Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 120327
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
827 PM PDT Mon Mar 11 2024


.UPDATE...A sub 980mb low sitting off the BC coast is draping an
occluded front across the PNW this evening. This is leading to
lowland rain and mountain snow ongoing across the area. Showers
are to remain in the forecast for tonight along with breezy winds
over the coast, Northern Interior, and San Juan Islands. Overnight
lows are forecasted to fall into the lower 40s. The previous
discussion remains below along with an updated marine/aviation
section.

&&


.SYNOPSIS...A front will move through Western Washington tonight.
Increasing rain and wind ahead of the front this afternoon. Upper
level trough behind the front Tuesday will be east of the Cascades
by early Tuesday evening. Upper level ridge building offshore
Wednesday nosing into Southern British Columbia Wednesday night
and Thursday. The ridge will slowly move east and be over Western
Washington for the weekend.

&&

.SHORT TERM /TONIGHT THROUGH THURSDAY/...Latest satellite and
radar imagery continue to show the frontal system working its way
into the region with steady rain and snow above 2000-2500 ft overtaking
the region from west to east. Winds are also beginning to
increase, with the highest winds along the coast and through the
north Interior. As such, Wind Advisories continue for these areas
through this evening. Wind, rain, and snow, will continue to
develop across the region this afternoon into this evening, with
the front reaching the coast between 03-06Z, then reaching the
interior between 06-09Z. Winds will drop off somewhat following
the frontal passage, and precipitation will become more showery in
nature. Some instability behind the front may allow for a few
lightning strikes in stronger showers late tonight into early
tomorrow morning. Low temperatures tonight around 40.

The threat for minor coastal flooding exists with high tide
tonight (late tonight along the Pacific coast, early tomorrow
morning for the Puget Sound). Along the Pacific, breezy onshore
flow and wave run-up will enhance the flooding threat.

Tomorrow, the upper level trough axis will pass over the region,
keeping conditions showery through most of the day. Hi-res models
show a convergence zone forming early afternoon, centered over
north Snohomish county before slowly descending southward through
the evening. Enough instability may be present for a few rumbles
of thunder along the coast and in the convergence zone. It will
also likely locally boost snow totals for Stevens and potentially
Snoqualmie Pass. Still a bit windy tomorrow but well below any
advisory criteria.

Through tomorrow afternoon, snow levels stay fairly steady in the
2000-3000 ft range as the incoming front is occluded. In total,
an additional 8 to 15 inches are possible through the Cascade
passes and at Hurricane Ridge, with higher amounts at Paradise
and Mount Baker, an additional 15 to 30 inches still possible. An
additional half-inch to three-quarters of an inch of rain through
the interior lowlands, with the highest amounts for the Olympic
Peninsula, between 1.5 and 2.5 inches. Winter Weather Advisories
remain in effect for all mountain zones, except the Cascades of
Whatcom and Skagit, which are under a Winter Storm Warning,
through Tuesday evening.

A large upper level ridge will quickly amplify and push out the
trough, which will clear things up and allow for the beginning of
a warmer and drier pattern. A warm front will try and clip the
northwestern part of the region, but the trend has been for the
ridge to win out and keep things dry, leaving only a slight chance
for some showers near Cape Flattery on Wednesday. Highs Wednesday
in the in the low 50s, increasing Thursday to the mid 50s. Lows in
the mid to upper 30s.

.LONG TERM /FRIDAY THROUGH MONDAY/...A sharp ridge of high pressure
will continue to amplify along the Pacific coast through the
weekend, maintaining dry and calm conditions over western Washington
as temperatures continue a warming trend. Temperatures across most
of the lowlands will reach 60 degrees by Friday, with continued
warming into at least Saturday and Sunday, depending on the strength
and location of the ridge. Ensembles show a high (70% to 90%) chance
of temperatures reaching or surpassing 65 degrees across the
lowlands on Saturday and Sunday, with areas including Seattle and
towards the Cascade foothills seeing a moderate (40% to 60%) chance
of reaching 70 degrees. Areas along the coast, including Quillayute,
are forecast to break temperature records towards the weekend, and
current ensembles even show a possibility (10% to 20% chance) of
reaching the daily temperature record for the Seattle area on
Saturday, set in 1947 at 72 degrees. Offshore flow is forecast to
weaken on Sunday as the ridge breaks down, allowing temperatures to
moderate back into the mid 60s by Monday. This weekend is on track
to be the warmest weather in western Washington since October 2023.

Lindeman


&&

.AVIATION...Cold front continues to approach the Washington mainland
from the Pacific Ocean. Widespread stratiform rain continues across
the region. This will trickle back to shower activity late tonight
into Tuesday. Ceilings have remained a mix of primarily VFR (with
some MVFR) at terminals receiving rain. As the precipitation slows
down, the ceilings will drop to MVFR (pockets of IFR are also
possible for terminals along Puget Sound and the Strait of Juan de
Fuca Tuesday morning). The heavier rain showers may bring
visibilities down to MVFR. Winds will remain out of the south
through the period, with gusty 20-30 kt winds subsiding to around 10
kt late overnight/Tuesday.

KSEA...Light rain continues across the terminal. Once the rain
lightens up 04-06Z, expect ceilings to drop to MVFR shortly after
with off and on post-frontal showers throughout the
overnight/Tuesday period. Heaviest showers may temporarily bring
visibilities down to MVFR. South winds at 10 kt gusting to 20 kt
will continue through this evening, but will hold steady around 10
kt (with minimal gusts) through Tuesday.

HPR


&&

.MARINE...Strong south-southeasterly winds continue this
evening across the coastal and interior waters ahead of an incoming
cold front. Gale force winds continue through the coastal waters,
the East Entrance to the Strait of Juan de Fuca, the Northern Inland
Waters, and Admiralty Inlet. As the front passes through late
tonight/early tomorrow morning, winds will drop down somewhat
quickly. A push of westerlies down the Strait of Juan de Fuca will
allow for Small Craft Advisories to continue through tomorrow
evening. High pressure will build over the area Wednesday into
Thursday for tranquil conditions across the area for this weekend
and into the beginning of next week.

Seas will remain around 13 to 16 ft tonight, and may increase to
near 18 ft tomorrow. Seas will decrease down to 10 ft by Wednesday
evening into Thursday, and remaining 5 to 7 ft through the weekend.

LH/HPR


&&

.HYDROLOGY...Heavy rain over the south slopes of the Olympics this
afternoon through early Tuesday morning will likely push the
Skokomish River in Mason county above flood stage tonight. A flood
watch remains in effect for Mason County. Other rivers around the
area rising tonight through Tuesday but snow levels between
2500-3000 feet will limit the rises and keep the remaining rivers
below flood stage.


&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Wind Advisory until 2 AM PDT Tuesday for Admiralty Inlet Area-
     San Juan County-Western Skagit County-Western Whatcom
     County.

     Coastal Flood Advisory from 4 AM to 10 AM PDT Tuesday for
     Seattle and Vicinity-Tacoma Area.

     Flood Watch through Tuesday afternoon for Hood Canal Area-Lower
     Chehalis Valley Area-Olympics.

     Winter Weather Advisory until 5 PM PDT Tuesday for Olympics.

     Wind Advisory until 11 PM PDT this evening for Central Coast-
     North Coast.

     Coastal Flood Advisory from midnight tonight to 6 AM PDT Tuesday
     for Central Coast-North Coast.

     Winter Storm Warning until 11 PM PDT Tuesday for West Slopes
     North Cascades and Passes.

     Winter Weather Advisory until 11 PM PDT Tuesday for West Slopes
     North Central Cascades and Passes-West Slopes South Central
     Cascades and Passes.

PZ...Small Craft Advisory until 5 AM PDT Wednesday for Grays Harbor
     Bar-West Entrance U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory until 2 AM PDT Wednesday for Central U.S.
     Waters Strait Of Juan De Fuca.

     Gale Warning until 5 AM PDT Tuesday for Admiralty Inlet-East
     Entrance U.S. Waters Strait Of Juan De Fuca-Northern Inland
     Waters Including The San Juan Islands.

     Small Craft Advisory until 5 PM PDT Tuesday for Puget Sound and
     Hood Canal.

     Gale Warning until 2 AM PDT 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.

     Small Craft Advisory from 2 AM Tuesday to 5 AM PDT 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.

&&

$$


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