The Sourdough Fire was first reported on July 29, 2023, three days after a thunderstorm in the area with lightning strikes that caused nearby fires. It is named for
Sourdough Mountain in
North Cascades National Park. The fire grew to over by August 4 and prompted the immediate closure of the North Cascades Highway (
State Route 20) between
Newhalem and
Rainy Pass. It was initially reported on August 5 to be nearly but the estimate was revised down with the use of more accurate mapping. The North Cascades Highway reopened on August 9, but closed again two days later due to increased fire activity near the road. Evacuations were ordered at several campsites and recreational facilities in the park around
Diablo Lake. By August 11, the fire burned approximately and was 5 percent contained with 411 firefighters, 6 helicopters, and several aircraft dispatched to the area. The fire generated a large
pyrocumulus cloud on August 4 that was visible from the
Puget Sound region. Fire officials expect the Sourdough Fire to continue southeast towards Diablo Lake and
Gorge Lake and potentially west where "more continuous fuels exist". The fire, described as "long-duration", is not expected to be contained until October due to warm temperatures and low humidity.
Seattle City Light plans to continue operating the
three hydroelectric dams in the area and suspended its tours of Diablo Lake. During evacuations of staff on August 2, the Diablo and
Ross dams went offline while Gorge Dam continued with reduced output of about 50 percent; and several transmission lines were also shut down to prevent shorting. Power generation at the Diablo and Ross dams resumed on August 9. The fire was directed west towards Newhalem by firefighters using "burnout techniques"; the area near Newhalem includes burn scars from a 2015 wildfire that would slow progress. The strategy was paused after a
red flag warning was issued by the
National Weather Service for the Diablo area with a high temperature of recorded on August 13. Smoke from the fire moved southwest into the Puget Sound region, including
Seattle, on August 13 and caused worsened
air quality readings. The smoke from the Sourdough Fire and other fires in Washington and British Columbia returned to the Puget Sound region the following week and caused the air quality index in Seattle to reach 190 on August 20, the worst among major cities globally. The North Cascades Highway reopened on August 23 for through travelers, with stops prohibited and recreation areas remaining closed due to the Sourdough and Blue Lake fires. It closed a day later and was reopened on August 30 for travel with pilot vehicles to direct traffic. The
North Cascades Institute cancelled all of their programs for 2023 as a result of the fire, which forced their on-site employees to evacuate from dormitories. Management of the Sourdough Fire was transferred from the Northwest Incident Management Team 8 to the
National Park Service on August 29 following successful containment measures. The fire's spread slowed after rainfall in early September as containment reached 25 percent; several campsites and recreation areas in the North Cascades National Park Complex were reopened on September 11 due to improved conditions. ==References==