Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 260411
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
912 PM PDT MON APR 25 2016

.SYNOPSIS...HIGH PRESSURE WILL BRING MOSTLY DRY WEATHER TO THE
PACIFIC NORTHWEST THROUGH TUESDAY MORNING. AN APPROACHING FRONT
TUESDAY AFTERNOON INTO WEDNESDAY WILL SPLIT AS IT MOVES INLAND WITH
THE BULK OF MOISTURE DIVING SOUTH OF THE AREA. THERE IS A CHANCE OF
SOME LIGHT MEASURABLE RAIN OVER THE OLYMPIC PENINSULA TUESDAY
AFTERNOON SPREADING INTO PARTS OF THE INTERIOR TUESDAY NIGHT AND
WEDNESDAY...ESPECIALLY SOUTH PART. THURSDAY SHOULD BE DRY BETWEEN
SYSTEMS...THEN ANOTHER FRONT SWEEPS ACROSS THE AREA FRIDAY WITH A
BETTER SHOT AT RAIN. A RIDGE OF HIGH PRESSURE BUILDS AGAIN SATURDAY
THROUGH EARLY NEXT WEEK WITH DRY WEATHER AND TEMPERATURES WELL ABOVE
AVERAGE.

&&

.SHORT TERM...A WEAKENING UPPER LEVEL TROUGH OVER THE AREA THIS
EVENING WILL WEAKEN AND MOVE EAST OF THE CASCADES TONIGHT. SOME
RESIDUAL LIGHT SHOWERS ARE STILL SHOWING UP OVER THE NORTHERN
CASCADES...NEAR THE HOOD CANAL BRIDGE...AND IN THE SOUTH INTERIOR
FROM NORTH OF SHELTON TO AROUND MT RAINIER. THE SHOWERS WILL DIE OUT
QUICKLY BY 10 PM AS THE BOUNDARY LAYER STABILIZES.

A PROGRESSIVE UPPER LEVEL RIDGE OVER THE OFFSHORE WATERS THIS
EVENING WILL PUSH INLAND EARLY TUESDAY MORNING THEN EAST OF THE
CASCADES TUESDAY AFTERNOON. DRY CONDITIONS CAN BE EXPECTED FROM
LATER THIS EVENING THROUGH TUESDAY IN THE INTERIOR. SOME CLOUDS
MOVING OUT AHEAD OF A SPLITTING FRONTAL SYSTEM THAT WILL BE
APPROACHING THE WASHINGTON COAST LATE TUESDAY WILL GIVE SOME CLOUDS
TO THE INTERIOR TUESDAY AFTERNOON...BUT IT SHOULD BE NICE WITH THE
DRY CONDITIONS AND TEMPERATURES RISING TO AROUND THE 60 DEGREE MARK.

THE SPLITTING FRONTAL SYSTEM WILL HIT A WALL AS IT TRIES TO MOVE
ONSHORE...NEVER REALLY PUSHING INLAND. THE BULK OF THE MOISTURE AND
ENERGY WITH THIS FRONT WILL LIKELY NOT MAKE IT PAST THE OLYMPIC
PENINSULA OR THE SOUTH INTERIOR...BUT THERE WILL BE PLENTY OF CLOUDS
SPREADING INLAND. CURRENT FORECASTS THAT SHOW LOW CHANCE POPS
REMAINING MAINLY OVER THE SOUTH INTERIOR AND THE OLYMPIC PENINSULA
THROUGH WEDNESDAY LOOKS GOOD. NEAR NORMAL TEMPERATURES WITH LOWS IN
THE LOWER TO MID 40S AND HIGHS IN THE LOWER 60S WILL ALSO CONTINUE.

THE NEXT PROGRESSIVE RIDGE WILL MOVE ACROSS THE AREA ON THURSDAY
BRINGING DRY CONDITIONS AND HIGHS REACHING INTO THE 60S TO NEAR 70.

CURRENT FORECASTS ARE IN GOOD SHAPE. NO UPDATE IS REQUIRED. ALBRECHT

.LONG TERM...FROM THE PREVIOUS LONG TERM DISCUSSION...THE
GFS/ECMWF/CANADIAN ARE ALL IN GOOD AGREEMENT ON BRINGING A FRONTAL
SYSTEM ACROSS THE PAC NW FRIDAY. MODEL QPF LOOKS WIDESPREAD BUT NOT
HEAVY GIVEN THE PROGRESSIVE NATURE OF THE TROUGH KEPT POPS IN THE
HIGHER CHANCE CATEGORY BUT THIS MAY NEED TO GET BOOSTED IF
SUBSEQUENT MODEL RUNS CONTINUE TO SHOW A CONSOLIDATED FRONT. POST
FRONTAL ONSHORE FLOW LOOKS DECENT FRIDAY NIGHT AND A PUGET SOUND
CONVERGENCE ZONE IS A GOOD BET IN THE FAVORED CORRIDOR BETWEEN
EVERETT AND SEATTLE. HIGHS WILL FALL BACK TO NEAR OR BELOW AVERAGE
IN THE UPPER 50S.

LONG RANGE MODELS ARE ALSO IN GENERAL AGREEMENT ON BUILDING A RIDGE
OVER THE PAC NW SATURDAY INTO EARLY NEXT WEEK. SATURDAY WILL BE A
TRANSITION DAY WITH THE RIDGE AXIS STILL OFFSHORE AND SLOW TO BUILD
NORTHWARD AS A WARM FRONTAL FEATURE LIFTS INTO BRITISH COLUMBIA. LIGHT
ONSHORE FLOW AND SOME RESIDUAL CLOUDS WILL KEEP HIGHS MOSTLY LIMITED
TO THE 60S. BY SUNDAY AND MONDAY...THE RIDGE STRENGTHENS AND A
THERMALLY INDUCED LOW BUILDS NORTHWARD ALONG THE OREGON COAST. THIS SHOULD
PRODUCE A PERIOD OF NORTHERLY OR OFFSHORE FLOW WITH 500 MB HEIGHTS
ABOVE 5700M SUGGESTING HIGHS REACHING INTO THE 70S. DEPENDING ON THE
TIMING OF THE NEXT SYSTEM...THE HEAT LOW COULD SHIFT OVER INTERIOR
WRN WA MONDAY WHICH COULD BE THE WARMEST DAY OF THE NEXT 7. MERCER

&&

.AVIATION...A WEAK UPPER LEVEL RIDGE WILL PREVAIL OVER THE REGION
OVERNIGHT. STRONG NLY FLOW ALOFT WILL WEAKEN OVERNIGHT. CONTD LIGHT
LOW LEVEL ONSHORE FLOW. ANTICIPATING VFR CONDITIONS
OVERNIGHT...ALTHOUGH THERE MAY BE PATCHY SHALLOW FOG /VSBYS 4-6SM/
FROM ABOUT KOLM SWD AFTER 0900 UTC.

KSEA...VFR. LIGHT NLY WINDS WILL BECOME LIGHT SLY OVERNIGHT.

&&

.MARINE...AN AREA OF HIGH PRES ALONG THE WASHINGTON COAST WILL
RESULT IN WEAK ONSHORE FLOW THROUGH TUE. EXPECT A WEAKENING OCCLUDED
FRONT TO APPROACH THE COASTAL WATERS TUE NIGHT. THE FRONT IS
EXPECTED TO DISSIPATE BEFORE REACHING THE WASHINGTON COASTAL WATERS.
ONSHORE OR WESTERLY FLOW WILL STRENGTHEN ON WED.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS UNTIL 11 PM PDT THIS
     EVENING FOR COASTAL WATERS FROM CAPE FLATTERY TO JAMES
     ISLAND 10 TO 60 NM-COASTAL WATERS FROM CAPE FLATTERY TO
     JAMES ISLAND OUT 10 NM-COASTAL WATERS FROM JAMES ISLAND TO
     POINT GRENVILLE 10 TO 60 NM-COASTAL WATERS FROM JAMES
     ISLAND TO POINT GRENVILLE OUT 10 NM-COASTAL WATERS FROM
     POINT GRENVILLE TO CAPE SHOALWATER 10 TO 60 NM-COASTAL
     WATERS FROM POINT GRENVILLE TO CAPE SHOALWATER OUT 10 NM.

     SMALL CRAFT ADVISORY FOR ROUGH BAR UNTIL 11 PM PDT THIS EVENING
     FOR GRAYS HARBOR BAR.

     SMALL CRAFT ADVISORY UNTIL 11 PM PDT THIS EVENING FOR CENTRAL
     U.S. WATERS STRAIT OF JUAN DE FUCA-EAST ENTRANCE U.S.
     WATERS STRAIT OF JUAN DE FUCA.

&&

$$

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