Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26
000
FXUS66 KSEW 121635
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
935 AM PDT Tue Mar 12 2024

.SYNOPSIS...Upper troughing will move across the area through
today for continued showers and mountain snow. Ridging will begin
to build offshore Wednesday. The upper ridge will be located
across the Pacific Northwest through the weekend for dry, warmer
weather.

&&

.SHORT TERM /TODAY THROUGH THURSDAY/...Scattered showers continue
to translate across western Washington this morning as an upper-
level trough moves across the Pacific Northwest. These are
expected to gradually diminish in coverage through the day with
further development of a Puget Sound Convergence Zone into this
evening along the King-Snohomish County border. No changes to
current headlines aside from dropping the Flood Watch.

In addition to this convergence zone, at least some instability
(200-300 J/kg) may result in a few isolated thunderstorms today,
with the threat diminishing later this evening. Snow levels today
will range 2000 to 3000 feet resulting in continued snow
accumulation for the Cascades, including Stevens and Snoqualmie
Pass. Generally another 8-10 inches  is expected for the Passes,
with localized heavier snowfall amounts in areas of convergence
later today.

The upper trough will move east of the area tonight with ridging
building offshore of western Washington. Precipitation potential
will diminish for much of the area later tonight into Wednesday
morning, with some lingering showers possible, especially in the
Cascades with a period of NW winds aloft. The ridge will build
further in extent into western Washington later Wednesday into
Thursday for drier conditions and warming temperatures. Clouds
will likely be around for a good portion of Wednesday before
clearing Wednesday night into Thursday, other than areas of fog
during the morning hours on Thursday. Highs will slowly warm into
the mid to upper 50s by Thursday.

.LONG TERM /FRIDAY THROUGH MONDAY/...An impressive upper ridge
will be the main theme for western Washington during this period,
resulting in dry conditions and warm temperatures. Offshore
flow will increase later this week, and likely peak later Friday
and into early Saturday. Temperatures will range in the low to mid
60s on Friday, however, areas in the Cascade Valleys, as well as
western slopes of the Olympics (such as Forks) may reach near 70
due to increased easterly flow. The warmest days for most areas
will likely be Saturday and Sunday with the ridge axis overhead.
NBM suggests a 40-70% of 70 degrees for areas away from the water
across the interior both days, with the highest probabilities in
the Cascade Foothills and south of Olympia. At this time, the best
potential for record breaking max temps is at KUIL, but have
trended towards 50PCT NBM for the forecast which suggests KBLI and
KHQM may reach record temperatures as well. All this is semantics
of course, as this will be a beautiful March weekend across
western Washington. Onshore flow may increase on Monday, but
continued dry weather and warmer temperatures are expected across
the area.

Davis/JD

&&

.AVIATION...Southwest flow aloft will become west to
northwesterly this afternoon as an upper trough axis shifts
onshore over Western Washington. The air mass will remain moist
and somewhat unstable today with scattered showers across the
region. Showers will diminish tonight as a building upper ridge
offshore begins to move toward the area. A typical mix of VFR/MVFR
ceilings in scattered post-frontal showers will be the story
today. Ceilings will likely settle into predominantly MVFR tonight
as onshore flow continues and surface winds ease.

KSEA...A mixed bag of VFR and high end MVFR in scattered showers
expected today. Showers diminish tonight with ceilings expected to
settle into a BKN-OVC025-035 layer. Surface winds S/SW 8 to 12
knots with a few higher gusts to 20-25 knots continuing into the
afternoon. Winds will ease further tonight.

27/14

&&

.MARINE...Small craft advisory conditions continuing today as
onshore flow continues in the wake of yesterday`s frontal system.
A surface ridge will amplify over the coastal waters on Wednesday
before shifting inland on Thursday. A thermally induced trough of
low pressure will expand northward along the coast on Friday for
offshore flow. The thermal trough shifts inland over the weekend
and dissipates for light onshore flow but tranquil conditions for
area waters. Seas will continue to hover between 12-15 feet over
the inner coastal waters and closer to 15-20 feet over the outer
coastal waters today, but will gradually subside and fall below
10 feet midweek. Seas will remain below 10 feet there into the
coming weekend.

27/14

&&

.HYDROLOGY...Heavy rain across the southern slopes of the Olympics
Monday has lead to rises in area streams and rivers, with the
Skokomish River rising above flood stage earlier this morning.
Opted to drop the Flood Watch with the ongoing Flood Warning now
that the river is above flood stage. Other rivers around the area
rising into Tuesday but snow levels between 2500-3000 feet will
limit the rises and keep the remaining rivers below flood stage.

Davis/JD

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Coastal Flood Advisory until 10 AM PDT this morning for Seattle
     and Vicinity-Tacoma Area.

     Winter Weather Advisory until 5 PM PDT this afternoon for
     Olympics.

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

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

PZ...Small Craft Advisory until 2 PM PDT Wednesday for Grays Harbor
     Bar.

     Small Craft Advisory until 5 AM PDT Wednesday for 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.

     Small Craft Advisory until 10 AM PDT this morning for 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 this afternoon for Puget
     Sound and Hood Canal.

     Small Craft Advisory until 5 PM 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.

&&

$$


USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.