Quantitative Precipitation Forecast
Issued by NWS

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FOUS30 KWBC 281410
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1010 AM EDT SUN SEP 28 2014

...VALID 15Z SUN SEP 28 2014 - 12Z MON SEP 29 2014...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
10 W 1B7 HSA 25 WNW OZR 15 ENE ABY 15 SSE VLD CTY 60 SW CTY
40 WSW AAF KVKY 10 W 1B7.


...COLORADO/WYOMING ROCKIES...

THE ANOMALOUS DEEP UPPER TROUGH/CLOSED LOW ACROSS THE LOWER GREAT
BASIN WILL SHIFT ONLY SLIGHTLY EASTWARD TODAY...THEREBY
MAINTAINING FAVORABLE DYNAMIC SUPPORT (UPPER
DIFFLUENCE/DIVERGENCE) VIA THE WARM CONVEYOR BELT (WCB) ALONG WITH
THE MOIST...S/SE LOW-LEVEL FLOW AND UPSLOPE ENHANCEMENT ACROSS THE
CENTRAL ROCKIES. THE LACK OF DEEP-LAYER INSTBY (MUCAPES 250-500
J/KG) ALONG WITH THE GRADUAL REDUCTION OF PRECIPITABLE WATER WITH
TIME (AS THE MID/UPPER LEVELS BECOME INCREASINGLY CUT OFF FROM ANY
SUBTROPICAL MOISTURE FEED) WILL LIMIT THE EXCESSIVE RAINFALL
POTENTIAL TODAY. NEVERTHELESS...THE FAVORABLE DYNAMICAL SUPPORT
(WIDESPREAD RAINFALL)...UPSLOPE ENHANCEMENT...WEAK INSTBY...AND
STILL FAVORABLE MOISTURE PROFILES (PWS 2-3 STANDARD DEVIATIONS
ABOVE THE NORM FOR LATE SEPTEMBER) WILL SUPPORT THE POTENTIAL OF
ISOLATED EXCESSIVE SHORT TERM RAINFALL RATES AND THUS RUNOFF
ISSUES...ESPECIALLY OVER THE MORE SLOPED TERRAIN WHERE THE 1-3
HOURLY FLASH FLOOD GUIDANCE WILL BE LOWER.


...CENTRAL/EASTERN GULF COAST...

WHEREAS THERE WAS DECENT MODEL QPF AGREEMENT OUT WEST..SUCH IS NOT
NECESSARILY THE CASE THRU THE GULF COAST AND SOUTHEASTERN
STATES...LEADING TO A LOWER THAN AVERAGE CONFIDENCE FORECAST.  THE
MODELS HAVE BEEN HAVING TROUBLE THRU THIS REGION FOR THE PAST DAY
OR SO...WITH 00Z GUIDANCE FROM LAST NIGHT TOO QUICK TO BRING SOME
HEAVIER RAINS INLAND..AND THIS IS THE CASE AGAIN TONIGHT WITH AT
LEAST A FEW OF THE GLOBAL MODEL QPFS..LIKELY CAUSED IN PART BY
FEEDBACK ISSUES.  GIVEN THAT THE FLOW PATTERN IS FORECAST TO
REMAIN QUITE FLAT ALOFT THIS PERIOD THRU THIS AREA..AND WITH ONLY
A VERY WEAK AREA OF LOW PRESSURE MOVING ALONG THE SURFACE BOUNDARY
THAT WILL PROBABLY REMAIN IN THE NORTHERN GULF OF MEXICO..HAVE
KEPT THE MORE SIGNIFICANT RAINS CONFINED TO NEAR THE CENTRAL AND
EASTERN GULF COAST..AT LEAST INTO MONDAY MORNING.  GAVE VIRTUALLY
NO CREDENCE TO THE 00Z GFS..OLD 12Z ECMWF HIRES AND TO A LESSER
EXTENT THE 00Z UKMET HIRES QPFS..ALL OF WHICH APPEARED TO HAVE
FEEDBACK PROBLEMS..AND INSTEAD WENT CLOSER TO THE HIRES ARW AND
NMMB..CANADIAN GEM REGIONAL AND EVEN THE NAM QPFS FOR THIS
FORECAST. DO SEE THE POTENTIAL FOR SOME 1-2+ INCH AREAL AVERAGE
RAINS ALONG THE IMMEDIATE CENTRAL/EASTERN GULF COAST..WITH
ISOLATED HEAVIER AMOUNTS POSSIBLE.  WENT WITH A SLIGHT RISK THREAT
OF FLASH FLOODING HERE..BUT WITH THE FF GUIDANCE VALUES QUITE HIGH
AND THE POTENTIAL FOR THE HEAVIEST OF RAINS TO REMAIN OUT IN THE
GULF..DO BELIEVE ANY FLOODING CONCERNS WILL BE QUITE ISOLATED.

TERRY/HURLEY
$$




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