Quantitative Precipitation Forecast
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FOUS30 KWBC 150021
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
720 PM EST TUE NOV 14 2017

...VALID 01Z WED NOV 15 2017 - 12Z WED NOV 15 2017...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
80 S CWEB 55 NW UIL 30 W CWSP CWSP CLM 10 SW CLM 15 SW CLM
20 SW CLM 30 SSW CLM 35 SSW CLM 30 NW SHN 15 NW SHN 10 WNW SHN
15 W OLM 30 WNW TDO 25 WNW KLS 20 E AST 20 SE AST 15 N S47
15 WNW S47 35 W S47 60 W S47 80 W S47.


01Z UPDATE...

NO CHANGES FOR MARGINAL RISK AREA OVER THE PAC NW COASTAL AREAS.
LATEST SATL/RADAR IMAGERY CONTINUED TO SHOW A FAIRLY INTENSE AND
SLOW MOVING NE/SW ORIENTED BAND OF MDT TO HEAVY RAIN WITH EMBDD
CONVECTIVE ELEMENTS DIRECTED INTO THE UPPER WA COAST/OLYMPICS IN
ADVANCE OF A VERY SLOW MOVING COLD FRONT ASSOCD WITH DEEP OFFSHORE
UPPER LOW.  18Z GUIDANCE CONTINUE TO SUPPORT EARLIER MODEL TRENDS
IN FOCUSING SOME VERY HEAVY RAINS ACROSS THE LOWER ELEVATIONS OF
THE OLYMPIC RANGE AND COASTAL RANGES FOR THE REMAINDER OF THE
OVERNIGHT PD WITH ADDITIONAL RAINFALL AMOUNTS OF 3 TO 6 INCHES
POSSIBLE AS STG LEFT EXIT REGION JET FORCING DVLPS OVER THE
REGION.  THESE AMOUNTS COULD LEAD TO RAPID SURFACE RUNOFF IN SOME
LOCATIONS.   SULLIVAN   PREVIOUS DISCUSSION FOLLOWS...

...OLYMPIC PENINSULA SOUTHWARD INTO FAR NORTHERN OREGON COAST
RANGE...

IN THE WAKE OF THE LEAD AREA OF HEIGHT FALLS THAT EJECTED OUT OF
THE MEAN TROF POSITION OFF THE PACIFIC NORTHWEST COAST AND INLAND
THROUGH THE PACIFIC NORTHWEST ON MONDAY---ADDITIONAL UPSTREAM
HEIGHT FALLS WILL RE-AMPLIFY THE MEAN CLOSED LOW POSITION OFF THE
SW COAST OF BRITISH COLUMBIA/VANCOUVER ISLAND THIS UPCOMING
PERIOD. THE AMPLIFICATION WILL HELP FOCUS STRENGTHENING
SOUTH-SOUTHWESTERLY LOW LEVEL FLOW INTO THE PACIFIC NORTHWEST. PW
VALUES IN THIS ONSHORE FLOW AXIS ARE NOT EXPECTED TO BE
ANOMALOUS---GENERAL AT OR SLIGHTLY BELOW SEASONAL NORMS. AS THE
CLOSED LOW AMPLIFIES...HOWEVER...THE LOW LEVEL INFLOW WILL REMAIN
FOCUSED INTO PORTIONS OF THE PACIFIC NORTHWEST FROM THE NORTHERN
OREGON COAST RANGE NORTHWARD INTO THE OLYMPIC RANGE AND INTO THE
NORTHERN WASHINGTON CASCADES. THIS WILL SUPPORT POTENTIAL FOR VERY
HEAVY PRECIPITATION AMOUNTS ACROSS THESE AREAS...ESPECIALLY INTO
THE OLYMPIC RANGE WHICH WILL HAVE THE GREATEST UPSLOPE ENHANCEMENT
TO THE DEEP LAYER ASCENT. ADDITIONALLY...THE 12Z SOUNDING AT
QUILLAYUTE WASHINGTON SAMPLED STEEP LAPSE RATES THROUGH THE DEPTH
OF THE COLUMN...AND EARLY MORNING RADAR IMAGERY AND LIGHTNING
DETECTION INDICATED THUNDERSTORMS WITH LOCALLY ENHANCED RAINFALL
RATES. LAPSE RATES ARE LIKELY TO CONTINUE SUPPORTING THUNDER AND
EMBEDDED THUNDER WELL INTO THE EVENING AS SYNOPTIC FORCING
INCREASES TO THE LEFT OF AN UPPER JET STREAK.

MAX 24-HOUR PRECIP AMOUNTS IN THE 5 TO 8 INCH RANGE ARE EXPECTED
IN THE OLYMPIC RANGE...WITH 2 TO 4 INCHES SOUTH OF THIS INTO THE
NORTHERN OREGON COASTAL RANGE. HOURLY RAINFALL RATES ARE FORECAST
TO REACH AT LEAST 0.50 INCHES. RAPID SURFACE RUNOFF MAY DEVELOP.




BURKE/ORAVEC

$$





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