Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 011019
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
319 AM PDT TUE SEP 1 2015

.SYNOPSIS...A WEAK COLD FRONT WILL BRING RAIN AT TIMES TO WESTERN
WASHINGTON TODAY. A LARGE UPPER LOW WILL BE OVER THE REGION WEDNESDAY
THROUGH FRIDAY FOR COOL SHOWERY WEATHER. THE UPPER LOW WILL MOVE
EAST THIS WEEKEND FOR A GRADUAL DRYING AND WARMING TREND.

&&

.SHORT TERM...A WEAK COLD FRONT EXTENDS SOUTHWEST FROM SOUTHERN
BRITISH COLUMBIA ACROSS WESTERN WASHINGTON AND INTO THE OFFSHORE
WATERS OF OREGON. THE FRONT IS WITHIN THE DEEP BROAD UPPER TROUGH
OVER THE REGION WITH ITS 5330 METER LOW CENTER JUST NORTHWEST OF
HAIDA GWAII. THE FRONT IS BRINGING AREAS OF LIGHT PRECIPITATION TO
THE FORECAST AREA EARLY THIS MORNING...MAINLY NORTH AND WEST OF
SEATTLE.

THE COLD FRONT WILL MOVE SLOWLY ACROSS WESTERN WASHINGTON TODAY...
WHILE THE UPPER LOW DIGS SOUTHEAST JUST OFF THE COAST OF BRITISH
COLUMBIA. THE FRONT SHOULD BRING MEASURABLE PRECIPITATION TO MOST
ALL OF WESTERN WASHINGTON TODAY...WITH THE HEAVIEST AMOUNTS OVER
THE NORTH CASCADES. THE SNOW LEVEL WILL BE AROUND 9000 FT TODAY...
ALTHOUGH THE HIGHS IN THE LOWLANDS WILL BE ONLY IN THE 60S.

THE UPPER LOW WILL MOVE SLOWLY SOUTHEAST TONIGHT THROUGH THURSDAY.
THE UPPER TROUGH EXTENDS SOUTH FROM THE LOW...AND IT WILL MOVE
INTO OUR OFFSHORE WATERS TONIGHT AND WEDNESDAY AND THEN INLAND ON
THURSDAY. THE COOL MOIST AND UNSTABLE AIR MASS WITH THE UPPER
TROUGH WILL BRING SHOWERY WEATHER TO WESTERN WASHINGTON. WE ARE
ALSO FOLLOWING THE SPC GUIDANCE AND ADDING A CHANCE OF AFTERNOON
AND EVENING THUNDERSTORMS TO MOST OF THE FORECAST AREA WEDNESDAY.

DAYTIME HIGHS WILL BE IN THE LOWER TO MID 60S -- A GOOD 5 TO 10
DEGREES BELOW NORMAL. TOTAL RAINFALL FOR THE LOWLANDS TODAY
THROUGH THURSDAY WILL BE MOSTLY IN THE 0.25 TO 0.75 INCH RANGE.
THE SNOW LEVEL WILL BE AROUND 5500 TO 6000 FT WEDNESDAY THROUGH
THURSDAY. WATER EQUIVALENT PRECIPITATION AMOUNTS OF 0.50 TO 1.50
INCHES WILL FALL OVER MUCH OF THE HIGHER MOUNTAINS...WITH THE
HEAVIEST AMOUNTS NEAR MT BAKER. THAT MEANS THERE WILL BE LOCAL
ACCUMULATIONS OF A HALF FOOT OF SNOW ABOVE 6000 FT...WITH A FOOT
OR MORE OF SNOW NEAR THE TOP OF MT BAKER. MCDONNAL

.LONG TERM...THE LONGER RANGE MODELS HAVE FALLEN INTO BETTER
AGREEMENT FOR THE EXTENDED PERIOD FRIDAY THROUGH MONDAY. THE
UPPER TROUGH WILL REMAIN OVER THE REGION FRIDAY...THEN DRIER
NORTHWEST FLOW WILL DEVELOP SATURDAY AS THE TROUGH MOVES EAST OR
SOUTHEAST AND CONTINUE INTO MONDAY. LIGHTER SHOWERS FRIDAY WILL
BECOME LIMITED TO THE CASCADES BY SATURDAY NIGHT...WITH MOSTLY
SUNNY AND WARMER WEATHER SUNDAY AND MONDAY. MCDONNAL

&&

.AVIATION...A FRONTAL SYSTEM WILL DRAG ACROSS THE AREA TODAY. A COOL
UPPER LEVEL TROUGH WILL FOLLOW THE FRONT LATER TONIGHT INTO
WEDNESDAY. CEILINGS GENERALLY 3500-5000 THIS MORNING WITH BRIEF
CEILINGS AROUND 2000 FEET AND VISIBILITIES 3-5SM IN MODERATE RAIN.
LITTLE IF ANY IMPROVEMENT IN THE CEILINGS BEHIND THE FRONT LATER
THIS AFTERNOON INTO THE EVENING HOURS BEFORE THE UPPER LEVEL TROUGH
ARRIVES.

KSEA...CLOUDY WITH RAIN AT TIMES THROUGH THIS AFTERNOON. CEILINGS
35000-4500 FEET WITH POSSIBLE BRIEF CEILINGS NEAR 2000 FEET IN
MODERATE RAIN MID MORNING TO EARLY AFTERNOON. SOUTHERLY WINDS 6 TO
10 KNOTS. FELTON

&&

.MARINE...A FRONTAL SYSTEM OVER THE NORTH PORTION OF THE AREA WILL
MOVE THROUGH THE INLAND WATERS LATER TODAY. THE FRONT IS NOT STRONG
ENOUGH TO CAUSE SMALL CRAFT ADVISORY WINDS. A COOL UPPER LEVEL TROUGH
WILL MOVE INTO THE AREA LATER TONIGHT INTO WEDNESDAY WITH SMALL
CRAFT ADVISORY WINDS OVER THE NORTHERN AND CENTRAL PORTION OF THE
OUTER COASTAL WATERS. THE TROUGH WILL KICK OUT OF THE AREA ON
THURSDAY. HIGH PRESSURE WILL BUILD OVER THE WATERS FRIDAY AND
SATURDAY. FELTON

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...SMALL CRAFT ADVISORIES NORTHERN AND CENTRAL OUTER COASTAL
WATERS...GRAYS HARBOR BAR.

&&

$$

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