Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000
FXUS66 KSEW 271117
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
330 AM PST TUE JAN 27 2015

.SYNOPSIS...A WEAK FRONT WILL MOVE INTO WESTERN WASHINGTON TODAY AND
DISSIPATE OVER THE AREA TONIGHT. AN UPPER RIDGE WILL PROVIDE DRY AND
MILD WEATHER WEDNESDAY THROUGH SATURDAY. THE NEXT FRONT BRINGS A
CHANCE OF RAIN BACK INTO THE AREA SUNDAY AND EARLY NEXT WEEK.

&&

.SHORT TERM...UPPER LEVEL HIGH PRESSURE OVER THE PAC NW WILL FLATTEN
TODAY AS A TROUGH PUSHES INTO BRITISH COLUMBIA. THE ASSOCIATED WEAK
SURFACE FRONT CURRENTLY OVER THE COASTAL WATERS WILL REACH THE COAST
LATER THIS MORNING AND THE INTERIOR THIS AFTERNOON. WV/IR SATELLITE
IMAGERY ARE NOT IMPRESSIVE SHOWING AN ELONGATED AND DIFFUSE CLOUD
BAND. RADAR IS ONLY PICKING UP BROKEN BANDS OF LIGHT PRECIP MOSTLY
OFFSHORE ALTHOUGH QUILLAYUTE HAD A TRACE EARLIER. THE HRRR DEPICTS A
SKINNY BAND OF DEEPER MOISTURE REACHING THE COAST BY DAYBREAK BUT
NOT PUSHING INTO THE INTERIOR UNTIL MIDDAY. BASED ON THE LATEST 00Z
MODELS...WILL REMOVE POPS FOR THE MORNING HOURS ACROSS MUCH OF THE
PUGET SOUND REGION EWD. BY AFTERNOON...THE FRONT WILL STALL OVER WRN
WA THROUGH TONIGHT AND DISSIPATE. QPF WILL BE LIGHT AND SPOTTY WITH
SOME LOCATIONS NOT MEASURING. WILL KEEP POPS LIMITED TO THE CHANCE
CATEGORY. IT WILL BE COOLER TODAY GIVEN THE ONSHORE FLOW WITH HIGHS
IN THE LOW TO MID 50S.

MODELS HOLD ONTO SOME LOW LEVEL MOISTURE WEDNESDAY BUT THERE IS A
LACK OF VERTICAL MOTION. THE ECMWF AND SOME OF THE GFS RUNS HOLD
ONTO SOME RESIDUAL SPOTTY QPF BUT OTHER MODELS ARE DRY. GIVEN THE
LACK OF DISCERNIBLE LIFT...THE FORECAST WILL REMAIN DRY. IT WILL
LIKELY BE CLOUDY THROUGH THE DAY SO HIGHS WILL BE LITTLE CHANGED IN
THE LOW TO MID 50S.

THE RIDGE BEGINS TO REBUILD ON THURSDAY LIFTING THE STORM TRACK N
INTO BRITISH COLUMBIA. LIGHT FLOW AND AFTERNOON SUNSHINE SHOULD
RESULT IN HIGHS WARMING BY AROUND 2-3 DEGREES.

.LONG TERM...A STRONG UPPER RIDGE WILL PROVIDE DRY WEATHER AND ABOVE
AVERAGE TEMPERATURES THROUGH SATURDAY. HIGHS WILL WARM SLIGHTLY EACH
DAY WITH MOSTLY SUNNY SKIES...EXCEPT FOR SOME LATE NIGHT AND MORNING
FOG. THE RIDGE AXIS MOVES DIRECTLY OVER WRN WA ON SATURDAY WITH THE
MID/UPPER LEVEL FLOW TURNING SLY AS A FRONT APPROACHES OFFSHORE.
HIGH TEMPERATURES ON SATURDAY HAVE THE POTENTIAL TO SURPRISE TO THE
UPSIDE. HOWEVER...IF INVERSIONS REMAIN INTACT IT WILL BE COOLER
WHICH IS INDICATED BY BOTH THE ECE/MEX GUIDANCE. WILL GO WITH HIGHS
IN THE UPPER 50S WHICH IS ABOVE MOS BUT BELOW THE POTENTIAL IN THIS
SLY FLOW PATTERN.

THE FIRST IN A SERIES OF FRONTAL SYSTEMS WILL REACH THE AREA
WEDNESDAY. ANOTHER SYSTEM WILL PROBABLY FOLLOW EARLY NEXT WEEK.
THERE IS SOME UNCERTAINTY ON TIMING AND STRENGTH GIVEN THE AMPLIFIED
RIDGE OVER THE WRN U.S. SO THE CHANCE POPS WILL REMAIN IN PLACE.
MERCER

&&

.HYDROLOGY...FLOODING IS NOT EXPECTED FOR THE NEXT 7 DAYS.

&&

.AVIATION...A BROAD UPPER LEVEL RIDGE CENTERED OVER IDAHO TODAY WILL
MAINTAIN SW FLOW ALOFT OVER W WA. A WEAK FRONT JUST OFFSHORE WILL
MOVE SLOWLY INLAND ACROSS W WA TODAY BEFORE WEAKENING OVER THE
CASCADES.

THE FRONT WILL SPREAD LOW LEVEL MOISTURE INLAND TODAY BUT NOT A LOT
OF RAIN. AREAS OF MVFR CIGS ARE ALREADY FORMING ACROSS THE INTERIOR
AT 10Z...AND SHOULD INCREASE IN COVERAGE THIS MORNING WITH AREAS OF
IFR CIGS DEVELOPING BY THIS AFTERNOON. THERE HAS BEEN PATCHY FOG
AROUND EARLY THIS MORNING...PARTICULARLY OVER THE N INTERIOR AND
AROUND OLM...WITH VISIBILITIES 1/2SM OR LOWER. SO FAR THE FOG HAS
BEEN COMING AND GOING. IT WILL PROBABLY CONTINUE THROUGH 16Z UNTIL
THE STRATUS FINALLY SETTLES OVER THE AREA. A WEAK PUGET SOUND
CONVERGENCE ZONE MAY FORM AFTER 21Z.

KSEA...NOW THAT MVFR CIGS BELOW 2000 FT HAVE FORMED OVER THE
TERMINAL...THEY SHOULD CONTINUE THROUGH TODAY. THE CIGS MAY LOWER TO
IFR LATE THIS MORNING AS A WEAK FRONT CROSSES THE AREA. SURFACE
WINDS WILL REMAIN SOUTHERLY 5-8 KT. KAM

&&

.MARINE...A VERY WEAK FRONT WILL MOVE INLAND OVER W WA THIS MORNING
THEN WEAKEN OVER THE CASCADES THIS AFTERNOON. POST-FRONTAL WESTERLY
FLOW DEVELOPING OVER THE COASTAL WATERS THIS MORNING WILL SPREAD
INLAND BY MID DAY. W FLOW WILL INCREASE IN THE STRAIT THIS EVENING
AND MAY REACH BORDERLINE SCA LEVELS FOR A SHORT TIME.

A SURFACE RIDGE BUILDING OVER THE COASTAL WATERS BEHIND THE FRONT
TODAY WILL EXPAND INLAND TONIGHT...ALLOWING THE ONSHORE FLOW TO
WEAKEN. THE RIDGE WILL SHIFT OVER E WA ON WEDNESDAY...SHIFTING THE
WINDS TO WEAK OFFSHORE FLOW THAT WILL PERSIST THROUGH SATURDAY.

00Z GFS AND ECMWF ARE IN AGREEMENT FOR AT LEAST THIS RUN...WITH THE
NEXT WEAK FRONT ARRIVING SATURDAY NIGHT. KAM

&&

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


&&

$$

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