Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 021023
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
323 AM PDT WED SEP 2 2015

.SYNOPSIS...A LARGE UPPER LOW WILL MOVE SLOWLY SOUTH OVER WESTERN
WASHINGTON TONIGHT THROUGH THURSDAY...BRINGING COOL SHOWERY
WEATHER. THERE IS ALSO A CHANCE OF THUNDERSTORMS MAINLY THROUGH
THIS EVENING. THE LOW WILL MOVE SOUTHEAST OF THE AREA BEGINNING
FRIDAY...FOR A GRADUAL DRYING AND WARMING TREND OVER THE WEEKEND.
A WEAK SYSTEM MAY BRING A CHANCE OF SHOWERS EARLY NEXT WEEK.

&&

.SHORT TERM...A 5410 METER UPPER LOW IS ALONG THE CENTRAL BRITISH
COLUMBIA COAST EARLY THIS MORNING...WITH ITS TROUGH AXIS EXTENDING
SOUTH ACROSS THE OFFSHORE WATERS. SCATTERED SHOWERS CONTINUE
ACROSS WESTERN WASHINGTON IN THE MOIST UNSTABLE SOUTHWEST FLOW
AHEAD OF THE TROUGH.

THE UPPER LOW WILL CONTINUE TO DIG SLOWLY SOUTHEAST TODAY AND
TONIGHT...ENDING UP NEAR VANCOUVER ISLAND LATE TONIGHT. THE UPPER
TROUGH WILL MOVE EAST TO THE PACIFIC NORTHWEST COAST OR JUST
INLAND. IT WILL PRODUCE MORE SHOWERS ACROSS THE FORECAST AREA.
THERE ARE CURRENTLY THUNDERSTORMS NEAR THE TROUGH AXIS JUST SOUTH
OF THE UPPER LOW...AND THERE IS CERTAINLY A CHANCE THAT THEY WILL
SPREAD INTO OUR FORECAST AREA THROUGH THIS EVENING. HIGHS TODAY
WILL BE IN THE 60S.

THE UPPER LOW SHOULD TRACK SOUTH INTO WESTERN WASHINGTON THURSDAY
AND THURSDAY NIGHT. INSTABILITY AND MOISTURE WILL PRODUCE
SCATTERED SHOWERS...ESPECIALLY DURING THE AFTERNOON AND EVENING...
BUT PRECIPITATION AMOUNTS SHOULD BE LESS. ON FRIDAY AND FRIDAY
NIGHT THE LOW WILL MOVE INTO OREGON...WITH SHOWERS OVER WESTERN
WASHINGTON TAPERING OFF AND EVENTUALLY BECOMING LIMITED TO THE
CASCADES. HIGHS BOTH DAYS WILL AGAIN BE MAINLY IN THE 60S.

THE SNOW LEVEL WILL BE AROUND 5500 TO 6000 FT TODAY THROUGH
FRIDAY WITH SHOWERS IN THE MOUNTAINS...FALLING AS SNOW ABOVE THE
SNOW LEVEL. MOST OF THE PRECIPITATION WILL OCCUR TODAY THROUGH
THURSDAY NIGHT...WITH SEVERAL INCHES OF ADDITIONAL SNOW OVER THE
HIGH TERRAIN OF THE OLYMPICS AND CASCADES. MCDONNAL

.LONG TERM...THE UPPER LOW WILL MOVE EAST OF THE REGION
SATURDAY...AND A SMALL UPPER RIDGE WILL MOVE OVER THE PACIFIC
NORTHWEST. IT SHOULD BE A MOSTLY SUNNY DAY AND A BIT WARMER. ONCE
AGAIN...CONFIDENCE IS NOT ESPECIALLY HIGH FOR SUNDAY THROUGH
TUESDAY AS MODEL SOLUTIONS HAVE BEEN INCONSISTENT. THE LATEST RUNS
OF THE GFS...EUROPEAN...AND CANADIAN MODELS ARE NOW SHOWING A WEAK
PROGRESSIVE TROUGH MOVING THROUGH THE AREA SUNDAY...FOLLOWED BY
ANOTHER SMALL RIDGE EARLY NEXT WEEK. OUR FORECAST REFLECTS EARLIER
RUNS...WHICH SHOWED A WEAK RIDGE OVER THE AREA THROUGH THE END OF
THE WEEKEND AND A WEAK UPPER TROUGH ARRIVING AROUND MONDAY NIGHT
OR TUESDAY. WE WILL SIT ON THE CURRENT FORECAST FOR NOW GIVEN THE
UNCERTAINTY. MCDONNAL

&&

.AVIATION...SHOWERS CONTINUING OVER THE AREA EARLY THIS
MORNING AS AN UPPER LEVEL TROUGH TO THE NORTHWEST CONTINUES
TO SAG SOUTH. TROUGH WILL CONTINUE TO MOVE SOUTH AND EAST
TODAY KEEPING SHOWERS AND POSSIBLE THUNDERSTORMS IN THE
FORECAST. WIDE VARIETY OF CEILINGS EARLY THIS MORNING. IN
GENERAL MULTIPLE CLOUD LAYERS FROM 1500 TO 7000 FEET. CEILINGS
GENERALLY NEAR 1500 FEET KPAE TO KSEA WITH CEILINGS 5000-
7000 FEET ELSEWHERE. LITTLE CHANGE IN THE CEILINGS THROUGH
THE MORNING. WITH SHOWER ACTIVITY INCREASING 1500 FOOT
CEILINGS WILL BECOME MORE WIDESPREAD. THERE IS A CHANCE OF
THUNDERSTORMS OVER THE NORTHERN PORTION OF THE AREA EARLY
THIS MORNING AND OVER THE ENTIRE AREA LATER THIS MORNING
INTO THIS AFTERNOON. CEILINGS WILL SLOWLY LIFT THIS AFTERNOON INTO
THIS EVENING WITH THE SHOWER ACTIVITY DECREASING THIS EVENING.


KSEA...CEILINGS NEAR 1500 FEET FOR THE MOST PART THOUGH THE
MORNING HOURS. CEILINGS LIFTING INTO THE 3000-4000 FOOT RANGE
THIS AFTERNOON INTO THE EVENING HOURS. SOUTHERLY WINDS 10-15 KNOTS.
FELTON

&&

.MARINE...LOW LEVEL ONSHORE FLOW CONTINUING TODAY. SHOWER
ACTIVITY WILL KEEP THINGS BLUSTERY THROUGH THE AFTERNOON
HOURS BUT WINDS WILL STAY JUST BELOW SMALL CRAFT ADVISORY
CRITERIA. WINDS WILL EASE LATE TONIGHT INTO THURSDAY WITH LOW LEVEL
ONSHORE FLOW CONTINUING. THE ONSHORE FLOW WILL WEAKEN THURSDAY NIGHT
INTO FRIDAY AS A WEAK SURFACE LOW MOVES THROUGH THE OFFSHORE WATERS.
HIGH PRESSURE WILL BUILD OVER THE WATERS FRIDAY INTO THE WEEKEND.
FELTON

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...SMALL CRAFT ADVISORY GRAYS HARBOR BAR.

&&

$$

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