Washington State Forecast Discussion

Western Washington


295
FXUS66 KSEW 260357
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
857 PM PDT Tue Mar 25 2025

.SYNOPSIS...High pressure and southwest flow aloft will result in
unseasonably warm temperatures today. A strong storm system will
lift a front across western Washington on Wednesday, bringing in a
chance for widespread thunderstorms. A cold front Thursday will
bring cooler temperatures while maintaining unsettled conditions.
Active weather is favored to continue through the period with
near-normal temperatures.

&&

.SHORT TERM /TONIGHT THROUGH FRIDAY/...High pressure continues to
amplify over the region this evening with a deep low pressure
system approaches the Pacific coast. Temperatures today warmed
considerably under southwest flow aloft, with many locations
warming into the 70s and several sites setting record high
temperatures for the date. Overnight low temperatures will also
remain mild under the continued southwest flow, and patchy and
locally dense fog will likely develop once again across the Puget
Sound lowlands once again Wednesday morning. Otherwise, the focus
turns to the potential for strong and isolated severe
thunderstorms on Wednesday. The remainder of the previous short
term discussion remains unchanged and describes this well.

The focus then shifts to convection on Wednesday, with impactful
weather on tap for all of western Washington. The offshore low
will approach the Pacific Coast on Wednesday, bringing a variety
of weather impacts throughout the day:

* MID MORNING: An initial wave of moisture will move towards the
Olympic Peninsula, and showers and embedded thunderstorms may
develop west of the Puget Sound. The primary threats of this
initial wave will be lightning and the potential for small
hail/graupel. However, a large amount of uncertainty exists over
the intensity of this precipitation and how far inland these
showers will develop.

* EARLY AFTERNOON: Activity will decrease across western
Washington with a lull in shower and thunderstorm activity mid-
day. Southerly flow aloft will continue to advect warm air into
the region, and daytime heating with some cloud clearing will
allow the environment to become very unstable by the early
afternoon. Ensembles show peak CAPE values ranging between
500-1500 J/kg, with the highest CAPE values over the Cascade
foothills and south of the Puget Sound towards Centralia.

* AFTERNOON/EVENING: The offshore low will lift a vigorous front
northward across western Washington throughout the afternoon and
evening hours, bringing a round of strong to potentially severe
thunderstorms across the region from the south moving northward.
The primary threats of these storms will be hail and gusty
winds alongside frequent lightning and locally heavy rain. The
strongest storms are favored to develop east of the Puget Sound
Wednesday evening along the I-5 corridor, potentially impacting
the evening commute. The strongest storms that develop could
become severe and capable of producing hail up to 2 inches or
more in diameter, outflow wind gusts as high as 60 mph or more,
and/or an isolated brief tornado.

A cold front will shift inland late Wednesday evening, shifting
the precipitation eastward. While the threat of thunderstorms
quickly decreases into the overnight hours, the low offshore will
continue to inject moisture inland for additional rounds of shower
activity throughout the day Thursday before shifting inland on
Friday. Thunderstorms are possible once again on Thursday, but
will not be as strong as Wednesday, will be more isolated in
nature, and are not expected to become severe. Breezy conditions
are also favored to develop along the coast and northern interior
on Thursday with southerly gusts to 30 to 40 mph. With large seas
building offshore, the potential for high surf conditions along
the Pacific coast will need to be closely monitored. Temperatures
will lower back to near- normal towards the end of the week, and
with snow levels returning to 3500-4500 feet, higher elevations
will see a few inches of accumulating snow to round out the week.

.LONG TERM /SATURDAY THROUGH TUESDAY/...Active weather will
continue into the weekend and early next week as a series of
systems pass over the Pacific Northwest. Temperatures will return
to near-normal in the mid 50s across much of the lowlands.
Forecast models continue to show weak ridging on Sunday, which may
allow some areas along the Cascade foothills to see high
temperatures in the 60s. However, mild conditions will be short
lived with another storm system bringing in wet and windy
conditions at the start of next week.

15/12

&&

.AVIATION...As the upper level ridge shifts slowly eastward, current
southwesterly flow aloft will shift more southerly by late Wednesday
morning. North Sound terminals, including SEA, currently favoring
northerly direction with speeds generally 4 to 8 kts. South Sound
terminals /OLM and PWT/ favoring more easterly direction with
similar speed. HQM stands alone with westerly winds, again with
similar speeds. Winds overall expected to become largely light and
variable away from the coast and remain that way at least into early
Wednesday morning. Coastal sites will see speeds ramp up sooner as
an incoming front approaches...as early as the overnight hours.

Widespread VFR conditions tonight likely to erode during the
overnight hours as the combination of abundant low-level moisture
from previous weather system coupled with the ridge aloft may
facilitate inversion development and thus, low clouds and/or fog
during the early morning hours Wednesday. This development will
result in widespread MVFR to IFR conditions throughout W WA. The
approach of the front and the mixing it provides will allow for
recovery to VFR conditions by late morning, however showers and
thunderstorms along the front and associated precipitation likely to
drag cigs down again in the afternoon at least into widespread MVFR
conditions, with isolated IFR possible under heavy rain.

Models remain consistent with thunderstorm potential Wednesday
afternoon and evening, resulting in frequent lightning, gusty and
erratic winds, hail and brief periods of heavy rain for much of the
area during FROPA. It is highly encouraged to remain up to date with
latest forecasts during this time as amendments will likely be short-
fused.

KSEA...VFR with FEW/SCT high clouds this evening and early tonight,
with north winds 4 to 8 kt. Fog/mist likely to develop overnight
into Wednesday morning, with visibilities down to a mile or less
possible. Improvements to VFR will be brief late Wednesday morning
and into the afternoon prior to a line of thunderstorms arriving
early Wednesday evening. These storms may contain hail and gusty
winds. Outside of thunderstorms, winds will become southerly 5 to 10
kt after storms pass through.

HPR/18

&&

.MARINE...Surface high pressure offshore via a ridge will move
inland tonight. A temperature inversion ahead of a cold front
Wednesday morning will likely lead to widespread fog/low stratus
across much of the inland waters, with visibilities potentially
below 1 SM. A strong cold front will trigger widespread showers and
thunderstorms Wednesday afternoon and evening. Some storms may
produce hail and gusty winds. Behind the front, gusty south winds
will pick up early Thursday morning in the coastal waters and most
of the interior waters. The confidence for sustained gale winds
remains low, but several gusts may approach gale force. Will leave
the gale watch in place for the coastal waters at this time. Small
craft will be particularly susceptible to the gusty south winds of
20-30 kt. In addition to winds, seas will steepen to 18 to 22 feet
Thursday and Friday, decreasing to 9 to 12 feet Friday through
Saturday and 6 to 8 feet on Sunday.

Additional systems will be possible over the weekend, although the
threat for hazardous gusty winds and seas remains low over the
extend forecast period.

HPR/18

&&

.HYDROLOGY...Area rivers have largely receded today, with a
handful of rivers in Action Stage this afternoon and on the way
down. A storm system Wednesday will bring showers and
thunderstorms to the region, with potential for locally heavy
rainfall at times in stronger activity. However, due to the
convective and spotty nature of this precipitation, most area
rivers are expected to stay below Flood Stage. Precipitation will
continue throughout the week as active weather continues, but is
not expected to cause significant rises to area rivers.

The exception is the Skokomish River, where heavy showers mid-
week are favored to bring the Skokomish into Flood Stage by late
Thursday where it will likely remain through early Saturday. The
latest forecast has the river peaking into Moderate Flood Stage,
but large uncertainty exists over the amount of precipitation over
the basin. Conditions will continue to be closely monitored.

15

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Gale Watch from Wednesday evening through late Thursday night
for Coastal Waters From Cape Flattery To James Island 10 To
60 Nm-Coastal Waters From Cape Flattery To James Island Out
10 Nm-Coastal Waters From James Island To Point Grenville
10 To 60 Nm-Coastal Waters From James Island To Point
Grenville Out 10 Nm-Coastal Waters From Point Grenville To
Cape Shoalwater 10 To 60 Nm-Coastal Waters From Point
Grenville To Cape Shoalwater Out 10 Nm.

&&