Quantitative Precipitation Forecast
Issued by NWS

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FOUS30 KWBC 201848
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
148 PM EST SAT DEC 20 2014

...VALID 18Z SAT DEC 20 2014 - 00Z MON DEC 22 2014...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
15 E MFR 20 E RBG 30 SE EUG 25 ESE SLE TTD 35 NNW CZK 45 N CZK
40 NNE CZK 15 NNW DLS 25 SSW DLS 25 NW RDM 25 SSW RDM 60 SSW RDM
60 N LMT 20 NW LMT 30 WNW LMT 15 E MFR.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
15 WNW TDO 15 SW KLS HIO 15 WNW SLE 10 SW EUG 25 NW SXT
45 ESE CEC 30 WNW O54 10 SSE ACV 30 NNW CEC 30 SSW OTH
30 SSW ONP 15 S AST 15 SSE HQM 30 N HQM 20 E UIL 10 SW CLM
30 SSE CLM 10 S SHN 15 WNW TDO.



...WA TO NRN CA COASTAL RANGES AND THE OR/SOUTHERN WA CASCADES...

A POWERFUL 150+ KT UPPER LEVEL JET WILL TAKE AIM AT THE PAC NW
COAST THIS PERIOD AND WITH IT WILL COME A SIGNIFICANT HEAVY TO
POTENTIALLY EXCESSIVE RAINFALL EVENT FOR MUCH OF THE COASTAL
RANGES AND CASCADES. MODELS CONTINUE TO HAVE HAD A GOOD HANDLE ON
THIS SYSTEM FOR THE PAST SEVERAL RUNS... AND CONTINUE TO SHOW
RATHER GOOD MASS FIELD AGREEMENT. THE LATEST SATELLITE IR/WV LOOPS
SHOW AN ELONGATED MOISTURE FETCH (AXIS OF ANOMALOUS PRECIPITABLE
WATER VALUES) EMANATING FROM THE SUBTROPICS BEING RAPIDLY DIRECTED
INTO COASTAL AREAS OF WA INTO NRN CA. THE ANOMALOUSLY HIGH
MOISTURE TRANSPORT (3-4 STANDARD DEVIATIONS ABOVE NORMAL) WILL
CONTINUE TO FOCUS ACROSS THE PAC NW COAST... ESPECIALLY OVER
OREGON WHERE THE AXIS OF MAX PWATS (1.25 INCHES ALONG THE OR
COAST) WILL REMAIN FOCUSED. THE DEEP-LAYERED AND VERY STRONG
WESTERLY FLOW WITH 850 MB WINDS INCREASING TO 40-50 KTS WILL LEAD
TO VERY STRONG OROGRAPHIC LIFT THROUGH MUCH OF THE COASTAL RANGES
INTO THE CASCADES. WPC CONTINUED TO LEAN HEAVILY TOWARD THE HIGHER
RESOLUTION GUIDANCE AND CONTINUITY TO SMOOTH OUT SMALL MESOSCALE
DIFFERENCES WHILE MAINTAINING BETTER OROGRAPHIC DETAIL. SNOW
LEVELS WILL CONTINUE TO RISE WITH THE INCREASED PACIFIC ONSHORE
FLOW/WAA AND THE COMBINATION OF EXPECTED VERY HEAVY RAINFALL AND
SNOW MELT WILL LIKELY LEAD TO RUNOFF ISSUES OVER LOWER ELEVATIONS
OF THE CASCADES AS WELL AS OVER THE COASTAL RANGES. 30 HOUR
AREAL-AVERAGE RAINFALL AMOUNTS -- FROM 18Z SAT THROUGH 00Z MON --
ARE EXPECTED TO RANGE BETWEEN 3-5 INCHES ALONG THE
OROGRAPHICALLY-FAVORED COASTAL RANGES AND FROM 4-8 INCHES ACROSS
THE OR CASCADES... WITH HIGHER AMOUNTS EXPECTED (LOCALLY OVER 10
INCHES) PER THE HIGHER RESOLUTION GUIDANCE. THE LATEST SSEO MEAN
40 KM NEIGHBORHOOD PROBABILITIES OF 3-6 HOURLY QPF EXCEEDING 3-6
HOURLY FFG TOP OUT OVER 70% OVER THE OR AND SOUTHERN WA CASCADES.

HURLEY

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