Brier Weather Station
Latitude N 47° 46' 49" Longitude W 122° 16' 48" Elevation 341 ft
541
FXUS66 KSEW 311203
AFDSEW
Area Forecast Discussion
National Weather Service Seattle WA
403 AM PST Wed Dec 31 2025
.SYNOPSIS...
Upper level ridge over the area today will slide off to the
east tonight and Thursday. Weakening front arriving late
Thursday into Friday morning. Developing upper level trough
offshore Friday afternoon. System spinning out of the trough
moving through Saturday into Sunday. Upper level trough moving
across area Monday. Upper level ridge trying to build Tuesday
with warm front moving into British Columbia.
.SHORT TERM /TODAY THROUGH FRIDAY/...
Satellite imagery shows high clouds embedded in southwesterly
flow aloft over the northwest portion of the area. Dense fog
formed late last night/early this morning along the I-5 corridor
from the King/Snohomish county line down to south of Chehalis
and westward through the Lower Chehalis Valley to Grays Harbor.
Visibilities a quarter of a mile or less common in these areas.
In addition to the fog a stratus layer has set up along the
Strait of Juan de Fuca. Temperatures at 3 am/11z range from the
upper 20s to mid 30s.
Have issued a dense fog advisory for the I-5 corridor from Lewis
county through Seattle with widespread visibilities a quarter
of a mile of less until 10 am. Some temperatures are below
freezing in this area bringing up the possibility of a thin
sheet of black ice on the roads. Lets be careful out there.
Models have pretty sharp but shallow inversion over the area
this morning. Tops around 500 feet ( Top of Columbia Center
probably sticking out of the cloud tops for you early morning
photographers ). Cross Cascade gradient around -6 mb is keeping
the fog out of the Cascade foothills and the gradient will stay
near -6 mb through the morning hours. With the fog layer so
shallow some light slightly drying easterlies will help
dissipate the layer. On the flip side the high clouds could slow
down the breakout but at this point the high clouds look to be
moving mostly north of the foggy areas. End result midday
breakout with just some high clouds this afternoon. The
exception to this will be along the Strait where the stratus
will hang on a little longer. Highs in the mid 40s to lower 50s.
Upper level ridge over the area today shifting east tonight.
System embedded in the southwesterly flow aloft still well south
of Western Washington by 12z Thursday. High clouds spreading
over the southern portion of the area overnight but likely not
in time to prevent at least some areas of fog to form again
along the I-5 corridor south of Seattle. It will be another cool
night with lows in the upper 20s to mid 30s.
Increasing middle and high clouds Thursday as front continues
to move north through Western Oregon. Could be a good morning
for lenticulars off of Rainier. Rain out ahead of the front
still mainly south of Lewis county by late Thursday afternoon
with just a chance of rain from about Seattle south in the
afternoon. Increasing clouds will keep highs in the mid 40s.
What is left of the front moving into Western Washington Friday
with rain spreading over the area Thursday night. System
weakening with rainfall amounts for Thursday night into Friday
mostly in the tenth to a quarter of an inch range. Rain
decreasing Friday afternoon. Cloud cover keeping lows near 40
Friday morning with highs Friday near 50.
&&
.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
Some timing differences in the models with regard to when the
rain out ahead of the next system spinning out of the upper
level trough offshore will reach the area. The ECMWF is faster
then the GFS on the operational runs. Ensemble solutions leaning
toward the faster solution so will have rain likely in the
forecast for Friday night. With the system moving up from the
southwest away from the parent low it will be a slow mover
keeping rain in the forecast for Saturday and Saturday night.
Next forecast problem is where will the surface low associated with
the front end up. The GFS tracks the low well offshore while the
ECMWF brings the low up the coastline Saturday night into
Sunday morning ( where have we seen this before? ). The ECMWF
does have the low weakening as it moves inland which helps to
limit the wind impact. Still could be a little windy Sunday
morning as the rain comes to an end with the frontal passage.
Snow levels with the south southwesterly flow aloft starting out
above pass levels Saturday lowering down to around 3500 feet
Sunday. South southwesterly flow aloft not conducive to decent
snow amounts in the mountains.
Confidence low for the last two days of the extended with a lot
of variability in the solutions. The ECMWF has the upper level
trough moving through with an upper level ridge trying to build
over the area. The GFS has the trough retrograding back to the
southwest. For now will go with a broadbrush mostly cloudy
chance of rain forecast until there is more clarity in the
models. Felton
&&
.AVIATION...
An upper level ridge will continue to weaken over the region today
with light southwest flow aloft. Light offshore flow continues near
the surface. Strong surface based inversions have led to widespread
LIFR ceilings and visibilities in fog and low clouds from Puget
Sound southward into the Southwest Interior and Chehalis Valley.
These conditions will continue into midday before gradually lifting
and scattering out. Low clouds may linger much of the day across the
Southwest Interior. Additional IFR to LIFR low clouds are expected
to reform again tonight.
KSEA...LIFR fog with visibilities at or below 1/2SM will persist
through late morning before gradually lifting this afternoon.
LIFR/IFR stratus is expected to return again overnight. Surface
winds light and variable becoming N/NE under 6 knots late this
afternoon. 27
&&
.MARINE...
High pressure will weaken over the waters today. A system
moving up from the south will reach the area later Thursday into
Thursday night. A stronger frontal system will move through the
waters Saturday into Sunday.
Dense fog of portions of the inland waters this morning. Winds
increasing with system Thursday look to stay under small craft
advisory criteria. Small craft advisory winds over the outer
coastal waters with the next system later Friday into at least Saturday.
Small craft advisory winds in the outer coastal waters could
last into Sunday before easing.
Seas in the 5 to 8 foot range building Friday night with seas in
the 10 to 14 foot range over the weekend. Higher seas over the
outer coastal waters. Felton
&&
.HYDROLOGY...
No river flooding expected in the next 7 days. The Skokomish
River will rise back into action stage over the weekend.
&&
.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Dense Fog Advisory until 10 AM PST this morning for City of
Seattle-Eastside-Lowlands of Lewis and Southern Thurston
Counties-Lowlands of Pierce and Southern King Counties-
Middle Chehalis River Valley-Olympia and Southern Puget
Sound-Shoreline / Lynnwood / South Everett Area.
PZ...None.
&&
$$
NWS SEW Office Area Forecast Discussion