Grisdale, Washington Weather Forecast Discussion

974
FXUS66 KSEW 072141
AFDSEW
Area Forecast Discussion
National Weather Service Seattle WA
241 PM PDT Sun Sep 7 2025
.SYNOPSIS...Cool, cloudy, and unsettled conditions will continue
across western Washington through the first half of the week, with
periods of showers and thunderstorms at times. A brief period of
drier conditions is possible towards the end of the week, with
another system bringing increasing rain chances by next weekend.
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.SHORT TERM /TONIGHT THROUGH WEDNESDAY/...An upper low pressure
system will continue to slowly meander inland through the short-
term, maintaining cool and unsettled conditions across western
Washington. A shortwave in the southerly flow aloft will ripple
northward across western Washington this afternoon, generating
light showers and isolated thunderstorm activity over the
Cascades. The best chance for thunderstorms remains over the North
Cascades, where ensembles show a 20% to 30% chance of
thunderstorms through the evening near the Cascade crest. However,
with a marine layer stemming all the way to the crest, the ample
cloud cover and cooler temperatures will make it difficult for
storms to initiate. The lowlands will likely see little more than
cloudy skies this afternoon, with temperatures on track to reach
the 60s to low 70s.
Cloudy conditions will stick around into Monday, with another
round of marine stratus expanding inland in the morning and
eroding towards the coast by the afternoon. The low pressure
system will start to track inland over Oregon on Monday, with some
wrap around moisture favored to fire up shower and thunderstorm
activity Monday afternoon mainly south of the Puget Sound and over
the Cascades. The best chance for more widespread showers and
thunderstorms will be late Monday night into Tuesday as the low
continues to shift eastward and moisture continues to be advected
towards western Washington. Some uncertainty still exists over the
coverage and strength of precipitation Tuesday, but with
temperatures peaking in the 60s for most areas under cloudy skies,
instability may be fairly limited.
Cool and cloudy conditions will continue on into Wednesday as the
low slowly shifts eastward. More wrap around moisture will move
into western Washington, but resultant showers will likely be
confined to the Cascades with a few lightning strikes possible.
.LONG TERM /THURSDAY THROUGH SUNDAY/...The slow moving upper low
will continue to creep eastward on Thursday and Friday, with high
pressure building in behind. Ensembles continue to favor drying
across the lowlands on Thursday and Friday, with potential for
lingering showers once again over the Cascades. This will allow
temperatures to warm up several degrees, returning to near normal
for the middle of September. Highs will likely rebound to the mid
70s across the lowlands and the mid 60s along the coast.
Forecast models continue to hint at a pattern change heading into
next weekend, bringing increasing chances for more widespread
precipitation and slightly cooler temperatures on Saturday and
Sunday. The latest ensemble guidance shows potential for up to
half an inch of rain across the lowlands next weekend, and up to
an inch or more of rain over the mountains.
15
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.AVIATION...A broad upper trough remains centered offshore with
an upper ridge over the Rockies producing light southerly flow aloft
over Western Washington. The air mass is moist west of the Cascades
with multiple cloud layers and a few showers. Areas of MVFR ceilings
will gradually lift for period of VFR ceilings late this afternoon
into the evening before deteriorating back to low MVFR or occasional
IFR once again on Monday morning. Any isolated thunderstorm activity
this afternoon and evening will likely be limited to the Cascade
crest and points eastward.
KSEA...Ceilings will lift to VFR mid-afternoon into the evening.
Shower activity is expected to be limited today. Ceilings will fall
back to low MVFR or tempo IFR late tonight into Monday morning.
Surface winds will be S/SW 8 knots or less.
27
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.MARINE...A weak surface ridge over the coastal and offshore waters
will be replaced by a weak low today. This general pattern will
persist through the first half of this week before a stronger
surface ridge rebuilds offshore around mid-week.
Seas 2 to 4 ft through at least Tuesday night, increasing to 4 to 6
ft by Wednesday.
18/27
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.FIRE WEATHER...For today, thunderstorms have already begun to
fire along the eastern slopes of the Cascades. Marine stratus
remains in place all the way up to the crest, and with high clouds
overtop of that, convection will have a tough time getting started
this afternoon over western Washington.
As an upper level trough slowly inches eastward over the area, we
will see renewed chances for thunderstorms, with the highest chances
(15-25%) over the Cascades. The day with the highest chances will be
Tuesday, but the threat will be possible each day through Wednesday.
The primary threats from any thunderstorms will be gusty winds,
brief heavy downpours, and lightning. Luckily, increased moisture,
cloud cover, and more seasonal temperatures across the area will
help to alleviate significant fire weather impacts.
Looking forward, Thursday has the best chance to be the driest day
of the week, with more chances for cooler and showery weather going
into next weekend.
62
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.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...None.
&&
$$

NWS SEW Office Area Forecast Discussion