Brier Weather Station
Latitude N 47° 46' 49" Longitude W 122° 16' 48" Elevation 341 ft
988
FXUS66 KSEW 221040
AFDSEW
Area Forecast Discussion
National Weather Service Seattle WA
340 AM PDT Sat Aug 22 2026
.SYNOPSIS...
Weak upper level low off the Central Oregon coast this morning
will continue to weaken and move northeast today. The low will
be off the Washington coast tonight and move inland as an upper
level trough Sunday morning. Upper level ridge building in
behind trough later Sunday will move east Monday. Western
Washington on the backside of the ridge Tuesday. Another upper
level trough arriving Wednesday or Thursday hanging around into
Friday.
&&
.SHORT TERM /TODAY THROUGH MONDAY/...
Satellite imagery shows low clouds have spread inland overnight
and are moving east of Puget Sound at 3 am/10z. High clouds over
the area above the stratus. Mild early morning with the cloud
cover. Temperatures a couple of degrees either side of 60.
Some small differences in the pattern will make a big difference
in the forecast this morning. Upper level low off the Oregon
coast further back to the southwest than the models are
indicating. Shortwave spinning out of the low that would be
moving over Western Washington if the low was where the models
predicted is instead going by offshore leaving Western
Washington with just a marine push in progress. Low slowly
moving northeast later today. Instead of another shortwave
spinning out of the low, convective activity over the area will
be mostly the result of daytime heating helping to destabilize
the air mass more than the current levels. This pushes the
chances for convection into the late morning and afternoon hours
and mostly over the northern portion of the area where the
stratus will dissipate first. Still a chance for thunderstorms
over the Central and Northern Cascades this afternoon. Cooler
air mass will lessen the chances for thunderstorms over the
Olympics. Will modify the Red Flag warning changing the start
time in the Cascades portion to later this morning and drop the
Olympics from the warning. Black Hills visible on the satellite
imagery putting the tops of the marine layer below 2500 feet.
Stratus retreating to the coast this afternoon but with the
southerly flow aloft still middle and high level clouds over the
area. Highs in the mid 60s to mid 70s.
Low weakens to an upper level trough tonight. Trough moving
inland near the Canadian border after midnight keeping at least
a slight chance of showers over most of the area. Marine layer
moving inland again approaching the Puget Sound by 12z Sunday.
Lows in the 50s.
Trough moving off to the east with an upper level ridge building
into Western Washington Sunday afternoon. Shower activity
confined to the North Cascades Sunday afternoon. Low level
onshore flow with the marine layer returning to the coast in the
afternoon. Highs once again in the mid 60s to mid 70s.
Upper level ridge continuing to build Sunday night before moving
east Monday. Onshore flow weakening bringing up the possibility
that the marine layer does not get east of Puget Sound Monday
morning. Even if it does it will be shallow and be gone by mid
to late morning. More sunshine and warmer temperatures aloft
adding up to a warmer day Monday. Highs in the 70s to lower 80s.
Lows Monday morning in the 50s. Felton
&&
.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
Extended models in good agreement this morning. Western
Washington on the backside of the upper level ridge Monday night
into Tuesday for one more warm day. Highs in the 70s to mid 80s.
Upper level trough moving into the area Wednesday hanging
around into Friday. Best chance for showers later Wednesday
into Thursday. Much cooler with highs in the mid 60s to mid
70s all three days.
Through the 21st Seattle is only 0.5 degrees above normal for
the month of August. This cooler end to the month will make it a
close call if August ends up being above normal for
temperatures. July was slightly below normal. The last time July
and August had below normal temperatures in Seattle was 2011.
Felton
&&
.AVIATION...
Southerly flow aloft becoming variable later this
afternoon and tonight. Low level onshore flow into Sunday
morning. IFR to LIFR ceilings lifting to MVFR by late morning.
Ceilings continuing to improve over the interior with VFR
ceilings this afternoon. MVFR ceilings continuing along the
coast. Low end MVFR/IFR ceilings returning to the interior after
12z Sunday.
KSEA...LIFR ceilings lifting to IFR mid morning, MVFR late
morning and VFR by mid afternoon. IFR ceilings possible again
Sunday morning after 12z. Southwest wind 6 to 12 knots easing to
4 to 8 knots tonight. Felton
&&
.MARINE...
A weak surface low will move into the coastal waters today. The
low will dissipate tonight. High pressure will rebuild Sunday
and remain over the area through Tuesday. A weak frontal system
will move across the waters midweek.
Winds picking up later this morning but staying 20 knots or less
into the afternoon hours. Diurnal westerlies in the Strait of
Juan de Fuca each evening for the next few days but at this
point peak winds look to be around 20 knots.
Seas 3 to 5 feet for the next few days. Felton
&&
.FIRE WEATHER...
Red Flag warning will continue for the Northern and Central
Cascades today for the possibility of lightning and gusty
erratic outflow winds. Chances for thunderstorms have gone down
this morning in the Olympics and the warning for there will be
dropped. Elevated fire weather concerns will continue until the
upper level trough moves east of the area Sunday. Upper level
ridge building in later Sunday. Low level onshore flow pattern
later Sunday through Tuesday will result in good relative
humidity recoveries in the overnight hours easing fire weather
concerns. Another upper level trough arriving in the middle of
next week increasing the chances for convection. Felton
&&
.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Red Flag Warning from 11 AM this morning to 8 PM PDT this
evening for West Slopes of the North Cascades Generally
above 1500 Feet.
Red Flag Warning from 9 AM this morning to 5 PM PDT this
afternoon for West Slopes of the Central Cascades
Generally above 1500 Feet.
PZ...None.
&&
$$
NWS SEW Office Area Forecast Discussion