Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000
FXUS66 KSEW 151017
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
315 AM PDT WED OCT 15 2014

.SYNOPSIS...AN UPPER LEVEL TROUGH WILL LIFT NORTH ACROSS WESTERN
WASHINGTON TODAY GIVING SHOWERS AND A CHANCE OF THUNDERSTORMS.
SHOWERS WILL TAPER OFF LATER TONIGHT INTO THURSDAY MORNING. ANOTHER
FRONT WILL REACH THE AREA ON FRIDAY. CONDITIONS WILL SLOWLY DRY OUT
SATURDAY NIGHT INTO SUNDAY AS HIGH PRESSURE AND OFFSHORE FLOW BUILDS
INTO THE AREA. ANOTHER WET FRONTAL SYSTEM WILL ARRIVE EARLY NEXT
WEEK.

&&

.SHORT TERM...A VIGOROUS UPPER LEVEL TROUGH EXTENDING FROM AROUND
48N 135W SOUTHEASTWARD TO THE NORTHWESTERN OREGON COAST WILL LIFT
NORTHWARD ACROSS WESTERN WASHINGTON TODAY. A 997 MB LOW ASSOCIATED
WITH THIS UPPER TROUGH IS SEEN OVER THE WASHINGTON COASTAL WATERS
THAT IS MOVING NORTHWARD TOWARD CENTRAL VANCOUVER ISLAND. THE AIR
MASS WITH THIS UPPER TROUGH IS RATHER UNSTABLE...AND QUITE A
FEW LIGHTNING STRIKES HAVE BEEN OBSERVED OVER THE COASTAL WATERS
OVERNIGHT. EARLIER THIS EVENING THERE WERE SEVERAL THUNDERSTORMS
SEEN OVER SOUTHWESTERN OREGON AND NORTHWESTERN CALIFORNIA. WHILE
LIGHTNING HAS NOT BEEN SEEN WITH THIS BATCH OF SHOWERS OVER THE PAST
FEW HOURS...CLOUD TOPS HAVE BEEN COOLING AS THEY MOVE NORTHWARD
THROUGH THE WILLAMETTE RIVER VALLEY. THUNDERSTORM ACTIVITY IS
POSSIBLE OVER THE INTERIOR OF WESTERN WASHINGTON TODAY AS THE
SHOWERS TO OUR SOUTH ASSOCIATED WITH THE TROUGH AXIS LIFT NORTHWARD.
AS THE TROUGH MOVES NORTH OF THE AREA...SOUTHERLY PRESSURE GRADIENTS
WILL INCREASE AND PRODUCE A PERIOD OF BREEZY SOUTH TO SOUTHWEST
WINDS MOST LOCATIONS.

COOL AIR ALOFT ASSOCIATED WITH THE UPPER LEVEL TROUGH ALONG WITH
LOCALLY HEAVY SHOWER ACTIVITY WILL FORCE SNOW LEVELS DOWN TO AROUND
5500 FEET IN THE CASCADES TODAY AND TONIGHT. THIS SNOW LEVEL IS JUST
ABOVE THE HIGHER WASHINGTON PASS AND LOCATIONS SUCH AS ARTIST POINT
AT MOUNT BAKER AND PARADISE RANGER STATION AT MOUNT RAINIER.
LOCATIONS ABOVE 5500 FEET COULD CERTAINLY SEE 3-8 INCHES OF SNOW IN
HEAVIER SHOWERS TODAY THROUGH THIS EVENING. GIVEN THE RELATIVELY
HIGH SNOW LEVEL OF 5500 FEET OR SO...WILL NOT ISSUE ANY WARNINGS OR
ADVISORIES...BUT WILL ISSUE A SPECIAL WEATHER STATEMENT GEARED
TOWARD GETTING THE WORD OUT TO BACKPACKERS AND HIKERS.

SHOWERS WILL DIMINISH TONIGHT INTO THURSDAY MORNING AS THE TROUGH
LIFTS NORTHWARD THEN A RIDGE OF HIGH PRESSURE ALOFT BUILDS OVER
EASTERN WASHINGTON. THURSDAY APPEARS THAT IT WILL BE A RATHER NICE
DAY OVER THE INTERIOR OF WESTERN WASHINGTON AS LOW LEVEL FLOW TURNS
OFFSHORE. BUT WARM ADVECTION AND A PIVOTING FRONTAL SYSTEM THAT IS
BECOMING INCREASINGLY N-S ORIENTED WILL KEEP A CHANCE OF RAIN GOING
ALONG THE COAST.

THE OFFSHORE FRONT WILL MOVE CLOSER TO THE COAST THURSDAY NIGHT THEN
WILL PUSH SLOWLY INLAND FRIDAY EVENING. MODELS SHOW A PERIOD OF
RATHER HEAVY PRECIPITATION OCCURING OVER PORTIONS OF THE OLYMPIC
PENINSULA AND ALONG THE NORTH COAST AHEAD OF AND WITH THE FRONT
FRIDAY AFTERNOON AND EVENING. WINDY CONDITIONS CAN BE EXPECTED ALONG
THE COAST AND POSSIBLY OVER PORTIONS OF THE NORTH INTERIOR AS THE
FRONT PUSHES INLAND. ALBRECHT

.LONG TERM...THE OFFSHORE FRONT MOVES INLAND FRIDAY NIGHT AND POST
FRONTAL SHOWERS DECREASE EARLY SATURDAY. IN RESPONSE TO STRONG
DEVELOPMENT OVER THE WEST CENTRAL GULF OF ALASKA ON SATURDAY...ALL
LONG RANGE MODELS NOW DEVELOP A RATHER STRONG RIDGE AT THE SURFACE
AND ALOFT FROM THE CANADIAN ROCKIES SOUTHWARD INTO EASTERN OREGON.
OFFSHORE FLOW WILL LIKELY GIVE DRY CONDITIONS TO THE INTERIOR OF
WESTERN WASHINGTON ON SUNDAY...AND NICE OFFSHORE FLOW WILL ALLOW
TEMPERATURES TO RISE TO AROUND 70 DEGREES IN THE PUGET SOUND
LOWLANDS. THE OFFSHORE FRONT WILL BECOME INCREASINGLY N-S ORIENTED
SUNDAY THEN SLOWLY PUSH INLAND AND WEAKEN SUNDAY NIGHT INTO EARLY
NEXT WEEK. WINDY CONDITIONS WITH THE INCOMING FRONT SHOULD BE
LIMITED TO THE COASTAL AREAS AND PORTIONS OF THE NORTH INTERIOR.
ALBRECHT

&&

.AVIATION...AN UPPER LEVEL TROUGH WILL LIFT NORTH TROUGH WESTERN WA
TODAY FOR SHOWERS ACROSS THE REGION. THE FLOW ALOFT IS SOUTHERLY.
THE AIR MASS IS MOIST AND UNSTABLE AND ISOLATED THUNDERSTORMS ARE
POSSIBLE WITH THE PASSING OF THIS TROUGH AXIS. CIGS ARE MAINLY VFR
ALTHOUGH COULD SEE MVFR CIGS WITH -SHRA. SHOWERS ACTIVITY WILL TAPER
DOWN THIS EVENING AS THE TROUGH MOVES NORTH INTO B.C. 33

KSEA...EXPECT MORE SHOWERS TODAY...ISOLD T-STORMS POSSIBLE IN THE
INTERIOR. CIGS MAINLY VFR ALTHOUGH COULD DROP TO MVFR RANGE IN
-SHRA. SURFACE WINDS WILL REMAIN SLY...WITH BREEZY WINDS THIS
AFTERNOON AND EVENING 20015G25KT. 33

&&

.MARINE...WEST SWELLS ARE 10 TO 12 FT AND A SMALL CRAFT ADVISORY FOR
HAZARDOUS SEAS REMAINS IN EFFECT FOR THE COASTAL WATERS TODAY.

A SURFACE TROUGH...ASSOCIATED WITH A 983 MB LOW NEAR HAIDA
GWAII...WILL SHIFT INLAND TODAY. SOUTHERLY ONSHORE FLOW WILL
INCREASE AS THIS TROUGH MOVES NORTH TROUGH WESTERN WA THIS
AFTERNOON. STRONGEST WINDS ARE LIKELY OVER PUGET SOUND AND HOOD
CANAL - A SMALL CRAFT ADVISORY IS IN EFFECT. WINDS WILL EASE AFTER
MIDNIGHT TONIGHT.

A STRONGER PACIFIC FRONTAL SYSTEM WILL IMPACT THE REGION THU THROUGH
FRI. MODELS CONTINUE TO SHOW GALES OVER THE COASTAL WATERS DURING
THIS PERIOD WITH COMBINED SEAS OF 14 TO 20 FEET. GALES MAY ALSO
OCCUR AT THE WEST/EAST STRAIT OF JUAN DE FUCA. THIS SYSTEM WILL EXIT
FRI NIGHT WITH HIGH PRES MOVING INLAND ON SAT. ANOTHER STRONG FRONT
WILL APPROACH WA ON SUN. 33

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.

PZ...SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS COASTAL WATERS.
     SMALL CRAFT ADVISORY FOR ROUGH GRAYS HARBOR BAR.

&&

$$

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