FXUS66 KSEW 272139
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
239 PM PDT Fri Sep 27 2024

.SYNOPSIS...Drier conditions through Saturday as zonal flow aloft
prevails. A subtle trough will enter on Sunday increasing
precipitation chances. An upper-ridge looks to take hold to start
the new week however, a series of weak troughs will influence the
pattern but most precipitation should stay north of the area.


&&

.SHORT TERM /TONIGHT THROUGH MONDAY/...Mostly zonal flow aloft
over the PNW along with broad ridging over the Rockies and saggy
troughing off the coast of California. Conditions are drier
across the forecast area as surface high pressure builds within
this post-frontal environment. For tonight, we'll remain dry with
minimum temperatures falling into the 40s and 50s. Can't rule out
patchy fog developing due to residual surface moisture
particularly along the river valleys.

More dry weather expected into Saturday as the flow aloft backs
towards the southwest. Offshore, an upper-trough positioned over
the NE Pacific will track closer to cause the perturbation in the
flow aloft. Conditions are to remain dry before rain chances
return on Sunday. The aforementioned trough will swing into the
region with the best chance of showers north of I-90 during the
day before drying out at night. Then, upper-ridging will return to
start the week on Monday as subsidence brings clear skies and
abundant sunshine. Highs are to remain in the 60s with overnight
lows largely in the 40s.

.LONG TERM /TUESDAY THROUGH FRIDAY/...Ridging will persist into
Tuesday but an upper-low out of the Gulf of Alaska will help to
flatten it by midweek. Here we'll see the return of more rain
chances. There are questions on how the pattern will exactly
evolve around this time but rain amounts don't appear to be
impressive. Guidance has a cold front sweeping across the region
on Friday but uncertainty still exists in the track of its parent
low. Temps in the extended may cool slightly with most locations
seeing highs in the upper 50s to mid 60s.


McMillian


&&

.AVIATION...Mostly VFR with skies becoming mostly clear through the
afternoon. A weak marine push Saturday morning will result in
increased cloud cover with a 30% chance of terminals near the Puget
Sound seeing MVFR in low stratus. Patchy fog also likely to develop
early Saturday. Drier conditions will allow for a quick return to
VFR by the afternoon. Surface winds generally out of the N 5-15 kt,
switching to S/SW by Saturday evening.

KSEA...VFR with north flow generally 8 to 13 kt, with occasional
gusts to 15 kt through the evening. Winds will lighten overnight
with some incoming cloud cover and patchy fog possible. Ensembles
maintain a roughly 30% chance of conditions deteriorating below VFR
in the early morning hours. Improvement by the late morning with VFR
conditions through the rest of the day Saturday.

15

&&

.MARINE...A surface ridge will quickly build into the coastal and
offshore waters today in the wake of a deep surface low that swept
onshore near Haida Gwaii overnight. Surface ridging will build into
the interior of southern British Columbia by tonight turning the
flow northerly across area waters. A forecast surge of northerly
winds has resulted in the issuance of a SCA for the East Entrance of
the Strait of Juan de Fuca and Admiralty Inlet overnight into
Saturday morning. Small craft advisories will also remain in place
across the coastal waters and the west entrance to the strait as
hazardous double digit seas will continue before they subside below
10 feet by Saturday night. A system passing mainly to the north of
the area Saturday night and Sunday will enhance onshore flow with
likely small craft advisory westerlies in the strait. Otherwise,
conditions will remain fairly tranquil across area waters into early
next week as high pressure remains in control.

27/15


&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory until 5 AM PDT Saturday for Coastal Waters
     From Cape Flattery To James Island Out 10 Nm-Coastal Waters
     From James Island To Point Grenville Out 10 Nm-Coastal
     Waters From Point Grenville To Cape Shoalwater Out 10 Nm-
     Grays Harbor Bar-West Entrance U.S. Waters Strait Of Juan
     De Fuca.

     Small Craft Advisory from 11 PM this evening to 8 AM PDT
     Saturday for Admiralty Inlet-East Entrance U.S. Waters
     Strait Of Juan De Fuca.

     Small Craft Advisory until 3 PM PDT Saturday for Coastal Waters
     From Cape Flattery To James Island 10 To 60 Nm-Coastal
     Waters From James Island To Point Grenville 10 To 60 Nm-
     Coastal Waters From Point Grenville To Cape Shoalwater 10
     To 60 Nm.

&&

$$