Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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584
FXUS66 KSEW 252302
AFDSEW

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

.SYNOPSIS...HIGH PRESSURE WILL BRING MOSTLY DRY WEATHER TO THE
PACIFIC NORTHWEST THROUGH TUESDAY MORNING. THE APPROACHING FRONT WILL
SPLIT WITH THE BULK OF MOISTURE DIVING SOUTHWARD OFFSHORE. THERE IS
STILL 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...POSSIBLY
REACHING THE 70S FOR HIGHS SUNDAY AND MONDAY AFTERNOON.

&&

.SHORT TERM...RADAR SHOWS SOME RESIDUAL SHOWERS ALONG THE
CASCADES/FOOTHILLS AND DOWNWIND OF THE OLYMPICS ON THE WEST SIDE OF
PUGET SOUND. SHOWERS SHOULD MOSTLY DIMINISH AFTER SUNSET WITH
LOSS OF DIURNAL INSTABILITY. VISIBLE IMAGE SHOWS MOST OF WRN WA HAS
CLEARED OUT NICELY BUT RESIDUAL LOW LEVEL MOISTURE COULD STILL
SETTLE INTO SOME PATCHY LOW CLOUDS LATER TONIGHT/TUESDAY
MORNING AS HIGH PRESSURE AND SUBSIDENCE DEVELOPS OVER THE REGION.

THE NEXT SYSTEM APPROACHES THE COAST TUESDAY BUT ALL MODELS AGREE
THE FRONT RAPIDLY SPLITS AS IT MOVES INSIDE 130 W. THE BULK OF
MOISTURE AND DYNAMICS DIG SE INTO OREGON AND CA WITH RESIDUAL
NRN BRANCH MOISTURE BAND REACHING THE N WA COAST BY TUESDAY
AFTERNOON. REMNANTS FROM THIS FEATURE MOVE INLAND TUESDAY NIGHT AND
WEDNESDAY BUT NOT MUCH MORE THAN SPOTTY LIGHT MEASURABLE AMOUNTS ARE
EXPECTED. COASTAL AREAS AND THE SW INTERIOR HAVE THE BEST CHANCE OF
SOME LIGHT PRECIP WITH LITTLE OR NOTHING EXPECTED ACROSS THE FAR N.

A BREAK BETWEEN SYSTEMS DEVELOPS THURSDAY PROVIDING DRY WEATHER AND
WARMER TEMPERATURES WITH HIGHS REACHING INTO THE 60S....POSSIBLY
CLOSE TO 70 FAR SOUTH INTERIOR. ONSHORE FLOW DEVELOPS THURSDAY
NIGHT AHEAD OF THE NEXT SYSTEM.

.LONG TERM...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
NWD 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 NWD 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...SCATTERED CU THIS AFTERNOON...AND SOME AREAS OF BKN
CLOUDS OVER THE CASCADES...WILL GIVE WAY TO MORE CLEARING TONIGHT.
A FRONT JUST OFFSHORE WILL SPREAD CLOUDS INTO WRN WA BY ABOUT
DAYBREAK ON TUE...MID AND HIGH CLOUDS. THAT FRONT SHOULD STAY JUST
OFF THE COAST AND DISSIPATE THROUGH TUE NIGHT.

KSEA...SCATTERED CLOUDS THIS EVENING...MID LEVEL OVERCAST INCREASING
ON TUESDAY.

&&

.MARINE...ONSHORE FLOW WILL BECOME LIGHT OVERNIGHT. A FRONT WILL
APPROACH THE COASTAL WATERS ON TUESDAY BUT THEN SHIFT SOUTHEAST
AND DISSIPATE AS WEAK LOW PRESSURE MOVES INTO WRN OREGON TUE NIGHT
AND WED. AN EVEN WEAKER FRONT DISSIPATES AS IT REACHES THE COASTAL
WATERS AROUND DAYBREAK FRIDAY...THAT MAY NOT HAVE MUCH EFFECT ON
THE WINDS AT ALL.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...SMALL CRAFT ADVISORY COASTAL WATERS FOR HAZARDOUS SEAS.
     SMALL CRAFT ADVISORY CENTRAL AND EASTERN STRAIT.
     SMALL CRAFT ADVISORY FOR ROUGH BAR CONDITIONS GRAYS HARBOR BAR.

&&

$$

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