305
FXUS66 KSEW 051629
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
929 AM PDT Fri Jul 5 2024

.UPDATE...An upper ridge will continue to build offshore today for
dry conditions, and warming temperatures. Temperatures today will
reach the 80s with low 90s primarily south of King County and
across the Chehalis Valley. Make sure to stay hydrated! No major
forecast updates this morning.

&&

.SYNOPSIS...Very warm week ahead for Western Washington as an
upper level ridge slowly drifts over the area. Temperatures will
peak Sunday through Tuesday with highs over the interior in the
mid 80s to near 100. The ridge will slowly exit to the east making
for a gradual cooling trend in the middle of next week.

Key Messages,

* HEAT...Continued warming will lead to hot conditions beginning
  today. Temperatures peaking Monday and possibly into Tuesday
  for the interior in the upper 80s to near 100. Highs will be
  cooler along the coast. A Heat Advisory is in effect for the
  entire region beginning this afternoon, ending Sunday evening
  for the coast, Monday evening elsewhere. If the trend continues
  the heat advisory for the interior will be extended into
  Tuesday.

* FIRE WEATHER...Increasing dry and unstable conditions for this
  weekend has warranted the issuance of a Fire Weather Watch for
  the Cascades. These conditions could also extend into Monday
  and Tuesday. See the Fire Weather discussion below for details.

&&

.SHORT TERM /TODAY THROUGH SUNDAY/...Satellite imagery shows
clear skies over Western Washington with an upper level ridge
building well offshore. Temperatures at 3 am/10z were in the mid
50s to mid 60s.

Upper level ridge offshore continuing to build today through
Saturday. Ridge axis near 130W this morning will drift east
towards the coast but will still be offshore by 00z Sunday. 500 mb
heights in the mid 580 to lower 590 dms. Low level flow remaining
light northerly with the cross Cascade gradient remaining positive
into Saturday afternoon. Winds above the surface to 850 mb also
never turn easterly. Temperatures aloft warming with 850 mb
temperatures in the plus 18C to plus 22C range late this
afternoon. Little change in the temperatures aloft tonight and
Saturday. High temperatures today warming by about 5 degrees
across the area with 80s and lower 90s over the interior and upper
70s to mid 80s along the coast. Lows tonight in the mid 50s to
lower 60s. Highs Saturday similar to today.

Upper level ridge drifting east Saturday night and Sunday with
the ridge axis right off the coast by late Sunday afternoon. High
temperatures warming over the interior slightly Sunday with 80s to
mid 90s. Highs along the coast remaining in the upper 70s to mid
80s. Lows also slightly warmer Saturday night with upper 50s to
mid 60s interior and mid to upper 50s coast.

.LONG TERM /MONDAY THROUGH THURSDAY/...Extended model ensembles
in good agreement trending towards slower eastward movement of
the upper level ridge with the ridge axis not completely east of
the area until Tuesday night. This scenario would make high
temperatures Tuesday similar to Monday. 850 mb temperatures
peaking in the plus 22C to plus 26C late Monday into Tuesday.
Surface thermally induced trough over Western Oregon moving into
Western Washington Monday and Tuesday shifting east of the
Cascades Tuesday night. Highs both days for the interior upper 80s
to near 100. Thermally induced surface trough inland enough to
keep highs along the coast in the 70s. Lows will start to get a
little uncomfortable in the urban areas with mid 60s common. Lows
in the remainder of the area in the mid 50s to lower 60s.

Very weak shortwave moving by well to the north Wednesday into
Thursday. This combined with the upper level ridge axis to the
east will induce a little low level onshore flow cooling high
temperatures Wednesday and Thursday. With the shortwave well to
the north the marine layer/onshore push will not be that strong.
High temperatures for the interior cooling into the mid 70s to
upper 80s Wednesday with a couple more degrees of cooling
Thursday. Highs along the coast lowering to the mid 60s to lower
70s. With the low level flow onshore low temperatures will return
to a more comfortable 50s and lower 60s. Felton

&&

.AVIATION...High pressure and offshore flow will lead to a dry
and stable air mass across western WA with VFR conditions for the
TAF period.

KSEA...VFR and clear with north winds generally 6 to 12 kt.

15/Maz

&&

.MARINE...Light offshore flow through the weekend with a thermal
trough along the coast. The flow will turn onshore Monday and
Tuesday with stronger westerly pushes down the strait.

Seas generally 4 to 6 ft through the weekend and into early next
week.

15

&&

.FIRE WEATHER...Strengthening upper level ridge settling over the
region beginning today and continuing into the early next week.
Surface gradients light northerly through the weekend. High
temperatures rising today through Sunday with the highs Sunday in
the watch zones in the 80s and lower 90s. With the air mass drying
out critical RH values are likely over the Cascades with possibly
some isolated areas within the Olympic Mountain valleys over the
weekend. The hot and dry setting will be enough to create elevated
fire weather conditions especially with fuels expected to rapidly
dry out in the next couple of days. The air mass will be unstable
over the Cascades but the lack of moisture will keep the threat
of convection minimal. The Fire Weather Watch for dry and unstable
conditions remains in effect for fire weather zones 658 and 659
Saturday and Sunday.

Model trends are pushing back the improving fire weather
conditions into Monday and possibly Tuesday. While RH recoveries
will improve over the coastal fire zones beginning Monday with a
thermally induced surface trough over the interior enhanced fire
weather conditions could continue especially in the Cascades into
Tuesday. Felton

&&

.CLIMATE...Record high temperatures for Seattle, Sunday 90 degrees
(2010), Monday 95 degrees (2010), Tuesday 93 degrees (2010).
Record highs for Olympia 95 degrees each day (1953), (2010) and
(1985). Record highs for Bellingham 88 Sunday and Monday (1953)
and (2010), Tuesday 85 degrees in 1979.

Record high low temperatures also possible for Seattle Sunday
through Tuesday with the record 64 degrees Sunday (2014), 63
Monday (2010) and 63 Tuesday (2006). Felton

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Heat Advisory until 10 PM PDT Monday for Admiralty Inlet Area-
     Bellevue and Vicinity-Bremerton and Vicinity-East Puget
     Sound Lowlands-Eastern Strait of Juan de Fuca-Everett and
     Vicinity-Hood Canal Area-Lower Chehalis Valley Area-
     Olympics-San Juan County-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-
     Western Whatcom County.

     Heat Advisory until 10 PM PDT Sunday for Central Coast-North
     Coast-Western Strait of Juan De Fuca.

     Fire Weather Watch from Saturday morning through Sunday evening
     for West Slopes of the Central Cascades Generally above
     1500 Feet-West Slopes of the North Cascades Generally above
     1500 Feet.

PZ...None.
&&

$$