FXUS66 KSEW 241017
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
317 AM PDT Thu Oct 24 2024

.SYNOPSIS...An upper-ridge will settle overhead through Friday
with drier and warmer conditions. Then, upper-troughing returns
with unsettled weather through the weekend with rain, mountain
snow, and occasionally windy conditions into next week.


&&

.SHORT TERM /TODAY THROUGH SATURDAY/...A shortwave trough is
cutting through the Rocky Mountains currently. Upstream, a deep
area of low pressure is evident over the NE PAC. Here locally,
we're in between these features with quasi-zonal flow aloft
becoming more ridge-like for the next 24 to 36 hours. Radar
indicates spotty shower activity as a weak convergence zone
fizzles out along US-2 at this hour. Elsewhere, light showers are
dripping over the coastal waters to the peninsula but they too
are fizzling out, possibly in response to upper-level height
rises. We'll start the day off with areas of low clouds and fog
similar to yesterday. Clouds will decrease as the day progress
with skies gradually becoming sunny. High temperatures are to
range throughout the 50s.

Dry conditions are favored into Friday as the upper-ridge axis
tracks overhead. Highs will also trend warmer in the upper 50s and
60s with aid of large-scale subsidence. Looming offshore however
is a deep low pressure system. This feature will strengthen the
offshore gradient as east winds are expected to blow through the
Cascade gaps. A 40-50% chance exists for gusts to peak at 40 mph
during this time. Then, widespread unsettled weather will return
by Friday night as models depict a shortwave ejecting out of a
broader deep low off the BC coast. Its associated frontal system
is forecast to bring a shot of widespread rain and windy weather.
This action is likely to persist into Saturday morning before
lessening during the day but only to be replaced by an additional
front overnight with more active weather.

Low temperatures are to be chilly Thursday night with 30s and 40s
in the forecast. Increased cloud coverage and breezy winds will
keep them warmer for both Friday and Saturday night with values
in the 40s and 50s expected.

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...A deep trough will center
over the PNW as we start the new week. Colder air aloft is slated
to accompany it as snow levels fall to 3,500-4,000 ft and lapse
rates steepen. A slight chance (15%) of thunderstorms is in the
forecast for the coast and parts of the interior along with light
mountain snow accumulation for the mountain passes. High pressure
will briefly dry conditions out Tuesday night before another wet
system moves into the region on Wednesday.


&&

.AVIATION...Fog and areas of lower stratus are impacting much of
central Puget Sound early this morning. KPWT conditions presently
include one half mile visibility or less and fog. PWT and other
areas prone to lower cigs may enter a period of IFR between 10-12Z
before becoming MVFR. VFR cigs remain generally from PAE north, and
MVFR in the Sea-Tac area and south. Areas of lower clouds and fog
should begin to dissipate and rise by 11 AM or noon today. Light
southerly to southwesterly flow will give way to north - northwest
flow after 19Z with VFR conditions present thereafter.

KSEA...An overcast stratus deck is presently overhead the terminal
at around 015 and will likely remain until 17Z-18Z. As the stratus
scatters out and VFR cigs return after 19Z, the change will be
coincident with a turn to light northerly flow. Through 21Z, speeds
should be 5 kt or less, but will ramp up to 7 or 8 kts by 00Z and
persist at those speeds until the extended portion of the TAF
period.

Kristell

&&

.MARINE...Benign conditions for area waters today as high pressure
remains in the area. Northerly flow is expected throughout much of
the late morning and afternoon period, but should remain below
headline criteria today. That said, a more active period is in store
for the late Friday into the weekend time frame.

Winds over the coastal waters begin to increase ahead of the next
low pressure system early Friday afternoon. Initially, the stronger
gusts will remain over the outer coastal waters, with them filling
in closer to the coast by overnight Friday into early Saturday
morning. Small craft advisories have been posted for Friday
afternoon for the coast, but transition to a Gale Watch for the
overnight and early Saturday morning period. Additionally, seas will
be coming up over the outer coastal waters between 13-15 ft, and 8-
10 feet over the inner coastal waters. Grays Harbor will need to be
evaluated further if the 10 ft seas get closer to the bar. An
elevated sea state will persist throughout the weekend before coming
back down.

Inner waters such as Puget Sound, Strait of Juan de Fuca, and
Northern Interior waters may also reach headline criteria over the
weekend but nothing has been posted at this time.

Kristell


&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...None.
&&

$$