Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000
FXUS66 KSEW 271621 CCA
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
900 AM PDT WED APR 27 2016

.SYNOPSIS...A WEAK UPPER TROUGH WILL MOVE ACROSS WESTERN
WASHINGTON TODAY PRODUCING MAINLY CLOUDY SKIES AND A CHANCE OF LIGHT
SHOWERS FOR THE COAST...MOUNTAINS...AND SOUTH PART. AN UPPER RIDGE
WILL BRING MOSTLY SUNNY WEATHER THURSDAY...FOLLOWED BY AN UPPER
TROUGH AND SCATTERED SHOWERS FRIDAY. A STRONG UPPER RIDGE WILL BRING
DRY WEATHER AND A WARMING TREND SATURDAY THROUGH MONDAY.

&&

.SHORT TERM...AN ELONGATED UPPER LEVEL TROUGH OVER THE AREA THIS
MORNING WILL CONTINUE TO SPLIT AS A CLOSED LOW AT THE BASE SHIFTS
SWD INTO SW OREGON/NRN CA. THE BULK OF MOISTURE AND DYNAMICS REMAINS
WELL SOUTH OF OUR AREA WITH THE CLOSED LOW. THERE IS JUST ENOUGH
INSTABILITY AND MAINLY MID LEVEL MOISTURE OVER WRN WA TO SUPPORT
SOME SPOTTY LIGHT RAIN. THE ONLY MEASURABLE RAIN SO FAR HAS BEEN
OVER THE MOUNTAINS AND GENERALLY UNDER A TENTH. SOME SPRINKLES HAVE
BEEN OBSERVED OVER THE LOWLANDS BUT NOTHING MEASURABLE. THE FORECAST
APPEARS ON TRACK FOR TODAY INDICATING CLOUDS WITH LOW CHANCE POPS
CONFINED TO THE MOUNTAINS/COAST/AND SOUTH OF PUGET SOUND. HIGHS
WILL BE CLOSE TO AVERAGE...AROUND 60.

CLOUDS WILL GRADUALLY THIN OUT TONIGHT AS THE SPLIT TROUGH SHIFTS
FURTHER EAST. IT SHOULD REMAIN MOSTLY DRY THROUGH THURSDAY BETWEEN
SYSTEMS WITH HIGHS TOPPING OUT A FEW DEGREES WARMER THAN TODAY. SOME
CU COULD BUILD UP OVER THE MOUNTAINS THURSDAY AFTERNOON DUE TO
DIURNAL INSTABILITY. A FEW ISOLATED SHOWERS ARE POSSIBLE NEAR THE
CASCADE CREST BUT THE VAST MAJORITY OF THE AREA WILL SEE SOME
SUNSHINE AND REMAIN DRY.

MODELS REMAIN IN GOOD AGREEMENT THAT THE NEXT FRONTAL SYSTEM WILL
REMAIN MORE CONSOLIDATED BUT ALSO A FAST MOVER. LIGHT RAIN WILL
REACH THE COAST LATE TONIGHT OR EARLY FRIDAY MORNING...THEN SPREAD
INLAND. THE SURFACE FRONT AND DEEPER MOISTURE SHOWN BY MODELS SHOULD
RESULT IN WIDESPREAD MEASURABLE RAIN. BUT QPF WILL STILL BE LIGHT
GIVEN THE PROGRESSIVE NATURE OF THE SYSTEM. LOCAL AMOUNTS UP TO A
QUARTER INCH ARE POSSIBLE...MAINLY IN THE MOUNTAINS AND WHERE ANY
POST FRONTAL CONVERGENCE ZONE MAY FORM. MESO MODELS SHOW A POSSIBLE
CONVERGENCE ZONE IN THE FAVORED CORRIDOR BETWEEN EVERETT AND SEATTLE
BUT THIS WILL GRADUALLY DIMINISH LATER FRIDAY EVENING. MERCER




.LONG TERM...THE MODELS REMAIN IN FAIRLY GOOD AGREEMENT THAT AN
UPPER RIDGE WILL BUILD OFFSHORE ALONG 130W ON SATURDAY...SHIFT
SLOWLY TO THE COAST ON SUNDAY AND MONDAY. THIS SHOULD BE A PERIOD
OF MOSTLY SUNNY WEATHER WITH A WARMING TREND. THE UPPER RIDGE WILL
PROBABLY MOVE EAST OF THE AREA ON TUESDAY...AND SOUTHERLY FLOW
ALOFT WITH HIGH LEVEL MOISTURE AND WEAK INSTABILITY COULD PRODUCE
SOME SHOWERS. MCDONNAL

&&

.AVIATION...A WEAK UPPER LEVEL TROUGH WILL REMAIN OVER THE AREA
TODAY WITH LIGHT AND VARIABLE FLOW ALOFT. LOW LEVEL ONSHORE FLOW
WILL STRENGTHEN THIS AFTERNOON.

SCATTERED TO BROKEN CLOUD LAYERS BETWEEN 6000 AND 10000 FEET THROUGH
TONIGHT. THE EXCEPTION TO THIS IS A SCATTERED TO BROKEN LAYER NEAR
2000 FEET FROM KSEA-KBLI UNTIL 20Z.

KSEA...TEMPORARY CEILINGS NEAR 2000 FEET UNTIL 19Z OTHERWISE
CEILINGS AOA 5000 FEET. LIGHT WIND BECOMING NORTHERLY 4 TO 8 KNOTS
MID AFTERNOON. FELTON

&&

.MARINE...HIGH PRES BUILDING OVER THE OFFSHORE WATERS TODAY.
THIS COMBINED WITH LOWER PRES EAST OF THE CASCADES WILL RESULT IN
ONSHORE OR WESTERLY FLOW THROUGH THURSDAY. SMALL CRAFT ADVISORY
WESTERLIES ARE EXPECTED IN THE CENTRAL AND EASTERN STRAIT TONIGHT
WITH SMALL CRAFT NORTHWESTERLIES IN ADMIRALTY INLET.

STRONG ONSHORE FLOW WILL DEVELOP ON FRIDAY IN THE WAKE OF A COLD
FRONT. THIS WILL LEAD TO GALE FORCE WESTERLIES OVER THE CENTRAL AND
EASTERN STRAIT OF JUAN DE FUCA...AND THE POSSIBILITY GALE FORCE
NORTHWESTERLIES OVER PARTS OF THE COASTAL WATERS. FELTON

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...SMALL CRAFT ADVISORIES ARE IN EFFECT FOR THE CENTRAL/EASTERN
     STRAIT OF JUAN DE FUCA AND THE ADMIRALTY INLET TONIGHT.

&&

$$

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