423
FXUS66 KSEW 281829
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
1129 AM PDT Thu Aug 28 2025

.UPDATE...A band of light rain stretching from
Snohomish/Skagit/Whatcom to Clallam county continues to push west
this morning. Isolated showers possible this afternoon.
Otherwise, no significant updates to the inherited forecast.
Refer to updated aviation and marine sections below.

&&

.SYNOPSIS...An upper level disturbance will keep the chance for
showers over western Washington again today before upper level
ridging begins to rebuild over the area. Isolated thunderstorms
remain possible, mainly in the terrain of the Cascades and the
eastern Olympics. Dry and warmer Friday before a system brings some
slight cooling and another chance for rain for the weekend.

&&

.SHORT TERM /TODAY THROUGH SATURDAY/...An odd little shortwave
cutting into the overall ridge pattern over W WA will keep the
chances for showers over the area, which is already present on
current satellite and radar. The majority of the action is split,
with a northern arm stretching through much of Snohomish county and
continuing eastward into the Strait and the northern third of the
Olympic Peninsula. The southern arm stretches from northern Mason
county out to the coast via northern Grays Harbor county. Some
precip may have made it onto the Bear Gulch fire...but it seems that
the best precip may have passed just to the south as RAWS on the
incident only shows a couple of hundredths measured.

Models suggest clouds scattering out in the afternoon and early
evening, which could result in another potential round of scattered
showers with isolated thunderstorms. Thunder risk is largely
confined to the higher terrain of the Cascades and Olympics as they
will likely be the easiest to destabilize. The question arises that
if conditions do not clear out as advertised, this could limit any
thunderstorm development further...but given current slight chance
wording, this seems to best address the threat, not likely but non-
zero.

This feature is driven northward overnight Thursday and into Friday
morning as an upper level ridge builds over the area, bringing a
return to dry conditions and nudging temps up a little further. This
is short-lived as an organized low off the coast starts to creep
eastward, pushing the ridge axis into E WA and nudging up to the WA
coast by Saturday afternoon. This will take a degree or two off
daytime highs, but the chances for precip will likely hold off until
the late afternoon/early evening as the center of the low very
slowly progresses eastward, yet never coming ashore. It is worth
noting the the chances here are not terribly impressive, 30-40 pct
at best with much of the area being more around 10-20 pct.

18

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...There is a high degree of
uncertainty with regards to the path of this low in the long term,
although there is a consensus that it lifts northward with little if
any further movement east. This may allow for a continued slight
chance of showers with isolated thunderstorms for the North Cascades
Sunday afternoon, but game over everywhere else. The general trend
for the first half of next week is for upper level ridging to
reassert itself with dry conditions expected for the remainder of
the forecast period and gradually warming temperatures back into the
lower to mid 80s for interior locations.

18

&&

.AVIATION...A mix bag of ceilings this morning across the
terminals ranging from VFR to LIFR. Expecting improvement for the
interior terminals back to VFR late this morning. However, ceilings
along the coast will MVFR today before they deteriorate back again
to IFR/LIFR later this evening. A band of light rain continues to
move north across the region this morning impacting terminals north
of KBFI. Precipitation will continue to move northward this morning
with isolated showers developing near Puget Sound terminals this
afternoon and evening.

Another chance of thunderstorms this afternoon/evening along the
Cascades, but not expecting any impact to the terminals.

KSEA...VFR conditions will persist through the day with passing mid
level clouds. Showers are possible at the terminal this evening
after 01z Friday into early Friday morning, but confidence is low.
North/northwesterly winds 5 to 8 kt in the afternoon and will
shift southwest after 12z Friday morning.

15/29

&&

.MARINE...Southwesterly surface winds over the coastal waters
will continue through late in the week. Onshore flow will bring
westerly pushes across the Strait of Juan de Fuca each evening, with
the strongest push likely reaching SCA criteria on Saturday.

The Dense Fog Advisory has been cancelled for the coastal waters and
Grays Harbor Bar this morning as latest observations show visibility
has improved.

Combined seas will remain between 2-5 feet through the period.

15/29

&&

.FIRE WEATHER...A Red Flag Warning for dry thunderstorms/lightning
will remain in effect for zones 658, 659 and 661 as the combination
of the continued import of monsoonal moisture coupled with the
potential for clearing skies allowing for a return to unstable
conditions could result in lightning strikes in the late afternoon
and early evening hours. While storms may drift westward, any
significant departure from the higher terrain will hinder any
ability to tap into instability and thus limit the ability to remain
intact.

Area fuels remain in exceedance of 95th percentile ERC values,
increasing concerns for lightning strikes capable of producing new
fire starts. Outflow winds of 25 to 35 mph are possible both ahead
of and behind any storms that develop and can create erratic wind
situations that are exacerbated by complex terrain.

Atmospheric moisture and PWAT suggest some storms may be capable of
a wetting rain, but QPF forecasts definitely leaning toward this
being more the outlier than the norm. That said, given the prolonged
stretch of hot and dry weather and ongoing drought, any precip may
not be enough to temper ignitions in the dry nature of the fuels.

JBB/18

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Red Flag Warning until 9 PM PDT this evening for East Portion of
     the Olympic Mountains-West Slopes of the Central Cascades
     Generally above 1500 Feet-West Slopes of the North Cascades
     Generally above 1500 Feet.

PZ...None.
&&

$$