Forecast Discussion for SEW NWS Office
000
FXUS66 KSEW 071653
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
852 AM PST Tue Feb 7 2023

.SYNOPSIS...A strong front will cross the region today, bringing
lowland rain, mountain snow, and gusty winds across Western
Washington. Expect showers to continue early Wednesday with an
upper trough crossing the region, but becoming increasingly
limited to the mountains through the day. A brief lull lasts into
Thursday with high pressure briefly overhead, but another weak
front brings renewed moisture Friday. Somewhat drier conditions
return over the weekend, but still plenty of showers around.

&&

.SHORT TERM /TODAY THROUGH THURSDAY/...Today`s front is
moving into the coastal waters as of this writing. The
forecast remains on track. The main thing to monitor will
be snowfall totals in the mountain passes with a post-frontal
convergence zone expected later this afternoon and tonight.
Previous discussion follows with updates to marine and aviation
portions.   27


Widespread rain and high elevation snow evident on NWS radar early
this morning ahead of the advancing frontal system. Snow levels have
risen in response to the warm southerly flow in advance of the
front, with the NOAA PSL profiler at Forks indicating a jump from
4000 to near 5500 ft over the last several hours. That said, cooler
air will return behind the front as it pushes across the interior
portions of the area by late morning or early afternoon today.
Meanwhile, gusty southerly winds continue across northern Whidbey
Island and north through San Juan and Whatcom counties.
Additionally, the strong dynamics and deep moisture content
associated with this front are quite evident as it begins to push
onshore. Quillayute airport picked up more than a half inch of rain
in about 90 minutes already today. These rainfall rates may lead to
some minor ponding of water as it pushes inland into the urban areas
and some rises on area rivers and streams can be expected. See the
hydrology section for more details on this, as well as potential for
flooding on the Skokomish River.

Behind the front, modest instability may even be sufficient to
bring a few flashes of lightning in heavier showers, especially
along the coast and inner coastal waters. Strong onshore flow
behind the front will likely induce a Puget Sound Convergence Zone
by Tuesday evening. This could also bring a few lightning strikes,
but more significantly could bring fairly heavy snow. Current
winter weather headlines remain unchanged with a Winter Storm
Warning on track for the North Cascades/Mt. Baker area and
advisory amounts most likely at both Stevens and Snoqualmie
passes. Not much change to the forecast with this cycle, but still
have the potential for higher end amounts if the convergence zone
holds together and sits over either of the passes for an extended
period of time.

Weak high pressure aloft begins to build over the region late
Wednesday through early Thursday, which will bring a brief break
in the precipitation for much of the region. However, by late
Thursday, some leading rain likely reaches the Olympic Peninsula
as a weak front approaches. Temperatures generally hold near
seasonal normals for the next few days.   Cullen

.LONG TERM /FRIDAY THROUGH MONDAY/...Global ensemble guidance
continues to favor the development of an upper ridge far enough
east (over the Great Basin or east toward the Rockies) that will
enable the next frontal system, mentioned above, to spread another
round of precipitation across the region on Friday. As heights
begin to further rise into the weekend as the upper low tracks
south through California and toward the Four Corners region,
there`s still some mention of rain/mountain snow chances in the
forecast through the weekend. Confidence in the details remains a
bit lower as next week begins, with again some potential for
insufficient amplification of the ridge to shield the Pacific
Northwest from the impact of the next disturbance by Monday.
Cullen

&&

.AVIATION...An upper trough and an associated cold front will
move through the area today and then shift inland tonight. The
flow aloft will be westerly. Southerly flow near the surface ahead
of the front this morning will shift to westerly behind the front
this afternoon. The air mass will be moist and stable this
morning. It will become unstable this afternoon and evening as the
upper trough moves through with decreasing low level moisture. A
Puget Sound Convergence Zone will likely develop this afternoon
and evening over Snohomish County. The convergence zone should
shift into the Cascades and fall apart after midnight tonight.

KSEA...Low clouds this morning should lift and scatter this
afternoon and evening behind a cold front. Gusty southerly winds
today will ease later tonight. A Puget Sound Convergence Zone is
expected to remain to the north of the terminal this afternoon and
evening. 16

&&

.MARINE...A cold front will push through the area this morning.
There will be marginal gale force southerly winds ahead of the
front over the north interior waters and small craft advisory
strength winds most other waters.

Onshore flow behind the front should bring gale force west winds
to the Strait this afternoon and evening with small craft advisory
westerly winds most other waters. Onshore flow will ease on
Wednesday.

A second frontal system will move through the area Thursday and
Thursday night for another round of small craft advisory strength
winds. Onshore flow behind this system Friday and Friday night
will ease on Saturday.

Combined seas 10 to 13 feet over the Coastal Waters will briefly
subside below 10 feet later Wednesday and Wednesday night but then
rebuild to 12 to 15 feet on Thursday and remain in that general
range Friday and Saturday. 16

&&

.HYDROLOGY...Expect rises on area rivers today into Wednesday as a
round of heavy precipitation moves through the region. Snow levels
initially climb to around 4,000 feet, before lowering to 2,500 ft
behind the front tonight. The flood watch for Mason County remains
in effect, with the Skokomish River expected to rise above flood
stage later this morning. Elsewhere, river flooding is not expected
through the next week. While the lower snow levels may limit
potential impacts for the Bolt Creek Burn Scar area, will need to
closely monitor the rainfall rates with this front and especially
any convergence zone development later this evening and tonight.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Wind Advisory until 10 AM PST this morning for Admiralty Inlet
     Area-San Juan County-Western Skagit County-Western Whatcom
     County.

     Flood Watch from 7 AM PST this morning through Wednesday morning
     for Mason County.

     Winter Storm Warning until 10 AM PST Wednesday for West Slopes
     North Cascades and Passes.

     Winter Weather Advisory until 10 AM PST Wednesday for West Slopes
     North Central Cascades and Passes-West Slopes South Central
     Cascades and Passes.

PZ...Small Craft Advisory until 6 PM 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-Grays Harbor Bar-West Entrance U.S.
     Waters Strait Of Juan De Fuca.

     Gale Warning from noon today to 1 AM PST Wednesday for Central
     U.S. Waters Strait Of Juan De Fuca.

     Gale Warning until 1 AM PST Wednesday for East Entrance U.S.
     Waters Strait Of Juan De Fuca.

     Gale Warning until 10 AM PST this morning for Admiralty Inlet-
     Northern Inland Waters Including The San Juan Islands.

     Small Craft Advisory from 10 AM this morning to 1 PM PST
     Wednesday for Northern Inland Waters Including The San Juan
     Islands.

     Small Craft Advisory until 4 AM PST Wednesday for Puget Sound
     and Hood Canal.

&&

$$

NWS SEW Office Area Forecast Discussion