A 600dm ridge of high pressure centered over the Desert Southwest in mid-June retrograded over to the West Coast/East-Central Pacific Ocean by the start of the 3rd week of June. The pattern began to amplify on June 20th, with the ridge axis building along the West Coast, coinciding with a large area of low pressure deepening over Hudson Bay to the east. This feature, along with deepening low pressure over the Gulf of Alaska were the primary factors in the omega block setting up off the Pacific Northwest Coast by the end of the week. The strength of the Hudson Bay vortex kept the 600dm ridge high centered over the Pacific Northwest for nearly a week, yielding record breaking temperatures (multiple days of over 100 degree temperatures in a row with low temperatures resembling the average high temperatures for the time of year).
The record-breaking heat from this anomalous pattern led to multiple heat-related fatalities (heat stroke and heat stress) across Western Washington is also expected to be related to numerous drownings across the area, largely in part due to hypothermia as people sought reprieve from the heat in local area lakes and large bodies of water. In addition, several brush fires were also ignited due to dry fuels present amidst hot temperatures. All fires were contained without major impacts.

Heat in SEATTLE AND VICINITY, WASHINGTON
From 27-JUN-21 17:00:00 to 29-JUN-21 12:00:00 (PST-8)
Reported by: Social Media

A section of pavement came loose/buckled on NB I-405 and I-5 in Tukwila, causing road and highway closures for several hours during the evening commute.

Heat in WESTERN WHATCOM COUNTY, WASHINGTON
From 27-JUN-21 17:00:00 to 28-JUN-21 12:00:00 (PST-8)
Reported by: Social Media

State route 544 milepost 7 near Everson was closed as asphalt roadway buckled and was deemed unsafe for travel. Detours were put in place with highway repair complete the morning following the incident.

Heat in TACOMA AREA, WASHINGTON
From 27-JUN-21 18:00:00 to 29-JUN-21 08:00:00 (PST-8)
Reported by: Social Media

Concrete panels along NB I-5 to I-705 experienced period damage and needed continuous repairs from Jun 27-Jun 29. This caused 3 lanes of the collector-distributor to close, causing traffic backups and detours.

Heat in CASCADES OF SNOHOMISH AND KING COUNTIES, WASHINGTON
From 28-JUN-21 18:00:00 to 29-JUN-21 12:00:00 (PST-8)
Reported by: Social Media

The left two lanes of I-90 eastbound five miles east of North Bend closed due to the highway buckling from the heat. This lead to traffic and difficult travel conditions.

Heat in SEATTLE AND VICINITY, WASHINGTON
From 26-JUN-21 14:00:00 to 29-JUN-21 07:00:00 (PST-8)
Reported by: ASOS

Record breaking heat across the Seattle metro area led to multiple heat related fatalities, numerous pavement buckles requiring road closures and repair, the closing of University bridge for marine traffic due to excessive heat, lowering of speed limits to Sound Transit, millions of gallons of water used, the highest energy usage in Seattle public utilities history during the summer months, the closing of the Seattle monorail, and the death of dozens of Caspian Terns.
Temperatures began to rise in the Seattle metro on 6/26 to 102 degrees, followed by an increase in several degrees to 104 on 6/27, with a peak and all time record high temperature on 6/28  of 108. Temperatures slowly began to cool as the month concluded.

Heat in TACOMA AREA, WASHINGTON
From 26-JUN-21 14:00:00 to 29-JUN-21 17:00:00 (PST-8)
Reported by: ASOS

Record breaking heat affected the Tacoma area for several days, beginning on 6/26 and peaking 6/27-6/28.  A high temperature of 99 was recorded on 6/27, with an (unofficial) all time record high temperature of 105 of 6/27. Temperatures then reached 99 and 97 on the afternoon of 6/28 and 6/29, respectively before a gradual cool down began at the conclusion of the month. Several reports of road buckling/road damage around Tacoma.

Heat in BREMERTON AND VICINITY, WASHINGTON
From 26-JUN-21 14:00:00 to 29-JUN-21 20:00:00 (PST-8)
Reported by: ASOS

Record breaking heat from 6/26-6/29. High temperatures at the Bremerton airport reached 90 degrees on 6/26, followed by a noticeable warmup on 6/27 at 100 degrees. An (unofficial) all time record high temperature was reported on 6/28 at 102 degrees. The heat stuck around for one more day on 6/29 where high temperatures reached 101 in the afternoon before a gradual cool down commenced at the conclusion of the month.

Heat in EVERETT AND VICINITY, WASHINGTON
From 26-JUN-21 14:00:00 to 29-JUN-21 07:00:00 (PST-8)
Reported by: ASOS

An extended period of hot temperatures affected the Everett area from 6/26-6/28. Temperatures reached the mid 90s on the afternoons of both 6/26 and 6/27, with temperatures then peaking on 6/28 over 100 degrees. The Everett-Paine Airport unofficially tied its all time record high temperature of 100, with a nearby COOP site reporting 101 degrees. Several heat related illness incidents were reported during this time frame as well as a brushfire on I-5 NB near MP 197. Temperatures then cooled down back into the low 80s at the conclusion of the month, ending the record breaking heat.

Heat in EASTERN STRAIT OF JUAN DE FUCA, WASHINGTON
From 26-JUN-21 14:00:00 to 29-JUN-21 07:00:00 (PST-8)
Reported by: ASOS

Record breaking heat affected the Port Angeles area and nearby land locations around the Eastern Strait of Juan de Fuca. The Port Angeles airport recorded an (unofficial) all time record high temperature of 99 degrees on 6/28. Temperatures from 6/26-6/27 were in the mid 90s, with temperatures dropping back into the 70s by 6/29, ended the heat wave.

Heat in WESTERN WHATCOM COUNTY, WASHINGTON
From 26-JUN-21 14:00:00 to 29-JUN-21 07:00:00 (PST-8)
Reported by: ASOS

An extended period of hot temperatures affected western Whatcom County at the end of June. High temperatures reached the mid 90s on the afternoons of 6/26 and 6/27 according to the Bellingham Airport ASOS. Temperatures then peaked on 6/28 with a high temperature of 99 at the Bellingham Airport. This then became an all time record high temperature. By 6/29, temperatures cooled back into the upper 70s, ending the extended period of record breaking hot weather. In addition to the heat, there were some reports of road buckling on SR 544 near MP 7 near Everson.

Heat in NORTH COAST, WASHINGTON
From 26-JUN-21 14:00:00 to 29-JUN-21 07:00:00 (PST-8)
Reported by: ASOS

Record breaking heat affected the North Coast of Washington at the end of June as a strong area of high pressure built into the region. The hottest afternoon temperatures were reported on the afternoon of 6/28, with the Quillayute Airport reporting an all time record high temperature of 110 degrees. The following day, onshore flow led to rapid cooling back into the upper 60s.

Heat in SAN JUAN, WASHINGTON
From 26-JUN-21 14:00:00 to 29-JUN-21 07:00:00 (PST-8)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: ASOS

An extended period of hot weather affected the San Juan Islands at the end of June. The ASOS at Friday Harbor recorded high temperatures in the mid 90s from 6/26-6/28 before temperatures finally began to cool on 6/29.

Heat in WESTERN SKAGIT COUNTY, WASHINGTON
From 26-JUN-21 14:00:00 to 29-JUN-21 07:00:00 (PST-8)
Reported by: Unknown

An extended period of hot temperatures affected Western Skagit county at the end of June. The official COOP site was not active during the heat wave, but observations at KAWO reported a high temperature of 103 on 6/28. Temperatures peaked on 6/28, with hot conditions present from 6/26-6/27. Temperatures began to cool on 6/29 through the rest of the month.

Heat in SOUTHWEST INTERIOR, WASHINGTON
From 26-JUN-21 14:00:00 to 29-JUN-21 07:00:00 (PST-8)
Reported by: ASOS

Record breaking heat led to multiple days of high temperatures above 100 degrees. On 6/26 high temperatures rose to 102 degrees, with 6/27 several degrees warmer at 105. On 6/28 an all time record high temperature was set at the Olympia Airport of 110 degrees. Temperatures then began to cool during the final two days of June.
Centralia also unofficially tied its all time record high temperature of 107 degrees on 6/28.

Heat in CENTRAL COAST, WASHINGTON
From 26-JUN-21 14:00:00 to 29-JUN-21 07:00:00 (PST-8)
Reported by: ASOS

Recorded breaking heat affected the central Coast of Washington at the end of June as a strong area of high pressure became centered over the region. Temperatures began to increase into the upper 80s on 6/26, with temperatures peaking on 6/27 and remaining hot through 6/28. The Hoquiam airport recorded an all time record high temperature  on 6/27 of 103 degrees. At the conclusion of the month, temperatures began to cool back into the upper 60s as onshore flow strengthened and high pressure weakened.
Aberdeen also recorded an unofficial all time record high temperature on 6/28 of 108 degrees.

Heat in CASCADES OF PIERCE AND LEWIS COUNTIES, WASHINGTON
From 26-JUN-21 14:00:00 to 30-JUN-21 20:00:00 (PST-8)
Reported by: Park/Forest Service

An extended period of heat affected the Cascades of Pierce and Lewis Counties at the end of June. Temperatures began to climb  into the upper 70s and lower 80s at Paradise on 6/26 and continued through 6/28. On 6/29, the Paradise Ranger Station recorded an unofficial all time record high temperature of 90. Temperatures then remained above normal through the end of the month but were not as hot as the previous several days.
Longmire also unofficially tied its all time record high temperature on both 6/29 and 6/30 at 105 degrees.
Due to the extended period of extreme heat, flooding from glacial/snow melt washed out the Nisqually bridge near Cougar Rock. This affected hiking near Mount Rainier National Park.