Carlisle, Washington Weather Forecast Discussion

191
FXUS66 KSEW 081036
AFDSEW
Area Forecast Discussion
National Weather Service Seattle WA
336 AM PDT Mon Sep 8 2025
.SYNOPSIS...An upper level low offshore will push inland over the
region late tonight into Tuesday, maintaining cooler conditions
and chances for showers and thunderstorms at times through the
first half of the week. A brief period of drier conditions will be
possible Thursday into Friday, before another system brings
increasing rain chances to western Washington over the weekend.
&&
.SHORT TERM /TODAY THROUGH WEDNESDAY/...Unsettled conditions will
continue across western Washington through the first half of the
week as an upper level low offshore gradually moves inland late
tonight into Tuesday and meanders across the Pacific Northwest.
Temperatures today will remain close to seasonal norms, with highs
along the coast generally expected to be in the upper 60s to near
70 and highs across the interior expected to be in the low to mid
70s. Some showers and isolated thunderstorms will be possible across
the Cascades and areas south of the Sound this afternoon and evening
as moisture moves into the area from the approaching low.
Convection potential looks greater on Tuesday as the low slowly
pushes inland, with latest hi-res guidance currently indicating a
25-35 percent chance of thunderstorm development across the
Cascades. The highest likelihood for development will be across
the North Cascades, with guidance highlighting a few spots with a
35-40 percent chance of development. While uncertainty still
exists in regards to the extent of coverage and intensity expected
with these storms, the main threats will be gusty outflow winds,
small hail, brief heavy downpours, and frequent lightning. Afternoon
high temperatures on Tuesday will be the coolest within the short
term period, with highs generally expected to be in the mid 60s
along the coast and mid 60s to near 70 across the interior.
Cool and cloudy conditions will persist into Wednesday as the low
resides across the Pacific Northwest. Afternoon high temperatures
will be in the mid 60s to low 70s areawide. Showers and isolated
thunderstorms will be possible across the Cascades again during
the afternoon and evening hours, but expect coverage to be less
than that of Tuesday.
.LONG TERM /THURSDAY THROUGH SUNDAY/...The upper low will slowly
continue to push eastward Thursday and Friday while weak high
pressure starts to build in its wake offshore. At this time,
Thursday and Friday look to be the driest days for the lowlands.
Showers will still be possible across the Cascades, however, as
wrap-around moisture from the low continues to move into the
region. Temperatures will be close to seasonal norms.
The drier period looks to remain short-lived, however, as
guidance still hints at a return to more widespread shower
activity by the weekend as another system moves into the area from
the Pacific. At this time, the latest NBM 50th percentile
indicates roughly a quarter of an inch to half an inch of rain
falling across the interior lowlands and around an inch of rain
falling for areas along the coast and in the mountains.
14
&&
.AVIATION...A broad upper trough remains centered offshore with
an upper ridge over the Rockies producing light southerly flow aloft
over Western Washington before shifting southeasterly as the upper
level low moves inland late tonight or early Tuesday morning.
Surface winds largely southerly again today before shifting to
northwesterly in the early evening. Speeds will remain consistent at
generally 4-8 kts, although some terminals may experience light and
variable winds early this morning and overnight tonight.
The air mass over the area remains moist with multiple cloud layers.
At the time of this writing /0830Z/ majority of terminals reporting
VFR conditions with some MVFR conditions in the south Sound area and
IFR conditions at OLM and HQM. More widespread MVFR to IFR
conditions expected to emerge closer to 12Z and will linger into the
late morning, possibly early afternoon with a widespread return to
VFR conditions within the 18-20Z time frame. VFR ceilings return by
Monday afternoon and remain in place for what is left of the TAF
period.
KSEA...Low-end VFR cigs this early morning should erode to MVFR by
12Z and remain there through the morning before lifting around 17Z
or 18Z. VFR conditions return for the afternoon and for the
remainder of the TAF period. Winds generally south to southwest this
morning and afternoon before shifting northwesterly this evening.
Speeds expected to remain 4-8 kts.
18
&&
.MARINE...Weak surface low pressure over the coastal and offshore
waters will remain in pace through the first half of this week with
minimal impacts to area waters. 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
&&
.FIRE WEATHER...Thunderstorm chances will continue across the
Cascades through Wednesday as an upper level low slowly moves
across the Pacific Northwest. The day with the highest probability
of storm development will be Tuesday, with guidance indicating
roughly a 25-40 percent chance of development, with the most
likely area being across the North Cascades. The primary threats
from any thunderstorms will be gusty outflow winds, brief heavy
downpours, small hail, and frequent lightning.
Outside of thunderstorm activity, increased moisture, cloud cover,
and more seasonal temperatures across the area will help to alleviate
significant fire weather impacts through much of the week.
62/14
&&
.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...None.
&&
$$

NWS SEW Office Area Forecast Discussion