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332
FXUS66 KSEW 160319
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
819 PM PDT Sun Sep 15 2024

.SYNOPSIS...Upper level trough moving southward tonight with
gradually clearing skies tonight. Monday will be dry as well with
the trough well to the south and an approaching front still north
of Vancouver Island. Front moving through Tuesday night with rain
out ahead of the front spreading over the area Tuesday. Upper
level ridge trying to build in later Wednesday into Thursday but
the ridge is not strong enough to eliminate the possibility of
systems brushing the area into next weekend.

&&

.SHORT TERM /TONIGHT THROUGH WEDNESDAY/...
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Mostly clear skies
tonight with lows tonight in the mid 40s to low 50s. The previous
discussion can be found below along with updated aviation and
marine sections:

Some patchy fog may develop Monday morning with mostly clear
skies, but should evaporate in the morning. Split flow aloft with
a weak ridge trying to nudge into the region will keep Monday
dry. Partly cloudy skies will allow temperatures to warm into the
upper 60s to low 70s. This is still a bit below normal, but it
will be the warmest day of the week. High clouds will filter in
Monday night as the next upper level trough and associated
frontal system approaches the region on Tuesday.

Tuesday will be much cooler with highs in the 60s with widespread
rain through much of the day. Rainfall amounts should remain
light, a few tenths of an inch possible across the interior, with
0.5 to near 1 inch possible along the Pacific Coast and the
windward Olympic mountains. Rain will devolve into showers Tuesday
night into Wednesday before tapering off Wednesday evening.

.LONG TERM /THURSDAY THROUGH SUNDAY/...The evolution of the long-
term forecast remains uncertain as models struggle to converge on
a solution. The trough will dip south in to California on
Wednesday with a ridge centered over the east-central Pacific
trying to build over the area. The ridge moves south, resulting in
more zonal flow by the end of the week. For this weekend, ensemble
cluster analysis shows about a 60% lean towards ridging for the
weekend, with warmer and drier conditions, with 40% of model runs
indicating additional troughs moving through for cooler and wetter
conditions. The mean solution shows temperatures slowly climbing
into the mid to upper 60s and a broad-brushed chance for showers
from Friday into the weekend across western Washington.

LH
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.AVIATION...
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An upper low located over the Southwest US will linger
with continued N/NE flow aloft at 700mb. Generally VFR cigs for most
areas this evening with lingering stratus along the Cascades. Mostly
clear skies will continue into early tonight. Low LIFR/IFR stratus
will likely develop across portions of central Puget Sound,
especially towards Snohomish and eastern King County into Monday
morning. Additional LIFR/IFR stratus expected along the coast near
KHQM. Patchy fog may also develop, particularly in river valleys
near KPAE as well as KBLI. Otherwise, cigs will likely clear late
Monday morning with VFR in the afternoon. Generally lighter winds
tonight will increase northerly on Monday.

KSEA...VFR continues into tonight. Stratus is likely to develop NE
of the terminal tonight near the Cascade Foothills. IFR cigs may
drift towards SEA Monday morning, generally from 13 to 18z. There
also remains approximately a 15% of LIFR cigs during this period.
N/NE winds tonight at 4 to 7 knots, increasing midday Monday. JD
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&&

.MARINE...Generally benign conditions today as high pressure builds
over the coastal waters. North to northwest winds across the waters
today with gusts just below SCA over the far outer coastal waters
and through the Strait of Georgia across the San Juan Islands
northwestward. Building high pressure will generate a westerly push
through the Strait of Juan de Fuca on Monday, though confidence is
not high enough that it will reach SCA criteria. Low pressure will
move southward across area waters on Tuesday with high pressure
rebounding through the remainder of the week.

Seas 5 to 7 feet today through Tuesday, dropping to 4 to 5 feet
Tuesday before rising again around 6 to 8 feet as a trough moves
through mid-week. Seas will return to 4 to 5 feet by the end of the
week as conditions calm.

15

&&

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

$$