778
FXUS66 KSEW 052149
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
249 PM PDT Tue Aug 5 2025

.SYNOPSIS...A relatively wet weather system will move through
the region tonight through early Thursday bringing widespread
precipitation to western Washington. Isolated thunderstorms will
also be possible Wednesday afternoon and evening. Dry and
warming conditions are then expected through this weekend into
early next week. By early next week, daytime highs may reach
the 80s to low 90s in the lower elevations of western
Washington.

&&

.SHORT TERM /TONIGHT THROUGH THURSDAY NIGHT/...Mid and high
level clouds continue to stream into the region this afternoon
ahead of a trough that will impact the area over the next couple
of days. Precipitation chances will increase and hang along the
coast later this afternoon and evening then spread across the
region overnight into Wednesday morning. 48-Hour QPF forecasts
are reasonably consisted with the inherited forecast. Generally
0.5-1.0 inches in the mountains with locally higher amounts and
then 0.25-0.50 in the lower elevations. By Wednesday afternoon,
post-frontal instability may be enough to kick off a few
isolated thunderstorms. The highest chances (20-30%) will be in
the North Cascades and lower (10-20%) chanced across the rest of
western WA. Shower activity will wane Thursday with some
sun likely by the afternoon.

&&

.LONG TERM /FRIDAY THROUGH TUESDAY/...The long term will
primarily be characterized by the development of a ridge of high
pressure across the eastern Pacific. That said, a weak
disturbance may move through the flow Friday/Saturday bringing a
period of increased cloud coverage. Otherwise, increasing
heights will result in dry and warming conditions into early
next week.

Confidence is reasonably high that temperatures will warm to
widespread moderate (orange) HeatRisk levels by Monday next
week. There is lower confidence in how long that level of heat
will linger. The most likely scenario appears to be 1-3 days.
Compared to the inherited forecast, the peak temperatures have
come down 1-2 degrees, but widespread 80s to low 90s remain in
the forecast early next week.

&&

.AVIATION...Southwesterly flow to westerly flow aloft as a upper
level trough moves through western Washington. VFR conditions at
all area terminals this afternoon will start to lower later this
evening (07z-10z) to MVFR as a front moves over the area bringing
widespread rain across area terminals. Rain will continue through
the overnight and into Wednesday morning and may locally limit
visibilities (4-6SM) at times with brief IFR conditions. Guidance
suggests low ceilings (MVFR/IFR) hanging out through Wednesday
afternoon before slowly lifting back to VFR.

KSEA...VFR conditions at the terminal this afternoon. Ceilings
will begin to lower to MVFR late tonight and into Wednesday
morning as rain moves through the terminal. Surface winds S/SW 8
to 12 knots this afternoon will lessen overnight before kicking
back up after 17z Wednesday around 10 to 15 knots. Ceilings may
lower to IFR at times throughout Wednesday morning as steadier
rain moves over the terminal.

Mazurkiewicz

&&

.MARINE...Surface high pressure weakening over the waters this
afternoon will make way for a frontal system to cross through this
evening. The westerly push down the Strait this evening will not
reach Small Craft Advisory criteria as winds calm slightly. A
stronger push Wednesday evening may warrant at Small Craft
Advisory but confidence is low at this time.

High pressure will rebuild over the coastal waters on Thursday and
will remain throughout the weekend for generally benign marine
conditions.

Coastal seas becoming 5 to 7 feet this afternoon and will remain
for the next couple of days before decreasing to 3 to 5 feet by
Friday.

Mazurkiewicz

&&

.FIRE WEATHER...A frontal system will move across the region tonight
into Wednesday, with conditions becoming increasingly cooler,
cloudier, higher humidities, and bringing rainfall into Thursday.
Widespread wetting rain is expected, with amounts of 0.25" to 0.5"
for the lowlands and 0.5" to 1.5" in the mountains with locally
higher amounts. This will generally lower fire weather concerns over
the region with some exceptions.

Wind gusts 20 - 30 mph will accompany the frontal passage for some
areas of the lowlands and could occur before much of the rain has
fallen. This would only briefly be a concern for ongoing fires.

There will also be a chance of thunder Wednesday through the
evening, highest probabilities for the norther half of WA Cascades
and foothills, lower for the lowland areas. With an upper ridge
expected to build into the region next weekend for the return of dry
and hot weather, any holdover lightning starts that persist through
the rainfall could come alive then.
jbb

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...None.

&&

$$