Lake Tapps, Washington Weather Forecast Discussion

364
FXUS66 KSEW 150840
AFDSEW
Area Forecast Discussion
National Weather Service Seattle WA
140 AM PDT Mon Sep 15 2025
.SYNOPSIS...High pressure will build through Tuesday for a brief
return of warmer and drier conditions. A weather system will
brush the area on Wednesday, with temperatures returning to near
or a little below seasonal normals and a chance for rain. Cooler
and rainy conditions may continue into the weekend.
&&
.SHORT TERM /TODAY THROUGH WEDNESDAY/....Upper level ridging will
begin to build over the area today with drying and warm
conditions. Areas of patchy fog and low clouds will linger
early this morning before dissipating by the afternoon, with high
temperatures warming into the upper 60s to low 70s.
Thermally induced low pressure will start to expand northward
along the Oregon coast tonight into Tuesday, which will help
boost temperatures along with easterly offshore flow. High
temperatures on Tuesday will be noticeably warmer, with highs in
the low to mid 80s, with the Cascade valleys seeing temperatures
in the upper 80s. With easterly offshore flow on Tuesday, will
have to monitor the potential for degraded air quality as easterly
winds may push wildfire smoke into the area from existing fires
east of the Cascades. Please refer to your local clean air agency
for more information. The thermally induced trough looks to only
influence the area throughout Tuesday, with easterly flow peaking
early Tuesday morning. Could see easterly gusts throughout the
gaps around 25 to 30 mph at times. These enhanced winds could
elevate fire weather conditions in the Cascade foothills - see
Fire Weather section below for more info.
Progressing into Wednesday, weak troughing with a front looks to
brush by the area, with the return to onshore flow for cooler,
seasonal temperatures across the area. This will help mitigate
any fire weather concerns. The aforementioned front looks rather
weak as well, with minimal PoPs - so expect the day to remain
mostly dry.
.LONG TERM /THURSDAY THROUGH SUNDAY/...Ensembles continue the
upper level troughing pattern over the Pacific Northwest, with
temperatures cooling further into the week - along with renewed
precipitation chances. Guidance has been suggesting a system
potentially crossing over western Washington by the weekend, which
could bring steady precip over the area. As of now, confidence is
low in exact QPF amounts, but it could be more rain than we`ve
seen for a while. This could be an indication of a more active
pattern as we enter the fall months.
Mazurkiewicz
&&
.AVIATION...Northerly flow aloft through this morning will become
lighter this afternoon as an upper ridge builds into Western
Washington. High-end MVFR and low-end VFR cigs continue this morning
across portions of the interior due to residual moisture and the
upper trough sliding east. These cigs will continue into this
morning, with localized IFR possible as well. Although fog is not
expected to be widespread, patchy fog may develop, mainly along the
coast due to clearing. Clouds will clear late morning into the early
afternoon as high pressure builds. Haze may also increase tonight
into Tuesday as flow transitions offshore. Light winds this morning
will increase from the north this afternoon before becoming more
E/NE tonight.
KSEA...VFR conditions early this morning. Cigs are expected to
slowly lower towards MVFR this morning. There remains approximately
a 30% chance of MVFR cigs between 12 to 18z. Lingering clouds will
then clear late morning through the afternoon. Light S/SE surface
winds will transition more N/NE around 14 to 16z and increase from
the north this afternoon. JD
&&
.MARINE...High pressure will rebuild offshore today. A thermal
trough will develop along the coast later today into Tuesday,
resulting in a period of offshore flow over the waters. Easterly
winds are expected to peak during the day on Tuesday. Although winds
will be primarily below SCA threshold, will need to monitor the
central and western Strait of Juan de Fuca, as well as the coastal
inner northern waters, where localized SCA winds may occur for a
brief period. Otherwise, offshore flow will subside Tuesday night
before onshore flow resumes on Wednesday. Northerly winds will also
increase later Wednesday through Thursday for the Coastal Waters,
potentially resulting in SCA winds for the outer Coast. In addition,
increasing westerly winds are expected through the Strait of Juan de
Fuca Wednesday into Wednesday night.
Seas will range 4 to 6 feet through early Wednesday. Seas then look
to build to 8 to 10 feet later Wednesday into Thursday, with steeper
seas during this time due to a period of 10 to 12 seconds. Seas will
subside late week. JD
&&
.FIRE WEATHER...Conditions will start to warm and dry out today
as an upper level ridge starts to build back into the region.
The attention turns to Tuesday as a thermal trough at the surface
creeps northward along the coast early in the day, allowing for
flow to transition to offshore. Latest hi-res guidance continues
to indicate easterly winds picking up across the Cascades during
the early morning hours and persisting through the afternoon, with
gusts to 25-30 mph possible. Easterly winds will help to warm and
dry conditions out further and could result in relative
humidities falling into the mid 20s to low 30s across portions of
the central and southern Cascades. This combination of gusty
easterly winds and low RHs has led to the issuance of a Fire
Weather Watch for the Cascade and Cascade foothill zones for
Tuesday.
Overall, expect these heightened fire weather conditions to remain
short-lived, as winds are anticipated to transition back to onshore
by midweek. Increasing onshore flow, cooler conditions, and the
potential for additional weather systems to move across the area
will help mitigate fire weather concerns later in the week.
14/Mazurkiewicz
&&
.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Fire Weather Watch from late tonight through Tuesday evening for
     Black Hills and Southwest Interior Lowlands-Northeast Puget
     Sound Lowlands Generally Below 1500 Feet-Southeast Puget
     Sound Lowlands Generally Below 1500 Feet-West Slopes of the
     Central Cascades Generally above 1500 Feet-West Slopes of
     the North Cascades Generally above 1500 Feet.
PZ...None.
&&
$$

NWS SEW Office Area Forecast Discussion