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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS66 KSEW 282157
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
257 PM PDT Tue Mar 28 2023

.SYNOPSIS...
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Mostly cloudy and dry conditions will persist through
tonight as weather impacts from a strong area of closed low
pressure near OR/CA remain to the south. Wednesday will be the
warmest day of the week as weak high pressure sets in ahead of a
shift back to cooler and wetter conditions the latter half of the
week and through the weekend. A seasonally strong front will cross
the area late Friday into Saturday, with showers continuing
through the weekend. Additional rain chances and cool weather will
then persist through early next week.
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&&

.SHORT TERM /TONIGHT THROUGH FRIDAY/...
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The upper level pattern
continues to feature a strong area of closed low pressure centered
just offshore the southern OR/northern CA border this afternoon.
Both upstream and downstream from this feature exists a ridge of
high pressure, with cyclonic flow noted around Hudson Bay and the
Bering Sea. Near the surface, strong low pressure just offshore
the southern OR/northern CA is essentially stacked with its upper
level parent low. It`s associated frontal system is making inland
progress this afternoon, spreading moderate to locally heavy rain
across parts of CA. Outside of this feature, high pressure extends
from W Canada into the N Great Plains, with high pressure also
accompanying much of the central US.

Quiet weather across much of W WA this afternoon given the above
analysis. Broad cyclonic flow around the center of the strong
closed low off the W Coast is helping spread mid and high clouds
across the area, making for mostly cloudy skies. Some moisture had
moves into southern counties earlier today, but provided continues
easterly winds in favor of an E-W oriented pressure gradient,
conditions have been pretty dry across most of the area,
keeping most of the moisture south. The pressure gradient will
relax this evening, hence resulting in a weakening of the
easterly/downslope winds. This may allow some light rain to creep
northward all the way towards central Puget Sound and the
Olympics. The atmosphere will likely be slow to even attempt any
saturation so thinking at best there could be some sprinkles
around the Seattle metro westward towards the Kitsap Peninsula.
Before winds ease this evening, downsloping effects will allow
afternoon temps to peak around 60 degrees despite increasing cloud
cover.

The upper level low and its associated sfc reflection will weaken
some and slide south towards the N CA Coast tonight, allowing a
weak ridge of upper level high pressure to approach the area. This
should help begin to clear skies from the north tonight, with any
moisture over the southern half of the area pushing further south
towards the WA/OR border. Expect skies to then clear more from
north to south Wednesday morning as high pressure arrives, with
lingering moisture mostly confined to central and eastern Lewis
County, particularly the southern Cascades. Weak subsidence aloft
and clear skies should allow Wednesday to become the warmest day
of the week with high temps reaching the low 60s. Some cloud cover
is expected to advect in as a subtle shortwave approaches the
southern BC Coast.

Wednesday night will be dry with ridging slowly becoming replaced
by weak troughing in the mid/upper levels. More cloud cover and
the development of isolated showers (mostly along the coast and
higher terrain) will lead to an overall cooler day with highs in
the mid/upper 50s. Current forecast could still be a bit
aggressive with rain chances given the shortwave trough`s largely
continental trajectory and overall lack of impressive dynamics
and moisture.

Conditions will then noticeable change on Friday as the next
organized, seasonally strong frontal system approaches the area.
Pre-frontal showers should increase in coverage Thursday night
into Friday with rain arriving along the Coast sometime Friday
afternoon or evening. Precip will then spread inland overnight and
through Saturday morning, resulting in measurable lowland rain and
heavy mountain snow. Winter headlines appear likely to be issued
in future forecast updates for this system, with travel impacts
likely across the Passes.

Kovacik

.LONG TERM /SATURDAY THROUGH TUESDAY/...The local area will be in
an unstable post-frontal environment in the wake of Friday night`s
frontal system to begin the long term. Upper level trough
influence will increase as the day progresses on Saturday,
resulting in widespread shower activity across the area. This
activity is likely to be convective, resulting in the potential
for a few lightning strikes and small hail. This general pattern
will hold strong through Sunday, likely enhanced at times by
subtle vort maxes within the broader trough, resulting in
widespread showers through the entire weekend. Colder air aloft
and the cooler post-frontal airmass will result in weekend high
temperatures in the upper 40s to around 50, with lows back in the
30s.

Ensemble guidance is in good agreement with upper level troughing
continuing to be the primary weather influence through early next
week. There is some discrepancy in the strength of the trough,
but despite this, it is a fair bet that the weather will remain
cool and wet through at least Tuesday.

Kovacik
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&&

.AVIATION...
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A broad upper trough centered over southern Oregon
and northern California offshore waters will gradually shift
southward into Wednesday with easterly flow continuing over Western
Washington. Low level easterly flow will weaken overnight.
VFR conditions to continue with mainly high and mid level moisture
streaming across the area. Isolated showers will be restricted to
far southern portions of the area this evening.

KSEA...VFR today with mid/high clouds. Gusty E/NE surface winds will
gradually ease this evening then become light NE overnight. Winds
becoming W/NW 7 knots or less Wednesday PM.   27
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&&

.MARINE...
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Moderate to strong offshore flow will gradually weaken
overnight as a surface low west of the OR/CA border continues to
shift southward and fill over the next 24 hours. The flow will turn
onshore Wednesday afternoon as surface ridging builds into the
coastal and offshore waters. This might be enough to produce small
craft advisory westerlies in the central/eastern strait for a period
Wednesday evening. A weak surface trough over the interior waters on
Thursday will keep winds across the waters under advisory levels.
The next in the series of fronts emerging from the Gulf of Alaska
will reach the area by later Friday and is likely to generate
additional headlines for area waters. The active pattern will
persist into the coming weekend.

S/SW swell over the coastal waters will approach 10 feet over
southern areas this evening before subsiding later tonight and
Wednesday. Coastal seas are then expected to remain below 10 feet
before building again this weekend.   27
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&&

.HYDROLOGY...


&&

.SEW WATCHES/WARNINGS/ADVISORIES...
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WA...Wind Advisory until 5 PM PDT this afternoon for East Puget Sound
     Lowlands.

PZ...Gale Warning until 2 PM PDT this afternoon for Coastal Waters
     From Cape Flattery To James Island Out 10 Nm-West Entrance
     U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory until 6 PM PDT this evening for Coastal
     Waters From Cape Flattery To James Island Out 10 Nm-West
     Entrance U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory until 9 PM PDT this evening for Central
     U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory until 5 AM PDT Wednesday for Northern
     Inland Waters Including The San Juan Islands.

     Small Craft Advisory until 6 PM PDT this evening 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 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-Puget Sound and Hood Canal.
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&&

$$