Quantitative Precipitation Forecast
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000
FOUS30 KWBC 090843
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
342 AM EST FRI DEC 09 2016

...VALID 12Z FRI DEC 09 2016 - 12Z SAT DEC 10 2016...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
30 E MHR 10 S AUN 10 NNW BAB CIC 20 E RBL 10 E RDD 20 E O54
20 SW MHS 15 E MHS 35 ESE MHS 40 ENE RDD 50 NE CIC 25 NNE BLU
15 WNW TVL 25 SW TVL 30 E MHR.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
25 S STS 30 W STS 35 W UKI 25 SSW O87 35 NW O87 15 NNW ACV
10 N CEC 25 NNE CEC 35 E CEC 50 NNW O54 20 WNW O54 35 SW O54
45 WSW RBL 20 ENE UKI 15 ENE STS 25 S STS.


...NORTHWEST CA COASTAL RANGES AND NORTHERN SIERRA-NEVADA...

A FAST-MOVING SHORTWAVE TROUGH AND ASSOCIATED JET STREAK WILL BE
APPROACHING NORTHERN CA FRI NIGHT ALONG WITH A WAVE OF LOW
PRESSURE. THIS WAVE OF LOW PRESSURE AND THE ASSOCIATED UPPER
DYNAMICS WILL DRIVE A RATHER SIGNIFICANT SURGE OF PACIFIC MOISTURE
WITH SOME SUBTROPICAL CONNECTION INTO THE COASTAL RANGES OF
NORTHWEST CA AND INTO THE FOOTHILLS OF THE NORTHERN SIERRA-NEVADA
BY LATE FRI NIGHT. THE 00Z ECMWF AND 00Z GFS BOTH AGREE IN
BRINGING RATHER HEAVY RAINFALL INTO THESE AREAS BETWEEN 00Z AND
12Z SAT. A CONSENSUS OF THE 00Z HIRES ARW/NNMB AND NSSL-WRF
SUPPORTS THIS SCENARIO AS STRONG WEST-SOUTHWEST LOW TO MID LEVEL
ONSHORE FLOW ARRIVES ALONG WITH ROBUST LARGE SCALE ASCENT AHEAD OF
A 130 TO 150 KT 250 MB JET STREAK. THE RELATIVELY ORTHOGONAL
COMPONENT OF THE LOW TO MID LEVEL FLOW RELATIVE TO THE
TERRAIN...COUPLED WITH 850/700 MB MOISTURE FLUX ANOMALIES OF
LOCALLY AS MUCH AS 3 TO 5 STANDARD DEVIATIONS ABOVE NORMAL...AND
PRECIPITABLE WATER VALUES OF AS MUCH AS 2 TO 3 STANDARD DEVIATIONS
ABOVE NORMAL SHOULD FOSTER HEAVY RAINFALL RATES BY LATE FRI NIGHT.
RAINFALL AMOUNTS OF AS MUCH AS 2 TO 3 INCHES WILL BE POSSIBLE
THROUGH 12Z SAT...WITH LOCALLY HEAVIER AMOUNTS OVER THE
WEST-FACING TERRAIN. GIVEN THAT MUCH OF THIS WILL BE FALLING OVER
THE LAST 6 TO 12 HOURS OF THE PERIOD...SOME ISOLATED RUNOFF
PROBLEMS WILL BE POSSIBLE.

ORRISON

$$





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