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287
FXUS66 KSEW 221551
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
851 AM PDT Mon Jul 22 2024

.SYNOPSIS...High pressure continues to move east of Washington,
with deep low pressure to the northwest in British Columbia,
influenced by a strong and slow moving upper level low. This
pattern will bring various degrees of onshore flow throughout the
week. Persons in western Washington can expect to see various
degrees of cloud cover in the morning, with sunshine in the
afternoon throughout the week. Temperatures return to around
average with highs in the 70s for much of Puget Sound through the
work week. Aside from a slight chance of showers in the north
Cascades Wednesday afternoon, remaining areas will continue to
stay dry this week.


&&

.SHORT TERM /TODAY THROUGH WEDNESDAY/...
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No major changes to the
forecast this morning. Temperatures will be slightly below average
for this time of year thanks to increased cloud cover and cooler
air moving in from the Pacific. Rest of previous discussion will
follow.

The forecast will sound like a broken record with the slow
movement of the previously mentioned upper-level features. For the
next few days, cloud cover will fill in most inland areas during
the overnight and morning hours, clearing out by late morning and
afternoon. The marine push Monday morning may be accompanied by a
post frontal convergence zone over Snohomish County. Threat of
showers is extremely low, but will most likely see lower cloud
cover for a longer duration this morning.

The low will swing an embedded shortwave trough over northern
Washington/southern British Columbia Monday night/Tuesday morning.
Despite good vorticity advection, this trough will past through
dry (but will increase cloud cover early Tuesday morning). An
embedded shortwave trough will bring more cloud cover Wednesday
afternoon (mix of clouds and sun).

For temperatures and winds, Monday will be the coolest day in the
interior/Puget Sound with highs in the low to mid 70s. This will
increase to the mid and upper 70s Tuesday and Wednesday. Highs
along the coast and waters will top out in the 60s. Lows will drop
into the 50s for all areas (few 40s at higher elevations). A few
gusty winds to 20 mph are possible areas along I-5 north of
Everett (with a strong push down the Strait of Juan de Fuca by
Monday afternoon/evening). Outside of this, winds will remain out
of the northwest at 5 to 10 mph.

Side note: in addition to smoke aloft, HRRR near-surface smoke was
still picking up on heavier smoke close to the Cascade crest due
to new wildfires (and fires east of the crest). Added haze to the
forecast for these areas affected by the fires. The onshore flow
will push the majority of this smoke east of the Cascades.

.LONG TERM /THURSDAY THROUGH SUNDAY/...The upper level ridge will
propagate eastward as the low moves onto land Wednesday into
Thursday. As the low moves ashore, an embedded shortwave trough
will swing over the northern part of Washington. This will be the
best chance of precipitation in the forecast, with a chance of
showers in the north Cascades Thursday morning. Will have to also
monitor the chance of thunder with this activity (temperatures
aloft are still a bit warm). The flow aloft will become more
northwesterly by Friday. This will weaken some of the onshore
flow from the Pacific, resulting in less cloud cover from any
marine push that tries to materialize. High temperatures as a
result will start to lean back towards 80 degrees next weekend.

HPR
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&&

.AVIATION...
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Upper level troughing digging southward over the
northeastern Pacific will produce southwest flow aloft over
Western Washington today. Low level onshore flow continues at the
surface and will become moderate to strong later today into this
evening. Satellite this morning shows stratus across much of the
interior of western Washington. Conditions at area terminals are
primarily MVFR in stratus and VFR for areas not under stratus.
Ceilings will lift by mid afternoon except in the vicinity of
KPAE where a convergence zone is expected to develop with possible
light shower activity.

KSEA...MVFR ceilings under stratus. Expect stratus to lift
between 18-20Z, with conditions becoming VFR this afternoon.
Surface winds S/SW rising to 6 to 11 knots...then veering to N/NW
this evening. Current best estimate of shift to northerly is
between 01-03Z tonight. 27/14
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&&

.MARINE...
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Onshore flow will continue through much of the week with
high pressure situated over the offshore waters and lower pressure
situated east of the Cascades. A series of weak troughs moving
into British Columbia will increase onshore flow at times over the
next several days. Models remain consistent with another strong
onshore push late this afternoon and evening for another round of
gales in the central and east strait. Small craft advisory
northwesterlies are expected in the adjacent waters of Admiralty
Inlet for a period this evening. Seas generally persisting at 4-6
ft across the coastal waters this morning. Seas look to hover
within this range through midweek. 27/14
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&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Gale Warning until 4 AM PDT Tuesday for Central U.S. Waters
     Strait Of Juan De Fuca-East Entrance U.S. Waters Strait Of
     Juan De Fuca.

     Small Craft Advisory from 5 PM this afternoon to 3 AM PDT
     Tuesday for Admiralty Inlet.

&&

$$