Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
000
FXUS66 KSEW 230404
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
900 PM PDT Mon May 22 2017

.SYNOPSIS...Strong onshore flow will develop on Tuesday with as an
upper level trough rapidly moves toward Western Washington. Clouds
and cooler conditions will spread into the area Tuesday. The upper
trough will weaken and shift east Thursday and an upper ridge will
arrive next weekend.

&&

.SHORT TERM...An upper ridge over the region will shift inland
tonight. Low clouds will reach the coast late tonight or Tuesday
morning as onshore flow increases. An upper trough will move over
the Pacific Northwest on Tuesday. This will induce a strong onshore
push. The coast will be mostly cloudy but the interior will be
mostly sunny again on Tuesday with some high clouds. The main impact
from the onshore push will be too lower high temperatures 10-15
degrees on Tuesday. There will also be some windy conditions for a
few hours over the Admiralty Inlet Area late Tuesday afternoon and
into the evening as strong west winds develop. It looks like at
least a wind advisory will eventually be needed to for this.

An upper trough and low level onshore flow will keep things mostly
cloudy on Wednesday. Clouds will likely lift and scatter a bit by
afternoon with daytime heating. There could be a few showers but
nothing significant. Highs will cool to near normal. Thursday looks
similar to Wednesday. A broad upper trough will remain over the
Pacific Northwest with low level onshore flow. The onshore flow will
weaken however and turn more northerly by afternoon. This should
result in more afternoon sunshine and highs warming a few degrees.
Schneider/Burke

.LONG TERM...Previous discussion...An upper ridge will move over the
area on Friday and remain in control into early next week. This will
bring another extended dry spell with temperatures above normal. A
few showers might bubble up over the Cascades Sunday and Monday
afternoon as the ridge axis shifts slightly inland and southerly
flow aloft increases across the area. Schneider

&&

.AVIATION...The upper level ridge over Western Washington this
evening will drift E tonight. Light northerly flow aloft will
gradually become westerly overnight. At low levels high pressure
over the offshore waters will maintain moderate onshore flow
tonight. The air mass will remain dry through tonight with VFR
conditions.

An approaching upper level system will help trigger a marine push
with strong onshore flow developing Tuesday morning and persisting
through Tuesday night. The onshore flow will spread low stratus onto
the WA coast tonight and through the Strait after 10Z resulting in
areas of IFR conditions. Surface winds at airports near the Strait
could see gusty winds particularly Tuesday afternoon and evening.

KSEA...VFR conditions with northerly winds 4-10 KT.

&&

.MARINE...A surface ridge just offshore will maintain moderate
onshore flow tonight with SCA conditions over the coastal waters
and in the central and E Strait of Juan De Fuca.

An upper level trough approaching from the NW will result in a a
very strong marine push on Tuesday, with Gale force westerlies
developing through the Strait of Juan De Fuca around midday Tuesday
with peak winds of 35-45 KT possible late in the afternoon or early
evening. Gale force winds are also expected to spread into the north
interior and Admiralty Inlet Tuesday afternoon and evening. This
system will also support solid northwesterlies over the offshore and
coastal waters, resulting in SCA winds and seas through Tuesday
night as well as a steep fresh swell that will affect the coastal
waters through Wednesday night. Onshore flow will ease late Tuesday
night and linger through Friday.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory from 6 PM this evening to 5 AM PDT
     Wednesday for Coastal Waters From Cape Flattery To James
     Island 10 To 60 Nm-Coastal Waters From Cape Flattery To
     James Island Out 10 Nm-Coastal Waters From James Island To
     Point Grenville 10 To 60 Nm-Coastal Waters From James
     Island To Point Grenville Out 10 Nm-Coastal Waters From
     Point Grenville To Cape Shoalwater 10 To 60 Nm-Coastal
     Waters From Point Grenville To Cape Shoalwater Out 10 Nm.

     Small Craft Advisory from 6 PM this evening to 9 AM PDT Tuesday
     for Central U.S. Waters Strait Of Juan De Fuca-East
     Entrance U.S. Waters Strait Of Juan De Fuca.

     Gale Warning from 9 AM Tuesday to 5 AM PDT Wednesday for Central
     U.S. Waters Strait Of Juan De Fuca-East Entrance U.S.
     Waters Strait Of Juan De Fuca.

     Gale Warning from 2 PM Tuesday to 2 AM PDT Wednesday for
     Admiralty Inlet-Northern Inland Waters Including The San
     Juan Islands.

&&

$$

www.weather.gov/seattle

You can see an illustrated version of this discussion at
www.wrh.noaa.gov/sew/gafd/latest_webafd.html



USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.