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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS66 KSEW 301018
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
318 AM PDT Thu Mar 30 2023

.SYNOPSIS...
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A weak upper level trough will move across the region
today, bringing showers to portions of western Washington. A
seasonally strong frontal system will then move across the area
Friday night into Saturday, bringing gusty winds, lowland rain,
and periods of heavy mountain snow to the area. Cool upper level
troughing will remain over the region into early next week for
continued shower activity and below normal temperatures.
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&&

.SHORT TERM /TODAY THROUGH SATURDAY/...
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Conditions remain relatively
quiet across western Washington early this morning, with current
temperatures ranging in the upper 30s to mid 40s across the area
as of 09Z/2AM.

A weak upper level trough, embedded in the northwesterly flow
aloft, will move across the region today. Moisture with this
system remains limited, so expect the main story with this feature
to be an increase in cloud cover for the region throughout the
day. Afternoon high temperatures will cool a couple of degrees
from Wednesday`s highs as a result - and are expected to mainly
top out in the upper 40s to mid 50s across the region. Despite
limited moisture, a few light showers are still possible -
primarily along the coast and across any higher terrain. Overall
precipitation amounts will remain quite light, with lowland
locations across the Olympic Peninsula likely only seeing one or
two hundredths of an inch. Areas of higher terrain may see
precipitation amounts of a few hundredths of an inch to just over
a tenth of an inch.

A more substantial shift in the weather is then expected Friday
into Saturday as a seasonally strong frontal system moves across
the region and brings with it gusty winds, widespread lowland
rain, and heavy mountain snow. Showers look to move into western
Washington by Friday morning, with the more widespread precipitation
making its way along the coast by Friday afternoon and spreading
inland Friday night into Saturday. Snow levels will fall below
pass level for periods of heavy mountain snow across the Cascade
passes. Travel impacts will be possible - and a Winter Storm
Watch remains in effect at this time. Southerly winds will pick
up Friday afternoon and evening ahead of the frontal system, with
gusts between 30-40 MPH possible across the lowlands at times.
Afternoon high temperatures will cool a couple degrees again on
Friday and will be in the mid 40s to low 50s.

The upper level trough influence will then become greater over
the region on Saturday, maintaining shower activity across the
forecast area. Latest guidance still showing rather cold 500 mb
level temperatures at around -35C for this time of year. Thus,
with conditions becomingly increasingly unstable in the wake of
the front, may see some isolated thunderstorm activity in any
heavier showers across western Washington Saturday afternoon and
evening. Snow showers will continue for the mountains and highs
will trend 5 to 10 degrees below normal - only topping out in the
mid to upper 40s. 14

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...Cool and unsettled weather
will persist through much of the extended period. An upper level
low looks to swing through the region Sunday into Monday, which
will keep shower activity in the forecast. With a cold airmass
remaining in place, snow levels will be rather low (between 400-600
ft) by early Monday morning. Should enough moisture linger for
any heavier shower activity, cannot rule out a rain/snow mix for
some lowland locations during the early morning hours. Temperatures
will remain unseasonably cool Sunday and Monday, with highs generally
in the 40s to low 50s and overnight lows expected to dip into the
low to mid 30s.

The upper level low looks to exit the Pacific Northwest to the
south and east on Tuesday and looks to be replaced by an upper
level ridge building into the region near midweek. The GFS and
ECMWF ensemble solutions continue to show a reduction in the
number of wet solutions for the period, but do still have 20-30
percent of the solutions showing some light precipitation. Thus,
showers remain in the forecast for both days for now, but do not
expect conditions to be as wet as over the weekend. Afternoon
highs will warm a few degrees each day - and will be in the 50s.
Overnight lows look remain in the 30s. 14
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&&

.AVIATION...
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Low clouds are spreading inland this morning with
onshore flow with MVFR conditions possible. Low clouds will lift
this afternoon with ceilings around 4000-5000 ft. A weak upper
level disturbance may trigger a few showers, especially over the
coast and mountains. Low clouds will reform tonight with light rain
as a warm front moves in. Showers and gusty south winds will
follow on Friday with a cold front. 33

KSEA...Low clouds pushing into the region this morning with
possible MVFR conditions, with winds becoming more S/SW around 5
kt. Cigs lifting this afternoon around 4000-5000 ft. 33
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&&

.MARINE...
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Onshore flow continues today with strongest winds
through the Strait of Juan de Fuca - a Small Craft Advisory is in
effect. Southerly flow will increase on Friday as a strong
Pacific frontal system moves in. Small Craft Advisory winds are
likely over all waters. Winds will remain elevated through the
weekend as an active weather pattern continues. 33
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&&

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

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
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WA...Winter Storm Watch from Friday afternoon through Sunday
     afternoon for West Slopes North Cascades and Passes-West
     Slopes North Central Cascades and Passes-West Slopes South
     Central Cascades and Passes.

PZ...Small Craft Advisory until 11 PM PDT this evening for Central
     U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory until 11 AM PDT this morning for East
     Entrance U.S. Waters Strait Of Juan De Fuca.
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&&

$$