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000
FXUS66 KSEW 251653
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
953 AM PDT Mon Sep 25 2023

.UPDATE...A deep 960mb low and its associated front is readily
apparent on current satellite analysis. In the wake of the front,
low-topped thunderstorms are tracking north-northeastward in a
regime of steep low-level lapse rates. Widespread rain along with
locally breezy winds are being observed across the CWA. Rainfall
is still on track to gradually transition into showers along with
a few rumbles of thunder this afternoon. Highs today will rise
into the 60s. The previous discussion remains on track with an
updated marine/aviation section:

&&

.SYNOPSIS...A broad trough of low pressure over the Gulf of Alaska
will direct a series of frontal systems into the region bringing
wet and occasionally windy weather through the middle of the
week. A gradual trend toward drier conditions is expected by the
weekend as high pressure aloft briefly rebuilds over the
northeastern Pacific.

&&

.SHORT TERM /TODAY THROUGH WEDNESDAY/...Moderate to locally heavy
rain and breezy winds continue across much of Western Washington
this morning as a warm front slowly moves onshore. The trailing
cold front will move inland late this morning with a somewhat
unstable air mass in its wake. Steady rain will change over to
showers this afternoon along with a thunderstorm or two. Shower
activity will decrease later tonight before another impulse
rounding the broad upper trough offshore leads to an increase in
showers during the day Tuesday along with a continuing chance of
thunder...especially near the coast.

Another upper trough and associated front is expected to move
onshore late Tuesday into early Wednesday. Model differences
remain with respect to the exact track of this system, but the end
result will likely be another a good dose of rain and gusty
winds. Temperatures throughout the short term forecast period will
remain below normal.

.LONG TERM /THURSDAY THROUGH SUNDAY/...As we move into the long
term forecast period, upper ridging will temporarily rebuild over
the Northeast Pacific as an upper trough digs southward over the
western third of the lower 48. The weather will remain on the wet
and cool side on Thursday as another shortwave digs southward
along the British Columbia coast into Western Washington. This
system is expected to dig southward before eventually cutting off
over the Great Basin by the coming weekend. A few showers may
linger into Friday before upper ridging brings a return of drier
and somewhat warmer conditions by Saturday. Forecast confidence
begins to wane early next week with ensembles showing considerable
discrepancies as to how quickly precip may reenter the forecast
picture. 27

&&

.AVIATION...Deep upper level trough offshore with strong
southwesterly flow aloft easing this afternoon and evening. A cold
front is currently making its way onshore but will be weakening as
it moves across the area midday. The air mass behind the front is
somewhat unstable; thunderstorms cannot be ruled out this afternoon,
particularly along the coast.

Ceilings between 5000 and 8000 feet this morning. Ceilings may lower
slightly to MVFR just ahead and with the frontal passage around 20-
22Z. Winds will pick up behind the front to 10-15 kt gusting 20 to
30 kt out of the southwest.
Ceilings will improve later this afternoon into this evening back up
to VFR with showers. Gusty winds should ease up after 03Z.

KSEA...Ceiling near 6000 feet with light rain. Frontal passage is
expected at 20z with ceilings potentially (25-30%) lowering to MVFR.
Ceilings lifting back up to VFR 00z-03z. East to southeast winds 5
to 10 knots becoming south-southwest 12 to 18 knots gusting around
25 knots 20z-03z. Winds returning to southeasterly 8 to 12 knots
after 03z.

Felton/LH

&&

.MARINE...A 960 mb low will remain centered well west of the
coastal waters as it weakens and moves north today. The cold front
associated with the low is currently making its way onshore. A few
low-topped thunderstorms have developed behind the front and will
likely pose a threat to the coastal waters today. Another front
sweeps across the waters late Tuesday into Wednesday. A weak surface
low will move south of the area Thursday.

Gale force winds over the coastal waters will ease this evening
into early Tuesday morning down to Small Craft Advisory speeds.
Gale force winds at the east entrance to the Strait of Juan de Fuca
will ease behind the front this afternoon. Small Craft Advisory
winds over all the remaining waters will continue except over the
Puget Sound and Hood Canal today.

Small Craft Advisory conditions will continue along the coast later
tonight through Tuesday, and will develop over the Puget Sound for
Tuesday. Seas building this afternoon to 11 to 13 feet, tonight to
13 to 16 feet peaking Tuesday in the 16 to 18 foot range. Seas will
subside quickly Wednesday dropping below 10 feet Wednesday night.

Felton/LH

&&

.HYDROLOGY...The daily hydrology discussion has ended until the
start of the next rainy season; it will only be updated as needed.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory from 2 PM this afternoon to 6 PM PDT
     Tuesday for East Entrance U.S. Waters Strait Of Juan De
     Fuca-Grays Harbor Bar.

     Small Craft Advisory until 6 PM PDT Tuesday for Admiralty Inlet-
     Central U.S. Waters Strait Of Juan De Fuca-Northern Inland
     Waters Including The San Juan Islands-West Entrance U.S.
     Waters Strait Of Juan De Fuca.

     Gale Warning until 2 PM PDT this afternoon for East Entrance
     U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory from 2 AM to 2 PM PDT Tuesday for Puget
     Sound and Hood Canal.

     Gale Warning until 6 PM PDT this evening 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.

     Small Craft Advisory from 6 PM this evening to 6 PM PDT Tuesday
     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.

     Gale Warning until 2 AM PDT Tuesday 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.

     Small Craft Advisory from 2 AM to 6 PM PDT Tuesday 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.

&&

$$