Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA
FXUS66 KSEW 240351
Area Forecast Discussion
National Weather Service Seattle WA
851 PM PDT FRI SEP 23 2016
.SYNOPSIS...A strong ridge will bring dry and warmer weather
Saturday through Monday, with the warmest weather in September
possible on Monday. A marine push will cool things down on
Tuesday. An upper level trough moving out of the Gulf of Alaska
in the middle of the week will bring a threat of more rain to the
area by late in the week.
.SHORT TERM...The front that moved through Western Washington
earlier today left light showers in its wake -- mainly along the
west slopes of the Cascades and Olympics, and they have been
decreasing this evening. The flow aloft is veering to
northwesterly as an upper ridge starts to build over the region,
extending northeast from the large upper high over the northeast
Pacific near 33N/133W. There was a mix of cloud cover over the
forecast area at 8 pm with temperatures in the 50s to lower 60s.
The upper ridge will build over the region tonight and Saturday,
with 500 mb heights over Western Washington rising to around 5820
meters. The air mass will be moist in the lower levels Saturday
morning for a generally cloudy start to the day, and a weak front
moving over the north side of the ridge into British Columbia will
bring some mid to high cloud cover during the afternoon. So
sunshine will be somewhat limited on Saturday.
The upper ridge will continue to build Saturday night and Sunday,
and 500 mb heights will probably reach 5900 meters. Low level flow
will turn northerly or even weakly offshore Sunday. There could be
patchy fog in the morning, but Sunday will be a mostly sunny and
warmer day. Highs will be mainly in the 70s.
The upper ridge axis will move east of the Cascades Sunday night
and Monday, but the lower atmosphere should continue to warm.
Monday should be a sunny and slightly warmer day, with highs in
the 70s to lower 80s. McDonnal
.LONG TERM...Here is the long term section from the afternoon
forecast discussion -- A weak cold front will drag across Western
Washington on Tuesday for cooler conditions. Highs will drop back
into the 60s. This front may bring a little rain to the coast and
north Cascades...with dry weather elsewhere. An upper level trough
will dig offshore on Thursday then shift inland Thursday night or
Friday. This system will maintain a cool and unstable air mass
with a chance of showers. 33
.AVIATION...Low level onshore flow will become light Saturday as
high pressure builds over the area. Low level moisture in a stable
air mass will give morning low clouds and fog patches then afternoon
sun for Saturday.
KSEA...The breezy southwest wind will decrease overnight and low
clouds will redevelop. Morning clouds with afternoon sunshine for
Saturday with a light and variable wind.
.MARINE...High pressure is building into the area with onshore flow
this evening. Winds will decrease later tonight as the high pressure
area moves over the region and gradients become flat Saturday
afternoon and night.
PZ...Small Craft Advisory until 2 AM PDT Saturday for Coastal Waters
From Cape Flattery To James Island 10 To 60 Nm-Coastal
Waters From James Island To Point Grenville 10 To 60 Nm-
Coastal Waters From Point Grenville To Cape Shoalwater 10
To 60 Nm.
Small Craft Advisory for rough bar until 2 AM PDT Saturday for
Grays Harbor Bar.
Small Craft Advisory for hazardous seas until 2 AM PDT Saturday
for Coastal Waters From Cape Flattery To James Island Out
10 Nm-Coastal Waters From James Island To Point Grenville
Out 10 Nm-Coastal Waters From Point Grenville To Cape
Shoalwater Out 10 Nm.
Small Craft Advisory until midnight PDT tonight for Central U.S.
Waters Strait Of Juan De Fuca-East Entrance U.S. Waters
Strait Of Juan De Fuca-Puget Sound and Hood Canal.
You can see an illustrated version of this discussion at