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Area Forecast Discussion (AFD)

Issued by Seattle/Tacoma, WA (SEW)

FXUS66 KSEW 180306

Area Forecast Discussion
National Weather Service Seattle WA
806 PM PDT Sat Aug 17 2019

.SYNOPSIS...Onshore flow into Monday as a weak weather system
passes to the north of Western Washington. An upper level ridge 
will strengthen early next week for warmer temperatures and more 
sun. A front is expected around the middle of the week with a 
chance for showers and cooler temperatures.


.SHORT TERM /TONIGHT THROUGH TUESDAY/...Satellite imagery this
evening shows mostly cloudy skies across Western Washington with 
some clearing in spots. Generally dry conditions into Sunday with 
just a slight chance for a few showers mostly across the Olympic 
Peninsula as a system slides by north of the area. Temperatures 
through the weekend will be a few degrees below normal with highs 
in the mid 60s to mid 70s across the area.

An upper level ridge will build into the region on Monday with
weak offshore flow by Monday afternoon. Expect additional sunshine
Monday afternoon after morning stratus clouds. Temperatures will 
also be a few degrees warmer in the 70s with offshore flow.

The upper level ridge will start to slide east of the area into 
Tuesday ahead of the next system. Although there may be some 
stratus clouds Tuesday morning, they will be less widespread given
the generally weak offshore flow Tuesday morning. Dry weather into
Tuesday afternoon with showers along the coast by Tuesday night as
the front approaches. Temperatures on Tuesday will be warmer given
the ridge placement and weak offshore flow with highs in the 70s
to mid 80s in spots across the area. JD

onshore Wednesday with some showers around as the system slides 
through the area. Guidance is in general agreement on the timing 
of the system with the GFS being a tad bit wetter, especially 
across the northern tier, than the ECMWF. Either way, expect 
showers around Wednesday with generally drier weather by Thursday 
morning. Flow aloft following the system looks mostly zonal with 
guidance suggesting another chance of some POPs Friday or 
Saturday. Temperatures are expected to be near climo into the 70s 
across the area. JD


.AVIATION...Weak low level onshore flow continuing through the 
weekend. Northwesterly flow aloft becoming westerly on Sunday.
Stratus lingers this evening though several spots did see a bit of
clearing this afternoon. Ceilings across the area range from VFR
to MVFR where less clearing occurred. Tonight into Sunday looks
to be a repeat of today with ceilings lowering back down as
stratus becomes overcast overnight. Gradual improvement by mid 
afternoon on Sunday. 

KSEA...VFR conditions this evening, lowering back down to MVFR
overnight into Sunday morning. Gradual improvement expected again
by late morning to mid afternoon. South to southwest winds 4 to 8
kts. CEO


.MARINE...Weak onshore flow will continue through the 
weekend. No headlines are in place this evening though winds in
the central Strait are just below small craft advisory. Flow
becomes lighter on Monday and Tuesday before a weakening front
arrives Wednesday with stronger winds. CEO


.HYDROLOGY...The daily hydrology discussion has ended until the
start of the next rainy season; it will only be updated as needed
until then.