000
FXUS66 KSEW 252203
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
203 PM PST Mon Jan 25 2021

.SYNOPSIS...Western Washington will remain in a troughy pattern
over much of the next 7 days. We expect to see a series of frontal
systems move through the area this week. None of them are looking
particularly wet, at least for Western Washington. With this
pattern we expect temperatures to remain cool with highs in the
mid 40s for the lowland areas. With these weather systems moving
in and cooler temperatures there is a chance for snow to be
falling for any precipitation occuring overnight for the rest of
this week. Things will gradually warm up towards the start of next
week, so expect the threat of snow in the lowlands to go away

&&

.SHORT TERM /TONIGHT THROUGH THURSDAY/...As expected, the clouds
over much of Western Washington are scattering out slightly this
afternoon. While some convective showers still remain along the
coast and just off shore. These showers will taper off through the
evening, as the upper level trough moves inland with a weak ridge
building in behind it. As the trough moves inland scattered
showers will also move into the area. These showers will scatter
out Tuesday afternoon as a very brief and very weak ridge moves
in. With as slightly stronger and more moist system right behind
it, which will begin to impact the area Tuesday evening.

Now the difficult part about both tonight`s and Tuesday night`s
forecast - lowland snow possibilities.

With low temperatures hovering just around freezing at the surface
and slightly colder air aloft we certainly have the potential for
some snow to be falling. However, because temperatures are very
marginal at the surface and not much colder aloft (only a few
degrees below freezing at 850 hPa), the probability of snow
accumulation is low for much of the area.

For both tonight and tomorrow night the precipitation intensity is
going to be very light, so any dynamic cooling occuring is going
to be very minimal. Which furthers the idea that although snow may
fall the surface conditions will not cool enough to allow it to
accumulate in most places; particularly for tonight`s system.

Additionally, we are expecting down sloping easterly winds coming
out of the Cascades for the next couple of days. This does not
bode well for snow potential on the east side of the Puget Sound
and Northern Inland waters, as the air will remain a bit warmer.
However, as the air flow reaches the Olympic Peninsula it will be
forced upwards and will cool. With the topographic enhancement
areas just east of the Olympics have the greatest chance for snow
accumulation both tonight and Tuesday night.

In summary, we are confident that some areas of the lowlands will
see some snow falling the next couple of nights. What we are not
confident in are accumulation amounts, especially for the Eastern
side of the Olympic Peninsula.
As typically the case here in Western Washington, the higher you
are in elevation the greater the chance of snow, as well as snow
accumulation.

As this is a marginal event with lots of variables at play, the
forecast could easily change, so check back for updates.

Butwin

.LONG TERM /FRIDAY THROUGH MONDAY/...Snow levels in the long term
are expected to rise back up to 1000-1500 feet starting Thursday
and will continue to rise to around 2000-2500 feet by Sunday. A
wetter system is in store for the weekend, which will bring some
rain to the lowlands and mountain snow. Overall, this weekend
system is looking to be rather mundane at this point. The overall
trend for the extended is that the storms and the heaviest
precipitation will be to our south.

Butwin

&&

.AVIATION...There are areas of clearing the afternoon and an area
of showers near the coast associated with the cold upper trough
and that instability. The showers will become isolated overnight
into Tuesday--perhaps hanging on along the south and east side of
the Olympics. The snow level will continue to be quite low as the
cold upper trough moves ashore. Offshore/easterly offshore flow
will develop on Tuesday as the next front approaches the coast. A
mid level overcast should arrive and lower Tuesday afternoon with
rain and snow developing along the south coast by evening then
spreading inland. Downslope off the Cascades in the easterlies
should prevent much precip up and down the I-5 corridor but HQM-
OLM and perhaps the Port Angeles TAF could see some wintry precip
Tuesday night. 19

KSEA...So far this afternoon the showers along the coast haven`t
made much progress inland so the Seattle area is likely to be dry
tonight. Easterly flow Tuesday and Tuesday night should keep the
Seattle area mostly dry while a front moves in--this looks like a
typical Hood Canal snow with only a skiff for the Seattle through
Wednesday morning. 19

&&

.MARINE...A weakening trough is along the coast and that will fill
and dissipate overnight. The flow will turn ESE on Tuesday and gales
are likely for the afternoon and evening over the coastal waters.
For now I think a 20-30kt easterly wind is likely for the Strait of
Juan de Fuca, with a SE 20-30kt wind for Admiralty Inlet and the
northern waters. After the front passes later Tuesday night and
Wednesday gradients will become light again. At times the models
suggest a little Fraser outflow around Thursday and Thursday night,
that is not in the forecast right now and so far cold high pressure
has not been able to push down through B.C. much. Additional fronts
should arrive late in the week or over the weekend. 19

&&

.HYDROLOGY...River flooding is not expected for the next 7 days.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory until 8 AM PST Tuesday 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.

     Gale Warning from 8 AM Tuesday to 4 AM PST 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 until 4 AM PST Wednesday for Grays Harbor
     Bar-West Entrance U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory from 2 AM Tuesday to 4 AM PST Wednesday for
     Admiralty Inlet-East Entrance U.S. Waters Strait Of Juan De
     Fuca-Northern Inland Waters Including The San Juan Islands.

     Small Craft Advisory from 3 AM Tuesday to 4 AM PST Wednesday for
     Central U.S. Waters Strait Of Juan De Fuca.

&&

$$

www.weather.gov/seattle

NWS SEW Office Area Forecast Discussion