Quantitative Precipitation Forecast
Issued by NWS

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FOUS30 KWBC 301402
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1002 AM EDT TUE JUN 30 2015

...VALID 15Z TUE JUN 30 2015 - 12Z WED JUL 01 2015...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...



DAY 1...

15Z UPDATE

NO CHANGE TO PREVIOUS OUTLOOK AND REASONING.

...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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