Area Forecast Discussion Issued by NWS Seattle/Tacoma, WA
000
FXUS66 KSEW 130323
AFDSEW
Area Forecast Discussion
National Weather Service Seattle WA
823 PM PDT Tue Mar 12 2024
.UPDATE...Convergence zone showers have set up over northern King
and Kitsap Counties and will continue to drift eastward tonight
towards the Cascades. Stevens and Snoqualmie Passes will continue
to see light snow accumulations through the rest of the evening
with scattered rain showers elsewhere. Precipitation will taper
off overnight as a drier airmass amplifies northward along the
coast. This high pressure ridge will allow conditions to become
unseasonably warm by the weekend, with some lowlands on track to
see the first 70 degree day of the year by Sunday. The current
forecast captures the trends well, no updates.
&&
.SYNOPSIS...An upper level trough will slowly shift eastward over
the Pacific Northwest tonight, with continued showers and mountain
snow. Upper level ridging will then build along the West Coast
Thursday through this weekend with building warmth and dry
conditions.
&&
.SHORT TERM /TONIGHT THROUGH FRIDAY/...Scattered showers across
portions of western Washington this afternoon with the main focus
turning towards a developing Puget Sound Convergence Zone
extending from northeastern Jefferson County eastward across
Whidbey Island into central Snohomish County. Another more
organized collection of showers and downpours can be found across
the southern Puget Sound. Several lightning strikes have also
occurred across the East Puget Sound lowlands near the Issaquah
Alps along the I-90 corridor of central King County earlier this
afternoon. Can`t rule out additional lightning strikes through the
remainder of the afternoon and evening with several hundred J/kg
of CAPE, especially in the developing convergence zone.
Light snow will continue through the Cascades, especially across
the central Cascades in association with convergence zone
enhancement. Thus, Winter Weather Advisories continue across the
central Cascades with an additional 2 to 6 inches of snow possible
with highest totals across King County, where totals could trend
a little higher wherever the convergence band sits the longest.
At this time that looks to favor the area near Stevens Pass more
so than Snoqualmie Pass. Opted to drop the Winter Storm Warning
for the north Cascades of eastern Whatcom and Skagit Counties as
the main synoptic-scale forcing for snow ends and any lingering
snow transitions mostly to convergence banding south of these
areas. Can`t rule out additional light accumulations, though
mostly sub- advisory amounts.
We begin to dry into Wednesday as upper-level ridging slowly
builds north and east into western Washington. A few more high
clouds look to pass over the region thanks to a weakening warm
front located offshore, which may enhance some light snow or
flurries over the Olympics and north Cascades, but it looks to be
a dry day for the most part. High temperatures inch upward a
degree or two closer to 50 across most of the lowlands.
The ridge continues to build eastward over the Pacific Northwest
Thursday and Friday with a thermal trough building along the
Oregon coast northward along the Washington Coast. Surface high
pressure building over the Canadian Rockies will help induce
offshore flow, which will help enhance adiabatic warming through
the Cascade and Olympic Valleys. High temperatures warm into the
low to mid 60s by Friday with partly to mostly sunny conditions.
.LONG TERM /SATURDAY THROUGH TUESDAY/...Upper-level ridging
continues Saturday and Sunday, reaching peak amplitude this
weekend with greatest potential for record high temperatures
across the lowlands. Nudged highs slightly towards the NBM 90th
percentile Saturday and Sunday due to continued offshore flow an
anomalously strong mid-level heights. Record highs this weekend in
the upper 60s to low 70s. Overall, a period of mild spring-like
weather is in store this week.
The ridge begins to break down into early next week with surface
low pressure tracking into British Columbia and dragging a weak
front across western Washington. Moisture looks weak with this
system at this time with little to no rainfall.
Davis
&&
.AVIATION...An upper level trough continues on its way out of the
state this evening. Post frontal showers and convergence zone
activity is diminishing this evening over KPAE. The flow aloft and
at the surface will become more onshore. A weak warm frontal
boundary will stay over the Pacific and produce showers off the
Washington coast Wednesday. With precipitation ending over the
mainland however, ceilings will drop to borderline MVFR/VFR (around
3000 ft) overnight through at least the first part of Wednesday
(especially with a push down the Strait of Juan de Fuca). Winds will
remain out of the south through Wednesday morning at 5 to 10 kt, but
will switch to the north late Wednesday morning at around 2 to 5 kt.
KSEA...Mostly VFR this evening. Expectation is for ceilings to drop
to around 2,500-3,000 ft overnight with rain ending, but improvement
to VFR will occur mid to late Wednesday morning. Southwest winds 8-
12 kt with gusts to 20 kt will diminish overnight ti 6 to 9 kt, and
transition to the northwest around 21Z Wednesday at around 4 to 6 kt.
HPR
&&
.MARINE...Winds will continue to ease through the end of today in
the wake of a frontal system, with seas hovering between 10 to 15
feet over the coastal waters. Small Craft Advisories will remain
in effect along the Strait of Juan de Fuca through tonight with
gusty post-frontal westerlies persisting this afternoon. High
pressure will build over the area waters Wednesday and move inland
on Thursday, calming conditions. A thermal trough of low pressure
will expand northward on Friday, bringing light offshore flow to
the coast and along the Strait. The trough is expected to move
inland over the weekend. Overall, expect tranquil conditions to
persist over the waters through the weekend.
Seas will gradually subside and fall below 10 feet late Wednesday
and then look to generally hover between 6 to 8 feet heading into
the weekend.
Gordon/Borth
&&
.HYDROLOGY...The Skokomish River continues to drop below flood
stage this evening and will continue to fall through the week
with an extended period of dry weather. No additional flooding is
forecast over the next 7 days.
&&
.SEW WATCHES/WARNINGS/ADVISORIES...
WA...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-East Entrance U.S. Waters
Strait Of Juan De Fuca.
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.
&&
$$