FXUS66 KSEW 052221

Area Forecast Discussion
National Weather Service Seattle WA
321 PM PDT Mon Jun 5 2023

.SYNOPSIS...Upper level troughing will continue to influence the
region tonight into Tuesday before an upper level ridge nudges into
the region Tuesday afternoon. Dry conditions, unseasonably warm
temperatures, and elevated fire conditions will persist across much
of western Washington into Thursday. Upper level troughing then
looks to become the dominant influence again later in the week for
cooler temperatures and increased shower chances.


skies across the region this afternoon, with temperatures ranging in
the 60s to the low 70s. Afternoon highs are expected to remain
rather seasonal today with an upper level trough to the north of the
area and look to generally top out in the mid 60s to mid 70s across
western Washington. Breezy northerly winds will continue through the
evening hours, before easing overnight.

Upper level troughing will continue to influence the region into
early Tuesday, before ridging starts to nudge into the region
Tuesday afternoon from a strong area of high pressure situated over
the northern Plains and Canada. At the surface, a thermal trough
over Oregon and northern California will creep northward into the
area. Temperatures will rise a couple of degrees as a result,
primarily topping out in the upper 70s to mid 80s. Latest guidance
still indicates Tuesday will be the hottest day along the coast.
Northerly winds will pick up through the day, becoming breezy during
the late morning to afternoon hours. Dry and unstable conditions
accompanied by breezy winds will yield elevated fire weather
conditions across portions of the region. See the fire weather
section below for more details.

Upper level ridging then looks to amplify on Wednesday, allowing for
temperatures to climb roughly 10 to 15 degrees above normal for the
interior. Highs generally look like they will top out in the upper
70s to mid 80s across the majority of western Washington - with the
warmest temperatures expected along the Chehalis River Valley, the
Cascade foothills, and along the south Sound. The coast, however,
will be cooler under the influence of onshore flow - with
temperatures generally expected to top out in the low 70s. 14

.LONG TERM /THURSDAY THROUGH MONDAY/...Main focus is a cool down
after Wednesday with the chance of showers Friday through the
weekend. Upper level patterns continue to show an omega block over
the central CONUS with troughing still over the west coast. By
Thursday a low is ejected from a trough over the Pacific Ocean into
the coast of CA with a couple of weak shortwaves passing through the
PNW. This retrogrades the high over the Central Plains slightly to
the west. With this change the trough will progress slightly
eastward which should help bring temperatures below or around
average from Thursday through the weekend with most places seeing
60s. Some weak vorticity advection involved with the slight pattern
change this weekend along with the marine push leads to the
possibility of showers Friday into the weekend. These showers are
mostly orographic in nature staying primarily over the Cascades but
some of the showers could reach the Puget Sound lowlands. QPFs had
the Cascades receiving the most rain with up to 0.5 inches possible,
remaining areas see less than a tenth of an inch of precipitation.



.AVIATION...West-southwest flow aloft will continue with weak
ridging building into the area and an upper low over California.
Clear skies will continue through tonight with a few high clouds at
times this afternoon. North-northeast winds will continue tonight,
peaking this afternoon and evening before tapering off a bit tonight
into Tuesday morning. Gusts of 20-25 kts possible into this evening.

KSEA...Mostly clear, with a few VFR high clouds. North-northwest
winds remaining breezy into this evening before transitioning more
northeast tonight. JD


.MARINE...North-northwesterly gradient winds will continue through
through Tuesday with winds peaking each afternoon and evening
period. Small Craft Advisory winds will continue for the outer
Coastal Waters through Tuesday evening, likely tapering Wednesday
morning. In addition, winds will briefly subside for the inner
coastal waters late tonight into Tuesday morning before increasing
again Tuesday afternoon and evening. Continued northwesterly SCA
winds for the northern inland waters through Tuesday, with the
strongest winds north of the San Juan Islands.

Onshore flow will begin to increase Wednesday night with likely
Small Craft Advisory winds for the central and eastern Strait of
Juan de Fuca. Onshore flow will increase further Thursday evening
into Thursday night with elevated winds for the Strait and at least
the potential for gales, current probabilities around 10-20% for
gale force gusts in this area.

Seas generally ranging 5 to 8 feet through Tuesday, with seas up to
9 feet possible for the outer coastal waters. JD


.FIRE WEATHER...Dry and breezy conditions persist across the area
this afternoon as a thermal trough builds north along the CA and OR
Coast and high pressure resides across central BC and westward
across the far NE Pacific. Fire weather conditions remain elevated
in response to these conditions, with widespread RH values in the 20-
40% range this afternoon. While fire starts remain possible across
the entire area, the highest threat for isolated red flag conditions
through the rest of today remains across areas south of Puget Sound
to the OR border and across the southern Cascades, where RH values
remain lowest in tandem with breezy N winds in the 10-15mph range.

Some recovery is expected overnight as RH values reside in the 50-
70% range. The thermal trough will build north along the Coast on
Tuesday, with higher pressure maintaining itself to the north and to
the west over the open ocean. Gradients will relax some in response
to this, but will still maintain a northerly component generally in
the 5-10mph range, with slightly breezier conditions in the 10-15
mph range along Puget Sound and into the SW Interior. Winds may
shift to the east over the Cascades at 10 mph or less. While
slightly less breezy than Monday, winds will still be strong enough
that when combined with another afternoon of RH values in the 20-40%
range, fire weather conditions will be elevated again area-wide. In
addition to low RH values and breezy winds, the mid-level Haines
index will reach 6 east of Puget Sound into the Cascades. When
factoring all these conditions together, in addition to evaluating
current ERC values, red flag conditions appear probable across the
Southern and Central Cascades. As such, a warning has been issued
for much of Tuesday. It should be emphasized still that fire starts
and spreads still remain favorable area-wide!

By Wednesday, onshore flow will increase along the coast, pushing
the thermal trough towards Puget Sound. Hot afternoon temperatures
will materialize as this feature resides below a upper level ridge.
RH values from the Olympics, through the lowlands, and into the
Cascades will remain low on Wednesday, with mid-level Haines at 5-6
across this entire area. This will continue to make for favorable
fire weather conditions, with isolated red flag criteria possible,
especially across the Southern and Central Cascades and areas south
and east of Puget Sound.

An onshore push of marine area will spread further inland Wednesday
night into Thursday, helping promote a noticeable recovery in RH.
Fire weather conditions will become less favorable across the
lowlands and Olympic Peninsula on Thursday, however, unstable and
dry conditions will persist over the Cascades, possibly maintaining
elevated fire concerns. The chance for convection may then also
increase across the Cascades Friday into the weekend, which could
create a threat for lightning-induced fire starts. Confidence in
this scenario is currently low and will be monitored in the coming



.HYDROLOGY...The daily hydrology discussion has ended until the
start of the next rainy season; it will only be updated as needed.


WA...Red Flag Warning from 10 AM to 10 PM PDT Tuesday for West Slopes
     of the Central Cascades Generally above 1500 Feet.

PZ...Small Craft Advisory until 11 AM PDT Tuesday for Northern Inland
     Waters Including The San Juan Islands.

     Small Craft Advisory until 8 PM PDT this evening for Puget Sound
     and Hood Canal.

     Small Craft Advisory until 2 AM PDT Tuesday for Coastal Waters
     From Cape Flattery To James Island Out 10 Nm-Coastal Waters
     From James Island To Point Grenville Out 10 Nm-Coastal
     Waters From Point Grenville To Cape Shoalwater Out 10 Nm.

     Small Craft Advisory until 11 PM PDT Tuesday for Coastal Waters
     From Cape Flattery To James Island 10 To 60 Nm-Coastal
     Waters From James Island To Point Grenville 10 To 60 Nm-
     Coastal Waters From Point Grenville To Cape Shoalwater 10
     To 60 Nm.



NWS SEW Office Area Forecast Discussion

Discussion Script by Ken True at Saratoga Weather - WFO Script by SE Lincoln Weather