Washington State Forecast Discussion

Western Washington


953
FXUS66 KSEW 271047
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
347 AM PDT Sat Apr 27 2024

.SYNOPSIS...The active weather pattern will continue this weekend
into next week as a series of fronts and upper level troughs pass
through the region. Most of the activity will be in the form of
showers, with heavier precipitation possible along the coast,
Olympics and Cascades. Snow will also be possible in Snoqualmie
and Stevens Passes Monday as cold air brings the snow levels down.
Expect temperatures to top out in the 50s and 60s, with warmer
temperatures towards the end of next week.

&&

.SHORT TERM /TODAY THROUGH MONDAY/...A quiet start to the day with
a few showers ongoing along the coast and Cascades. Most of Puget
Sound remained dry overnight with low clouds. A shortwave trough
passed through yesterday, with a break in between troughs early
this morning. A couple additional troughs sit to the west that
will come over land in the short term. The first one today is weak
and will combined with an occluded front off the coast to produce
scattered showers today. Coverage will increase in the morning
hours as a line of light rain forms, which will break apart as it
moves inland and scatter out. The heaviest rainfall will be along
the coast with 0.50-0.75 inches of QPF possible through Sunday
morning. Remaining areas should get around one to two tenths of an
inch of QPF. Snow showers will be possible for the peaks of the
Olympics and Cascades, but amounts will remain light with just a
trace or an inch by Sunday morning.

Attention then turns to a more potent mid-latitude cyclone
dropping down from Alaska/Canada on Sunday/Monday. The center of
this low will slowly drop to the southeast, sitting in southern
B.C. on Monday, with a trough and jet core extending well south
into Oregon/northern California. With cool air aloft arriving with
this low (500 mb temps down to -35 C), snow levels will drop to
just under 2,000 ft Sunday night/Monday morning. Morning low
temperatures will dip into the upper 30s/low 40s in the lowlands,
with some areas below freezing at higher elevations. Moisture
coming in with the jet/westerlies will support the chance for snow
in some of the passes Sunday night/Monday (Snoqualmie and
Stevens), as well as areas higher than 2,000 ft. At this time,
impacts appear to be minor for roadways with this system
(considering warm grounds, and light snowfall rates). NBM 50th
percentile gave 5 inches for Snoqualmie and 4 inches for Stevens.
The higher end of the model brought both passes up a couple
inches (7 and 6 inches respectively). Given the upticks in QPF
with this system from the past couple days, will continue to
monitor changes and consider issuing headlines (if warranted).

For remaining areas below the snow level, the cool air aloft will
provide a conditional thunderstorm risk for shower activity that
develops on Monday (SPC has western Washington in a general
thunder up to the Cascade crest). QPF amounts are not expected to
be as heavy down in the lowlands (compared to the Cascades), but
shower/thunderstorm activity will be off and on for most of the
Sunday night/Monday period. High temperatures will remain cool in
the mid 50s in the lowlands (Saturday - Monday). Winds remain
light out of the southwest at 5 to 10 mph (few gusts possible near
Puget Sound/Strait of Juan de Fuca waters).

.LONG TERM /TUESDAY THROUGH FRIDAY/...The mid latitude low will
remain over Washington through mid week as it digs southward
through the state. Cool air will remain planted with this system
as it fills in and begins to dissipate to the east over the
Rockies by mid week. With less moisture available, the shower
chances will decrease Tuesday/Wednesday. Snow levels will begin to
increase Wednesday/Thursday as the trough departs to the
southeast. Ensemble/deterministic models are agreeing more for
drier and warmer weather to finish the week (although some still
showing a trough/frontal system passing through - so will keep a
conditional shower chance through the end of next week).
Temperatures will increase into the 60s by Wednesday, with a shot
of 70s by next Saturday. Winds will also remain light.

HPR

&&

.AVIATION...West-southwest flow aloft as an upper level trough moves
across the Pacific Northwest into this evening. Southwest flow
continues across the Puget Sound terminals and west-southwest at HQM
and CLM from 10 to 15 kt this morning into the early afternoon.

A mix of IFR and MVFR CIGs this morning with drizzle and scattered
showers across western Washington. Widespread light rain will move
back into the region in association with the next frontal system
from 18-20Z, with CIGs rising, potentially to low-end VFR levels
briefly for a few hours from 19-00Z, though confidence on this
evolution is low with a 30% chance for MVFR restrictions to continue
through the evening. Regardless, CIGs look to trend back towards
MVFR after 02Z this evening through much of tonight.

KSEA...IFR CIGs this morning with drizzle. A gradual improvement in
CIGs is expected through the morning with a brief period of low-end
VFR possible from 20-00Z, though there's a 30% chance we hang on to
MVFR through the afternoon. Widespread stratiform rain is expected
to move back into the region with the next frontal system after 20Z.
A gradual trend back to MVFR through the night is expected.
Southwesterly winds through the TAF period, with gusts to 20 kt
possible through 22Z this afternoon.

Davis

&&

.MARINE...Breezy southerly winds this morning into the early
afternoon along and ahead of an incoming occluded front that will
move over the area waters this evening, followed by onshore flow.
Expanded Small Craft Advisories into the inner waters with growing
confidence for wind gusts above 21 kt (60% chance) for all but the
West Entrance to the Strait of Juan de Fuca for a combination of
strong southerly pre-frontal winds and post-frontal surge through
the Strait. Strongest southerly winds mostly confined to central
Puget Sound northward through Admiralty Inlet and Possession Sound.
Marginal wind gusts to SCA thresholds possible Sunday afternoon (35%
chance) over the offshore waters with another round of Small Craft
Advisories likely through the Strait with another afternoon push.

Seas ranging from 5 to 7 feet this morning will increase to 6 to 9
feet this afternoon and through much of the day Sunday. Seas look to
increase to 7 to 9 feet Sunday night into Monday. Seas look to
remain below 10 feet Tuesday onward.

Davis

&&

.HYDROLOGY...No river flooding is expected over the next seven
days.


&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory from 8 PM this evening to 5 AM PDT Sunday
for Central U.S. Waters Strait Of Juan De Fuca.

Small Craft Advisory from 2 PM this afternoon to 5 AM PDT Sunday
for East Entrance U.S. Waters Strait Of Juan De Fuca.

Small Craft Advisory from 11 AM this morning to 11 PM PDT this
evening for Admiralty Inlet-Northern Inland Waters
Including The San Juan Islands.

Small Craft Advisory from 5 AM early this morning to 2 PM PDT
this afternoon for Puget Sound and Hood Canal.

Small Craft Advisory from 8 AM this morning to 8 PM PDT this
evening 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.

&&