NW GDJ 20 NNW SEP RPH 25 W 1F0.




...PLAINS/MS VALLEY...GULF COAST STATES...OH/TN
VALLEYS...MID-ATLANTIC...

0100 UTC UPDATE...

HAVE SCALED BACK THE MARGINAL AND SLIGHT RISK AREAS CONSIDERABLY
-- MOST NOTABLY ACROSS EASTERN KS/NE AND ACROSS THE OH VALLEY INTO
THE MID ATLANTIC REGION -- BASED ON THE CURRENT CONVECTIVE TRENDS
AS DEEP-LAYER INSTABILITY (MUCAPES) CONTINUES TO WANE. THE
ACTIVITY EAST OF THE MISSISSIPPI HAS EXHIBITED THE MOST PRONOUNCED
WEAKENING TREND OF LATE... GIVEN THAT THE ACTIVITY HERE (EAST OF
THE UPPER RIDGE AXIS) IS CLOSELY CORRELATED TO THE DIMINISHING
SURFACE-BASED INSTABILITY WHILE THE DEEP-LAYER SHEAR AND LOW LEVEL
INFLOW REMAIN WEAK.

HURLEY



1930 UTC UPDATE...

SOME SIGNIFICANT CHANGES TO THE EXCESSIVE RAINFALL OUTLOOK ARE
NECESSITATED AT THIS TIME GIVEN THE LATEST CONVECTIVE TRENDS ALONG
WITH HIRES MODEL SIGNALS.

THE STRONG CLOSED MID TO UPPER LOW CURRENTLY CROSSING THE CENTRAL
ROCKIES WILL EJECT EAST OUT ACROSS THE CENTRAL HIGH PLAINS
OVERNIGHT AND THIS WILL DRIVE SURFACE LOW PRESSURE FROM THE
SOUTHERN HIGH PLAINS NORTHEAST UP THROUGH THE LOWER MO VALLEY BY
12Z SAT. A VIGOROUS TRAILING COLD FRONT THAT WILL EJECT EAST
ACROSS THE SOUTHERN PLAINS FROM SOUTHERN KS DOWN ACROSS CENTRAL
TX. THIS STRONG SYNOPTIC SCALE SYSTEM WITH AN IMPRESSIVE ARRAY OF
JET FORCING/DYNAMICS WILL BE INTERACTING WITH PLENTY OF DEEPER
LAYER MOISTURE/INSTABILITY TRANSPORT FOR WIDESPREAD SHOWERS AND
THUNDERSTORMS WHICH WILL BE FOCUSED ALONG AND AHEAD OF THE COLD
FRONT. ONE OF THE MAJOR CHALLENGES TO THE FORECAST...ESPECIALLY
FOR OVERNIGHT...IS THE PRESENCE OF A PRE-FRONTAL DIFFERENTIAL
HEATING/OUTFLOW BOUNDARY OVER NORTHERN TX AND SOUTHEAST OK
INCLUDING THE RED RIVER VALLEY AREA. THIS BOUNDARY WILL BECOME AN
EFFECTIVE FRONT THIS AFTERNOON AND EVENING THAT IS EXPECTED TO
INTERCEPT SOME OF STRONGER SOUTHERLY LOW LEVEL FLOW AND ASSOCIATED
MOISTURE TRANSPORT WHILE ALSO REPRESENTING A NEW WELL-DEFINED
INSTABILITY GRADIENT FOR CONVECTION TO FOCUS ALONG. MEANWHILE...AN
UPSTREAM JET MAX EJECTING OUT OF THE SOUTHERN ROCKIES WILL PIVOT
THROUGH THE SOUTHERN HIGH PLAINS AND PLACE THE RED RIVER VALLEY
AREA IN A FAVORABLE REGION FOR STRONGER JET ASCENT/FORCING WHICH
SHOULD AID CONVECTION. WHILE THERE WILL STILL LIKELY BE CONVECTION
FARTHER NORTH ALONG THE COLD FRONT...IT IS EXPECTED THAT THE MORE
ORGANIZED CONVECTION WILL BE FARTHER SOUTH CLOSER TO THE RED RIVER
VALLEY OVERNIGHT AND THROUGH EARLY SAT...WITH A CONVECTIVE AXIS
THAT EXTENDS NORTHEAST UP ACROSS CENTRAL/EASTERN AR AND MUCH OF
EASTERN MO BEFORE THEN GRADUALLY ADVANCING EAST INTO THE OH VALLEY
DOWNSTREAM. PWATS OF 1 TO 2 STANDARD DEVIATIONS ABOVE NORMAL AND A
GOOD SET-UP FOR TRAINING/BACK-BUILDING CELLS WILL PROMOTE AS MUCH
AS 2 TO 4 INCH RAINFALL TOTALS...WITH ISOLATED 5+ INCH AMOUNTS NOT
OUT OF THE QUESTION. THE HEAVIEST TOTALS ARE LIKELY TO BE IN THE
NEW MODERATE RISK AREA WHICH INCLUDES NORTHERN TX AND SOUTHEAST
OK. THIS IS WHERE THE GREATEST FLASH FLOOD THREAT IS AT THIS TIME.
AN OTHERWISE LARGE AREA OF 1 TO 2 INCH AMOUNTS ARE STILL EXPECTED
ELSEWHERE INCLUDING MUCH OF THE MID MS AND OH VALLEY AREA WHERE
MULTIPLE ROUNDS/CLUSTERS OF THUNDERSTORMS THIS EVENING AND
OVERNIGHT WILL RESULT IN SOME ELEVATED CONCERNS FOR FLASH
FLOODING...AND THIS AN EXPANSIVE SLIGHT RISK AREA IS MAINTAINED TO
ACCOMMODATE THIS THREAT. FARTHER EAST WITH THIS UPDATE...WE HAVE
INCLUDED THE GREATER MID-ATLANTIC REGION IN A MARGINAL RISK GIVEN
THE HIGHER PWAT ENVIRONMENT AND EXPECTATION OF THUNDERSTORMS
ADVANCING EAST OF THE APPALACHIANS THIS EVENING AND OVERNIGHT.
THESE LATEST CHANGES ARE WITH RESPECT TO THE LAST SEVERAL RUNS OF
THE HRRR/HRRRX AND THE 12Z WRF-ARW AND NSSL-WRF SOLUTIONS...WHICH
IN PARTICULAR SUPPORT THE AFOREMENTIONED ADJUSTMENTS OVER THE
CENTRAL/SOUTHERN PLAINS AND MID MS VALLEY.

ORRISON
$$





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