Quantitative Precipitation Forecast
Issued by NWS

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FOUS30 KWBC 301841
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
241 PM EDT TUE JUN 30 2015

...VALID 1841Z TUE JUN 30 2015 - 12Z WED JUL 01 2015...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...



DAY 1...

18Z UPDATE SPECIAL


OH VALLEY...NRN MID ATLC/SRN NY...

PLEASE SEE MPD #281 VALID UNTIL 23Z WITH REGARD TO HEAVY RAIN
POTNL ACRS THIS REGION.

VERY LOW FFG VALUES ACRS PARTS OF THIS AREA AND WITH THREAT OF
PSBL STG CONVECTION WED AFTN/EVENG AHEAD OF OH VALLEY UPR
TROF...POTNL WILL EXIST FOR ISOLD RUNOFF PROBLEMS FROM THE HEAVIER
RAIN PRODUCING TSTMS.  LATEST MESO ANALYSIS SHOWS SB CAPES OF 1000
TO 2500 J/KG  WITH GPS PWS INDICATING VALUES OF NEAR 1.5
INCHES...ESPECIALLY EAST OF THE APLCNS.  WITH DEEP LAYERED SWLY
FLOW ...PONTL WILL EXIST FOR SOME TRAINING BANDS THAT COULD
PRODUCE SOME SHORT TERM RAINFALL AMOUNTS THAT COULD EXCEED THE
LOWER FFG VALUES.


...LOWER MISSOURI VALLEY / MID MISSISSIPPI VALLEY...

THE SHORTWAVE CURRENTLY ALONG THE U.S.-BC/ALBERTA BORDER WILL
CONTINUE TO BREAK DOWN THE UPPER RIDGE...WHICH OVER THE LATTER
HALF OF THE FORECAST PERIOD (00-12Z WED) WILL ALLOW A MORE
SOUTHEASTERLY TURN OF THE SHORTWAVE INTO THE NORTHERN PLAINS.
OVERNIGHT OUT AHEAD OF THIS SHORTWAVE...INCREASING UPPER LEVEL
(300/250 MB) DIFFLUENCE ACROSS THE LOWER MISSOURI VALLEY INTO THE
MID MS VALLEY WILL FAVOR THE FORMATION OF A NOCTURNAL MCS...WITH
THERMODYNAMIC PROFILES BECOMING QUITE FAVORABLE ALONG WITH
STRENGTHENING LOW-LEVEL INFLOW (DEVELOPING LLJ). THE MODELS SHOW
PWS OVER THIS REGION INCREASING TO 1.5-1.75+ INCHES FROM LATE
AFTERNOON TUE THROUGH THE OVERNIGHT AND INTO EARLY WED... ALONG
WITH THE ELEVATED DEEP-LAYER INSTABILITY AS MUCAPES CLIMB TO
1000-2000 J/KG. QUITE A BIT OF SPREAD REMAINS IN THE MODELS WITH
RESPECT TO THE QPF...INCLUDING THE HIGH-RES GUIDANCE...DUE TO THE
FACT THAT SOME (LIKE THE NAM/NAM CONEST) ARE MORE ROBUST WITH THE
EXIT-REGION FORCING AHEAD OF THE WEAK UPPER LEVEL JET
STREAK/LOW-AMPLITUDE SHORTWAVE...AND (THUS) NOTICEABLY STRONGER
WITH THE SOUTHWESTERLY LOW LEVEL JET OVERNIGHT (50+ KTS PER THE
NAM VS. 30-40 KTS PER THE GFS/ECMWF). FOR NOW...WPC OPTED FOR A
MULTI-MODEL BLEND WITH THE QPF...LEANING A BIT TOWARD THE HIGH-RES
GUIDANCE (ESPECIALLY THE NSSL-WRF) WITH RESPECT TO LOCATION/TIMING
OF THE AXIS OF MAXIMUM RAINFALL AMOUNTS. OVERALL...INCREASED MAX
AMOUNTS UP A CAT FROM THE PREVIOUS FORECAST (20 KM AREAL-AVERAGE
BETWEEN .50 AND 1.00 INCH)...HOWEVER AGAIN THE POTENTIAL EXISTS
FOR MUCH HIGHER AMOUNTS (2-4+ INCHES) WITHIN THIS STRIPE PER SOME
OF THE MESOSCALE GUIDANCE...AGAIN DEPENDING ON THE STRENGTH OF THE
LLJ OVERNIGHT. IF THESE HIGHER AMOUNTS MATERIALIZE...ANTICIPATE AT
LEAST ISOLATED AREAS OF POTENTIALLY EXCESSIVE SHORT-TERM RAINFALL
RATES...CONSIDERING THE FFG VALUES BETWEEN 2-2.5 INCHES WITHIN 3
HOURS.

HURLEY/SULLIVAN
$$




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