391
FXUS66 KSEW 031157 CCA
AFDSEW

Area Forecast Discussion...CORRECTED
National Weather Service Seattle WA
457 AM 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.

&&

.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...An upper level low off the coast of BC this morning
will swing across the Pacific Northwest today, allowing for
southwesterly flow aloft to become more westerly through the day.
At the surface, a frontal system just offshore early this morning
will continue to push inland over the next few hours. Moderate to
heavy rain, lower ceilings, and gusty winds will persist through
the early morning hours, with more widespread precipitation
transitioning to scattered showers near mid morning in the wake of
the front. 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 to 25 kt possible. Another
front will approach the region tonight, bringing another round of
more widespread rain, which is expected to reach the coast between
00-03Z. Southerly surface winds will become gusty again tonight
into Tuesday.

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 25 kt expected at
times through the day. 14

&&

.MARINE...A strong frontal system continues to push inland early
this morning, still bringing gusty winds to portions of the 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. Guidance still indicating a marginal push of
post-frontal westerlies along the Strait today, so have added a
Small Craft Advisory for the central Strait through this evening.
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 issuances 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. Will keep the
flood watch up for one more run of the river models this morning.
If the forecast trend continues look for the watch to be taken
down later today. Felton

&&

.CLIMATE...Record daily rainfall records were broken Sunday in
Seattle 0.65 inches versus old record of 0.48 inches in 2001,
OLympia 1.08 inches versus the old record of 0.68 inches set in
2010 and at Hoquiam with 1.87 inches breaking the old record of
1.35 inches set in 1962. The 1.87 inches in Hoquiam was the
wettest June day on record. The old record wettest June day in
Hoquiam was 1.77 inches on June 8th, 1956. The 1.08 inches at
Olympia was the 6th wettest June day. The record is 1.60 inches
set on June 6, 1985. Felton

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
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 until 5 PM PDT this afternoon for Grays
     Harbor Bar.

     Small Craft Advisory from 8 AM this morning to 8 PM PDT this
     evening for Central U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory until 8 PM PDT this evening for 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 from 1 PM this afternoon to 2 AM PDT
     Tuesday for Northern Inland Waters Including The San Juan
     Islands.

     Small Craft Advisory from 11 PM this evening to 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.

&&

$$