Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000
FXUS66 KSEW 261552
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
855 AM PDT FRI SEP 26 2014

.SYNOPSIS...A LARGE UPPER LEVEL TROUGH OFFSHORE WILL MOVE INLAND
LATE TODAY. WEAK HIGH PRESSURE WILL BUILD THIS WEEKEND FOR PARTLY TO
MOSTLY SUNNY SKIES. A WEAK COLD FRONT WILL BRING SOME RAIN MONDAY.
COOLER NORTHWEST FLOW ALOFT WILL MAINTAIN MOSTLY CLOUDY SKIES AND A
CHANCE OF SHOWERS NEXT TUESDAY.

&&

.SHORT TERM...AN UPPER TROUGH IS MOVING INTO THE WRN U.S. AND THERE
IS A SURFACE LOW PRESSURE TROUGH NEAR THE WA COAST THIS MORNING.
SHOWERS OVER WRN WA ARE ASSOCIATED WITH A DISTURBANCE THAT SHOWS UP
WELL ON SATIMG. SHOWERS WILL TAPER OFF THROUGH THIS EVENING EXCEPT
PERHAPS IN A PSCZ WHICH THE UW MM5NAM SHOWS. AN UPPER RIDGE WILL
BUILD INTO THE REGION OVER THE WEEKEND SO MORNING CLOUDS SATURDAY
SHOULD GIVE WAY TO CLEARING. AREAS OF MORNING LOW CLOUDS AND FOG ON
SUNDAY SHOULD GIVE WAY TO SUNNY SKIES AS 500MB HEIGHTS PEAK AROUND
5780M

.LONG TERM...00Z EXTENDED MODELS IN GOOD AGREEMENT AND SHOWING GOOD
RUN TO RUN CONTINUITY WITH THE TIMING OF THE NEXT SYSTEM TO REACH
WESTERN WASHINGTON. THE LAST 3 RUNS HAVE STAYED WITH THE IDEA OF THE
FRONT MOVING INTO WESTERN WASHINGTON MONDAY AFTERNOON. WILL GO WITH
CHANCE POPS IN THE MORNING AND WILL UP THE POPS TO LIKELY FOR THE
AFTERNOON HOURS. UPPER LEVEL TROUGH FOLLOWING THE FRONT MONDAY NIGHT
KEEPING SHOWERS IN THE FORECAST. A PUGET SOUND CONVERGENCE ZONE IS
ALSO POSSIBLE OVER THE CENTRAL SOUND. UPPER LEVEL TROUGH EAST OF THE
AREA ON TUESDAY WITH NORTHWESTERLY FLOW ALOFT. THIS WILL CONFINE
MOST OF THE SHOWER ACTIVITY TO THE COAST AND MOUNTAINS BY TUESDAY
AFTERNOON. BOTH THE GFS AND THE ECMWF SHOWING SOME WEAK RIDGING FOR
WEDNESDAY ON THE 00Z RUN. WANT TO SEE A COUPLE MORE RUNS WITH THIS
SOLUTION BEFORE TAKING THE LOW POPS OUT OF THE FORECAST. MODELS
SOLUTIONS DIVERGE WEDNESDAY NIGHT AND THURSDAY. THE ECMWF BUILDS THE
RIDGE STRONG ENOUGH TO PUSH A FAIRLY WET WARM FRONT NORTH OF THE
AREA. THE GFS IS MUCH WEAKER INITIALLY WITH THE RIDGE WITH A WEAKER
WARM FRONT MOVING INTO WESTERN WASHINGTON WEDNESDAY NIGHT. THE GFS
THEN BUILDS A STRONGER AND HIGHER AMPLITUDE RIDGE OVER WESTERN
WASHINGTON ON THURSDAY WITH 500 MB HEIGHTS APPROACHING 580
DECAMETERS BY 00Z FRIDAY. GIVEN THE LACK OF MODEL CONSENSUS WILL
STAY WITH THE CLIMATOLOGY FORECAST OF LOW CHANCE POPS FOR WEDNESDAY
NIGHT AND THURSDAY. FELTON

&&

.AVIATION...SHOWERS WILL CONTINUE ACROSS WESTERN WA THIS MORNING AS
A SURFACE TROUGH MOVES INLAND. EXPECT MVFR TO IFR CONDITIONS IN
-SHRA. AN UPPER LEVEL TROUGH WILL MAINTAIN MOIST WESTERLY FLOW AND A
FEW MORE SHOWERS THIS AFTERNOON. EXPECT MOIST AND STABLE CONDITIONS
TONIGHT WITH LOW CLOUDS AND/OR FOG THROUGH SAT MORNING. 33

KSEA...SHOWERS WILL REMAIN IN THE VICINITY THIS MORNING AND
AFTERNOON WITH MVFR CONDITIONS POSSIBLE. SURFACE WINDS WILL REMAIN
LIGHT SOUTHERLY. THE AIR MASS WILL REMAIN MOIST TONIGHT WITH LOW
CLOUDS OR FOG SAT MORNING. 33

&&

.MARINE...A SURFACE TROUGH IS MOVING INLAND THIS MORNING WITH
SOUTHERLY WINDS ACROSS WESTERN WA. A SMALL CRAFT ADVISORY REMAINS IN
EFFECT FOR THE COASTAL WATERS...ADMIRALTY INLET...EASTERN STRAIT AND
NORTHERN INLAND WATERS. WINDS WILL EASE THIS AFTERNOON. SEAS ARE
NEAR 10 FT BUT WILL SUBSIDE THIS AFTERNOON. WEAK HIGH PRES WILL
BRING GENERALLY LIGHT WINDS TO WESTERN WA SAT AND SUN. AN ONSHORE
PUSH MAY BRING SMALL CRAFT ADVISORY WINDS TO THE STRAIT SUN NIGHT.
THE NEXT COLD FRONT WILL CROSS WESTERN WA ON MON. ONSHORE FLOW WILL
PREVAIL THROUGH MID WEEK. 33

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...SMALL CRAFT ADVISORY COASTAL WATERS...EAST ENTRANCE STRAIT...
       ADMIRALTY INLET...NORTHERN INLAND WATERS.

&&

$$

YOU CAN SEE AN ILLUSTRATED VERSION OF THIS FORECAST DISCUSSION AT
WWW.WEATHER.GOV/SEATTLE/GAFD/LATEST_WEBAFD.HTML







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