Quantitative Precipitation Forecast
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FOUS30 KWBC 100035
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
734 PM EST FRI DEC 09 2016

...VALID 01Z SAT DEC 10 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
50 NNW O54 25 NW O54 20 WSW O54 30 SW O54 50 WSW RBL 45 NNE UKI
30 NNE UKI 20 E UKI 20 NE STS 20 ESE STS 25 S STS 25 SSW STS
25 WSW 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.


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

01Z UPDATE...
NO SIGNFICANT CHANGES TO TIMING OF PCPN BASED ON 12Z GUIDANCE AND
RECENT HRRR/SATL TRENDS.  ALL BRING HEAVIER RAINS INTO THE COASTAL
AREAS BY AROUND 03Z WITH THE HEAVIEST RAINFALL AMOUNTS LIKELY TO
IMPACT THE NRN SIERRA RANGE OVERNIGHT WITH SNOW LEVELS RISING TO
NEAR 10000 FEET.  STILL LOOKING FOR RAINFALL AMOUNTS PSBLY
REACHING UP TO 4 INCHES BY MORNING IN SOME OF THE MORE FAVORED
UPSLOPE AREAS.   SEE MPD#791 IN EFFECT UNTIL 0915Z FOR ADDITIONAL
INFORMATION.  SULLIVAN

PREVIOUS DISCUSSION FOLLOWS...

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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