FXUS66 KSEW 172320

Area Forecast Discussion
National Weather Service Seattle WA
320 PM PST Mon Jan 17 2022

.SYNOPSIS...Upper level trough moving down from the northwest
reaching Western Washington later tonight into Tuesday. Weak upper
level ridge building offshore Tuesday night dissipating Wednesday.
Warm front moving into Western Washington Wednesday night with the
trailing cold front moving through Thursday. Upper level ridge
building Friday and remaining over the area into the first part of
next week.


.SHORT TERM /TONIGHT THROUGH THURSDAY/...Satellite imagery shows a
little bit of clearing this afternoon with clouds associated with
an approaching upper level trough already moving into Northwest
Washington. Doppler radar has a line of showers from about
Quillayute to Bellingham. Temperatures at 2 pm/22z were in the

Weak upper level trough embedded in the northwesterly flow aloft
moving down over Western Washington late tonight into Tuesday
morning. Shower activity associated with the trough already over
Northwest Washington will spread down over the entire area
overnight. Snow levels remaining above the passes. Lows tonight
in the lower to mid 40s.

Upper level trough moving through the area Tuesday morning with
shower activity decreasing in the afternoon. Possible weak
convergence zone near the east Entrance of the Strait of Juan de
Fuca behind the trough passage later Tuesday morning into the
afternoon hours. Highs mostly in the upper 40s.

Weak upper level ridge building offshore Tuesday night. Could have
a few residual showers lingering around Tuesday evening but for
the most part this period looks fairly dry. Middle and high level
clouds out ahead of an approaching warm front streaming through
the top of the ridge keeping skies mostly cloudy. Lows near 40.

Warm front fighting its way through the upper level ridge offshore
Wednesday with rain out ahead of the front reaching the coast in
the afternoon with a chance of rain inland. Highs near 50.

Warm front moving over Western Washington Wednesday night with
the trailing cold front arriving Thursday morning. This time frame
will have the heaviest precipitation in the next week but not
enough to cause any flooding on the area rivers. Snow levels will
remain above the passes. Lows in the mid 40s and highs in the
lower 50s.

.LONG TERM /FRIDAY THROUGH MONDAY/...Models and ensembles still
in good agreement with an upper level ridge building Friday and
remaining over the area through the weekend. This is the strongest
ridge we have seen for awhile with 500 mb heights getting into
the 580 dms. Surface gradients and low level flow remaining light
which combined with the decent inversion as a result of the ridge
and the low level moisture present over the area to produce areas
of night and morning fog. Blend high temperatures starting to
trend down a little and are slightly below normal meaning the
solutions are slowly trending towards more fog over the weekend.
Some of the ensemble solutions starting to break down the ridge
Monday with an upper level trough moving into the top of the
ridge. A majority of the solutions keep the ridge intact for
another night and morning low clouds and fog with some afternoon
sunshine day Monday. Felton


.AVIATION...An upper trough will slide north of the area with west
flow over the area. VFR cigs for most this afternoon with areas of
IFR/MVFR. VFR mainly into this evening with MVFR/IFR along the
coast. Rain will increase over the area tonight into Tuesday.
MVFR/IFR cigs tonight into Tuesday with the light rain. Winds will
be light southerly tonight.

KSEA...VFR cigs this afternoon with MVFR cigs tonight and increasing
rain chances, mainly into early Tuesday. IFR will be possible
Tuesday morning. Winds will be light southerly through tonight. JD


.MARINE...A weak weather system will move across the area tonight
and through Tuesday. A stronger weather system will move across the
area later Wednesday and Thursday for increasing winds. Small Craft
Advisory winds for most areas with this weather system. A ridge will
build into the area later in the week with northerly, offshore flow
through the area. JD


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





NWS SEW Office Area Forecast Discussion

Discussion Script by Ken True at Saratoga Weather - WFO Script by SE Lincoln Weather