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473
FXUS66 KSEW 200221
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
721 PM PDT Thu Sep 19 2024

.UPDATE...
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No major forecast updates have been made this evening.
Check below for the previous discussion with some timing updates,
as well as an update to the aviation and marine segments.
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.SYNOPSIS...Weak high pressure remains in place for the next few
days with a few passing disturbances and weakening fronts bringing
some deeper marine clouds and cooler temperatures at times through
the weekend. Stronger high pressure may build and bring some light
offshore flow early next week, bringing temperatures back above
normal.


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.SHORT TERM /TONIGHT THROUGH MONDAY/...
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A weak disturbance may induce a few light
showers in portions of the interior (especially toward the
Cascades) on Friday, but most areas will stay dry and some
additional cloud cover (and resulting cooling in temperatures)
will remain the most notable impact to sensible weather. Yet
another front approaches and likely fades away as it stalls over
British Columbia, again leaving most of western Washington dry.
Temperatures trend a little warmer into Saturday as a result,
making it closer to seasonal normals. Sunday will likely be a
return to cloudy cool and somewhat wetter across the region as the
next front is likely able to hold together better and bring some
additional moisture. While ensembles still have a fair amount of
variability with this system, we`re likely to see rainfall in the
one quarter to half inch range near the coast and in the mountains
(especially to the north). Confidence remains lower in the
lowlands of the Puget Sound region and especially south along I-5
through Lewis County.

.LONG TERM /TUESDAY THROUGH FRIDAY/...Ensemble guidance has
consolidate to favor a building ridge across the western U.S.
early next week, which would support warming temperatures and
decreasing cloud cover. This could bring temperatures back into
the mid to upper 70s through much of the interior, with the
warmest locations approaching 80. Offshore low-level flow would
likely bring this warming to the coast as well, as the sea-breeze
will be limited or eliminated. Fortunately the antecedent
moisture will likely hinder any significant fire weather concerns,
but will need to continue to monitor the evolution of the
pattern. The ridge likely breaks down by Wednesday or Thursday,
again opening the door for cooler temperatures and increasing
clouds and rain chances. That said, spread in the ensemble
guidance does increase once again in this time period and forecast
confidence decreases again. Cullen
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.AVIATION...
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Northwesterly flow aloft will continue tonight into
Friday as an upper level trough moves eastward allowing for ridging
to build along the coast. Onshore flow persists at the
surface...generally light for most interior terminals however those
along the coast and Strait could see winds up to 10-15 kts with
occasional gusts this evening before starting to taper off after
midnight.

Widespread VFR conditions this evening although starting to see some
stratus creep onto the coast, resulting in isolated MVFR conditions
there. Cigs gradually eroding overnight with widespread MVFR
conditions in place over W WA by 12Z Friday morning. Locations that
favor lower cigs may see IFR conditions emerge from time to time.
Model guidance also suggesting the potential for fog around PAE,
with both IFR cigs and some vis restrictions expected there mainly
between 12-18Z. Widespread VFR conditions expected to return early
Friday afternoon in the 18-21Z time frame.

KSEA...VFR conditions expected to remain in place tonight and into
early Friday. MVFR conditions expected to emerge at or around 12Z
and persist through the remainder of the morning. VFR conditions
expected to return by 20Z with skies clearing by 00Z. West to
southwesterly winds 4-8 kts this evening becoming light and variable
tonight. Switch to southerly winds early Friday morning before
becoming more northwesterly by 10Z. Speeds returning to 4-8 kts for
remainder of TAF period.

18
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.MARINE...
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Ridging will remain offshore through this weekend,
keeping onshore flow in place with northwesterly winds over the
coastal waters. Gusty winds to 25 kt are expected over the outer
coastal waters tonight into Friday as well as over the central and
eastern portions of the Strait of Juan de Fuca. That said, inherited
SCA looks good and will remain in place. These winds will also allow
seas to build up to 8 to 9 feet at 8 to 10 seconds in the outer
coastal waters. In addition, areas of patchy to dense fog are
possible over the east Strait of Juan de Fuca, Admiralty Inlet, and
Northern Inland Waters Friday morning. The fog may bring
visibilities down to a quarter of a mile in some spots.

The remainder of this weekend into next week will see calmer winds
out of the west or southwest as the ridge moves inland. A couple of
weak frontal systems will move through the area next week, but are
not expected to produce significant winds. Seas will drop to 4 to 6
feet over the weekend, increasing to 5 to 7 feet next week.

HPR/18
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.SEW WATCHES/WARNINGS/ADVISORIES...
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WA...None.
PZ...Small Craft Advisory until 3 AM PDT Friday for Central U.S.
     Waters Strait Of Juan De Fuca-East Entrance U.S. Waters
     Strait Of Juan De Fuca.

     Small Craft Advisory from 11 PM this evening to 5 PM PDT Friday
     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.
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