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452
FXUS66 KSEW 021049
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
349 AM PDT Sun Jun 2 2024

.SYNOPSIS...
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Atmospheric river pattern setting up over Western
Washington today with the pattern continuing through Tuesday. Two
separate waves of heavier rain will move through the area. The
first one will begin this afternoon and continuing until the early
morning hours Monday. The second one will arrive Monday evening
and continue into Tuesday. The second wave will be weaker than the
first one. An upper level ridge will build over Western
Washington quickly Wednesday. The ridge will remain in place
through at least the weekend bringing dry and much warmer weather
to the region.

...Key Messages for Upcoming Active Weather Pattern...

* A late season atmospheric river pattern will develop today and
  continue with breaks through Tuesday.

* Heavy rainfall amounts of 3 to 5 inches in the mountains, with
  possible 6 inch event totals over the southern slopes of the
  Olympics, and 2 to 4 inches along the coast.

* Moderate to heavy rainfall of 1 to 2 inches across the lowlands
  during this timeframe.

* Snow levels above 6500 feet will promote additional runoff with
  several area rivers flowing out of the Cascades forecast to
  enter action or even minor flood stage. A Flood Watch remains in
  effect across portions of Western Washington.
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.SHORT TERM /TODAY THROUGH TUESDAY/...
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Satellite imagery shows
leading edge of an atmospheric river just off the coast this
morning. This long band of moisture extends all the way back to
near Asia. Rain still offshore as of 3 am/10z. Under cloudy skies
temperatures were on the mild side, in the 50s.

Forecast on track this morning with rain beginning along the coast
this morning spreading inland late morning. PWAT values continue
to be in the 1.0 to 1.2 inch range. If anything the models are a
touch stronger with the 850 mb winds on the 00z run versus
previous runs which will slightly enhance the precipitation over
the mountains. Snow levels rising to 7000 to 8500 feet so only the
higher elevations of the volcanoes will be seeing any snow. With
the clouds and rain temperatures will change little during the day
with highs a couple of degrees either side of 60.

First of the two waves embedded in the atmospheric river moving
through with the area late tonight/ early Monday morning. 24 hour
rainfall totals from this first wave in the 1.5 to 3 inch range in
the mountains, 1.5 to 2 inches along the coast and 0.75 to 1.5
inches over the interior. Good chance most locations in the
interior will see over half the normal monthly June rainfall in
less than 24 hours. Even with the first wave going through the
combination of orographics and and very moist air mass will keep
rain going in the mountains. Rain rates however will decrease
significantly. In the lowlands with the flow aloft becoming west
southwesterly the Central and Northern Puget Sound area could be
rain shadowed for a few hours. Lows tonight near 50.

Second wave of the atmospheric river arriving Monday morning and
continuing into Tuesday morning. The feature will be a little
weaker than the first wave with with PWAT values 0.8 to 1.0 inches
and winds above the surface to around 700 mb a little lighter.
This will give the area less rainfall than the first round, but
still a big amount for the first week of June. Snow levels
lowering but still remaining above the passes. Second waves will
be east of the area Tuesday afternoon with the steady rain winding
down. Rainfall totals for Sunday through Tuesday ranging from 3
to 5 inches in the mountains, with possible 6 inch event totals
over the southern slopes of the Olympics, 2 to 4 inches along the
coast and 1 to 2 inches in the interior. Highs MOnday and Tuesday
near 60 with lows Monday night near 50.

With the heavy rain, burn scars in the Cascades will be closely
monitored through the period.

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...In a version of weather
whiplash, an upper level ridge builds over the area Wednesday with
the ridge remaining in place through the weekend giving Western
Washington dry and increasing warmer weather as we get to the
weekend. 500 mb heights rising into the lower 580 dms by Friday.
Low level flow never turns strongly offshore and model 850 mb
winds don`t turn easterly for much of the period Friday and
Saturday. There are a few ensemble solutions that put highs well
into the 80s Saturday but most of the solutions are are in the
lower to mid 80s. With the lack of strong offshore flow in the
models right now will stay with this idea and keep the warmest
temperatures Saturday in the mid 80s. Highs Wednesday in the mid
60s to lower 70s with 70s to lower 80s by Friday and the mentioned
mid 70s to mid 80s Saturday. Lots of the ensemble solutions are
showing an upper level blocking pattern developing over the
Eastern Pacific over the weekend. Blocks are hard to break down
this time of year. If this pattern does develop Western Washington
could be in for the longest dry spell since last August. Felton
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&&

.AVIATION...
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Southwesterly flow will persist aloft as an upper
level low over the Gulf of Alaska digs southward towards the coast
of southern BC today. At the surface, an approaching frontal
system will bring periods of moderate to heavy rain, lower
ceilings, and gusty winds to the area TAF sites today. Rain looks
to move inland along the coast between 12-15Z and make its way
into the interior terminals between 16-18Z. Southerly surface
winds will increase through the mid to late morning hours,
becoming gusty to 20-25 kts at times. KHQM along the coast could
see some gusts to 30 kt. Conditions currently a mix of VFR and
MVFR across the TAF sites early this morning, though expect a
gradual lowering of conditions down to MVFR over the next couple
of hours. Widespread MVFR conditions expected for much of the day,
with periods of IFR to LIFR possible in moderate to heavy rain.

KSEA...MVFR conditions early this morning. Expect MVFR ceilings to
persist through much of the day, though could see some periods of
IFR or even LIFR in any moderate to heavy rainfall. Rain looks to
move into the terminal between 15-18Z. Southerly winds will increase
to 8-12 kt between 15-17Z and will become gusty to 20-25 kt during
the afternoon hours. Gusty winds will persist through tonight. 14
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&&

.MARINE...
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More active conditions commence across the area waters
today as a strong frontal system approaches the area. Winds have
already started to increase towards small craft strength across
the coastal waters this morning. Guidance does still hint at the
possibility of a few isolated gusts to gale, especially for the
coastal waters south of Point Grenville should a coastal jet
develop ahead of the front. Gusts to gale will also be possible
in the vicinity of the front, but guidance still suggests that
these will be short-lived, with more of the widespread, persistent
gales remaining south of Cape Shoalwater. Thus, have maintained
the small craft advisories in effect for the coastal waters. Seas
will sharply build in response to the winds with this front and
will be rather steep today and will persist into Monday.

Small craft advisories also remain in effect for the eastern
Strait of Juan de Fuca, as southeasterly winds are expected to
ramp up ahead of the front this morning. Expect winds to then
transition to westerly in the wake of the frontal passage late
tonight into Monday. Though winds look marginal, have also issued
an SCA for post-frontal westerlies for the central Strait. May
have to extend SCAs with additional pushes expected down the
Strait through early this week.

SCAs have also been issued for the Northern Inland Waters and
Admiralty Inlet, as latest guidance indicates SCA strength winds
should be widespread in these zones. Have held off on Puget Sound
for now, but will need to monitor this through the day.

Overall, expect the pattern to remain active through the first
half of the week, with yet another frontal system expected to
move across the region on Tuesday. Latest guidance suggests the
winds with this next system could be stronger, with more
widespread gales possible. Seas are expected to build towards
10-13 ft. Wave periods look to remain rather short, near 8
seconds, and will maintain steep seas at times.

High pressure then looks to build into the coastal waters near
midweek for overall calmer conditions the second half of the week.
High pressure will persist into Thursday and looks to interact
with lower pressure inland through late in the week. 14
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&&

.HYDROLOGY...
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Today through Tuesday forecasted rain totals are
still 3 to 5 inches for the Olympics and the Cascades, with the
possibility of 6 inch bullseyes along the southwest slopes of the
Olympics. Snow levels will be in the 7000 to 8500 foot range for
for the first wave of the atmospheric river and just a little
lower for the second round. West southwesterly flow aloft favors
the heaviest rainfall to be along the southwest slopes of the
Olympics and the Central Washington Cascades. Several rivers
flowing out of the Central Cascades and Southern Olympics are
forecast to reach action stage. The river with the best chance to
reach flood stage is the Skokomish River in Mason county. Even
with some of the rivers only reaching action stage, these levels
would be records for this time of the year. The flood watch for
Skagit, Snohomish, King, Pierce, Mason and Lewis county remains in
effect.

In addition to the high flows on area rivers, the water
temperatures in the rivers continues to be very cold. Most rivers
flowing out of the Cascades are still in the mid 40s to lower 50s
for water temperature. Felton
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&&

.CLIMATE...
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Here are some daily rainfall records for around the
area today, Seattle 0.48 inches in 2001, Olympia 0.68 inches in
2010, Bellingham 0.48 inches in 1962, Quillayute 1.63 inches in
2010 and Hoquiam 1.35 inches in 1962. Felton
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&&

.SEW WATCHES/WARNINGS/ADVISORIES...
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WA...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 from 8 PM this evening to 2 AM PDT Monday
     for Central U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory from 8 AM this morning to 2 AM PDT Monday
     for East Entrance U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory from 8 AM this morning to 8 PM PDT this
     evening for Admiralty Inlet-Northern Inland Waters
     Including The San Juan Islands.

     Small Craft Advisory until 5 AM PDT Monday 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.
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&&

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