Brier Weather Station
Latitude N 47° 46' 49" Longitude W 122° 16' 48" Elevation 341 ft
239
FXUS66 KSEW 150959
AFDSEW
Area Forecast Discussion
National Weather Service Seattle WA
259 AM PDT Fri May 15 2026
.SYNOPSIS...A very cool upper level trough will move over
Western Washington today and remain over the area through
Saturday night. Upper level ridge building offshore Sunday with
Western Washington on the backside of the ridge through the
middle of next week.
&&
.SHORT TERM /TODAY THROUGH SUNDAY/...
Satellite imagery shows mostly cloudy skies over Western
Washington early this morning. Doppler radar has widely
scattered showers mainly over the northern portion of the area.
Temperatures at 2 am/09z were in the mid 40s to lower 50s.
Main story for the next two days is the very cool upper level
trough over Western Washington. The trough will move over the
area today and remain into Saturday night. Temperatures aloft
very cold for this time of year with 500 mb temperatures
dropping below -30C tonight into Saturday. Even with plenty of
cloud cover and little daytime heating the very cold air aloft
will create unstable conditions especially this afternoon
through Saturday. Lifted indexes in the plus 2 to minus 2 range,
convective temperatures both this afternoon and Saturday
afternoon below the predicted high temperatures, lapse rates
with the very cold air aloft in the plus 7 to 8C/km. All this
adds up to showers through Saturday with a chance of afternoon
and evening thunderstorms. Snow levels, already low near 4000
feet this morning, lowering to 3000 to 3500 feet tonight and
Saturday. Could see a couple of inches of snow at the summit of
Stevens Pass while higher up Paradise on Mount Rainier looking
at 4 to 8 inches of new snow the next two days. Highs in the
lower to mid 50s today and mid to upper 50s Saturday. Highs
today will only be a couple of degrees warmer than record low
maximums. Lows tonight in the upper 30s to mid 40s.
Upper level trough weakening Saturday night and moving out of
the area Sunday. Convective activity coming to an end Saturday
evening. A few breaks in the clouds cover will allow
temperatures to drop into the mid 30s in the colder locations
Sunday morning. Lows in the upper 30s to mid 40s for the
remainder of the area.
Upper level ridge building offshore Sunday. Plenty of low level
moisture over Western Washington combined with light flow in the
lower levels will make it hard for the sun to break through
especially in the morning. As the marine layer thins in the
afternoon some sunshine will get highs into the upper 50s to
mid 60s. Felton
&&
.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
Models in good agreement with the upper level ridge remaining in
place at least through Tuesday. Differences in the model
solutions beginning Wednesday with some solutions moving the
ridge inland over Western Washington while other solutions keep
the ridge axis offshore. Either scenario keeps the weather dry
over the area. The ridge axis moving overhead would result in a
little warmer days. For now with the uncertainty will keep highs
just a couple of degrees above normal Wednesday and Thursday,
in the mid 60s to lower 70s. Highs Monday and Tuesday in the
60s. Lows in the 40s through the period.
&&
.AVIATION...
Mostly westerly flow aloft into tonight with perhaps a slight shift
to southwesterly in the late morning and early afternoon as an upper
level trough begins to dig into the area. Flow will shift more
northwesterly by Saturday morning as the trough axis passes east of
the Cascades. Surface winds remaining southerly for most terminals
although HQM and CLM are reporting more westerly winds. Speeds this
morning are varied, as some locations have gone light and variable,
however majority of terminals reporting speeds 8-12 kts. Like
yesterday, these speeds are expected to pick up in the late
morning/early afternoon generally ranging 10-15 kts with gusts up to
25 kts. The only exception here may be CLM, as they may be shielded
from the southwesterly winds by the Olympics...so their speeds may
remain fairly uniform to what is being observed at the time of this
writing.
Majority of stations reporting VFR conditions save for PAE where a
PSCZ is producing persistent precipitation and thus lowering cigs
down into MVFR. SEA and BFI likely will not see the precip, however
low clouds have nestled in here too with MVFR conditions also
present here. Models suggest that cigs should see some improvement a
little later in the morning, getting these sites back up to VFR with
the rest of the crowd...yet none of them are handling the current
conditions well. May split the difference on the 12Z forecast, allow
for some improvement, but keeping these two terminals in a high-end
MVFR scenario. As showers become more widespread with the incoming
trough, any terminal or location under falling precip will likely
see cigs dip into MVFR. Latest progs suggest some recovery after
22Z, which may nudge conditions back up into low-end VFR, except for
those locations more prone to lower cigs /HQM, maybe OLM and PWT/.
KSEA...MVFR conditions in place. While some improvement may be
possible this morning, not sure cigs lift enough to get the terminal
out of this category. See above ceiling discussion for more detail.
Southwesterly winds throughout the TAF period with speeds 8-12 kts
this morning, becoming 10-15 kts with gusts to 25 kts this afternoon
and early evening before easing tonight.
18
&&
.MARINE...
Onshore flow will continue over the weekend which will allow for
daily pushes through the Strait of Juan De Fuca. However, given the
more southwesterly flow of winds...they may not see such a strong
push today...that remains on track for Saturday though. These
southwesterly winds however do look to trigger advisory level winds
for the Puget Sound for much of the day today before easing by this
evening. As such, an SCA has gone out with the morning forecast
package.
Near-shore seas will steadily increase today, likely topping out at
7 to 9 ft. The outer waters however will see more significant
increases, reaching 9 to 12 ft late tonight and persisting
throughout much of Saturday. As such, have issued an SCA this
morning to cover this high seas threat. Seas might be slow to
regress, but they are expected to slowly ease back down to 7 to 9 ft
Sunday morning.
18
&&
.HYDROLOGY...
The daily hydrology discussion has ended until the start of the
next rainy season; it will only be updated during this time as
needed.
&&
.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...None.
&&
$$
NWS SEW Office Area Forecast Discussion