567
FXUS66 KSEW 080920
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
220 AM PDT Mon Jul 8 2024

.SYNOPSIS...Unseasonably hot conditions will continue through
the first half of the week under a strong upper level ridge. Some
relief is expected mid-week as the ridge pivots eastward and
weekend, though above normal temperatures and dry conditions will
persist through the forecast period.

* HEAT...Warming will continue through Tuesday, with temperatures
  nearing or surpassing daily records across much of the lowlands
  apart from the coast. A Heat Advisory remains in effect for the
  entire region, ending Tuesday morning along the coast and
  Tuesday evening elsewhere.

* FIRE WEATHER...Dry, hot, and unstable conditions have led to a
  Red Flag Warning for the Cascades through Tuesday evening.
  Fuels across the area continue to dry out rapidly, raising fire
  weather concerns for much of the region.

&&

.SHORT TERM /TODAY THROUGH WEDNESDAY/...Hot and dry conditions
will continue to intensify across western Washington to start the
week as a strong high pressure ridge remains firmly in place over
the southwestern US. High temperatures will increase a few
degrees today and again into tomorrow, with areas of Moderate
(orange) to Major (red) HeatRisk for much of the region apart from
the coast. Overnight low temperatures will also remain elevated
in the mid 60s for much of the lowlands, providing little relief
from the hot daytime temperatures.

The upper ridge axis will slowly push eastward through Tuesday,
allowing for weak onshore winds to develop along the coast.
However, a thermal trough building overhead will keep inland areas
hot with little in the way of surface winds to cool things off.
Warming will continue today and again into Tuesday, allowing
temperatures to peak roughly 15-20 degrees above normal with much
of the region seeing highs in the mid 90s. Additionally, a
strengthening subsidence inversion over the mountains will
maintain warmer conditions over the Cascades. Despite clear skies,
temperatures Tuesday morning will stay well above normal in the
mid 60s and providing a warm starting point for even warmer
temperatures Tuesday afternoon.

Temperatures are on track to continue to increase throughout the
day Tuesday for inland areas, which will be the hottest day of
the period, peaking in the upper 90s for most lowlands surrounding
the Puget Sound. Areas southeast of the Sound will also see a
moderate chance (30% to 40% probability) of temperatures reaching
100 degrees. Several daily high temperature records will likely be
broken Tuesday. However, areas along the coast will see a
different story as onshore flow continues to develop as the ridge
shifts eastward, allowing temperatures along the shores to begin
to moderate. Some uncertainty remains over how strong the onshore
flow will be once it develops, and areas as far as Chehalis,
Olympia, and Shelton may see some moderation in temperatures by
early Wednesday morning.

Forecast models show good agreement over conditions finally
beginning to cool down on Wednesday as a weak shortwave brings
onshore flow further inland. Inland areas will see highs in the
upper 80s, still roughly 10-15 degrees above normal, but enough
for HeatRisk to decrease into the Minor (yellow) category for
most areas outside of the Seattle/Tacoma metro areas. Areas of
urban heat stress may persist on Wednesday, especially after
another night of elevated temperatures, and the need for heat
related headlines continues to be monitored for areas from
Seattle east into the Cascade valleys.

.LONG TERM /THURSDAY THROUGH SUNDAY/...Warm temperatures are
favored to continue through the rest of the week as western
Washington remains on the periphery of a strong ridge drifting
eastward over the southern US. While light onshore flow will keep
the coast in the low 70s, areas inland will see highs in the low
to mid 80s through the period. Ensembles also remain in good
agreement over dry conditions through the week, with virtually no
signal of incoming precipitation.

Lindeman

&&

.AVIATION...A strong upper ridge remains in place over Western
Washington with light west to northwest flow aloft. Clear skies will
prevail apart from a very shallow marine layer along the immediate
coast which may produce some tempo LIFR/IFR conditions at KHQM this
morning.

KSEA...Clear skies. Surface winds N/NE 5 to 10 knots backing to NW
this afternoon.

27

&&

.MARINE...Thermally induced low pressure remains in place across the
interior of Western Washington with broad surface ridging over the
coastal and offshore waters. Onshore flow is light. By midweek, the
surface ridge offshore will strengthen and the thermal trough will
shift east of the Cascades in response to a weak weather system
passing well north of the area. This will lead to an increase in
onshore flow by Tuesday night into Wednesday. Small craft advisory
westerlies are expected in the central/east strait by Tuesday
evening with possible gales Wednesday afternoon/evening. Small craft
advisory conditions are also expected for the second half of the
week over the outer coastal waters with the expected increase in
onshore flow.

27

&&

.FIRE WEATHER...Strong high pressure will continue to bring very
warm and dry conditions to the region. Instability over the
Cascades will allow the Red Flag Warning for the Cascade Zones
(658 and 659) to continue unchanged. Elsewhere, critical afternoon
relative humidities will persist for the lower elevations and
foothills south and east of the Puget Sound, but uncertainty
remains over fuel readiness and instability paired with relatively
calm winds and the threat for critical fire weather conditions
will continue to be monitored for these areas. Onshore flow will
bring somewhat higher humidities for the coastal and Olympics
zones Monday, but it could be as late as Wednesday before portions
of the Cascades see notable improvement.

15

&&

.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 11 AM PDT Tuesday for Central Coast-North
     Coast-Western Strait of Juan De Fuca.

     Red Flag Warning until 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.
&&

$$