531
FXUS66 KSEW 032241
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
341 PM PDT Mon Jun 3 2024

.SYNOPSIS...A second atmospheric river event will arrive in
western Washington late Monday into Tuesday as a frontal system
moves through. Moderate to heavy rainfall remains possible between
the lowlands and mountains, and a few thunderstorms are also
possible with heavier bands of precipitation. Gusty winds are also
expected as the system moves through overnight. High pressure will
build in the second half of the week, with temperatures increasing
to above average levels.

&&

.SHORT TERM /TONIGHT THROUGH THURSDAY/...Western Washington
remains situated under a strong 300 mb jet core with the max still
off the coast. This continues to funnel in plenty of moisture in
the region from the remnants of tropical activity in the East
Pacific. The shortwave trough from yesterday at the mid levels
sits over Idaho/Montana, with the next broad trough/mid level low
sitting well off the B.C. shoreline. Cool air remains aloft with
temperatures at -18 to -24 degrees celsius. A weak mid-level ridge
also sits in between troughs over western Washington this
afternoon. This has helped to break out some of the cloud cover
seen over the weekend.

Behind the first front, popcorn showers have continued in north
Puget Sound, and have also now been developing in the Kitsap
Peninsula this afternoon. There have been a couple of lightning
strikes early in the day, although instability remains limited
(50-100 J/kg). Still, there is an isolated thunder chance this
afternoon, but the threat remains low.

As the next frontal system approaches, southwest flow aloft is
expected to tap in additional low/mid level moisture (via the
initial warm front). The showers this afternoon are expected to
converge into stratiform rain late tonight through Tuesday. The
frontal system will occlude as it moves inland. The heaviest of
the rain is expected to remain in the mountains, with an
additional 1-2 inches of rain likely in the Olympics and Cascades.
There remains half an inch to an inch of rain expected along the
coast, and for remaining lowland areas (Puget Sound), amounts have
decreased overall to around a quarter of an inch to half an inch.
Higher amounts are possible (especially if convective banding
occurs with the rainfall). See the hydrology section for concerns
on the rivers.

With the weak ridging that developed in between troughs, gusty
winds have been an issue for many across the region. Winds this
morning caused several power outages, as well as downing branches
and blowing leaves. The wind advisory that went out earlier today
will continue through Tuesday morning 11 am PDT. Gusty winds have
continued through the afternoon (with occasional gusts closer to
40 mph observed at a few of the observation sites). More
widespread winds of 15 to 25 mph (with gusts over 35 to 40 mph)
are expected late tonight into Tuesday morning. This is expected
to be the windiest time as the system progresses inland. The
windiest area is expected to be around Bellingham and western
Whatcom County, where there is a 40% chance that wind gusts may
exceed 50 mph.

Once the system moves out late Tuesday night, the jet stream
pattern will shift north, becoming zonal and will eventually build
into a ridge over the northern U.S. states and Canada. Skies will
clear out significantly on Wednesday and Thursday, with flow
weakening significantly aloft (and down at the surface).
Temperatures will start to increase from the 50s and 60s Monday
through Wednesday, into the low 70s by Thursday.

.LONG TERM /FRIDAY THROUGH MONDAY/...Ensemble/deterministic models
have a ridge continuing to build over the Pacific coast going into
the weekend. This will result in above average temperatures with
weak offshore flow. The warmest days are expected to be Friday and
Saturday, where high temperatures could pop out in the upper 70s
to low 80s. At this time, the heat risk remains minor for all
areas expect for the immediate Seattle metro (which has a moderate
heat risk on Saturday). The ridge will move out of the region
Sunday into Monday, and a weak shortwave trough will bring the
next chance of showers into the mountains Sunday and Monday.

HPR

&&

.AVIATION...Mainly VFR to MVFR with post-frontal showers and breezy
southwest winds 10-20 kt with gusts to 35 kt. IFR conditions
possible in heavier shower activity in the vicinity of area
terminals, and a lightning strike or two cannot be ruled out this
afternoon. A strong cold front will cross the region later this
evening, bringing in more widespread rain and stronger winds after
03z with gusts to 40-45 kt. Ceilings will lower to MVFR/IFR in
heavier showers and low stratus before improving in the afternoon as
precipitation slowly tapers off.

KSEA...Low-end VFR conditions will continue through the afternoon
with scattered shower activity. South to south winds will taper off
through roughly 05z, then increase by 09z/10z as the front crosses.
A round of heavier rain will come through with the front, lowering
ceilings for a few hours below 2k feet. Winds will pick up to 20 kt
sustained and 30-35 kt gusts through the morning with continued
showers before easing throughout the afternoon.

15

&&

.MARINE...Winds remain elevated this afternoon behind a strong
frontal passage, with seas building towards 10-13 feet over the
coastal waters. Another strong front will move across the region
later tonight and into Tuesday morning, bringing in even stronger
winds. SCAs will be upgraded to Gale Warnings overnight as winds
continue to increase, especially offshore and through the Strait of
Georgia and into the east entrance of the Strait of Juan de Fuca and
Admiralty Inlet. SCAs will continue across the Puget Sound and
through the western and central Strait of Juan de Fuca. Seas over
the coastal waters will remain above 10 ft and will remain rather
steep through Tuesday, so it is likely Small Craft Advisories for
the coastal waters will continue despite winds easing.

High pressure will build across the coastal waters on Wednesday and
persist into late week for an overall less active weather pattern.
Seas, however, look to build towards 12-14 ft over the coastal
waters on Wednesday, so it is likely headlines will continue. Seas
then look to subside below 10 ft again late in the week, but breezy
northerlies developing over the coastal waters may maintain steeper
seas through the second half of the week.

14/15

&&

.HYDROLOGY...Rivers are rising although at a slower pace this
afternoon with a few rivers like the Snoqualmie at Carnation and the
Skokomish near Potlatch forecast to crest near action stage.
Forecasted rainfall amounts with the second wave of this atmospheric
river event later tonight through Tuesday are for an additional 0.50
to 1 inch along the coast, 1.0 to 1.5 inches in the Olympics, 0.25
to 0.50 inches for the interior and 0.50 to 1 inches in the
Cascades. Rivers will continue to rise through Tuesday but this
break in the action today along with the lower future rainfall
forecast will help lower forecast crest values Tuesday into
Wednesday. The Flood Watch will remain in place to account for
additional swells on the rivers, as well as overland and small
stream flooding on account of some drains being clogged with tree
debris due to overnight wind speeds. Kristell

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Wind Advisory until 11 AM PDT Tuesday for Admiralty Inlet Area-
     Bellevue and Vicinity-Bremerton and Vicinity-Central Coast-
     East Puget Sound Lowlands-Eastern Strait of Juan de Fuca-
     Everett and Vicinity-Hood Canal Area-Lower Chehalis Valley
     Area-North Coast-San Juan County-Seattle and Vicinity-
     Southwest Interior-Tacoma Area-Western Skagit County-
     Western Strait of Juan De Fuca-Western Whatcom County.

     Flood Watch through Wednesday morning for Bellevue and Vicinity-
     East Puget Sound Lowlands-Everett and Vicinity-Hood Canal
     Area-Lower Chehalis Valley Area-Olympics-Seattle and
     Vicinity-Southwest Interior-Tacoma Area-West Slopes North
     Cascades and Passes-West Slopes North Central Cascades and
     Passes-West Slopes South Central Cascades and Passes-
     Western Skagit County.

PZ...Small Craft Advisory until 5 PM PDT this afternoon for Grays
     Harbor Bar.

     Small Craft Advisory until 5 PM PDT Tuesday for Central U.S.
     Waters Strait Of Juan De Fuca-Puget Sound and Hood Canal-
     West Entrance U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory until 8 PM PDT this evening for Admiralty
     Inlet-East Entrance U.S. Waters Strait Of Juan De Fuca-
     Northern Inland Waters Including The San Juan Islands.

     Gale Warning from 8 PM this evening to 5 PM PDT Tuesday for
     Admiralty Inlet-East Entrance U.S. Waters Strait Of Juan De
     Fuca-Northern Inland Waters Including The San Juan Islands.

     Small Craft Advisory until 11 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.

     Small Craft Advisory from 8 AM to 5 PM PDT Tuesday 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.

     Gale Warning from 11 PM this evening to 8 AM PDT Tuesday 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.

&&

$$