Quantitative Precipitation Forecast
Issued by NWS

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FOUS30 KWBC 241839
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
238 PM EDT THU JUL 24 2014

...VALID 18Z THU JUL 24 2014 - 00Z SAT JUL 26 2014...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
20 NE BLH 45 W EED 30 SW HND 30 NNE LSV 25 NW SGU 30 NE CDC
40 NE BCE 20 NNE 4HV 50 NE U28 40 SE VEL 10 WSW HDN 25 ENE 20V
30 ENE MYP 20 ENE CPW 15 E DRO 70 S 4BL PRC 20 NE BLH.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
50 SSE HSE 50 SE MRH 40 ESE ILM 15 SE EYF FAY TTA 10 NW RDU LHZ
10 SSW RWI 20 ESE ISO 35 NE NKT 20 NW HSE 25 NE HSE 35 E HSE
50 SSE HSE.


...EASTERN NORTH CAROLINA...

A FRONTAL BOUNDARY WILL SLOWLY DESCEND THROUGH NORTH CAROLINA
DURING PEAK HEATING TODAY. AN MCS THIS MORNING HAD LAID OUT AN
OUTFLOW BOUNDARY FROM CENTRAL TO EAST-CENTRAL NC WHICH IS LIKELY
TO FOCUS LOCALLY GREATER COVERAGE OF THUNDERSTORMS WITH HEAVY
RAINFALL. AT 18Z MIXED LAYER CAPE WAS IN EXCESS OF 2000 J/KG PER
THE SPC MESOANALYSIS. MID LEVEL ASCENT WILL DEEPEN AND STRENGTHEN
TO THE REAR OF AN INTENSIFYING JET STREAK IN THE WESTERN
ATLANTIC...AND AHEAD OF AN ANOMALOUSLY DEEP TROUGH AXIS EXITING
THE APPALACHIANS. WITH SUSTAINED LOW LEVEL INFLOW A TICK ABOVE
CLIMATOLOGICAL NORMS...ORGANIZED CONVECTION IS LIKELY TO OCCUR
WITHIN AN ENVIRONMENT CHARACTERIZED BY PRECIPITABLE WATER OF NEAR
2 INCHES AND LITTLE OR NO OPPORTUNITY FOR HAIL PRODUCTION.

FLASH FLOOD GUIDANCE IN THIS REGION IS ON THE HIGH SIDE...AS IS
TYPICAL...BUT THE ENVIRONMENT DOES FAVOR PARTICULARLY HEAVY
RAINFALL...POTENTIALLY REACHING THE 2.5 TO 3.0 INCH IN 1-3 HOURS
GUIDANCE NUMBERS IN A FEW LOCATIONS.


...COLORADO/UTAH...

PER EARLY MORNING RAOBS...AND SATELLITE AND MODEL ANALYSES...A
MOISTURE PLUME WAS BEING DRAWN UP AROUND THE IMMEDIATE WEST SIDE
OF THE UPPER RIDGE CENTER...AND INTO EASTERN UTAH/WESTERN
COLORADO. NAM/RAP/HRRR FORECASTS INDICATE RESPECTABLE CAPE OF
500-750 J/KG BY MIDDAY...WHILE ASCENT AND INFLOW AT CLOUD BASE
BECOMES SLIGHTLY ENHANCED BY THE DEEP NORTHWESTERN U.S. CYCLONE
BRUSHING ACROSS THE PERIPHERY OF THE UPPER RIDGE. THIS SUGGESTS
SOME ORGANIZATION OF CONVECTIVE STORMS TODAY A BIT GREATER THAN
USUAL...WITH SOME POTENTIAL FOR BACK-BUILDING AND BRIEF TRAINING
EPISODES AS THE ENHANCED 700-600 MB SOUTHWESTERLIES SUPPORT
REDEVELOPMENT ALONG OUTFLOWS. PRECIPITABLE WATER WILL LIKELY
INCREASE TO ABOUT 1.10 INCHES...OR 1.5 TO 2 STANDARD DEVIATIONS
FROM CLIMATOLOGY. THOUGH THIS REGION HAS NOT BEEN PARTICULARLY WET
RECENTLY...BASED ON 14-DAY DEPARTURES FROM NORMAL...THE TYPICALLY
FLASHY TERRAIN FEATURES MAY RECEIVE QUICK DOSES OF 0.75 INCHES OR
MORE OF RAINFALL. GIVEN THE WELL DEFINED SYNOPTIC SITUATION AND
CLUSTERING OF HIGH RESOLUTION MODEL QPFS...WE INTRODUCED A SLIGHT
RISK OF EXCESSIVE RAINFALL FOR UT/CO TODAY.

A SECOND SLIGHT RISK AREA WAS INTRODUCED OVER AZ/NV/CA IN
ANTICIPATION OF AN EVENT FRIDAY AFTERNOON. BOTH THE GFS AND ECMWF
FORECAST A MODERATELY BROAD PLUME OF GREATER PRECIPITABLE
WATER...ABOVE 1.5 INCHES...TO NOSE NORTHWARD INTO THE LOW DESERTS
AND REACHING SOME OF THE MOUNTAINOUS TERRAIN BETWEEN
FLAGSTAFF...VEGAS...AND SOUTHEAST CA. ASIDE FROM INCREASED
CONVECTIVE COVERAGE FRIDAY AFTERNOON...SOME SLIGHT ENHANCEMENT OF
SOUTHERLY INFLOW IS FORECAST NEAR CLOUD BASE...PERHAPS AIDING
UPSCALE GROWTH OF SOUTHWARD PROPAGATING STORM CLUSTERS.


...SD/MN/IA...

THE 12Z RUNS OF THE ARW...NMM...AND NSSL WRF AT LEAST HAD SOME
PRECIPITATION SIGNAL THROUGH THIS AFTERNOON...BUT NO MODEL WAS
HANDLING CONVECTION PARTICULARLY WELL ALONG A NNW-SSE ORIENTED
BAROCLINIC ZONE. WITH 850 MB INFLOW AND MID LEVEL ASCENT GRADUALLY
INCREASING AHEAD OF THE VIGOROUS NORTHWESTERN U.S.
SHORTWAVE...THERE MAY BE LESS DEPENDENCE ON THE DIURNAL LOW LEVEL
JET CYCLE...ALLOWING THUNDERSTORMS TO PERSIST THROUGH THIS
AFTERNOON. ESTABLISHMENT OF A BROAD COLD POOL ALONG THE BORDER OF
SD WITH MN/IA...AND EXTENDING DOWN INTO IA...IF IT OCCURS BASED ON
EARLY TRENDS...COULD REINFORCE THE BAROCLINIC ZONE AND CAUSE A
MORE FOCUSED INTERCEPT OF THE INCREASED INFLOW LATER THIS EVENING.
THE 12Z RUNS OF THE MODELS MENTIONED ABOVE DO PREDICT A FOCUSED
SWATH OF HEAVY RAINFALL TONIGHT ACROSS MAINLY CENTRAL IOWA. FLASH
FLOOD GUIDANCE HAS RECOVERED OVER THIS REGION DURING A RELATIVELY
DRY STRETCH OF WEATHER IN THE PAST TWO-PLUS WEEKS. THE ENVIRONMENT
LENDS ITSELF TO SOME SEVERE WEATHER...INCLUDING HAIL...AND
MARGINAL PRECIPITABLE WATER VALUES MAY LIMIT THE INSTANTAENOUS
RAIN RATES...BUT AREA WILL NEED TO BE WATCHED FOR A POTENTIALLY
LENGTHY DURATION TRAINING EVENT...AND POSSIBLE UPGRADE TO SLIGHT
RISK.

BURKE
$$




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