641
FXUS66 KSEW 061042
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
342 AM PDT Sat Jul 6 2024

.SYNOPSIS...Upper level ridge centered offshore will move over
Western Washington Monday into Tuesday. The center of the ridge
will shift east of the area Tuesday night with Western Washington
remaining on the back side of the ridge Wednesday. Weak trough
moving through Thursday with southwesterly flow aloft Friday.
High temperatures for the interior peaking Monday and Tuesday
while the coast begins to cool down. Increasing low level onshore
flow will cool temperatures in the interior Wednesday but highs
will still be above normal.

&&

Key Messages:

* HEAT...Continued warming will lead to hot conditions into next
  week. Temperatures will peak Monday and 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, ending Sunday evening for the coast, and Tuesday
  evening elsewhere.

* FIRE WEATHER...Increasing dry and unstable conditions for this
  weekend has warranted the issuance of a Red Flag Warning for the
  Cascades through Tuesday. Fuels are drying out rapidly across
  the area. It is possible the Southeast Puget Sound lowlands may
  be added to the warning Sunday or Monday. See the Fire Weather
  discussion below for details.

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

Little change in the pattern today with the upper level ridge
with the ridge axis offshore, remaining over the area. Light
northerly gradients in the lower levels. Cross Cascade gradients
never do turn negative this afternoon and 850 mb winds continue to
be light northwesterly. Temperatures aloft also showing little
change with 850 mb temperatures in the plus 18C to plus 22C
range. Similar daytime warming today versus yesterday but with
morning lows this morning slightly warmer expecting high
temperatures to be a couple of degrees warmer than Friday. For the
interior highs in the 80s to mid 90s with upper 70s to mid 80s
along the coast.

Upper level ridge axis starts to drift towards Western Washington
tonight and Sunday with the ridge axis close to the coast by 00z
Monday. Even with the ridge axis approaching, temperatures aloft
not warming with 850 mb temperatures remaining in the 18C to 22C
range. Winds at 850 mb also remaining northwesterly. Highs once
again for the interior in the 80s to mid 90s with upper 70s to
mid 80s along the coast. Low temperatures Sunday morning in the
Seattle metro area in the mid 60s. For the remainder of the area
mid 50s to lower 60s.

Upper level ridge axis moving over Western Washington Sunday night
into Monday. Thermally induced surface trough moving up the
coastline Sunday night will shift inland Monday. The increasing
onshore flow along the coast will result in high temperatures
in the early afternoon hours, mid 70s to lower 80s. For the
interior with the thermally induced trough in the area surface
gradients will go flat allowing high temperatures to warm another
couple of degrees. Warmer locations like the Southwest Interior
and Cascade foothills could get into the upper 90s. For the
rest of the interior highs in the mid 80s to mid 90s. Low
temperatures Monday morning similar to Sunday morning with mid
60s in the Seattle metro area and mid 50s to lower 60s elsewhere.

.LONG TERM /TUESDAY THROUGH FRIDAY/...While the deterministic
models move the upper level ridge axis east of the area Tuesday
the ensembles are a little slower with this process. This will
keep highs in the interior Tuesday near the readings Monday, mid
80s to upper 90s. The increasing difference in temperature between
the coast and the interior will increase the onshore flow along
the coast cooling high temperatures there into the lower to mid
70s.

The combination of the upper level ridge moving east and a very
weak shortwave riding by well to the north will increase the low
level onshore flow over the interior Tuesday night and Wednesday.
The increasing onshore flow will cool high temperatures Wednesday
around 10 degrees for the interior with mid 70s to mid 80s in the
forecast. Highs along the coast will also continue to cool, back
into the 60s. The increasing onshore flow will cool morning lows
Wednesday into the 50s and lower 60s.

Very weak upper level trough moving through Western Washington
Thursday. 500 mb heights only lowering to the lower to mid 580
dms. The trough will maintain the low level onshore flow pattern
keeping highs in the mid 70s to mid 80s for the interior and in
the 60s along the coast.

Southwesterly flow aloft Friday with low level onshore flow
continuing. Persistence a good forecast with little change in the
temperatures from Thursday. Felton

&&

.AVIATION...VFR conditions will continue with light winds and clear
conditions as high pressure continues to build over the region.

KSEA...VFR. North surface winds generally 6 kt or less overnight,
increasing to 8-12 kt this afternoon.

15

&&

.MARINE...High pressure will continue to build over the area waters,
resulting in north to northwest winds over the area waters. Fairly
benign conditions will continue over the weekend and into early next.

A surface front will move across the region on Wednesday, bringing
in stronger pushes through the Strait of Juan de Fuca and bringing
stronger northerly winds over the offshore waters. These elevated
winds are likely to persist through the end of next week as a more
progressive weather pattern returns.

Seas generally 4 to 6 feet into the weekend and through early next
week, rising to 6 to 8 feet towards the second half of next week.

15

&&

.FIRE WEATHER...One of the most concerning things about this spell
of hot weather is the rapid drying out of fuels across Western
Washington, especially in the interior.

Red flag warning will remain in effect through Tuesday for fire
weather zone 658 ( West Slopes of the North Cascades Generally
above 1500 Feet ) and fire weather zone 659 ( West Slopes of the
Central Cascades Generally above 1500 Feet ) with hot, dry and
unstable conditions. Fuels are quickly reaching critical
thresholds of dryness in other parts of Western Washington. The
most concerning is the Southeast Puget Sound foothills. Minimum
relative humidity values Sunday through Tuesday could drop below
20 percent. If the trends continue look for a watch or possible
Red Flag warning to be issued for this location as well as early
as Sunday.

Critical relative humidity values are also possible in the
Olympic Mountain valleys through the weekend but at this point
does not look to be widespread enough to add this area to the
warning. Decent relative humidity recovery for the Olympic and
coastal zones Monday but interior zones will have to wait until
Tuesday night into Wednesday to see some improvement.

Let`s be careful out there! Felton

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Heat Advisory until 10 PM PDT Tuesday 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.

     Red Flag Warning from 11 AM this morning to 11 PM PDT Tuesday
     for West Slopes of the Central Cascades Generally above
     1500 Feet-West Slopes of the North Cascades Generally above
     1500 Feet.

PZ...None.
&&

$$