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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS66 KSEW 252158
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
258 PM PDT Sat Mar 25 2023

.SYNOPSIS...
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Upper level troughing over the area through the
weekend will make for cool and showery weather before giving way
to drier conditions as a storm system remains displaced to the
west over the ocean on Monday. Temperatures will rebound through
mid-week back into the 60s with dry weather and sunshine. An
active pattern then looks to return towards then end of the week
and into next weekend, with wet weather, cool temperatures, and
lowering snow levels likely.
-- End Changed Discussion --

&&

.SHORT TERM /TONIGHT THROUGH TUESDAY/...
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Broad upper level
troughing extends from the Pacific Northwest southeastward through
the Central Rockies this afternoon, containing within it numerous
shorter wave troughs/vort maxes. Cyclonic flow then extends
across much of the CONUS, with another potent shortwave trough
across the Great Lakes. At the surface, troughing was noted along
the WA/OR coast, with high pressure over the Canadian Prairies and
into the Northern Great Plains, with strong low pressure over the
Great Lakes.

Given upper level troughing over W WA this afternoon, the
atmosphere remains unstable and favorable for shower development.
As of 2PM, shower coverage is highest along the Coast, which
corresponds nicely with the sfc troughing and near the WA/Canada
border which corresponds to the area just downstream of a subtle
vort max embedded within the broad upper trough. For the rest of
the day, as the subtle vort max rotates towards the Olympic
Peninsula, should see coverage increase slightly, especially
during the remaining daylight hours as sunbreaks provide some
added instability (latest SPC mesoanalysis shows up to 500 J/kg
MUCAPE over portions of the area as of 2PM). Isolated lightning
strikes will also remain possible into the mid-evening hours
(especially near the Coast and in the vicinity of the Olympics),
before diminishing into the overnight period. Isolated to
scattered showers will then remain possible into Sunday morning
as the vort max swings across the area. There could be pockets of
a rain/snow mix or brief transition to snow in the lowlands given
temperatures in the low-mid 30s, however, recent model guidance
has suggested snow levels will remain slightly higher than
previously forecast, now more towards the 700-900ft range. Showers
are likely to become more isolated into the morning hours Sunday,
but with continued troughing aloft and favorable shortwave
energy, coverage will likely increase through the day, making for
a very similar day to today. High temperatures will remain nearly
identical in the upper 40s to right around 50.

The upper level trough will then exit to the SE Sunday evening and
Sunday night, with high pressure attempting to very briefly take
its place, however, its influence is likely to be minimal. After
midnight Sunday into very early Monday, a strong area of closed
low pressure will sink S/SW from Haida Gwaii over the open ocean,
west of the outer coastal water zones of WA and OR. Surface low
pressure associated with the closed low will quickly merge with a
separate area of low pressure off the coast of southern OR,
creating a strong Pacific storm system with plentiful moisture.
Confidence is high that the bulk of this moisture will remain to
the west and south of W WA, resulting in a mostly dry day through
Monday and high temps rebounding back into the low to mid 50s.
Increasing easterly flow from this system looks to contribute to
upslope flow on the eastern side of the Cascades, with the
potential for shower development and for some of this activity to
drift west of the Cascade crest.

The upper level closed low will then begin to head towards the N
CA Coast Monday night into Tuesday, with some of the moisture on
its northern periphery skirting Lewis County, and possibly
portions of Thurston and Pierce Counties. There could be some
snow mixed with rain if moisture does make it into the area, but
overall the amount of moisture is not impressive. Aside from
maybe some lingering showers across these counties on Tuesday, dry
conditions persist over the area, with more spring-like
temperatures returning as afternoon highs approach 60.

Kovacik

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...An E-W oriented upper
level ridge will temporarily build into the area on Wednesday as
the closed upper low near the CA Coast continues to drift south.
This will make for a very nice spring day across W WA, with added
sunshine allowing for temperatures in the low 60s, maybe even mid
60s. High clouds will begin to spread in at some point during the
day as the next upper level trough approaches.

A shortwave trough is expected to move across the area on
Thursday, however, moisture appears limited. A few showers may
materialize, primarily near the Coast and across the higher
terrain before a more promising chance of rain arrives at the end
of the week, along with a return to colder temperatures. A deep
trough is expected to build into the area from the Gulf of Alaska
on Friday, carrying with it an organized frontal system. Showers
and areas of light rain are likely ahead of the front, with high
temps dropping back into the low 50s. Widespread rain is then
likely Friday night into Saturday, with widespread showers in the
front`s wake. Expect a return to temps in the upper 40s to around
50 on Saturday, with snow levels dropping to at or just below 2000
ft. Potentially heavy mountain snow is expected with this system,
and may affect the Passes.

Kovacik
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&&

.AVIATION...
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Light north flow aloft with broad upper troughing across
the Pacific Northwest. Generally VFR this afternoon with MVFR across
portions of the Olympic Peninsula and Southwest Interior with a few
showers in this area. Mainly VFR into this evening with MVFR at
times in periods of showers. Cigs will lower to MVFR tonight into
Sunday morning with IFR possible in portions of the central and
southern Puget Sound. Generally south to southwesterly winds.

KSEA...VFR cigs this afternoon into this evening. A few showers may
move through this evening into early tonight. Cigs lower to MVFR
tonight and through Sunday morning. Winds generally south to
southwesterly, may briefly become variable this evening. JD
-- End Changed Discussion --

&&

.MARINE...
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Mainly lighter south to southwesterly winds across the
interior through tonight with Northwesterly winds for the Coastal
Waters. Small Craft Advisory winds continue for the Coastal Waters
into this evening, with seas above 10 feet through tonight before
subsiding on Sunday. Mainly light southwesterly winds Sunday into
Sunday night. A surface low will slide south along the Offshore
Waters Monday and linger south of the area on Tuesday. Winds will
increase offshore Monday and continue to remain elevated through
Tuesday. Small Craft Advisory winds are likely for most waters,
particularly for the Coastal Waters and the Strait of Juan de Fuca.
Offshore winds will ease and transition a bit northerly on
Wednesday. Seas of 9 to 11 feet through tonight will subside to 6 to
8 feet for Sunday. JD

Generally south to southwesterly winds for the interior
waters today with northwesterly winds continuing for the Coastal
Waters. Small Craft Advisory winds and seas for the Coastal Waters
will continue through tonight. Winds will subside further Sunday
morning through Sunday night. Another weather system will slide
south across the offshore waters on Monday, with increasing offshore
winds Monday and Tuesday. Additional headlines are likely during
this period, especially for the Coastal Waters and the Strait of
Juan de Fuca with increasing easterly winds. Seas of 11 to 14 feet
today will slowly subside to 6 to 8 feet on Sunday. JD
-- End Changed Discussion --

&&

.HYDROLOGY...
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No river flooding over the next 7 days.
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&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory until 4 AM PDT Sunday 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.

     Small Craft Advisory until 5 PM PDT this afternoon for West
     Entrance U.S. Waters Strait Of Juan De Fuca.

&&

$$