A strong upper level ridge of high pressure began to build into the region around August 11, remaining in place through August 13 before pushing eastward. As the upper level ridge influence increased over the region, the lower level flow turned easterly, creating a downsloping effect across much of Western Washington.
Deaths and injuries are direct and indirect together, as the offices filed them. Damage is property and crops in the dollars of the year, not adjusted for inflation, and only where an office estimated it.
The episode as NWS SEW wrote it up.
A strong upper level ridge of high pressure began to build into the region around August 11, remaining in place through August 13 before pushing eastward. As the upper level ridge influence increased over the region, the lower level flow turned easterly, creating a downsloping effect across much of Western Washington. As a result of this setup, very warm temperatures were forecast for most of the area, with 850mb temperatures expected to peak near 25C during the heart of the event, with surface temperatures ranging from the mid 80s to near 100 and low temperatures during the overnight period ranging from the mid 60s to low 70s.
Excessive Heat Watch was issued on August 8, several days prior to the event, valid for all included zones beginning 12PM on Wednesday August 11 and continuing for some zones through Friday August 13 at 8PM and others Saturday August 14 at 7PM. The Watch was upgraded to a warning during the afternoon of August 10.
Fire weather was also a concern during the event, along with air quality impacts from smoke, however, no major impacts were noted during the period of unusually warm weather.
The local office's own words before the first event, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.
NWS Seattle, WA wrote its last area forecast discussion before the first event at Aug 11, 8:24 AM PST, 3 hours 36 minutes earlier.
Area Forecast Discussion
National Weather Service Seattle WA
924 AM PDT Wed Aug 11 2021
.UPDATE /0900 AM/...The newest heatwave is beginning today, with
temperatures expected to be in the 90s for the interior and 80s
near the waters. Hot temperatures will continue through the rest
of the week. Not much relief is expected during the overnight in
the interior as low temperatures are expected to be in the upper
60s. We urge people to take proper heat precautions during this
time. These can include not doing strenuous activity during the
hottest parts of the day, staying cool and keeping hydrated.
The previous forecast with updated aviation and marine sections
are below.
Butwin
&&
.SYNOPSIS...Upper level ridge over the area through Friday with
the ridge centered over Western Washington Thursday. The ridge
will move southeast over the weekend. High temperatures warming
each day through Friday for most of the area with record highs
possible Thursday and Friday. Increasing low level onshore flow
over the weekend. A weak system moving down from the northwest
will reach the area later Sunday into Monday. Upper level trough
moving through Monday night into Tuesday.
&&
.SHORT TERM /TODAY THROUGH FRIDAY/...Satellite imagery shows low
clouds and fog right along the coastline and down the Strait of
Juan de Fuca to near Whidbey Island at 3 am/10z. Just a few high
clouds over the remainder of the area. Temperatures at 3 am were
in the mid 50s to mid 60s.
Heat wave for Western Washington still on track this morning.
Upper level ridge centered offshore over Western Washington today.
Temperatures aloft continue to warm with 850 mb temperatures
rising from plus 18 to 20C Tuesday evening to plus 22 to 24C by
late this afternoon. Low level flow remaining light onshore. This
will keep high temperatures in the upper 70s to lower 90s.
Upper level ridge continuing to build over the area tonight with
the center of the ridge moving over Western Washington Thursday.
Temperatures aloft not warming much more with model 850 mb
temperatures around plus 25C. Low level flow turning offshore
Wednesday night with the low level offshore flow continuing
Thursday. The switch to offshore flow will keep overnight lows in
the mid and upper 60s especially in locations with a little
exposure to easterly winds like the Cascade foothills. For the
remain of the area lows in the upper 50s to mid 60s. Highs
Thursday warming into the mid 80s to near 100. Hottest
temperatures will be over the Southwest Interior and in the
Cascade foothills and valleys. The transition to offshore flow
will dry out the lower levels of the air mass Thursday increasing
fire weather concerns. See fire weather discussion below for
details.
Upper level ridge sliding east Thursday night into Friday with the
flow aloft becoming southerly. Not much change in the
temperatures aloft into Friday afternoon. Low level flow turning
back onshore Friday afternoon. Not in time to make a dent in the
high temperatures over the interior. The coast will see
considerable cooling Friday with highs lowering back down into
the 70s. For the interior another round of mid 80s to near 100.
With the light flow in the lower levels overnight Thursday night
and the warm air aloft it will be another warm night with most
places only dropping into the 60s Friday morning.
The excessive heat warning for the interior beginning at noon
today continuing through Friday evening for the northern portion
of the interior and through Saturday evening for the southern
portion of the interior. Heat advisory also in effect for the
Olympics beginning today at noon and continuing through Friday
evening. Heat advisory for the North Coast beginning at noon today
will end Thursday evening.
.LONG TERM /SATURDAY THROUGH TUESDAY/...Some small changes in the
extended solutions overnight. Upper level ridge moving a little
further south Saturday with the upper level flow becoming
southwesterly. This will reduce the chances for convection over
the Cascades and reduce the possibility of elevated smoke getting
into the area. Temperatures aloft still warm and low level onshore
flow looks weak. This combination will result in just a few
degrees of cooling for the interior Saturday with highs still in
the 80s and lower 90s. Lows will continue on the warm side
Saturday morning for the interior with another round of 60s.
Upper level ridge continuing to move southeast Sunday with a weak
system approaching from the northwest. Low level onshore flow
increasing ahead of the system Sunday cooling temperatures over
the interior back down to around normal, mostly in the 70s. There
is a slight chance of rain over the northern portion of the area
in the afternoon and evening. Weak system sliding through the area
Sunday night into Monday for a chance of rain over the entire
area. If we do get any rain, amounts will be light. Just a few
hundredths. Upper level trough trailing the front moving through
Monday night into Tuesday keeping the low level onshore flow
intact. Slight chance of showers over the northern portion of the
area. Highs Monday in the mid 60s to mid 70s, Tuesday upper 60s to
upper 70s. Felton
&&
.AVIATION...Northerly flow aloft will back to the northwest
overnight. At low levels, light onshore flow will transition to
offshore late tonight with persistent northerlies, 5-10 kts, through
the interior. Low level winds will strengthen to 8-12kt this
afternoon and evening before easing late. The atmosphere remains dry
and generally stable.
Generally clear skies and VFR conditions will remain in place over W
WA with the only exception being KHQM where marine stratus may
redevelop with IFR conditions early Thursday morning.
KSEA...Clear skies and VFR conditions will persist through Thursday.
Northerly winds 5-7 kts will strengthen to 7-10 kts this afternoon,
then ease late this evening.
&&
.MARINE...Persistent northerly winds at small craft advisory levels
over the outer coastal waters will linger through early Thursday
morning. Northwesterly swell may peaking around 10-11 ft. Onshore
flow will transition to easterly flow late tonight's a thermally
induced surface trough develops offshore. Seas may return to 8-10
feet later in the the week.
&&
.FIRE WEATHER...The combination of very hot and dry conditions,
resulting in RH values down around 20 pct, and a thermal pressure
trough over the area Thursday could result in red flag conditions as
mid-level Haines values of 6 will be expected over the Cascades
/Fire Wx Zones 658 and 659/. As such, will go ahead and issue a Fire
Weather Watch with the morning forecast package to get the ball
rolling on this potentially dangerous situation. Remainder of CWA
will certainly be hot and dry, but the instability does not look to
be widespread as the thermal pressure trough shifts eastward
throughout the day...and thus not foreseeing including any other
additional fire wx zones at this time, however, will continue to
monitor. 18
&&
.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Excessive Heat Warning from noon today to 7 PM PDT Saturday for
Bellevue and Vicinity-Cascades of Pierce and Lewis Counties-
Cascades of Snohomish and King Counties-Cascades of Whatcom
and Skagit Counties-East Puget Sound Lowlands-Seattle and
Vicinity-Southwest Interior-Tacoma Area.
Fire Weather Watch from Thursday morning through Thursday
evening for West Slopes of the Central Cascades Generally
above 1500 Feet-West Slopes of the North Cascades Generally
above 1500 Feet.
Heat Advisory from noon today to 8 PM PDT Friday for Olympics.
Excessive Heat Warning from noon today to 8 PM PDT Friday for
Bremerton and Vicinity-Everett and Vicinity-Hood Canal Area-
Lower Chehalis Valley Area-Western Skagit County-Western
Whatcom County.
Heat Advisory from noon today to 8 PM PDT Thursday for North
Coast.
PZ...Small Craft Advisory until 2 AM PDT Thursday 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.
&&
www.weather.gov/seattle10 heat. Local standard time, as filed.
A period of much above normal temperatures affected the Seattle area around mid-August. High temperatures ranged from the mid 80s to low 90s during this period, with the temperature peaking August 12-August 13 at 93 degrees, both of which were record high temperatures. Low temperatures during this period ranged from the mid to upper 60s.
The Southwest Interior experienced a stretch of heat towards mid August. The ASOS sensor at Olympia showed high temperatures in the low to mid 90s through the duration of the heat event, with a record high temperatures of 96 recorded on August 12. Low temperatures through the event ranged from the mid to upper 50s.
Centralia also recorded temperatures in the low to mid 90s. A high temperature of 95 was recorded on August 12 and August 13. Low temperatures stayed in the mid 60s.
A warm stretch of weather affected Western Whatcom County towards the middle of August, high temperatures consistently reached the mid to upper 80s for much of the duration of the heat stretch, however, temperatures soared to 100 degrees at the Bellingham Airport on August 12, setting a new record. Low temperatures during the event remained right around 60.
Very warm weather affected the Bremerton Area and the Kitsap Peninsula around the middle of August. Observations from Bremerton Fire showed high temperatures ranging from the mid 80s to low 90s through the duration of the event. Temperatures peaked on August 13, where a record high temperature of 93 was set. Low temperatures ranged from the low to mid 60s.
A warm stretch of weather affected the Everett area towards mid August. Temperatures ranged from the upper 80s to low 90s during the event, with a record high temperature of 92 degrees. Low temperatures ranged from the mid to upper 60s.
Everett-Paine Field airport had temperatures range from the upper 80s to low 90s, with a record high temperature set on August 13 of 91.
Warm weather affected the Tacoma area around mid August. Temperatures ranged in the upper 80s through the duration of the event, with the highest temperature recorded on August 12 at 89 degrees. This set a new record high temperature for that day. Low temperatures ranged from the mid to upper 60s.
A stretch of unusually warm weather affected the Lower Chehalis valley in mid August. Temperatures ranged from the upper 90s to low 100s during the event. A record high temperature of 101 was set on both August 12 and August 13, per a source sited from Elma, WA. Low temperatures ranged from the mid to upper 50s.
Warm weather affected The Cascades valleys during mid August. Temperatures observed at Darrington ranged from the upper 80s to mid 90s, with lows in the upper 50s to near 60. Concrete observed temperatures in the mid 80s to low 90s, with a record high of 93 on August 13. Low temperatures ranged from the upper 50s to mid 60s.
A stretch of warm weather affected the valleys and lower elevations of the Central Cascades of King and Snohomish Counties. Monroe recorded temperatures in the upper 80s to low 90s during the event, with a record high of 91 on August 13 and August 14. Low temperatures ranged from the mid 50s to around 60.
A stretch of unusually warm weather affected the valleys and lower elevations of the Cascades of Lewis and Pierce Counties. Temperature recordings at Longmire at Mount Rainier National Park showed temperatures ranging from the mid 80s to upper 90s through the event, with record high temperatures of 98 degrees set on August 13 and August 14. Low temperatures ranged from the mid to upper 50s.
Cedar Lake also recorded temperatures in the mid to upper 80s, with a record high of 87 on August 14.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Washington in 2021Every state in 2021This day in weather historyWarnings in Washington, August 2021
NOAA National Centers for Environmental Information, Storm Events Database, compiled from the National Weather Service’s monthly Storm Data. Complete through 2026-06; NCEI adds each month about 75 days after it ends and revises past years a few times a year. Rebuilt 2026-09-24. Each event’s entry at NCEI: 982357, 982358, 982360, 982361, 982363, 982364, 982366, 982382, 982384, 982385.