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FXUS66 KSEW 050521 AAA
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
921 PM PST Tue Feb 4 2025

.UPDATE...No changes made to the inherited forecast for this
evening`s update. The upper-low remains offshore as showers wrap
around it. Current radar and hi-res guidance suggests most of the
moisture remains over the offshore waters, coast, and peninsula
but stragglers may make their way inland with spotty bouts of
snow showers and flurries into early Wednesday morning. No
widespread major accumulation is expected. In addition, Cold
Weather Advisories remain for W Whatcom and San Juan Counties
where Fraser Outflow continues with gusts up to 30-35 mph possible.
Widespread 20s are expected for overnight lows with isolated
teens, mainly for places like Bellingham, Lynden etc.


&&


.SYNOPSIS...An upper level low spinning off the Pacific
coast will continue to bring chances of snow showers to western
Washington for much of the week before pushing inland on Friday.
This will keep temperatures cold as well as allowing gusty Fraser
outflow winds to drag wind chills into the single digits for
northern portions of the area at least into Thursday.

&&

.SHORT TERM /TONIGHT THROUGH FRIDAY/...Radar has largely calmed from
this morning, with only two areas worth monitoring. The first being
a band of precip moving northward in Grays Harbor county and another
nearly stationary band in and around Port Angeles...likely due to
upward forcing by terrain of persistent Fraser outflow winds. For
the former, it is traveling in areas that should be seeing temps
north of freezing, and as such is either a mix of rain and snow or
if it is all snow, nothing at this point is likely to stick. The
latter merits watching mainly for its persistence...even though the
echo is not terribly strong. Additionally, temps there only cracked
above 32 as of 1 PM PST and any further warming is going to be
inhibited by the cloud deck present there. Will continue to monitor,
as an additional headline may be warranted there.

W WA is looking at a relatively quiet period this afternoon and
tonight. However, the upper level low responsible for this wintery
weather will shift eastward and as such putting the area back in
line with moisture associated with the feature. This will allow for
the resumption of the prospects for lowland snow. Even though PoPs
will increase throughout the day Wednesday, the main timeframe of
concern will be as early as Wednesday afternoon but likely holding
off until Wednesday evening and into Thursday. On the bright side,
this will bring clouds into the area and thus warming overnight
lows, however said lows will still have a difficult time getting to
30 or higher. With that being the case, any precip from this
incoming moisture will fall as snow. The forecast problem of the day
remains snowfall amounts during this time period and what, if any,
headlines need to be in play. Unfortunately, the multitude of
ensemble members all have different locations that lean toward
greater snowfall amounts. Zooming out and taking these solutions as
a whole, the entire area running from Everett through to Olympia
could see significant snowfall amounts. However, such a broad area
conveys a high level of uncertainty...which is to be expected for
the showery activity expected. Complicating matters will be
temperatures...how quickly or slowly temps fall below 32...and the
prospects for banding. These factors alone create sufficient
uncertainty to postpone any headline issuance for the afternoon
package, in the hopes that a clearer solution presents itself in
future model runs. That said, afternoon forecast will still indicate
that most locations should prepare for amounts ranging from a half
to one inch throughout the overnight period Wednesday before
tapering off Thursday morning. As one might expect, this will likely
result in at least some impact on the Thursday morning commute.

With the upper low sinking southward through the day Thursday,
taking much of its moisture with it, clearing skies are expected
which will only facilitate significant cooling Thursday night,
bringing overnight lows down into the lower to mid 20s. Friday sees
the upper level low finally shifting inland, however the track it
will take will make a huge difference as to whether or not the area
will see precip to go with it. Most solutions take this feature to
the south of the area...keeping PoPs low.

18

.LONG TERM /SATURDAY THROUGH TUESDAY/...Long term models continue to
show a shortwave disturbance in the flow aloft approaching the area
Saturday, nudging PoPs upward to low-end chance /approx 30-ish pct/.
Once this feature passes, solutions still lean toward W WA remaining
in a troughy pattern for the remainder of the weekend. This would
keep temperatures pretty similar to those of the short term and, as
such, would keep the risk of lowland snow in the forecast. Now, that
being said, solutions still keep any moisture in the area fairly
showery, so as to not only keep PoPs fairly low, but any snowfall
amounts during this time frame pretty limited for the most part. For
the start of the next work week, solutions remain diverse as to
whether or not a strong ridge over the Pacific will shift eastward
into the area. As such, while PoPs remain low...they never go away
either. As the positioning of the ridge will also factor into temp
forecasts, some solutions showing continued cold while other suggest
a warm-up...this uncertainty lends itself well to persistence
forecasting, keeping temps largely unchanged for the remainder of
the forecast period...until a stronger signal in one direction or
the other emerges.

18

&&

.AVIATION...Southwesterly flow aloft as low level flow turns
northerly with an upper level low churning offshore. This will
maintain largely VFR conditions this evening with local MVFR/IFR in
showers near the coastline. Latest high-res guidance continues to
support a lull in the showers inland this evening, but another band
will bring snow showers north in the 09-15z range. A another found
of moisture brings more showers from south to north Wednesday
afternoon to the region with additional periods of MVFR to localized
IFR in snow and fog. Gusty northerly/northeast winds continue in
regions impacted by Fraser outflow including KBLI and the terminals
in the San Juan Islands, but otherwise more modest north/northeast
winds across the remainder of the region.

KSEA...VFR conditions continue this evening with a lull in shower
activity. Another round of light snow showers in and around the
terminal area through the 09-13z window, but confidence is low in if
these are heavy enough to cause significant reduction in ceilings
and visibility. Showers Wednesday afternoon may contain a rain/snow
mix initially before changing to all snow after 3z Thurs. Surface
winds generally northeasterly around 6 to 10 knots shifting more
easterly overnight. A brief switch to light southerly winds early
Wednesday morning (12z-17z) before switching back to E/NE 6 to 10 kt
Wednesday afternoon.

&&

.MARINE...A surface trough will continue to remain over the
coastal waters with surface ridging in place over British Columbia.
Fraser River outflow winds will continue through Wednesday morning,
where a Small Craft Advisory remains for the Northern Inland waters,
the Central/West Strait of Juan De Fuca, and the adjacent inner
coastal waters. Light offshore flow will persist through the end of
the week, with low pressure offshore and higher pressure inland.

Combined seas generally around 3 to 6 feet will continue throughout
the rest of the week.

&&

.HYDROLOGY...No river flooding is forecasted over the next seven
days.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Cold Weather Advisory until 10 AM PST Wednesday for San Juan
     County-Western Whatcom County.

PZ...Small Craft Advisory until 10 AM PST Wednesday for Central U.S.
     Waters Strait Of Juan De Fuca-Coastal Waters From Cape
     Flattery To James Island Out 10 Nm-Northern Inland Waters
     Including The San Juan Islands-West Entrance U.S. Waters
     Strait Of Juan De Fuca.

&&

$$