FXUS66 KSEW 232120
Area Forecast Discussion
National Weather Service Seattle WA
220 PM PDT Wed May 23 2018
.SYNOPSIS...Onshore flow will prevail for the next week for morning
clouds and at least partial afternoon sunshine most days. A weak
upper disturbance will bring a chance of showers and thunderstorms
to the Cascades this evening.
.SHORT TERM...There will be a threat of thunderstorms over the
Cascades early this evening, mainly near the crest. A weak upper
ridge will move over the area tonight and Thursday which will
stabilize the air. This should end the shower and thunderstorm
threat. Low level onshore flow will be stronger tonight which
should allow clouds to spread into the interior and then burn
partially back to the coast later Thursday. Highs will cool a few
degrees Thursday but they will still be a little above normal.
A dry upper trough will move over the area on Friday. Low level
onshore flow will continue for another day of morning clouds and
some afternoon sunshine. Highs will cool a few more degrees and be
close to normal. The upper trough will shift inland with weak high
pressure aloft moving over the area on Saturday. Low level onshore
flow will continue and it should be a day similar to Friday.
.LONG TERM...A weak upper ridge over the area this weekend will
give way to an upper trough next Tuesday and Wednesday. Low level
onshore flow will continue. The ECMWF shows a dying front
reaching the area later Monday with spotty light rain and then a
few showers Tuesday and Wednesday. The GFS and GEM are essentially
dry through the period. The forecast leans toward the dryer
solutions for now which also matches neighboring offices.
Temperatures should be seasonable through the period. Schneider
.AVIATION...Coastal marine stratus will spread inland overnight--
probably reaching the I-5 corridor around midnight. There are a few
showers and thunderstorms near the Cascade Crest this afternoon,
those will dissipate later this evening. A few towering CU over the
Olympics will also dissipate this evening. After morning clouds,
there should be some afternoon sunshine on Thursday.
KSEA...The low clouds ought to get in here by midnight. The wind
this evening could be variable for awhile, but by late evening a SSW
wind is a good bet as the marine air pushes in.
.MARINE...Strong onshore flow this evening with gale force west
winds likely in the central and eastern Strait of Juan de Fuca. A
gale warning is in effect for that, with small craft advisories in
effect for the adjacent waters of Admiralty Inlet and the Northern
High pressure will remain offshore Thursday through Sunday, with
lower pressure east of the Cascades, for continuing onshore flow
through the period. Solid small craft advisory winds are likely in
the central and eastern Strait during the diurnal peak each late
afternoon through early morning. Gales are possible, especially
Friday afternoon and evening.
PZ...Small Craft Advisory until 3 PM PDT this afternoon for Central
U.S. Waters Strait Of Juan De Fuca-East Entrance U.S.
Waters Strait Of Juan De Fuca.
Gale Warning until 3 AM PDT Thursday for Central U.S. Waters
Strait Of Juan De Fuca-East Entrance U.S. Waters Strait Of
Juan De Fuca.
Small Craft Advisory until 3 AM PDT Thursday for Northern Inland
Waters Including The San Juan Islands.
Small Craft Advisory until midnight PDT tonight for Admiralty
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