305
FXUS66 KSEW 290921
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
220 AM PDT Fri Aug 29 2025

.SYNOPSIS...Upper level ridging will bring dry conditions to western
Washington today before shifting eastward by this evening. An upper
level low off the coast will influence the area this weekend,
bringing slightly cooler temperatures and only a slight chance for
showers. Upper level ridging returns Monday, bringing a return to
warming temperatures and dry conditions.

&&

.SHORT TERM /TODAY THROUGH SUNDAY/...Latest satellite imagery
continues to show the upper level center or circulation still in
place over W WA this early morning, however shifted northward from
24 hours ago. For the southern three-quarters of the CWA, this has
resulted in a more typical west-to-east steering flow. From the
Skagit/Whatcom county line and on northward, a more monsoonal east-
to-west steering flow remains. While this impacts the mid to high
level clouds over the area, it has little effect on the low
clouds/marine stratus along the coast. Switching over to radar,
there is a curious band of echoes located over northern Pierce and
southern King counties as of 145 AM PDT...stubbornly in between any
ASOS stations, so it is difficult to see if they are actually
precipitating. Their very presence, yet low intensity, suggests that
at least some isolated spots in the south Sound and around the
immediate Seattle metro area could see a stray sprinkle before
sunrise...but no significant rainfall is expected.

As stated in the synopsis, the main weather feature today will be
upper level ridging building over the region which will slowly burn
off any cloud cover for the interior while coastal stratus appears
to be a little more stubborn, in at least some part due to the upper
level low off the coast, but that will be discussed more in-depth
momentarily. High temps today will be on average 1-3 degrees warmer
than yesterday with most inland locations in the upper 70s to lower
80s while water-adjacent spots will run in the mid 60s to around 70.

The main feature for the weekend, the upper level low off the coast,
continues to remain organized but subsequent model runs from 24
hours ago to current have been persistent in associating less and
less moisture with the feature. So while some slight cooling, down
into the mid 70s to around 80 for the interior, is still on tap for
Saturday...the chances for showers have dipped with only slight
chance wording /10-20 pct/ in the forecast...and the higher end of
that is mainly over the higher terrain of the Olympics and Cascades,
with possibly similar chances over the islands. Timing for this
remains more of an overnight Saturday/early Sunday morning event, if
it occurs. Generally dry conditions resume for most of the day
Sunday, even though the proximity of the upper low will still keep
daytime highs below 80.

18

.LONG TERM /MONDAY THROUGH THURSDAY/...Intensifying upper level
ridging to the east of the area looks to cause the upper low to
retrograde back out over the Pacific waters, resuming its influence
over W WA for the remainder of the forecast period. Daytime highs
are expected to increase each day, with 90s returning to inland
locations as early as Wednesday for Cascade valleys...becoming more
widespread in the interior lowlands Thursday. The coast and other
water-adjancent locations will generally remain in the lower to mid
70s for most of the long term period...the only exception could be
Thursday where some potential offshore flow could nudge temps into
the mid to upper 70s.

18

&&

.AVIATION...IFR/MVFR stratus along the coastline with VFR conditions
and mid level cloud ceilings elsewhere. Light onshore flow early
this morning will allow stratus to gradually fill in inland, but is
favored to stay west of the Puget Sound and I-5 corridor over the
Southwest Interior. Any marine stratus that makes it way inland will
retreat back to the coastline by 18z. Mid level clouds will thin out
by the late morning as the upper level disturbance overhead
dissipates.

KSEA...VFR conditions with some passing mid level clouds early this
morning. Could see scattered clouds around 500 feet 13z-16z.
Northwest wind 4 to 6 knots becoming southwest around 12z. Winds
trying to become northwesterly late this afternoon with the wind
direction ending up in the 250-280 degree range.

15

&&

.MARINE...Light south to southwesterly surface winds will
continue over the coastal waters today. Periodic onshore flow will
bring westerly pushes across the Strait of Juan De Fuca each
evening, with the strongest push Saturday evening that may reach
Small Craft Advisory criteria.

Combined seas around 2 to 4 feet look to continue through the
weekend and into the first half of next week before building to 4 to
6 feet.

15

&&

.FIRE WEATHER...Drier and warmer conditions today as upper level
ridging becomes the main weather influence over the area. Weak
onshore flow into the weekend is expected to keep temperatures in
check with good to excellent nightly relative humidity recoveries.
An upper level low parked offshore over the weekend could trigger
isolated thunderstorm activity over the north Cascades, but latest
model runs continue to shrink that possibility...associating less
and less moisture with the feature.

This offshore low will shift away from the area and back out to sea
early next week with strong upper ridging rebuilding across the
area. As a result, temperatures are expected to climb once again to
well above average. Afternoon relative humidities in the 25-35%
range are expected, with some higher terrain locations could get as
low as 15-25%. Fuel moisture levels are already low across much of
Western Washington and the upcoming very warm and dry weather will
further cure both live and dead fuels.

Felton/18

&&


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.SEW WATCHES/WARNINGS/ADVISORIES...

WA...None
PZ...None.

&&

$$