Physt, Washington Weather Forecast Discussion

400
FXUS66 KSEW 061544
AFDSEW
Area Forecast Discussion
National Weather Service Seattle WA
844 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/...The latest forecast remains
on track with no updates this morning. 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.
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...An upper ridge axis over the Northern Rockies and
a broad upper trough offshore continue to promote south to southeast
flow aloft over Western Washington. Light low level onshore flow
continues near the surface with LIFR stratus/fog and reduced surface
visibility encompassing much of the lowlands. Widespread wildfire
smoke and haze aloft will persist across the region. An upper level
disturbance entering the area will lead to elevated instability for
scattered showers and isolated thunderstorms across southern
portions of the area this morning. A combination of daytime heating
and upper level diffluence/divergence will lead to a renewed threat
of scattered showers and isolated thunderstorms later today. Some of
this could impact Puget Sound area terminals...especially 00Z to 06Z
this evening. Coastal stratus will spread inland once again tonight
with widespread LIFR or IFR ceilings expected west of the Cascades
on Sunday morning.
KSEA...LIFR ceilings and surface visibility below 3SM at times is
expected to persist into mid-morning before gradually lifting and
scattering late this morning. Convective activity southeast of the
terminals appears to be weakening as it moves from the higher
terrain into the lowlands. However, there is concern for a renewed
threat of thunder...especially 00Z to 06Z this evening as the
environment becomes favorable for thunderstorms to develop over the
Cascades and drift into the lowlands east of Puget Sound. It may be
warranted to include a PROB30 -TSRA in the upcoming TAF for the
period around 00Z-04Z. LIFR/IFR stratus is expected to return to the
terminal 09Z-12Z Sunday morning. Surface winds S/SW 5 to 7
knots...except locally gusty and erratic around any thunderstorms.
27
&&
.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