Washington State Forecast Discussion

Western Washington


081
FXUS66 KSEW 210412
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
812 PM PST Mon Jan 20 2025

.SYNOPSIS...High pressure will dominate the weather into the
middle of this week, bringing dry conditions and cold overnight
temperatures. Lows will fall below freezing over much of Western
Washington at least into mid-week while daytime highs will remain
below normal.

&&

.SHORT TERM /TONIGHT THROUGH THURSDAY/...Models have remained
virtually unchanged in regards to the short term forecast. An
upper-ridge is centering over the PNW as its axis cuts precisely
over the Olympic Peninsula. We'll remain dry and cool tonight with
high pressure at the surface. Mid to high level cloud coverage
will stream overhead, keeping those overnight lows relatively
(much emphasis on "relatively") warmer than seen previously.
Nevertheless, values are forecast to fall into the mid to upper
20s. Coastal spots will be the warmest with values in the lower
to mid 30s.

Transient shortwave trough briefly overhead during the first half
of the day on Tuesday. This feature will be followed by the
redevelopment of more upper-ridging by Tuesday night into
Wednesday. It'll last through most of the remaining short term
period. However, conditions are beginning to converge on another
incoming shortwave trough but this time is accompanied by
moisture. Deterministic guidance still has some disagreement in
exact timing but the NBM has widespread PoPs painted across W WA
by Thursday night. Below normal temperatures remain favorable with
highs in the lower to mid 40s and lows in the mid 20s to lower
30s.

.LONG TERM /FRIDAY THROUGH MONDAY/...Guidance agrees on the
development of an amplified ridge over the weekend and into early
next week. A rex block pattern looks to set up shop around this
time so a period of sustained ridging could be at play. To reflect
this, the Climate Prediction Center has temperatures and
precipitation trending below normal throughout the next 6 to 10
days.

McMillian

&&

.AVIATION...The upper ridge over Western Washington will flatten
tonight as a weak trough aloft moves through the area. Westerly flow
tonight will then become more northwesterly on Tuesday afternoon as
the ridge builds back offshore. VFR cigs with high clouds through
this evening. Localized LIFR cigs and vsbys will be possible again
later tonight into Tuesday morning, mostly from Olympia southward
and along spots of south Puget Sound. Otherwise, VFR cigs with high
clouds at times and increasing mid to high clouds along the Olympic
Peninsula on Tuesday. Light winds will continue through Tuesday.

KSEA...VFR conditions with high clouds into tonight. Low clouds and
LIFR vsbys are expected to remain south of the terminal on Tuesday
morning, with only a 10% chance of LIFR. Otherwise, VFR on Tuesday
with high clouds at times. Light north winds of 3 to 7 kts are
expected through this evening, with winds becoming light S/SE
tonight into Tuesday. JD

&&

.MARINE...High pressure will remain over the waters into this
evening. A weak system will move by to the north into Tuesday, but
no impact is expected for the waters. High pressure will then build
back into the waters Tuesday night and remain through Thursday
morning. A weakening front will move southwards through the area
Thursday night into Friday for increasing northerly winds,
especially for the Coastal Waters. Small Craft Advisory winds will
be possible during this period for at least the Coastal Waters.
Increasing Fraser Outflow is expected later early Saturday, with
more north to northeasterly winds over the weekend.

Seas will be 4 to 7 feet through Tuesday before subsiding to 3 to 5
feet on Wednesday. Seas will then build with the next front Thursday
night into Friday to 9 to 13 feet. JD

&&

.HYDROLOGY...No river flooding in the next 7 days.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...None.
&&