Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 241042
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
342 AM PDT TUE MAY 24 2016

.SYNOPSIS...Weak high pressure aloft will be over the area today
into Wednesday for mostly dry weather. An upper low will bring
showers Thursday into the weekend.

&&

.SHORT TERM...Satellite imagery shows cloudy skies over
western Washington early this morning. Isolated shower activity
dried up Monday evening. With the cloud cover temperatures were in
a narrow range at 3 am...in the 50s.

Quiet day across western Washington today. Onshore flow and light
flow in the lower levels will continue with weak high pressure
aloft. With the light flow it will be hard to dissipate the cloud
cover over the area. The late May sun will burn off some of the
low level moisture but only enough for partly sunny conditions
this afternoon. Weak instability over the higher terrain this
afternoon will keep a chance of showers in the forecast for the
mountains. Highs in the 60s and lower 70s will be common late this
afternoon.

Little change in the pattern overnight with low level onshore
flow continuing with weak high pressure aloft. Cloud cover will
fill back in overnight. Lows will once again mostly be in the
lower to mid 50s.

Onshore flow increasing on Wednesday in response to an upper level
low beginning to dig south along the British Columbia coast. The
increasing onshore flow will limit the amount of afternoon
sunshine on Wednesday. More cloud cover in the afternoon will
result in slightly cooler max temperatures versus today...mostly
in the 60s.

Upper level low continuing to sag south Wednesday night with low
level onshore flow continuing. Low close enough by 12z Thursday
for a small chance of showers over the area with the best chances
near the Canadian border. Lows will be in the mid 40s to lower
50s.

Low continuing to drop south on Thursday with the low just north
of the Canadian border by Thursday afternoon. Low level onshore
flow continuing and with the added lift from the upper level low a
chance of showers will remain in the forecast. Best chances once
again will be over the northern portion of the area. In addition a
convergence zone is possible near the east entrance to the Strait
of Juan de Fuca. The slow cooling trend will continue with highs
in the upper 50s to mid 60s.

.LONG TERM...00z extended models showing a little better
consistency early on in the extended period with the upper level
low moving into western Washington Thursday night and then
drifting over eastern Washington on Friday. Beyond Friday the
models continue to be inconsistent with the GFS keeping an
elongated trough over western Washington extending back up into
the British Columbia coast Saturday then dropping another upper
level low down into the area Sunday night with the low moving
south of the area on Memorial day. The ECMWF keeps the low over
eastern Washington Saturday with a weak ridge building into the
British Columbia coast on Sunday and Monday with much drier
Northwesterly flow aloft over the area. With the lack of
consistency in the extended models will stay with the broad brush
chance of showers forecast with some areas of showers likely on
Friday. Temperatures will remain near or just a little below
normal for the end of May with highs mostly in the 60s and lows in
the mid 40s to lower 50s. Felton

&&

.AVIATION...Broad upper level trough remains over much of the
western US resulting not much change in the weather pattern from
days previous. Air mass remains moist and stable...making for
another round of BKN to OVC clouds out there...but cigs remain
generally VFR this early morning. Some locations may see cigs dip
down into MVFR through about mid-morning...but lifting back up and
breaking up by the afternoon. Lingering moisture may result in some
light showers or sprinkles...but looks like that will limited to the
Cascades for the most part.  Will see clouds increase and cigs start
to lower tonight and into Wednesday morning...as has been the
pattern.  SMR

KSEA...Cigs expected to remain VFR with BKN cloud cover. Low clouds
present throughout the morning...lifting by afternoon as cloud cover
becomes more SCT. Light winds out of the north this early
morning...becoming more westerly this afternoon before turning
more southwesterly this evening.  SMR

&&

.MARINE...Onshore flow will continue to give rise to borderline
small craft advisory conditions this early morning before tapering
off around sunrise. SCA in the east and central strait will remain
up...as obs at Race Rocks remain right at the threshold for advisory
winds. East strait is not doing that much...but why break up the
pair. High pressure over the NE Pacific will maintain onshore flow
across western WA through the end of the week. Small Craft Advisory
west winds are likely through the Strait of Juan de Fuca each day,
mainly during the late afternoon and evening hours. 33/SMR

&&

.SEW Watches/Warnings/Advisories...
WA...None.
PZ...Small Craft Advisory until 5 AM PDT early this morning for
     Central U.S. Waters Strait Of Juan De Fuca-East Entrance
     U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory from 5 PM this afternoon to 5 AM PDT
     Wednesday for Central U.S. Waters Strait Of Juan De Fuca-
     Coastal Waters From Cape Flattery To James Island 10 To 60
     Nm-East Entrance U.S. Waters Strait Of Juan De Fuca.

&&

$$

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You can see an illustrated version of this discussion at
www.weather.gov/seattle/gafd/latest_webafd.html



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