Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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942
FXUS66 KSEW 031915 AAA
AFDSEW

Area Forecast Discussion...UPDATED
National Weather Service Seattle WA
1215 PM PDT Mon Jun 3 2024

.SYNOPSIS...First wave in this atmospheric river event moving into
the Cascades early this morning. Upper level trough over the area
this morning moving east by afternoon. Increasing low level
onshore flow this morning with convergence zone near East Entrance
to the Strait of Juan de Fuca. Second wave arriving later tonight
with the wave moving through Tuesday. Upper level ridge building
over Western Washington Wednesday through Friday. Ridge shifting
east Saturday with a weak upper level trough Sunday.

&&

.UPDATE...Convergence showers across Snohomish/Skagit counties
are weakening (there were rainfall rates of up to an inch an hour
this morning). A Wind Advisory was issued through Tuesday morning
for all lowland areas. There are increasing probabilities that we
will see wind gusts exceeding 40 mph in several areas. See the
full discussion below for further details.

HPR

&&

.SHORT TERM /TODAY THROUGH WEDNESDAY/...Satellite imagery shows
first wave of this atmospheric river event moving into the
Cascades early this morning with rain ending behind the wave.
Temperatures at 3 am/10z were mostly in the mid 50s.

First wave in atmospheric river event will be east of the area
later this morning. Fast moving upper level trough behind the wave
moving through Western Washington this morning keeping showers in
the forecast. There was a lightning strike offshore earlier this
morning. Cloud top temperatures showing no signs of cooling on
the satellite imagery and the trough will move through quickly
so have left the mention of thunderstorms out of the forecast.
Convergence zone developing near the East Entrance to the Strait
later this morning with increasing low level onshore flow behind
the trough. Breezy southerly winds will peak midday then slowly
ease this afternoon. The convergence zone looks to stay in place
for most of the day extending eastward into the Cascades. Not much
change in temperatures with highs near 60.

Rain out ahead of the second wave in this atmospheric river event
arriving along the coast this evening with the rain spreading
inland overnight. This wave is not as juicy as the first one with
PWAT values peaking near 1.0 inches for a few hours. The first
wave had PWAT values as high as 1.4 inches. Lows tonight in the
50s.

Second wave moving through Western Washington late Tuesday making
for another wet June day. Rainfall amounts with this feature
forecasted to be from 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 inch in the Cascades. Snow levels will still be
elevated, at least 6000 feet for most of the event so the
precipitation will fall mainly as rain in the mountains.

Showers behind the second wave drying up pretty fast Tuesday night
as the weather pattern over the area begins to make a quick
transition to drier and warmer. With less cloud cover by Wednesday morning
lows will drop into the 40s.

Upper level ridge building over Western Washington Wednesday
clearing skies out and warming daytime temperatures. 500 mb
heights in the 570 dms by late Wednesday afternoon. Highs getting
back to near normal, mid 60s to lower 70s.

.LONG TERM /THURSDAY THROUGH SUNDAY/...The idea of a blocking
upper level pattern setting up over the Eastern Pacific this
weekend only lasted a model run or two. Models in good agreement
that the upper level ridge will continue to build Thursday and
Friday with 500 mb heights in the lower to mid 580 dms Friday
afternoon. Low level flow never really turns offshore and 850 mb
winds do not turn easterly for any significant length of time. The
lack of offshore flow will keep temperatures from getting too
warm with highs Thursday in the mid 60s to mid 70s and Friday in
the 70s to lower 80s. Models also in good agreement with the upper
level ridge axis shifting into Eastern Washington Saturday and a
weak upper level trough moving through Western Washington Sunday.
With the trough will mention a slight chance of showers in the
Cascades. For the lowlands highs cooling from the 70s and lower
80s Saturday to the mid 60s to mid 70s Sunday.

Felton

&&

.AVIATION...Mainly MVFR with post-frontal showers continuing to
stream inland this morning. Conditions look to remain more
widespread MVFR through much of the morning and afternoon, though
could see some slight improvement towards VFR for interior terminals
near 00Z. However, temporary reductions to IFR and even LIFR
conditions cannot be ruled out in any heavier shower activity in the
vicinity of any area terminals. Southerly surface winds look to
remain breezy through much of the day, with gusts up to 30-35 kt
possible into the evening before a stronger front brings gustier
winds and more widespread rain, which will reach the coast between
00z-03z.

KSEA...Primarily MVFR conditions will persist in steady rain
through the morning hours, however could see temporary reductions
to IFR in heavier showers though the day. A brief rebound to VFR
will be possible by late afternoon, before ceilings look to lower
back towards MVFR tonight as another front approaches. Southerly
winds look to remain breezy, with gusts to 30 kt expected at times
through the day.

14/15

&&

.MARINE...A strong frontal system continues to push inland
this morning, maintaining gusty winds to most area waters. The
current small craft advisories for the Coastal Waters, Puget Sound,
and the Eastern Strait of Juan de Fuca remain in good shape and
continue to cover current conditions as the front progresses
eastward. Multiple rounds of SCA strength westerlies look likely
over the next 24-36 hours, with brief lulls in between, so can
expect additional small craft issuance or extensions at times for
the Strait through Tuesday. In addition to the breezy winds, seas
across the coastal waters have remained rather steep this
morning, and generally persist at 8 to 9 feet at 8 seconds. Seas
will then build towards 10-13 feet over the coastal waters
throughout the day.

Another strong front will move across the region on Tuesday.
Guidance continues to suggest that the winds with this system will
be stronger, with more widespread gales possible, so have issued
a Gale Watch for the Coastal Waters, the eastern Strait, and the
Northern Inland Waters through Tuesday morning. Winds will
gradually ease through the afternoon and evening hours. 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 then 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 12-15 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

&&

.HYDROLOGY...Rainfall amounts with the first wave of this
atmospheric river event were as follows, 1 to 2 inches along the
coast, 1.5 to 3 inches in the Olympics, 0.50 inches to an inch in
the north half of the interior with 0.75 inches to 1.5 inches in the
southern half of the interior and 1.5 to 2.5 inches in the Cascades.
Rivers are rising this morning with a few rivers like the Snoqualmie
at Carnation and the Skokomish near Potlatch forecast to crest above
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.

Felton/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-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 8 PM PDT this evening for Central
     U.S. Waters Strait Of Juan De Fuca-East Entrance U.S.
     Waters Strait Of Juan De Fuca.

     Gale Watch from late tonight through Tuesday morning for East
     Entrance U.S. Waters Strait Of Juan De Fuca-Northern Inland
     Waters Including The San Juan Islands.

     Small Craft Advisory until 2 AM PDT Tuesday for Northern Inland
     Waters Including The San Juan Islands.

     Small Craft Advisory until 11 AM PDT Tuesday for Admiralty Inlet.

     Small Craft Advisory until 5 AM PDT Tuesday for Puget Sound and
     Hood Canal.

     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.

     Gale Watch from this evening through late tonight 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.

&&

$$