Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000
FXUS66 KSEW 281634
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
830 AM PST SAT FEB 28 2015

.SYNOPSIS...AN UPPER RIDGE AND OFFSHORE FLOW WILL BRING SUNNY DAYS
AND COOL NIGHTS TO WESTERN WASHINGTON THIS WEEKEND. A WEAK WEATHER
SYSTEM WILL MOVE THROUGH THE AREA SUNDAY NIGHT AND MONDAY FOR A
CHANCE OF LIGHT PRECIPITATION. DRY WEATHER WILL PREVAIL AGAIN
TUESDAY AND WEDNESDAY...AND ANOTHER WEAK SYSTEM COULD REACH THE AREA
LATE IN THE WEEK.

&&

.SHORT TERM...AN UPPER RIDGE AND LOW LEVEL OFFSHORE FLOW WILL GIVE
DRY SUNNY WEATHER THIS WEEKEND. MODELS SHOW SOME HIGH CLOUDS MOVING
INTO THE AREA TONIGHT AND SUNDAY HOWEVER. A WEAK SHORT WAVE IN THE
NORTHWEST FLOW ALOFT WILL BRING A LEAST A CHANCE OF RAIN SUNDAY
NIGHT. THE ECMWF CONTINUES TO BE WETTER WITH THIS COMPARED TO OTHER
MODELS AND SLOWER TO DRY THINGS OUT ON MONDAY. SCHNEIDER

.LONG TERM...PREVIOUS DISCUSSION...DRY NORTHERLY FLOW WILL CONTINUE
TUESDAY AND WEDNESDAY AHEAD OF AN OFFSHORE UPPER RIDGE...FOR MORE
DRY WEATHER. THE RIDGE WILL WEAKEN AND SHIFT INLAND THURSDAY...AND A
WEAK UPPER SHORTWAVE COULD BRING SOME LIGHT PRECIPITATION TO THE
AREA THURSDAY THROUGH FRIDAY.   MCDONNAL

&&

.HYDROLOGY...FLOODING IS UNLIKELY FOR THE NEXT 7 DAYS.

&&

.AVIATION...A LARGE UPPER LEVEL RIDGE CENTERED OVER THE NE PACIFIC
ALONG 140W WILL MAINTAIN DRY NORTHERLY FLOW OVER W WA THROUGH
SUNDAY. A SURFACE RIDGE OVER INTERIOR B.C. WILL MAINTAIN DRY N-NE
LOW LEVEL FLOW TODAY...ALTHOUGH WEAKENING PRESSURE GRADIENTS WILL
ALLOW LOCALLY GUSTY N-NE SURFACE WINDS TO SLOWLY DIMINISH.

THE AIR MASS WILL REMAIN DRY THIS WEEKEND WITH UNRESTRICTED VFR
CONDITIONS...ALTHOUGH THERE COULD STILL BE SOME ISOLATED RIVER
VALLEY FOG DURING THE EARLY MORNING HOURS.

KSEA...UNRESTRICTED VFR THIS WEEKEND. SURFACE WINDS WILL REMAIN N
8-15 KT TODAY. KAM

&&

.MARINE...A 1032 MB SURFACE HIGH REMAINS OVER THE INTERIOR OF B.C.
THIS MORNING WITH A WEAK SURFACE TROUGH ALONG THE B.C. AND WA
COASTS. THE OFFSHORE GRADIENTS HAVE BEEN SLOWLY WEAKENING AND SHOULD
CONTINUE TO DO SO AS THE LOW OVER CA CONTINUES MOVING S. SMALL CRAFT
ADVISORIES OVER THE INTERIOR HAVE BEEN SET TO END AT NOON TODAY
BASED ON THE WEAKENING PRESSURE GRADIENTS...CURRENT CONDITIONS...
AND THE LATEST HRRR GUIDANCE. THE SCA OVER THE COASTAL WATERS WILL
END AS PLANNED AROUND MID AFTERNOON.

THE B.C. HIGH WILL WEAKEN AND SLIDE OVER THE N ROCKIES TONIGHT
LEAVING BROAD HIGH PRESSURE EXTENDING FROM THE LARGE HIGH OVER THE
NE PACIFIC ACROSS THE PACNW TO THE HIGH OVER THE NORTHERN ROCKIES.
RELATIVE TO THE TWO SURFACE HIGHS THIS WILL LEAVE A WEAK SURFACE
TROUGH OVER THE PACNW ON SUNDAY...BUT WITH WEAK PRESSURE GRADIENTS
ACROSS THE AREA.

AN UPPER LEVEL TROUGH IS STILL EXPECTED TO MOVE SE ACROSS THE AREA
SUNDAY NIGHT. MESOSCALE MODELS STILL SHOW A BRIEF PERIOD OF SCA
LEVEL N WINDS DEVELOPING AS THE TROUGH CROSSES THE AREA.

ANOTHER SURFACE RIDGE WILL MOVE OVER INTERIOR B.C. MONDAY NIGHT AND
TUESDAY FOR ANOTHER ROUND OF MODERATE N-NE FLOW. KAM

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...

&&

$$

YOU CAN SEE AN ILLUSTRATED VERSION OF THE FORECAST DISCUSSION AT
WWW.WEATHER.GOV/SEATTLE/GAFD/LATEST_WEBAFD.HTML





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