Quantitative Precipitation Forecast
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000
FOUS30 KWBC 150809
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
309 AM EST WED FEB 15 2017

...VALID 12Z WED FEB 15 2017 - 12Z THU FEB 16 2017...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
65 W OTH 10 W OTH 25 SW RBG 25 W MHS 35 S O54 30 E UKI
20 SSW STS 85 SW STS.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
55 WNW UIL 30 W CWSP CLM 25 ESE CLM 15 N PWT TIW 10 SSE SEA
15 ENE PAE 15 NNE BVS 10 E CYXX CWZA 40 SE CWZA 55 E AWO
15 SSE SMP 30 NNE DLS 15 NW DLS 20 SSE CZK UAO 10 S MMV
15 NW CVO 20 S ONP 40 W ONP.


...PACIFIC NORTHWEST SOUTHWARD INTO NORTHERN CALIFORNIA...

HEAVY PRECIPITATION ACROSS THE PAC NW WILL BE EXPANDING SOUTHWARD
INTO NORTHERN CA THIS PERIOD PER THE APPROACHING BROAD UPPER
TROUGH AND INCREASINGLY EXPANSIVE AREA OF UPPER DIFFLUENCE. ROBUST
WARM CONVEYOR BELT MECHANICS AND ATTENDANT ELONGATED ATMOSPHERIC
RIVER WILL DIVE SOUTHWARD INTO NORTHERN CA THIS PERIOD PER THE
APPROACHING UPPER TROUGH AND HEIGHT FALLS.   STRENGTHENING
SOUTH-SOUTHWESTERLY LOW-LEVEL FLOW IN AN AXIS OF PW VALUES 2 TO 3
STANDARD DEVIATIONS ABOVE THE MEAN WILL SUPPORT WIDESPREAD
OROGRAPHICALLY-ENHANCED HEAVY PRECIP TOTALS ACROSS THE COASTAL
RANGES FROM WA SOUTHWARD INTO NORTHERN CA...ALONG WITH THE WA
CASCADES. HIGHEST TOTALS...AVERAGING BETWEEN 3-4+ INCHES WITH
ISOLATED TOTALS OF 5-7 INCHES...ARE AGAIN EXPECTED OVER THE
OLYMPIC AND CASCADE RANGES IN NORTHERN WA.

GIVEN THE LONG-DURATION OF THIS EVENT...THE THREAT FOR SHORT-TERM
RUNOFF ISSUES WILL BE MINIMAL (I.E. THE EXCESSIVE RAINFALL RISK
"MARGINAL"). THE MARGINAL ERO RISK WILL DROP SOUTH INTO NORTHERN
CA LATER IN THE PERIOD (00-12Z THU)...CORRESPONDING TO THE
SOUTHWARD SHIFT OF THE ATMOSPHERIC RIVER/PW AXIS AND STRENGTHENING
LEFT-EXIT REGION UPPER JET FORCING. SOME OF THE HIGH-RES CAM
GUIDANCE (PARTICULARLY THE WRF-ARW...NAM-CONEST...AND EXPERIMENTAL
NAM-CONEST) IN FACT SHOW ISOLATED POCKETS OF HOURLY RAINFALL RATES
BETWEEN 0.50-0.75" OVER NORTHERN CA WEDNESDAY NIGHT.

HURLEY
$$





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