Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000
FXUS66 KSEW 291141
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
441 AM PDT SAT AUG 29 2015

.SYNOPSIS...A POWERFUL PACIFIC STORM FOR THIS TIME OF THE YEAR
WILL BE STRONG WINDS AND LOCALLY HEAVY RAIN TO THE AREA TODAY.
LOOK FOR WET AND UNSETTLED CONDITIONS TO PERSIST THROUGH MONDAY
DUE TO LOW PRESSURE ALOFT REMAINING OVER THE REGION.

&&

.SHORT TERM...
SATELLITE IMAGERY SHOWED AN IMPRESSIVE LOOKING SYSTEM APPROACHING
THE PACIFIC NORTHWEST AT THIS TIME. THIS SYSTEM HAS A WELL
DEFINED BENT BACK OCCLUSION AND DECENT WARM FRONT. BASED ON
SATELLITE DATA AND LIMITED SURFACE OBSERVATIONS...IT APPEARED THAT
THE SURFACE LOW WAS NEAR 993 MB...QUITE IMPRESSIVE FOR AUGUST
29TH. THE MOST SIGNIFICANT IMPACT THIS SYSTEM WILL HAVE ON THE CWA
WILL BE ATYPICALLY STRONG WINDS FOR THIS TIME OF THE YEAR. WE
WOULD NORMALLY EXPECT A SYSTEM LIKE THIS DURING AUTUMN AND WINTER.

SOUTHERLY WINDS OF 20 TO 35 MPH WITH GUSTS OF 45 TO 50 MPH ARE
STILL LIKELY ACROSS MUCH OF THE LOWLANDS TODAY. SOME PLACES ON THE
COAST AND IN THE ADMIRALTY INLET AREA COULD HAVE GUSTS NEAR 55
MPH. THIS IS UNUSUAL FOR LATE AUGUST. THEREFORE...THIS WIND EVENT
COULD CREATE MORE PROBLEMS BECAUSE OF TREES BEING UNDER STRESS
DUE TO DRY CONDITIONS AND DECIDUOUS TREES STILL HAVING THEIR
LEAVES. THESE FACTORS WILL ONLY INCREASE THE RISK DOWNED TREES
AND BRANCHES. THUS...THE WIND ADVISORY WAS UPGRADED TO A HIGH WIND
WARNING.

WINDS ARE EXPECTED TO RAPIDLY DIMINISH LATE TODAY...WITH GENERALLY
BREEZY CONDITIONS ANTICIPATED THIS EVENING.

MEANWHILE...THE PACIFIC STORM HAS TAPPED INTO A PLUME OF MOISTURE
THAT EXTENDS WELL INTO THE SUBTROPICS. THE SATELLITE DERIVED TOTAL
PRECIPITABLE WATER /TPW/ SHOWED CLOSE TO 2 INCHES OF PRECIPITABLE
WATER BEING FEED INTO THE SYSTEM. RAINFALL AMOUNTS DURING THE 24
HOUR PERIOD ENDING AT 5 AM SUNDAY ARE FORECAST TO BE /LOCALLY/ IN
THE 2-4 INCH RANGE IN THE MOUNTAINS. MUCH OF THE LOWLANDS ARE
FORECAST TO RECEIVE 1-2 INCHES OF RAIN. THIS SYSTEM WAS QUITE
DYNAMIC...WITH EMBEDDED TSTMS OCCURRING WITH THE WARM FRONT OVER
OREGON EARLY THIS MORNING. WHERE TSTMS OCCUR...AMOUNTS WILL BE
HIGHER.

THE COLD OR OCCLUDED FRONT WILL SWEEP ACROSS THE CWA DURING THIS
AFTERNOON...WITH THE STEADY RAIN CHANGING OVER TO SHOWERS. THE
SHOWERS WILL BE LOCALLY HEAVY.

LOOK FOR AN UPPER TROF TO MOVE ACROSS THE REGION ON SUNDAY...
THEREBY KEEPING THE WEATHER PATTERN WET AND UNSETTLED. TEMPS ARE
FORECAST TO BE BELOW NORMAL ON SUNDAY AFTER BEING NEAR NORMAL
TODAY.

THE PACIFIC NORTHWEST WILL REMAIN UNDER THE INFLUENCE OF AN UPPER
TROF ON MON. IT LOOKS LIKE A FRONTAL BOUNDARY MAY STALL OVER THE
NORTHERN PART OF THE CWA OR OVER FAR SOUTHERN BRITISH COLUMBIA ON
MON. IF THE FRONT STALLS OVER THE CWA...THERE COULD BE A PERIOD OF
HEAVY RAIN ON THE WEST FACING SLOPES OF THE OLYMPICS AND NORTH
CASCADES.

.LONG TERM...
NO MAJOR CHANGES TO THE THINKING DURING THIS PERIOD. THE PACIFIC
NORTHWEST WILL REMAIN UNDER THE INFLUENCE OF A MEAN UPPER LEVEL
TROF...RESULTING IN BELOW NORMAL TEMPS AND ABOVE NORMAL PRECIP.

&&

.AVIATION...MID LEVEL DECK OVER WESTERN WASHINGTON EARLY THIS
MORNING WITH CEILINGS NEAR 10000 FEET. CEILINGS LOWERING DOWN TO
2000-3000 FEET 12Z-15Z COAST AND 15Z-18Z INTERIOR WITH RAIN AS A
STRONG FRONT APPROACHES THE AREA. THE CEILINGS WILL IMPROVE SOMEWHAT
BACK TO LOW END OF VFR BEHIND THE FRONT IN THE AFTERNOON HOURS. THE
TRAILING COLD FRONT WILL ARRIVE THIS EVENING WITH CEILINGS POSSIBLY
LOWERING BACK DOWN INTO MVFR. SOUTHERLY WINDS WILL INCREASE ALONG
THE COAST EARLY THIS MORNING WITH THE WINDS INCREASING OVER THE
INTERIOR MIDDAY. SUSTAINED WINDS 20 TO 30 KT ARE POSSIBLE ESPECIALLY
DURING THE LATE MORNING AND AFTERNOON HOURS.

KSEA...CEILINGS AROUND 10000 FEET LOWERING DOWN TO NEAR 2000 FEET
15Z-18Z WITH RAIN. SLIGHT IMPROVEMENT IN THE CEILINGS IN THE
AFTERNOON WITH CEILINGS NEAR 3000 FEET WITH THE COLD FRONT TONIGHT.
EAST TO SOUTHEAST WIND 5-10 KNOTS SWITCHING TO SOUTHWEST AND RISING
QUICKLY TO 15-25 KNOTS LATE THIS MORNING. WINDS EASING THIS
EVENING. FELTON

&&

.MARINE...A 992 MB LOW ABOUT 250 NM W OF ASTORIA EARLY THIS MORNING
WILL MOVE NORTHEAST THROUGH CENTRAL VANCOUVER ISLAND MIDDAY. WARM
FRONT ASSOCIATED WITH THE LOW MOVING THROUGH THE AREA THIS MORNING
BRINGING GALE FORCE WINDS TO ALL BUT THE WEST ENTRANCE AND CENTRAL
STRAIT. WINDS EASING TONIGHT WITH THE WEAKER TRAILING COLD FRONT
MOVING THROUGH THE WATERS. ADDITIONAL SYSTEMS WILL MOVE THROUGH THE
WATERS MONDAY AND TUESDAY BUT THESE SYSTEM ARE MUCH WEAKER THAN
TODAYS WARM FRONT. FELTON

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...HIGH WIND WARNINGS ARE IN EFFECT FOR MUCH OF THE LOWLANDS
 FROM 8 AM THIS MORNING TIL 6 PM PDT THIS EVENING.

PZ...GALE WARNINGS ARE IN EFFECT FOR ALL WATERS EXCEPT THE
 CENTRAL 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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