Text Products for AFD Issued by SEW

Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000
FXUS66 KSEW 290942
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
242 AM PDT Wed Mar 29 2023

.SYNOPSIS...-- Changed Discussion --Warm and mostly dry conditions will persist today
as weak high pressure aloft nudges into the region. Conditions
get cooler and wetter again from Thursday onward as a weak upper
level trough moves into the region. A seasonally strong frontal
system will cross the area Friday night into Saturday, with
showers expected in its wake over the weekend. Upper level troughing
will then persist over the Pacific Northwest into early next
week, with another system slated to arrive Tuesday.-- End Changed Discussion --

.SHORT TERM /TODAY THROUGH FRIDAY/...-- Changed Discussion --
The upper level low that has
been responsible for advecting some moisture and light precipitation
into the southern portions of the forecast area yesterday currently
resides just off the southern OR/northern CA coast early this
morning. Latest radar shows showers across the local area tapering
and mostly becoming confined to the southern Cascades and coastal
waters at this hour. The upper level low and its associated surface
reflection will continue to progress southward along the California
coast today, allowing for weak upper level ridging to nudge into
western Washington. Overall, expect a dry and sunny day for the
majority of the area today - with the exception of a few showers
remaining possible across the southern Cascades. Today is still on
track to be the warmest day of the week, with high temperatures
expected to climb into the upper 50s to low 60s across the
lowlands.

Cloud cover will begin to advect into the area late this
afternoon as a subtle shortwave trough starts to approach the
region. This feature will then move into the area on Thursday.
While moisture remains rather limited with this system, can still
expect to see some light showers develop through the day -
primarily along the coast and across any higher terrain. High
temperatures on Thursday will cool a couple degrees, topping out
in the upper 40s along the coast and low to mid 50s across the
interior lowlands.

A more substantial shift in the weather is then on tap Friday
into the weekend as a seasonally strong frontal system approaches
and brings with it widespread rain and heavy mountain snow to the
region. Latest guidance still hints at pre-frontal showers moving
across the area Thursday night into Friday, with the more
widespread rain approaching the coast Friday night and moving
inland overnight into Saturday. Snow levels will fall to below
pass level, so can expect periods of heavy snow to potentially
yield travel impacts across the Cascade passes. At this time,
winter headlines still appear likely with future forecast
packages. High temperatures will be in the upper 40s to low 50s.
14

.LONG TERM /SATURDAY THROUGH TUESDAY/...Showery and unsettled
weather is expected to persist across the region Saturday and
Sunday in the wake of the aforementioned frontal system. The
upper level trough influence will become greater over the weekend
and conditions look to become increasingly unstable in the
cooler, post-frontal airmass. Thus, can expect some shower
activity to be convective - and cannot rule out some lightning
potential or small hail in any of the heavier post-frontal
showers. High temperatures over the weekend will primarily range
in the mid 40s to near 50, with lows expected to be in the mid 30s
to low 40s.

Guidance remains in good agreement with upper level troughing
remaining the dominant influence across the Pacific Northwest
headed into early next week. Another system then looks to drop
down along British Columbia and into our area on Tuesday, bringing
the potential for another round of lowland rain and mountain
snow. With a cool airmass in place and snow levels remaining low,
a rain/snow mix may still be possible for portions of the lowlands
during the early morning hours. High temperatures will be in the
upper 40s to low 50s, with overnight lows expected to be in the
low to mid 30s. 14-- End Changed Discussion --

.AVIATION...-- Changed Discussion --
An upper level low continues to spin to our south
today, leaving western WA dry and stable. The flow aloft is
easterly. VFR conditions expected with just mid/high level clouds
over the area. An onshore push may bring lower clouds inland early
Thursday morning for MVFR ceilings. 33

KSEA...VFR today with N/NE wind 5-8 kt. Winds turning more W to SW
after 00Z. Low clouds and MVFR conditions possible 12-15Z Thur. 33-- End Changed Discussion --

.MARINE...-- Changed Discussion --
Northerly flow prevails today then turns onshore
tonight. Strongest winds will be through the Strait of Juan de
Fuca where a Small Craft Advisory is in effect. The flow
gradually turns southerly ahead of another frontal system that
will move across the region Friday. Strong onshore flow will
follow Friday night and Saturday with gales possible down the
strait. 33-- End Changed Discussion --

.HYDROLOGY...-- Changed Discussion --
No river flooding is expected through the next seven
days.-- End Changed Discussion --

.SEW WATCHES/WARNINGS/ADVISORIES...
-- Changed Discussion --WA...None.
PZ...Small Craft Advisory from 6 PM this evening to 9 AM PDT Thursday
for Central U.S. Waters Strait Of Juan De Fuca-East
Entrance U.S. Waters Strait Of Juan De Fuca.-- End Changed Discussion --

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