Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000
FXUS66 KSEW 261615
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
900 AM PDT TUE AUG 26 2014

.SYNOPSIS...A HIGH PRESSURE RIDGE WILL BRING SUNNY WARM DAYS TO
WESTERN WASHINGTON TODAY AND WEDNESDAY. THE RIDGE WILL MOVE EAST AND
A SHORTWAVE UPPER LEVEL TROUGH WILL MOVE THROUGH THE AREA
THURSDAY...BRINGING COOLER WEATHER AND A CHANCE OF SHOWERS FOR THE
NORTH CASCADES. A LONGWAVE UPPER LEVEL TROUGH WILL MOVE THROUGH THE
AREA THIS WEEKEND...BRINGING A MORE WIDESPREAD CHANCE OF SHOWERS.

&&

.SHORT TERM...AN UPPER LEVEL RIDGE AXIS IS OVER THE REGION
TODAY...BRINGING WARM TEMPERATURES AND CLEAR SKIES. WE ARE IN AN
ONSHORE FLOW PATTERN...AND LATE TONIGHT/WEDNESDAY MORNING LOW CLOUDS
AND FOG WILL MOVE INLAND. THE NAM12 BOUNDARY LAYER RH SHOWS THE
CLOUDS REACHING ALL THE WAY TO THE PUGET SOUND REGION BUT NOT
COVERING ALL OF IT.

WEDNESDAY...THE UPPER LEVEL RIDGE AXIS WILL MOVE TO THE EAST...AND
TEMPERATURES WILL FALL A FEW DEGREES. HOWEVER...IT WILL STILL BE
WARM AND DRY. THURSDAY MORNING WE WILL SEE ANOTHER PUSH OF LOW
CLOUDS INLAND. THE MARINE LAYER WILL LIKELY BE A BIT DEEPER AND TAKE
LONGER TO BURN OFF. DURING THE DAY ON THURSDAY A SMALL UPPER LEVEL
SHORTWAVE TROUGH WILL MOVE OVER THE AREA...AND THERE IS A SLIGHT
CHANCE OF SHOWERS OVER NORTHWESTERN WASHINGTON...ESPECIALLY IN THE
NORTH CASCADES. JSMITH

.LONG TERM...AN UPPER LEVEL LONGWAVE TROUGH WILL BEGIN TO MOVE INTO
THE AREA ON FRIDAY...BRINGING A CHANCE OF SHOWERS FRIDAY NIGHT
THROUGH SUNDAY...WITH THE SHOWERS MOST WIDESPREAD ON SATURDAY. THE
GFS AND ECMWF DISAGREE BEGINNING MONDAY ON WHAT WILL HAPPEN
NEXT...THE GFS HAS SHOWERS CONTINUING OFF AND ON LABOR DAY AND
TUESDAY...BUT THE ECMWF SHOWS A TREND OF DRYING OUT WITH AN UPPER
LEVEL RIDGE BUILDING IN. BECAUSE OF THIS...THERE IS QUITE A BIT OF
UNCERTAINTY IN THE FORECAST FROM LABOR DAY ONWARDS. JSMITH

&&

.AVIATION...AN UPPER LEVEL RIDGE WILL REMAIN OVER THE PACIFIC
NORTHWEST THROUGH 06Z/11 PM TONIGHT WITH NW FLOW ALOFT BECOMING W.
THE UPPER LEVEL RIDGE WILL WEAKEN AND MOVE E OVER ID AFTER 06Z. WEAK
LOW LEVEL ONSHORE FLOW WILL CONTINUE. THE AIR MASS WILL REMAIN DRY
AND STABLE OVER THE INTERIOR. THE SMALL AREAS OF FOG AROUND KHQM
WILL DISSIPATE BY 19Z. MVFR/IFR STRATUS WILL CONTINUE OVER THE
COASTAL WATERS UP TO THE BEACHES AND WILL BEGIN SPREADING GRADUALLY
INLAND AND E THROUGH THE STRAIT OF JUAN DE FUCA AFTER 00Z AS ONSHORE
FLOW INCREASES.

KSEA...CLEAR SKIES THROUGH THIS EVENING. SURFACE WINDS BE W-NW 4-8
KT THROUGH 02Z THEN SHIFT N 3-6 KT. KAM

&&

.MARINE...HIGH PRES OVER THE NE PAC WILL MAINTAIN ONSHORE FLOW
ACROSS WESTERN WA THROUGH WED. ONSHORE FLOW WILL BE STRONGEST DURING
THE EVENING HOURS AND WEAKEST DURING THE MORNING. THE STANDARD SCA
IS IN EFFECT FOR THE CENTRAL/E STRAIT OF JUAN DE FUCA THIS EVENING.
AS ONSHORE FLOW INCREASES STRATUS AND AREAS OF FOG WILL MOVE E
THROUGH THE STRAIT.

A WEAK DISSIPATING COLD FRONT WILL MOVE OVER THE COASTAL WATERS LATE
WEDNESDAY NIGHT OR THURSDAY MORNING. ANOTHER SYSTEM WILL REACH THE
AREA FRIDAY NIGHT OR SATURDAY MORNING. KAM

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...SMALL CRAFT ADVISORY CENTRAL AND EASTERN STRAIT OF JUAN DE FUCA.

&&

$$

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






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