Artondale, Washington Weather Forecast Discussion

507
FXUS66 KSEW 051048
AFDSEW
Area Forecast Discussion
National Weather Service Seattle WA
348 AM PDT Fri Sep 5 2025
.SYNOPSIS...Upper level ridge over the area today will slowly move
east tonight into the weekend. Upper level low west of Haida
Gwaii this morning will move south and be off the Oregon coast by
Sunday. Upper level disturbances spinning out of the low moving
over Western Washington beginning tonight and continuing through
the weekend. Low moving east Monday stalling and weakening into a
trough over the Pacific Northwest Monday night through Wednesday.
&&
.SHORT TERM /TODAY THROUGH SUNDAY/...Satellite imagery shows low
clouds along the coast moving down the Strait of Juan de Fuca and
through the Lower Chehalis Valley to the southern portion of the
Hood Canal at 3 am/10z. High clouds approaching from the south. Up
on the roof the orange moon over Seattle indicates a smoke layer
aloft. Temperatures were in the mid 50s to mid 60s.
High amplitude upper level ridge over Western Washington today
with an upper level trough digging south well offshore. HRRR smoke
models have smoke aloft over the area all day. Stratus this
morning will continue to slowly move eastward and could get east
of Puget Sound for a couple of hours after sunrise before
retreating back to the coastline by late morning/early afternoon.
Weak upper level system spinning out of the offshore low
remaining south of the area but close enough for a chance of
showers around Mount Rainier late in the day. High temperature
forecast will be a little tricky with the upper level smoke. Have
knocked 3 to 5 degrees off the NBM highs due to the smoke. This
puts highs in the 70s and lower 80s inland and in the mid 60s
along the coast.
Upper level ridge axis east of the area tonight. Weak upper level
shortwave moving through overnight into early Saturday morning
with a chance for showers spreading north. Upper level smoke
remaining but will be obscured by the increasing cloud cover. Lows
in the mid 50s to lower 60s.
Upper level ridge continuing to drift east Saturday while the
upper level low offshore digs south and also moves a little east.
A stronger shortwave spinning out of the low reaching Western
Washington late in the afternoon. Air mass somewhat unstable with
lifted indexes well below 0, lapse rates in the plus 7 to 8C range
along with elevated CAPE values. On the flip side convective
temperatures are well above predicted high temperatures and model
soundings have a cap between 850-700 mb. For now will stay with
the slight chance of late day thunderstorms in the lowlands with a
better chance over the mountains in addition to the chance of
showers. With the cloud cover and increase in onshore flow highs
cooler than today, mid 60s to mid 70s.
Chance of showers with a slight chance of thunderstorms
continuing Saturday evening until the shortwave exits to the north
after midnight. Lows in the mid 50s to lower 60s.
Upper level low offshore drifting towards the coast Sunday with
the flow aloft becoming difluent over the area in the afternoon.
This will keep a chance of showers in the forecast. With plenty of
cloud cover highs will remain mostly in the 60s.
.LONG TERM /MONDAY THROUGH THURSDAY/...Extended models in pretty
good agreement with the upper level low weakening into a trough
and stalling over the Pacific Northwest later Monday into
Wednesday keeping the mostly cloudy chance of showers or showers
likely forecast going into the middle of next week. Temperatures
will remain below normal with highs in the 60s and lower 70s.
While the operational runs indicate some ridge building Thursday
the ensembles are not as emphatic with the ridge. Not many wet
solutions in the ensembles but enough to keep a chance of showers
in the forecast. Highs remaining just a little below normal, mid
60s to mid 70s.
&&
.AVIATION...An upper-ridge east of the Cascades and an
upper-trough will usher southerly flow aloft through the TAF period.
Weak low-level onshore flow is present. Shallow marine stratus
producing LIFR/IFR ceilings and reduced surface visibility along the
coast and southwest interior. This action will spread inland towards
Puget Sound and neighboring inland waters this morning before
burning off to VFR and hazy skies towards 18-20z. An additional
round of low stratus and patchy fog again possible Friday night into
Saturday across area terminals.
KSEA...Hazy conditions and variable amounts of high and mid clouds
has continued into this morning. A shallow marine layer producing
LIFR ceilings is expected to reach the terminal around 12-14z
Friday. Any lingering low stratus should burn off towards 18z. Light
surface winds this morning increasing out of the NNW this afternoon-
early evening. Another round of low stratus again possible into
Saturday morning.
McMillian
&&
.MARINE...A weak surface ridge will remain over the coastal and
offshore waters today with lower pressure over the interior
producing light onshore flow. A weak trough will gradually move into
the coastal waters over the weekend into early next week, but will
produce little in the way of impacts. Diurnal westerlies through the
strait may reach SCA criteria later over the weekend but confidence
is not high at this time.
McMillian
&&
.FIRE WEATHER...The Red Flag Warning came to an end Thursday.
Increasing onshore flow early this morning will increase the RH
values across the area including the foothills today. Late
afternoon RH values were 5 to 10 percent higher late Thursday
afternoon versus Wednesday afternoon and this trend will continue
today. There is a chance of showers over the weekend with a slight
chance ( 20% or less ) of widespread thunderstorms in the late
afternoon and evening Saturday. There is a slight chance for
thunderstorms possibly as early as late this afternoon for the
very southern end of the west slopes of the Cascades. Confidence
remains low with exact coverage and intensity of the convective
activity. Cool and showery weather Sunday into the middle of next
week will keep the fire danger suppressed. Felton
&&
.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...None.
&&
$$

NWS SEW Office Area Forecast Discussion