Oyhat, Washington Weather Forecast Discussion

804
FXUS66 KSEW 061127
AFDSEW
Area Forecast Discussion
National Weather Service Seattle WA
427 AM PDT Sat Sep 6 2025
.SYNOPSIS...An upper level low will remain offshore through the
weekend before moving inland early next week. A series of
shortwaves moving across the region from this system will maintain
shower and thunderstorm chances across western Washington through
the first part of the week. A brief period of drier conditions
will be possible later in the week as the low progresses further
inland, however showers return next weekend as another system
makes its way into the region.
&&
.SHORT TERM /TODAY THROUGH MONDAY/...An upper level low will
continue to deepen offshore today and Sunday before starting to
move inland on Monday. A series of shortwave disturbances will
move over the region in the southerly flow aloft and will bring
shower and thunderstorm chances to western Washington through the
short term.
Radar across the area remains rather quiet early this morning,
however some showers from Oregon have slowly started to creep
northward into Washington at this time. Hi-res guidance has had a
difficult time initializing the convection that continues to fire
up along the Oregon coast this morning. While most activity has
fizzled as it approaches Washington, the focus for the thunderstorm
threat over the next few hours looks to be mainly be along the
coast and across the coastal waters as these storms continue to
slowly progress northwestward.
Otherwise, the shortwave currently moving across the region will
continue to bring chances of showers and isolated thunderstorms
to the area this morning, primarily for areas along the coast and
from Puget Sound southward. A stronger shortwave moving across the
area later today will have the potential to bring more widespread
shower and thunderstorm activity to the area. The greatest potential
for thunderstorm activity remains across the Cascades at this time,
with guidance highlighting roughly a 25-40 percent probability of
thunderstorm development. Cannot rule out thunderstorms moving
over the lowlands this evening as well, where guidance maintains a
15-25 percent chance of convection. One factor to watch this
afternoon and evening will be the wildfire smoke across the area,
which could act to hinder the development of any potential
thunderstorms. Otherwise, expect conditions to be cooler today,
with highs expected to be in the 60s along the coast and low to
mid 70s across the interior.
Chances for showers and thunderstorms continue across western
Washington on Sunday and Monday as the upper low gradually makes
its way closer to pushing onshore. Thunderstorm chances lessen
across the region on Sunday, before becoming mostly confined to
the Cascades by Monday afternoon and evening. Shower chances will
continue across western Washington, along with cooler temperatures
with highs expected to mostly be in the 60s to low 70s areawide.
.LONG TERM /TUESDAY THROUGH FRIDAY/...Cool and unsettled conditions
look to persist through midweek as the upper level low pushes
inland and stalls over the region. A brief period of drier conditions
will be possible late in the week as the low then starts to sink
southward along the West Coast and ridging builds into British
Columbia and Alberta. Guidance then hints at shower chances
increasing again on Friday as another system approaches the
region from the northeastern Pacific. 14
&&
.AVIATION...South to southeasterly flow aloft due to an upper level
ridge centered over northern ID. Light westerly to southwesterly
onshore flow at the surface with wind speeds mostly 5 kts or less.
Surface winds will shift more south to southwesterly by noon today
with speeds increasing only slightly to 5-10 kts. The exceptions
will be CLM, where direction will be more W to NW and HQM where more
westerly is favored.
Cigs lowering a little quicker than forecast with terminals west of
the Sound and in the south Sound area, including SEA, seeing LIFR
conditions. These lower cigs are expected to impact all terminals by
12-14Z this morning and persist through around 18Z before cigs lift
back into at least MVFR. Smoke and haze could continue to pose
problems and vis restrictions into the late morning, possibly into
early afternoon. Models remain consistent on afternoon and evening
showers /with a slight chance for thunder/...however confidence on
where development will occur remains low enough where the inclusion
of a more definitive -RA or -SHRA does not seem warranted at this
time. This possibility however will continue to be reflected using
VCSH for now. As for thunder risk, this will largely remain confined
to the higher terrain of the mountains and as such, is not expected
to impact any terminals at this time. As similar lowering of cigs is
expected for late tonight and early Sunday morning.
KSEA...Hazy/smoky conditions playing into the lower cigs at the
terminal, with LIFR conditions present at the time of this writing
and expected to continue through around 18Z. Vis is gradually coming
down a little in last couple of obs...so while there will be some
reduction, should not get any worse than 5-6 SM. Convective showers
still possible this afternoon and evening, probably with an emphasis
on the late afternoon and early evening. The addition of low-level
moisture to the already present smoke and haze should make for a
return to MVFR to IFR conditions late Saturday/early Sunday. SW
winds generally 4-8 kts expected for the entire TAF period.
18
&&
.MARINE...A weak surface ridge will remain over the coastal and
offshore waters today and even though a weak low takes its place
Sunday, pressure differences are not significant enough to divert
from onshore flow. This pattern does not vary much even into the
first half of next week, although more pronounced surface ridging
will be possible for the second half of the week ahead.
Seas largely 2-4 ft in the near term before increasing slightly
Wednesday to 3-5 ft for the mid-week time frame. An increase to 5-7
ft is expected for the end of next week.
18
&&
.FIRE WEATHER...Upper level disturbances moving across the area
will bring chances of showers and thunderstorms across the region
through the weekend. The greatest chance for thunderstorm
development today remains across the Cascades, where there is a
25-40% chance of widespread thunderstorms developing during the
late afternoon and evening, though cannot rule out some thunderstorm
activity moving into the lowlands as well. The main hazards with
these thunderstorms are gusty erratic winds, brief heavy
downpours, and frequent lightning. At this time, confidence
remains low in the extent of coverage and its intensity, so have
opted to refrain from hoisting any fire weather headlines at this
time. Another factor to monitor will be the amount of wildfire
smoke within the region and how much that inhibits convection
across the area this afternoon and evening.
The thunderstorm threat will become more isolated and mostly
confined to the mountains by Monday. Outside of thunderstorm
activity, the cool and showery conditions lasting into midweek
should help to keep the overall fire danger suppressed.
&&
.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory from 8 PM this evening to 3 AM PDT Sunday
     for Central U.S. Waters Strait Of Juan De Fuca-East
     Entrance U.S. Waters Strait Of Juan De Fuca.
&&
$$

NWS SEW Office Area Forecast Discussion