Quantitative Precipitation Forecast
Issued by NWS

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000
FOUS30 KWBC 100840
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
340 AM EST SAT DEC 10 2016

...VALID 12Z SAT DEC 10 2016 - 12Z SUN DEC 11 2016...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
40 SSE TVL 35 NW MMH 25 WSW MMH 35 NNE FAT 35 NE MCE 35 NE MOD
25 ESE MHR 10 NE BAB 20 E CIC 35 NE CIC 55 N BLU 15 S TRK
40 SSE TVL.


...NORTHERN AND CENTRAL SIERRA-NEVADA...

A ROBUST ATMOSPHERIC RIVER WILL BE IMPACTING THE FOOTHILLS AND
HIGHER TERRAIN OF THE NORTHERN AND CENTRAL SIERRA-NEVADA THROUGH
SAT WITH VERY HEAVY RAIN AS A STRONG DEEP LAYER WESTERLY FETCH OF
PACIFIC MOISTURE AND ENHANCED FORCING CROSSES THE REGION. A
CONSENSUS OF THE 00Z HIRES ARW/NNMB AND NSSL-WRF SHOW ENHANCED LOW
TO MID LEVEL ONSHORE FLOW ARRIVING THIS MORNING OUT AHEAD OF A
SHORTWAVE IMPULSE AND AN ASSOCIATED 130 TO 150 KT 250 MB JET
STREAK. THIS WILL DRIVE STRONG LARGE SCALE ASCENT...AND
ADDITIONALLY THE ENERGY WILL BE DRIVING A WEAK AREA OF LOW
PRESSURE ALONG A FRONTAL ZONE THAT WILL CROSS NORTHERN CA BETWEEN
12Z AND 18Z. THE LARGELY ORTHOGONAL COMPONENT OF THE LOW TO MID
LEVEL FLOW RELATIVE TO THE TERRAIN ALONG WITH THE FRONT...COUPLED
WITH 850/700 MB MOISTURE FLUX ANOMALIES OF 3 TO 5 STANDARD
DEVIATIONS ABOVE NORMAL...AND PRECIPITABLE WATER VALUES OF OVER 3
STANDARD DEVIATIONS ABOVE NORMAL WILL FOSTER HEAVY RAINFALL RATES
FOR THE WEST-FACING SLOPES OF THE NORTHERN AND CENTRAL
SIERRA-NEVADA. RAINFALL RATES ARE LIKELY TO REACH UP BETWEEN A
0.50 TO 1 INCH/HR DURING THE HEIGHT OF THE ATMOSPHERIC RIVER
CONDITIONS THIS MORNING...AND THEN GRADUALLY BEGIN TO TAPER DOWN
THIS AFTERNOON. CONDITIONS WILL STEADILY IMPROVE SAT NIGHT WITH
HEAVY RAINS TAPERING OFF BY EARLY SUN. RAINFALL TOTALS OF AS MUCH
AS 5 TO 8 INCHES WILL BE POSSIBLE...WITH THE HEAVIEST AMOUNTS OVER
THE NORTHERN SIERRA-NEVADA. GIVEN THE HEAVY RAINFALL RATES DURING
THE HEIGHT OF THE EVENT AND THE OVERALL STORM TOTALS...SOME RUNOFF
PROBLEMS/CONCERNS ARE POSSIBLE.

ORRISON

$$




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