Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 200332

Area Forecast Discussion
National Weather Service Seattle WA
832 PM PDT Fri Jul 19 2024

.SYNOPSIS...Warm and dry conditions will persist into the weekend
as upper level ridging amplifies over the region on Saturday. A
shortwave will skirt the area on Sunday and may bring some light
showers to portions of western Washington. An upper level trough
moving into British Columbia early next week will cool temperatures
closer to seasonal norms.


.SHORT TERM /TONIGHT THROUGH MONDAY/...The forecast largely remains
on track this evening. Stratus will push inland overnight, but to
a lesser extent than previous days with weaker onshore flow. Overnight
lows will be in the 50s across much of western Washington. The
remainder of the previous discussion follows below, with updates
made to the aviation section. 14

Upper level ridging will amplify over the region on Saturday with
500 mb heights building into the 590 dms. Flow aloft will
transition to southerly and temperatures aloft will warm to 20C.
Onshore flow will weaken and expect a shallower marine layer to
allow for afternoon temperatures on Saturday to reach the upper
80s and low 90s across the interior. High temperatures near the
coast will be in the 70s.

The upper level ridge will slowly shift east Saturday night into
Sunday as an upper level trough approaches the area. Another upper
level shortwave looks to precede the trough and may bring some
light precipitation to the coast on Sunday. Latest high-res guidance
indicates roughly a 10-15% chance of isolated thunderstorms across
the mountains Sunday afternoon, so will need to keep an eye on
this trend over the next day. Temperatures on Sunday will cool a
few degrees along the coast, and generally look to top out in the
60s. Temperatures across the interior, however, look to remain
warm, generally climbing into the mid to upper 80s.

Guidance remains in good agreement with a pattern shift starting
Monday as a broad upper level trough starts to move into the
region. Increased onshore flow will allow for temperatures to
cool back down towards seasonal norms, with highs generally
expected to be in the 60s along the coast and 70s across the

.LONG TERM /TUESDAY THROUGH FRIDAY/...The aforementioned trough
will remain over the region through the long term period. This
will promote onshore flow, morning stratus, and temperatures close
to seasonal norms. Highs generally look to trend in the 60s for
the coast and 70s across the interior, with overnight lows
trending in the upper 40s to mid 50s. Not much expected in the
way of precipitation at this time, though could see a few very
spotty showers at times across the mountains late in the week.


.AVIATION...Southwest flow aloft with troughing upstream and ridging
downstream with weak low-level onshore flow. VFR/clear skies
continue this evening. LIFR/IFR stratus is expected to advance
inland along the coast tonight and possibly making it`s way to KSHN-
KPWT, and also close to KCLM/KPAE in the Strait of Juan de Fuca. Any
lingering stratus should return to the coast by 18z Saturday with
widespread VFR for the remainder of the day. Winds expected to
remain light out of the north and west at 4 to 8 kt.

KSEA...VFR for the remainder of the evening into Saturday. Marine
stratus is expected to remain well west of the terminal (might see a
few VFR level clouds in the morning). Surface winds north 4 to 8 kt
this evening before shifting back to the northwest Saturday



.MARINE...Surface high pressure offshore with lower pressure inland.
Because of this, we`ll see prevailing onshore flow of varying
strength. A SCA has been issued this evening into tonight with more
headlines likely into next week. Gales are possible Sunday evening
into Monday. Seas 3 to 5 ft into Saturday before rising to 4 to 7 ft
Saturday night through Monday.



.FIRE WEATHER...Warm and dry conditions through Sunday. Afternoon
minimum RHs again dipping close to critical thresholds Saturday
for the lowlands and through Sunday for the Cascades. Instability
may increase enough to keep a mention of elevated concern for the
Cascades especially Saturday afternoon and evening. Another
disturbance may bring a renewed threat for thunderstorms Sunday
across some portion of the mountains, with high resolution
ensembles including the NBM showing a 10-15% chance at this time.
A cooler more humid pattern develops Monday as the pattern
switches to be dominated by an upper level trough over the region.


PZ...Small Craft Advisory until 3 AM PDT Saturday for Central U.S.
     Waters Strait Of Juan De Fuca-East Entrance U.S. Waters
     Strait Of Juan De Fuca.