Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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852
FXUS66 KSEW 301032
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
332 AM PDT SAT APR 30 2016

.SYNOPSIS...HIGH PRESSURE ALOFT WILL BUILD OVER THE REGION THIS
WEEKEND. THIS COMBINED WITH THE LOW LEVEL FLOW BECOMING OFFSHORE
WILL RESULT IN TEMPERATURES CLIMBING ABOVE NORMAL FOR THIS TIME OF
THE YEAR. UNSEASONABLY WARM WEATHER WILL PERSIST ON MONDAY.

&&

.SHORT TERM...
AN UPPER LEVEL RIDGE WILL BUILD OVER THE REGION THIS WEEKEND. THIS
COMBINED WITH THE LOW LEVEL FLOW BECOMING OFFSHORE WILL RESULT IN
ANOTHER PERIOD OF WARM WEATHER. TEMPERATURES TODAY WILL BE ABOVE
NORMAL FOR THIS TIME OF THE YEAR OR GENERALLY FIVE TO DEGREES
WARMER THAN YESTERDAY. A THERMALLY INDUCED AREA OR LOW PRESSURE
ALONG OR JUST OFF THE COAST ON SUNDAY WILL RESULT IN UNSEASONABLE
WARM TEMPERATURES OR TEMPS ONE WOULD EXPECT DURING THE SUMMER.

THE FORECAST FOR MONDAY WILL BE A LITTLE TRICKY. THE SURFACE LOW
OFF THE OREGON COAST IS ANTICIPATED TO SHIFT NORTH DURING THE
DAY. THIS MAY INDUCE A LOW LEVEL SURGE OF MARITIME AIR UP THE
COAST IN THE AFTERNOON...THUS TEMPS ON THE COAST MIGHT BE A LITTLE
COOLER OR A LOT COOLER...DEPENDING ON WHICH MODEL ONE PREFERS. THE
NAM GUIDANCE FOR KHQM...FOR EXAMPLE...HAS A HIGH 68 DEGREES FOR
MONDAY...WHICH WAS ELEVEN DEGREES COOLER THAN ITS FORECAST FOR
SUNDAY. IN CONTRAST...THE GFS HAD A HIGH OF 73 DEGREES FOR KHQM
FOR MONDAY...OR ONLY FIVE DEGREES COOLER THAN ITS FORECAST FOR
SUNDAY. DECIDED TO GO WITH THE GFS SOLUTION FOR NOW DUE TO
UNCERTAINTY IN THE SURFACE FEATURES.

ACROSS THE INTERIOR...EXPECT TEMPS ON MONDAY TO BE A FEW DEGREES
WARMER THAN ON SUNDAY...WITH A FEW SITES HAVING A GOOD CHANCE OF
BREAKING RECORDS FOR THE DATE.

STRONG SOUTHERLY FLOW ALOFT IS EXPECTED TO DEVELOP MONDAY NIGHT.
THIS WILL ALLOW SOME MIDLEVEL MOISTURE AND INSTABILITY TO ADVECT
OVER MAINLY THE SOUTHERN PART OF THE FORECAST AREA FOR A LOW
THREAT OF SHOWERS. IF THE LATEST SREF IS CORRECT...THERE IS ALSO A
POSSIBILITY OF ISOLATED TSTMS MONDAY NIGHT OVER THE CENTRAL
CASCADES.

.LONG TERM...
THE WEATHER PATTERN OVER THE AREA TUESDAY THROUGH FRIDAY OF THE
UPCOMING WEEK WILL BE SOMEWHAT UNSETTLED. AN OMEGA BLOCK WILL
BE OVER THE USA...WITH UPPER LEVEL TROFS OVER THE WEST AND EAST
COASTS. IT APPEARED THAT MUCH OF THE ENERGY WITH THE WEST COAST
TROF WILL IMPACT THE SOUTHWEST USA BUT THERE WILL STILL BE A
THREAT OF SHOWERS OVER THE FORECAST AREA. OTHERWISE...EXPECT
ONSHORE FLOW ACROSS WESTERN WA DURING THIS PERIOD...WITH TEMPS
RETURNING TO NEAR NORMAL.

&&

.AVIATION...UPPER LEVEL RIDGING WILL CONTINUE TO BUILD OFFSHORE
TODAY. NORTHERLY FLOW ALOFT WILL TRANSITION TO BECOME NORTHEASTERLY
TONIGHT. LOW LEVEL ONSHORE FLOW IS EXPECTED TO PERSIST TODAY.

OBS FROM KSEA AND KBFI SHOW THAT CIGS ARE STARTING TO LOWER...WHILE
OBS FROM REMAINING TAF SITES CONTINUE TO SHOW GENERALLY CLEAR
CONDITIONS. IR SATELLITE IMAGERY HOWEVER DOES HINT AT AN INCREASE IN
CLOUD COVER...SO WOULD EXPECT A TRANSITION FROM GENERALLY CLEAR
SKIES TO MORE BROKEN TO OVERCAST CONDITIONS THIS EARLY MORNING. CIGS
WILL DIP BRIEFLY INTO MVFR TERRITORY THIS MORNING BEFORE REBOUNDING
DURING THE AFTERNOON. CURRENT MODELS INDICATE A FAIR AMOUNT OF
CLEARING THIS AFTERNOON AND TONIGHT. IF YESTERDAY AFTERNOON WAS ANY
INDICATION...WOULD LEAN TOWARD PROSPECT OF CLEARING BEING RIGHT ON
TRACK.

KSEA...CIGS DROPPING TO BETWEEN 2K AND 3K FT THIS MORNING BEFORE
STARTING TO LIFT BY NOON TODAY...LEADING TO MOSTLY CLEAR CONDITIONS
BY MID AFTERNOON. WINDS LIGHT AND VARIABLE THIS MORNING...BECOMING
NORTH 5-10 KNOTS BY NOON AND REMAINING THERE FOR THE REMAINDER OF
THE TAF FORECAST PERIOD. SMR

&&

.MARINE...LOW LEVEL ONSHORE FLOW PATTERN CONTINUING TODAY
WITH SMALL CRAFT ADVISORIES PERSISTING OVER COASTAL WATERS TODAY AND
THROUGH THE NIGHT TONIGHT WITH SMALL CRAFT WINDS ALSO PRESENT IN THE
CENTRAL AND EASTERN STRAIT DURING THE EARLY MORNING TODAY. THESE
SMALL CRAFT WINDS WILL RETURN TO THE ENTIRE STRAIT LATE THIS
AFTERNOON AND INTO TONIGHT BEFORE DIMINISHING ONCE MORE. CURRENT
ONSHORE FLOW WILL TURN NORTHWESTERLY THIS AFTERNOON AS HIGH PRESSURE
BUILDS INTO SOUTHERN BRITISH COLUMBIA. LOW LEVEL FLOW TURNING
OFFSHORE ON SUNDAY WITH THERMALLY INDUCED TROUGH ALONG THE COAST. A
RETURN TO LOW LEVEL ONSHORE FLOW WILL OCCUR LATER MONDAY INTO
TUESDAY. FELTON/SMR

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...SMALL CRAFT ADVISORIES ARE IN EFFECT FOR THE COASTAL WATERS
 AND STRAIT OF JUAN DE FUCA.

&&

$$

WWW.WEATHER.GOV/SEATTLE

AN ILLUSTRATED VERSION OF THIS FORECAST DISCUSSION CAN BE SEEN AT
WWW.WEATHER.GOV/SEATTLE/GAFD/LATEST_WEBAFD.HTML



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