Text Products for AFD Issued by SEW

Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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-- Discussion containing changed information from previous version are highlighted. --
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FXUS66 KSEW 271630
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
930 AM PDT Mon Mar 27 2023

.UPDATE...-- Changed Discussion --No changes to the current forecast this morning. A quiet
but chilly start to the new workweek. A strong sfc cyclone will
rapidly intensify today as it merges with another low offshore the
OR and CA Coast. This will increase the pressure gradient over W
WA through the day today, with the flow becoming offshore and
breezy. A wind advisory is still set to take a effect late this
evening over the East Puget Sound lowlands. Increasing upslope
flow on the E side of the Cascades still carries the potential to
spark a few showers this afternoon and evening, however, coverage
appears less impressive as compared to previous forecasts. An
overall dry day is in store for the local area, with high
temperatures rebounding into the mid and possibly upper 50s.

Previous discussion included below with an updated marine and
aviation section.

Kovacik-- End Changed Discussion --

.PREV DISCUSSION... -- Changed Discussion --/issued 359 AM PDT Mon Mar 27 2023/

.SYNOPSIS...A warming and drying trend will commence today and
persist through midweek as offshore flow develops across western
Washington and a low offshore tracks southward towards California.
Upper level ridging will nudge into the region Wednesday in its
wake. A return to cooler and wetter conditions is then expected
the latter half of the week and into the weekend as a seasonally
strong frontal system moves into the region.-- End Changed Discussion --

.SHORT TERM /TODAY THROUGH WEDNESDAY/...Radar early this morning
shows some light shower activity persisting over the coastal
waters and along portions of the Strait of Juan de Fuca and the
San Juan Islands. Overall, expect showers to wind down over the
next couple of hours. Temperatures early this morning are rather
chilly out there, currently ranging in the upper 20s to the upper
30s across the majority of the forecast area. Areas of fog have
also started to develop across portions of the south Sound overnight
with clear skies and ample moisture still present in the low levels.

A robust upper level low, will sink southward into the region
from British Columbia today, remaining well offshore. Its associated
surface low will merge with another low tracking towards southern
OR. This will act to strengthen the surface low - and aid in the
intensification of the upper level low through the day as well.
The bulk of the moisture will primarily remain well to the west
of the area today as the low continues to sink south. All in all,
expect a primarily dry day for the majority of western Washington
with low level flow transitioning to offshore and mid- level
cloud cover streaming overhead. Have kept a mention of POPs in
the Cascades, however- where upslope flow east of the crest may
spark some shower activity in the afternoon that drifts on over to
the west side. Temperatures will climb a few degrees today, with
afternoon highs expected to be in the low to mid 50s.

As the closed low sinks further southward towards the southern
OR/northern CA coast tonight into Tuesday, some wrap- around
moisture looks like it will start to make its way northward and
move into the southern fringes of the forecast area. Thus, have
maintained rain chances in the forecast, mainly for Lewis, Grays
Harbor, Thurston, Mason, and Pierce counties. Strengthening
offshore flow tonight will lead to locally windy conditions across
the Cascade gaps overnight and through Tuesday afternoon, mainly
for areas like Enumclaw and North Bend - where gusts to 45-50 mph
will be possible at times. Have issued a wind advisory for the
Puget Sound lowlands with this forecast package as a result.
Temperatures on Tuesday will climb a few degrees from Monday`s
highs - topping out in the upper 50s to near 60 across the area.

The upper level low will then continue to move south along the CA
coast on Wednesday, pulling its remaining moisture out of the
area and allowing for upper level ridging to nudge into the region
from the west. Wednesday is still trending as the sunniest and
warmest day of week, with afternoon highs expected to climb into
the upper 50s to low 60s across the area. 14

.LONG TERM /THURSDAY THROUGH SUNDAY/...A switch back to wetter
and cooler conditions is on tap in the extended period with an
upper level shortwave looking to brush the region on Thursday.
Although moisture continues to look rather limited, this feature
has the potential to bring a few showers to the region- mainly
along the coast and across the mountains.

A more organized frontal system then looks to approach the region
on Friday, bringing with it more widespread rain for the lowlands,
mountain snow, and cooler temperatures headed into the weekend.
Snow levels look to drop back down below pass level with periods
of heavy mountain snow possible. This may create some travel impacts
across the passes should current forecast trends hold. Thus, those
planning cross- Cascade travel this weekend will want to make sure
to stay updated to the latest regarding the forecast over the
next few days. 14

.AVIATION...-- Changed Discussion --An upper-level low will dig southward offshore through
Tuesday, promoting intensification of a strong surface low. This
will lead to the development of an easterly flow pattern over the
region through Tuesday. Patchy IFR in fog dissipating this morning,
then VFR with areas of high level moisture. Low level easterly winds
increasing tonight...especially near gaps in terrain.

KSEA...VFR conditions with building high clouds. Surface winds N/NE
7 to 12 knots knots...turning E/NE tonight with gusts of 20 knots
possible...especially around daybreak Tuesday. 27-- End Changed Discussion --

.MARINE...Light southerly winds will begin to turn offshore through
the day as a surface low rapidly intensifies well offshore and
slides southward into Tuesday. Small Craft Advisories will go into
effect this afternoon for the offshore waters then expand over the
coastal waters this evening. Fraser Outflow winds will lead to
strong gusts over the Northern Inland Waters into the Strait of Juan
de Fuca tonight through Tuesday night. Winds look to remain below
gale criteria with the stronger winds being closer to the surface
low well offshore then to our south as the low dives southward.
Winds will gradually ease into Tuesday night as the remaining SCAs
expire for the Strait and Northern Inland Waters.

Seas will increase in part with the offshore winds but look to
remain below 10 feet through Tuesday.

A weak surface trough will move across the area Thursday followed by
a stronger frontal system into Friday, both of which look to bring
another round of Small Craft Advisories to the area waters.

Davis

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

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Wind Advisory from 11 PM this evening to 5 PM PDT Tuesday for
East Puget Sound Lowlands.

PZ...Small Craft Advisory from 8 PM this evening to 8 PM PDT Tuesday
for Central U.S. Waters Strait Of Juan De Fuca-West
Entrance U.S. Waters Strait Of Juan De Fuca.

Small Craft Advisory from 11 PM this evening to 5 AM PDT
Wednesday for Northern Inland Waters Including The San Juan
Islands.

Small Craft Advisory from 8 PM this evening to 2 PM PDT Tuesday
for Coastal Waters From Cape Flattery To James Island Out
10 Nm-Coastal Waters From James Island To Point Grenville
Out 10 Nm-Coastal Waters From Point Grenville To Cape
Shoalwater Out 10 Nm.

Small Craft Advisory from 2 PM this afternoon to 2 PM PDT
Tuesday for Coastal Waters From Cape Flattery To James
Island 10 To 60 Nm-Coastal Waters From James Island To
Point Grenville 10 To 60 Nm-Coastal Waters From Point
Grenville To Cape Shoalwater 10 To 60 Nm.

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