000
FXUS66 KSEW 301748
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
948 AM PST Wed Nov 30 2022

.SYNOPSIS...A continued active pattern remains over the region
through early next week, with cooler conditions and lowered snow
levels remaining a dominant feature. Showers continue today with
snow levels again lowering tonight as another disturbance
approaches. Meanwhile, moderate to heavy mountain snow continues.
Additional lowland snow is possible through the remainder of the
week and beyond, with a cool and wet pattern remaining in place
into early next week.

&&

.SHORT TERM /TODAY THROUGH FRIDAY/...Update: We`re post-frontal
here across western Washington as showers continue to linger. Snow
levels are up to around 500-1,000 ft into the afternoon so
rainfall should be the dominant precip for lowland locations. A
notable concern for the remainder of the daytime hours would be an
active convergence zone currently positioned over Snohomish County.
Latest high-res guidance has it gradually sinking southward into
King Co. which seems to be line with 850mb winds taking a more
northwesterly component. Can`t rule out lowered snow levels if
precip rates are intense enough. But, with highs expected to warm
into low 40s, little to no accumulation is expected if wintry
precipitation do so falls. Higher hills and mountains will likely
see a better chance for accumulation for the remainder of the day
with lingering showers. The previous discussion below still
stands:


Well, 24 hours ago it was stated that this forecast was uncertain
and full of potential complications and at this point it`s safe
to say that lived up to expectations. At long last, the surface
warm front (or, at least what`s left of it as it occludes) has
reached Puget Sound, with a line of steady precipitation
stretching from near Lynden southwest through the south to near
Chehalis at this hour. However, the heavy, wet snow that piled up
in the corridor from Everett to north Seattle last night, coupled
with gusty southerly winds, has resulted in fairly widespread
power outages in addition to numerous downed trees and tree
branches. Therefore, expect to encounter some blocked roadways or
out traffic signals this morning and drive carefully if you must
be out this morning.

Temperatures have warmed across the south and most of the central
Sound region, with surface temperatures and public/spotter
reports suggesting primarily just rain across most areas. This
moisture will continue to push east into the Cascades, where the
snow level will briefly rise to around 1500 to 2000 feet early
this morning. Expect some continued showers in the unstable post-
frontal air mass, which could bring some flurries into the air
again as cooler air arrives and snow levels again lower down to
the surface. The NOAA PSL profiler at Forks clearly demonstrates
this progression that has already occurred along the coast: the
snow level jumped to near 3000 feet in the warm sector before
already trending back down this morning toward 2000 ft or lower.

In the mountains, the current Winter Storm Warnings will remain
for now, though rates will likely ease a bit later today as the
front clears the Cascades and steady precipitation becomes more
showery. For the lowlands, have elected to maintain the current
warnings and advisories through the morning commute hours to draw
attention to some of the higher snowfall totals that will remain
on untreated roads, sidewalks, and trails through the morning that
could pose a threat to travel. Expect that the heaviest snow is
done for the day, with a period of rain now continuing for most
before showers again bring rain and perhaps some snow through the
day today.

Much as was the case 24 hours ago, there is quite low certainty in
the evolution of the weather pattern for tonight across the
lowlands. Guidance continue to suggest another impulse will track
close to the region before another surface low forms and moves
onshore near or slightly north of the Columbia River. Confidence
in the potential for additional lowland snow and how widespread it
may be is quite low. The current forecast would suggest generally
rain this morning through early afternoon, but then a return to
the potential for snow. As a generally rule, have a forecast of
generally 0.5 to 1.5 inches of snow across most of the lowlands
from Wednesday evening through Thursday afternoon, but any
specific bands of snow could bring locally higher amounts while
nearby locations get mostly or entirely shut out. The higher hills
will be the most likely candidates for consistently higher
totals, but again expect snow amounts to be variable even over
somewhat small areas, and other areas may see light showers that
bring snow through the air but not accumulating.

Confidence is higher that temperatures will trend much colder
tonight through early Thursday, however, so any remaining liquid
on untreated surfaces will likely freeze. Additionally, a return
of Fraser outflow will bring this reinforcing colder air into the
region. Additional showers may bring some light snow showers early
Thursday, but the disturbance should track south to end the
widespread coverage. Will let the current warnings and advisories
run their course and then closely monitor trends through the
morning to consider the need for additional headlines for
tonight.

After a brief break in between systems later Thursday, the next
low drops south Thursday night into Friday along the coast of
Vancouver Island and off the Pacific coast. Current guidance
suggests the low will initially be positioned more offshore, with
some increase in easterly gap winds. This will bring another round
of mountain snow and rain or snow (or both) to portions of the
lowlands.

.LONG TERM /SATURDAY THROUGH TUESDAY/...The general trend of
models for the Saturday is that it will remain unsettled and it
will remain cold. What this means is that there is a non zero
chance of lowland snow showers. These will generally be post
frontal and scattered in nature. A brief dry period Sunday, before
the next system begins to move in Monday with another chance for
lowland snow for the start of next week. Temperatures will remain
near 40 during the day and near freezing during the overnight.

Cullen/McMillian

&&

.AVIATION...Strong southwest flow aloft continues over the region
today with a deep upper trough digging southward just offshore.
A mixed bag of ceilings this morning, both in rain and snow
showers. Lowered ceilings and precipitation will continue across
the region into the late afternoon in a cold and somewhat unstable
post- frontal air mass, but will gradually improve into the early
evening.  Gusty surface winds will ease into the late morning
hours.

KSEA...MVFR ceilings in rain showers to continue through the
morning. Shower activity is expected to wane later this afternoon
with a period of VFR conditions expected mid afternoon into this
evening. Surface winds southerly 6 to 12 knots this morning will
ease this afternoon, then veer N/NE 10 to 15 knots after 03Z
tonight. 27/Mazurkiewicz

&&

.MARINE...Small craft advisories remain in effect across most of the
waters this morning with post-frontal onshore flow as a surface
low gradually fills over Vancouver Island. Surface high pressure
expanding southward over interior British Columbia will lead
to another round of Fraser outflow winds later tonight into Thursday.
Another front will approach the area on Friday for another round of
potential gale force winds across the coastal waters as well as
portions of the inland waters Friday afternoon into Friday
night.

Coastal seas of 13 to 17 ft today will subside below 10 feet briefly
Thursday into Thursday night before building back into the double
digits again with another potent frontal system late in the week.

Mazurkiewicz

&&

.HYDROLOGY...There will be active weather this week with
significant amounts of precipitation, but snow levels will be low.
Rivers will rise, especially the Skokomish, but there will not
likely be enough storm runoff for river flooding due to the
snowfall over much of the area.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Winter Weather Advisory until 4 PM PST this afternoon for
     Admiralty Inlet Area-Bellevue and Vicinity-East Puget Sound
     Lowlands-Eastern Strait of Juan de Fuca-Western Skagit
     County-Western Strait of Juan De Fuca-Western Whatcom
     County.

     Winter Storm Warning until 11 AM PST this morning for Everett
     and Vicinity-Seattle and Vicinity.

     Winter Storm Warning until 4 PM PST this afternoon for Olympics-
     West Slopes North Cascades and Passes-West Slopes North
     Central Cascades and Passes-West Slopes South Central
     Cascades and Passes.

PZ...Small Craft Advisory until midnight PST tonight for Grays Harbor
     Bar-Northern Inland Waters Including The San Juan Islands.

     Small Craft Advisory until 3 AM PST Thursday for Central U.S.
     Waters Strait Of Juan De Fuca-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-East Entrance U.S. Waters Strait Of Juan De Fuca-West
     Entrance U.S. Waters Strait Of Juan De Fuca.

     Gale Watch from late tonight through Thursday morning for
     Northern Inland Waters Including The San Juan Islands.

     Small Craft Advisory until 1 PM PST this afternoon for Puget
     Sound and Hood Canal.

&&

$$

NWS SEW Office Area Forecast Discussion