Quantitative Precipitation Forecast
Issued by NWS

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FOUS30 KWBC 261849
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
148 PM EST FRI DEC 26 2014

...VALID 18Z FRI DEC 26 2014 - 00Z SUN DEC 28 2014...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
BPT 40 ESE ESF 35 NNW PIB 45 E HBG 20 SE NBG 15 NNE KVQT
25 W KCRH BPT.


...LOWER MISSISSIPPI VALLEY...

THE AMPLIFIED UPPER LEVEL TROUGH INCORPORATING BOTH THE NRN STREAM
AND SOUTHERN STREAM SHORTWAVES (CURRENTLY ACROSS THE NRN HIGH
PLAINS AND OVER THE 4 CORNERS REGION RESPECTIVELY) WILL MAINTAIN A
POSITIVE TILT THROUGH DAY 1 (00Z SUN)...AS THE NRN STREAM WAVE
PUSHES FASTER COMPARED TO THE ONE IN THE SOUTHERN STREAM. THE NET
AFFECT OVER TIME WILL BE AN EXPANDING AREA OF MOD-HEAVY RAINFALL
ACROSS THE LOWER MS VALLEY RESPONDING TO BOTH NRN/SRN STREAM
DYNAMICS. THE SOUTHERN STREAM DYNAMICS WILL BE RESPONSIBLE FOR THE
SURGE IN LOW-LEVEL SOUTHERLY INFLOW (30-40 KTS AT 850 MB) AND
CORRESPONDING ANOMALOUS MOISTURE FLUX/PRECIPITABLE WATER VALUES --
PARTICULARLY AFTER 12Z SAT. THE ENSEMBLES SHOW BOTH THE 850-700 MB
MOISTURE FLUX AND PWATS (1.75-2.00 INCHES) PEAKING AROUND 2.5
STANDARD DEVIATIONS ABOVE THE NORM FOR LATE DECEMBER.
MEANWHILE...MUCAPES OVER THE OUTLOOK AREA ARE EXPECTED TO CLIMB
BETWEEN 1000-1500 J/KG PER THE LATEST ARW. THESE PARAMETERS WILL
SET THE STAGE FOR A VERY FAVORABLE THERMODYNAMIC ENVIRONMENT FOR
THE TIME OF YEAR...WHILE THE COUPLED DYNAMICAL FORCING AHEAD OF
THE SOUTHERN STREAM TROUGH AND IN THE RIGHT-ENTRANCE REGION OF THE
BROAD NORTHERN STREAM UPPER CONFLUENCE ZONE (JET AXIS) WILL
MAINTAIN A PROLONGED PERIOD OF LOW-MID LEVEL FRONTOGENESIS AND
DEEP-LAYER ASCENT ON SAT. THIS AS UPPER LEVEL HEIGHT FALLS ARE NOT
EXPECTED TO MOVE INTO THE OUTLOOK AREA UNTIL EARLY SUN. GIVEN THE
DEEP LAYER S-SW FLOW (DIRECTIONAL SHEAR DECREASING WITH
TIME...PARTICULARLY AFTER 12Z SAT)... THE MODELS SHOW WEAKENING
CORFIDI VECTORS DURING THE PERIOD WHEN THE LOW LEVEL JET PEAKS
NEAR 40 KTS...SUPPORTIVE OF INCREASED UPWIND PROPAGATION AND
POTENTIAL FOR TRAINING OF HEAVIER SHOWERS AND TSTMS.  WPC
AREAL-AVERAGE QPF OVER THE OUTLOOK AREA RANGES BETWEEN 1.5 AND 3
INCHES...THOUGH SOME OF THE HIGHER RESOLUTION GUIDANCE (INCLUDING
THE NAM CONEST...WRF-NMMB...AND NSSL-WRF) NOTE LOCALIZED AMOUNTS
BETWEEN 3-6+ INCHES.

HURLEY
$$




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