Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 221721
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
920 AM PST SAT NOV 22 2014

.SYNOPSIS...SCATTERED SHOWERS AND ONSHORE FLOW WILL CONTINUE TODAY.
A FRONT WILL MOVE THROUGH WESTERN WASHINGTON SUNDAY. A WARM FRONT
WILL MOVE THROUGH THE AREA MONDAY NIGHT AND TUESDAY. ANOTHER WEATHER
SYSTEM WILL ARRIVE LATE IN THE WEEK.

&&

.SHORT TERM...A TROUGH WAS MOVING THROUGH THE AREA THIS MORNING WITH
SHOWERS. SCATTERED SHOWERS THIS AFTERNOON WILL TAPER OFF TONIGHT.
ANOTHER FRONT WILL PUSH THROUGH WESTERN WA SUNDAY MORNING. SCATTERED
SHOWERS BEHIND THAT FRONT WILL TAPER OFF SUNDAY AFTERNOON AND NIGHT.
A WARMER SYSTEM ARRIVES ON THE NRN B.C. COAST BEFORE DAYBREAK
MONDAY...WITH THE RAIN SHIFTING SOUTH ACROSS VANCOUVER ISLAND AND
THE MAINLAND SOUTH B.C. COAST BY MIDDAY MONDAY. THAT WARM FRONT WILL
GIVE SOME RAIN TO WRN WA MONDAY NIGHT.

.LONG TERM...LOOKING AT THE 12Z GFS: RAIN FROM THE WARM FRONT LATER
MONDAY NIGHT THRU TUE AND WED WILL MAINLY BE IN THE NORTH
CASCADES...WITH LIGHTER AMOUNTS INT THE OLYMPICS AND CENTRAL
CASCADES. THE LOWLANDS IN THE OLYMPIC RAIN SHADOW...SW WA...AND THE
SRN CASCADES PROBABLY WONT SEE MUCH RAIN. BY THU THERE IS A GOOD
CHANCE OF DRY WEATHER AND OFFSHORE FLOW...ALTHOUGH THE GFS HAS A
SHORT OF STATIONARY FRONT AND A LITTLE PRECIP STILL HUNG UP IN THE
IN THE AREA. THEN RAIN BECOMES MORE LIKELY AROUND THE END OF THE
WEEK AS A SPLITTY CUT OFF SYSTEM BREAKS UP OVER THE REGION. MOST OF
THE PRECIP MAY GO INTO SW OREGON AND NRN CALIF.

&&

.HYDROLOGY...RAIN WITH A HIGH SNOW LEVEL IS LIKELY IN THE NORTH
CASCADES LATER MONDAY NIGHT THROUGH TUESDAY AND PERHAPS INTO
WEDNESDAY. THE 12Z GFS SHOWS THE 850MB TEMP RISING TO AROUND +5C TUE
AFTERNOON AND EVENING AND IT DOESN`T COOL DOWN TIL THE SYSTEM
FINALLY PETERS OUT WED NIGHT. IF THAT LOOKS THE SAME IN THE 12Z
ECMWF WE WILL BE GETTING CLOSE TO DOING A HYDROLOGIC OUTLOOK FOR
SKAGIT AND WHATCOM COUNTIES.

&&

.AVIATION...MODERATE WESTERLY FLOW ALOFT TODAY...BECOMING STRONGER
TONIGHT. THE AIR MASS WILL REMAIN MOIST AND GENERALLY UNSTABLE FOR
THE NEXT 24 HOURS. A SHORTWAVE WITHIN THE UNSTABLE AIR MASS IS
MOVING ACROSS WRN WA RIGHT NOW...ENHANCING SHOWER ACTIVITY...
ESPECIALLY OVER SW WA. THIS FEATURE WILL HAVE PASSED EAST OF THE
CASCADES BY 20Z...LEAVING LESS WIDESPREAD SHOWER ACTIVITY THROUGH
THIS EVENING. AT THAT POINT...SHOWERS WILL MAINLY FOCUS ON THE
WINDWARD SIDE OF THE OLYMPICS AND CASCADES. THE NEXT FAST-MOVING
FRONT WILL ARRIVE FROM THE PACIFIC EARLY SUNDAY MORNING...LEADING TO
MORE WIDESPREAD SHOWER ACTIVITY ON SUNDAY MORNING FROM ABOUT 10Z-16Z.

KSEA...RAIN AND SHOWERS NEAR THE TERMINAL AS OF 17Z WILL EXIT THE
VICINITY BTWN 18Z-19Z. PREDOMINANTLY DRY WEATHER WILL THEN PREVAIL
THROUGH LATE TONIGHT...BUT A BRIEF PASSING SHOWER WILL BE POSSIBLE
AT ALMOST ANY TIME...REDUCING CIGS AND VSBYS FOR MERE MINUTES. NEXT
FRONT WILL ARRIVE EARLY SUNDAY MORNING...ENHANCING SHOWER ACTIVITY
FROM ABOUT 12Z-16Z AND CAUSING LOW-LEVEL S-SW WINDS TO PICK UP.
WINDS ALOFT AT 4500 FT MSL WILL PEAK FROM THE SW NEAR 50 KT ARND 15Z
SUNDAY.     HANER

&&

.MARINE...MODERATE ONSHORE FLOW IS EXPECTED TODAY. GRADIENTS WILL
BECOME MORE SOUTHERLY TONIGHT IN ADVANCE OF A FRONTAL PASSAGE ON
SUNDAY MORNING. THERE IS ABOUT A 30 PERCENT CHANCE THAT BRIEF GALE
FORCE WINDS WILL OCCUR OVER PORTIONS OF THE COASTAL WATERS IN
ADVANCE OF THE FRONT LATE TONIGHT AND THROUGH THE STRAIT OF JUAN DE
FUCA BEHIND THE FRONT BEGINNING MIDDAY SUN. THIS IS NOT HIGH-ENOUGH
CONFIDENCE YET TO WARRANT A GALE WATCH. LATER SUNDAY MORNING AND
SUNDAY AFTERNOON...THE FRONT WILL BE FOLLOWED BY ANOTHER SURGE OF
MODERATE TO STRONG ONSHORE FLOW.

ONSHORE FLOW MAY INCREASE AGAIN TUE NIGHT OR WED AS ANOTHER LOW
MOVES BY TO THE NORTH OF THE AREA.  HANER

&&


&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...WINTER WEATHER ADVISORY IN EFFECT TIL 5 PM TODAY FOR THE
     CENTRAL CASCADES ABOVE 2500 FEET.

     WINTER STORM WATCH IN EFFECT FROM LATE TONIGHT THROUGH SUNDAY
     AFTERNOON FOR THE CASCADES ABOVE 3000 FEET.

PZ...SMALL CRAFT ADVISORY COASTAL WATERS AND STRAIT OF JUAN DE FUCA.

&&

$$

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