Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 261040

Area Forecast Discussion
National Weather Service Seattle WA
340 AM PDT Sun Mar 26 2023

.SYNOPSIS...Upper level troughing over the region will keep
conditions cool and showery today, before conditions dry out on
Monday. Overall drier and warmer conditions are expected the first
half of the week, with temperatures expected to approach the low
60s by Wednesday. An active pattern returns late in the week as
another weather system moves into the region and brings wetter
conditions, cooler temperatures, and lowering snow levels.


.SHORT TERM /TODAY THROUGH TUESDAY/...Upper level troughing
persists over western Washington this morning, with latest radar
showing shower activity continuing along the coast and coastal
waters. Current temperatures as of 2AM/09Z are in the 30s for the
majority of the area. Expect morning lows to get down to near
freezing in spots, especially south of the Sound along the Chehalis
River Valley. Could still see some pockets of a rain/snow mix, or
even a brief transition to snow, in heavier shower activity for
areas south of Puget Sound through the early morning hours given
near freezing temperatures and lowering snow levels overnight.

The upper level trough will continue to influence the region
today, but is expected to push south and east of the area this
evening. Shower activity will continue through the day, increasing
in coverage with a vort max situated just along the coast.
Temperatures will remain cooler than normal and only look to top
out in the mid to upper 40s for the majority of the area.

A strong closed low will then drop southward into the region from
Haida Gwaii late tonight into Monday morning and looks to continue
to track southward, well offshore, throughout the day. Flow will
transition to offshore and confidence remains high that the bulk
of the moisture associated with this system will remain to the
west and south of western Washington, making for a primarily dry
day across the region. The only exception would be the Cascades,
where upslope flow may spark some shower activity east of the
crest that may drift westward. Overall, expect conditions to dry
out and for temperatures to rebound into the mid 50s.

The closed low will then sink further towards the northern CA
coast Monday night into Tuesday. Some wrap-around moisture may
brush the southern portion of the forecast area heading into
Tuesday, so have kept a mention for a slight chance of POPs for
Lewis, Grays Harbor, Thurston, and Pierce counties. That said,
however, expect the majority of areas to remain dry and for
temperatures to continue to climb a few degrees from Monday`s
highs - likely topping out in the upper 50s to near 60. 14

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...Weak upper level ridging
looks to nudge into the region on Wednesday as the aforementioned
upper low continues to track southward along the CA coast. Wednesday
looks to be the nicest day of the week- with ample sunshine and
afternoon highs expected to climb into the low to mid 60s for the
majority of the area.

A shortwave trough then looks to drop down into the region on
Thursday, however moisture continues to look limited. Nonetheless,
this feature may spark a few showers across the region, with the
most favorable spots being along the coast and across any higher

A switch back to wetter and cooler conditions looks likely late in
the week as a more organized frontal system approaches the region
Friday morning and brings with it more widespread rain, mountain
snow, and the return of cooler temperatures. Mountain snow may be
heavy at times with snow levels likely dropping below the passes. 14


.AVIATION...MVFR ceilings through the better portion of the morning
with most rain being confined to the coast at KHQM. Ceilings should
scatter to VFR levels by around 20Z. Additional scattered showers
are expected to develop this afternoon thanks to the upper-level low
over the region and weak instability, which may lead to brief
ceiling/visibility restrictions. Cannot rule out a few lightning
strikes either. Winds out of the south-southwest from 5 to 10 knots,
with periods of south-southeasterly wind at KBLI, KPAE and KBFI into
the afternoon.

KSEA...MVFR conditions this morning with ceilings ranging from 1500
to 2000 feet. The stratus deck should gradually mix out through the
late morning with VFR conditions returning around 19Z. The airmass
will be somewhat unstable this afternoon with scattered showers and
perhaps a few thunderstorms developing after 20Z. South-
southwesterly winds this morning from 5 to 10 knots. Winds will back
to the southeast then east through tonight from 5 knots or less.


.MARINE...Northwesterly swell over the offshore and coastal waters
has dropped below 10 feet, thus the Small Craft Advisory for these
areas will expire on time at 4 AM.  Otherwise, light northwest flow
over the coastal waters and southerly flow over the inland waters
today with weak high pressure keeping winds light. A surface low
will dig southward offshore Monday, moving toward the Northern
California Coast by Tuesday night. Offshore flow will develop Monday
into Tuesday with growing confidence for at least advisory-level
wind gusts across the coastal and offshore waters in addition to the
Strait of Juan de Fuca. Though seas build with increasing wind waves
and fresh swell with offshore flow Monday night into Tuesday,
combined seas should remain below 10 feet through the upcoming



.HYDROLOGY...No river flooding expected in the next 7 days.


PZ...Small Craft Advisory until 4 AM PDT early this morning 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.


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