Quantitative Precipitation Forecast
Issued by NWS

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FOUS30 KWBC 010100
QPFERD

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

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



DAY 1...

01Z UPDATE...

OVERALL FOR THE NORTHERN MID-ATL/NY AND THE LOWER MO/MID MS VALLEY
REGIONS...NO SIGNIFICANT CHANGES IN THINKING FROM THE PREVIOUS
ISSUANCES.  FOR THE LOWER MO/MID MS VALLEY REGION...THE LATEST
HI-RES MODEL CONSENSUS...INCLUDING THE 23Z HRRR...STILL PLACES THE
HEAVIEST AMOUNTS FURTHER TO THE SOUTHWEST THAN THE 12Z/18Z GLOBAL
MODELS...PLACING THE GREATER POTENTIAL FOR FLASH FLOODING ACROSS
CENTRAL-SOUTHWESTERN MO OVERNIGHT.  FOR PORTIONS OF EASTERN
PA...NORTHERN NJ AND SOUTHEASTERN NY...SEE MPD #0283 FOR FURTHER
INFORMATION REGARDING THE ONGOING HEAVY RAINFALL THREAT ACROSS
THAT AREA.  FOR THE NORTHERN PLAINS...A SEE TEXT WAS ADDED TO
ADDRESS THE CONVECTION WITH LOCALLY HEAVY RAINS THAT IS EXPECTED
TO DEVELOP DURING THE EVENING-OVERNIGHT HOURS.

...NORTHERN PLAINS...

OVER THE NEXT SEVERAL HOURS...CONVECTION WILL CONTINUE TO DEVELOP
ACROSS PORTIONS OF THE NORTHERN HIGH PLAINS AS A WELL-DEFINED
TROUGH DROPPING SOUTHEASTWARD OUT OF SOUTHWESTERN CANADA SLIDES
INTO PORTIONS EASTERN MT AND THE DAKOTAS DURING THE LATE EVENING
TO OVERNIGHT HOURS.  LATEST MESOANALYSIS SHOWS MUCAPES OF
2000-3000 J/KG PWS TO THE EAST OF A NORTHWEST-SOUTHEAST ORIENTED
BOUNDARY...WITH PWS EXPECTED TO INCREASE TO AT OR ABOVE 1.5 INCHES
AS SOUTHEASTERLY FLOW AMPLIFIES.  LATEST HI-RES GUIDANCE SHOWS
LOCALLY HEAVY AMOUNTS DEVELOPING ACROSS PORTIONS OF EASTERN MT AND
WESTERN-CENTRAL ND...SLIDING SOUTHEASTWARD INTO EASTERN SD DAKOTA
OVERNIGHT.  WHILE INDIVIDUAL CELLS ARE EXPECTED TO BE
PROGRESSIVE...TRAINING/BACKBUILDING CONVECTION MAY RAISE THE
THREAT FOR LOCALIZED FLASH FLOODING CONCERNS...PARTICULARLY ACROSS
AREAS WHERE THE LATEST 3-HR FFG IS UNDER 1.5 INCHES.

PREVIOUS DISCUSSION...

...NORTHERN MID-ATLANTIC/NY...

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.

PEREIRA/HURLEY/SULLIVAN
$$





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