This creates ideal conditions in the West for lightning sparked and wind driven storms to spread large-scale, seasonal wildfires.

[11][better source needed][13] Land was protected from fire, and vegetation accumulated near settlements, increasing the risk of explosive, smoky conflagrations.

[25] The Oregon Department of Forestry declared fire season beginning July 5, 2020, signaling the end of unregulated debris burning outdoors, a major cause of wildfires.

[29][30] Between August 14 and 16, Northern California was subjected to record-breaking warm temperatures,[31] due to anomalously strong high pressure over the region.

Early on August 15, the National Weather Service for San Francisco issued a Fire Weather Watch[32] highlighting the risk of wildfire starts due to the combination of lightning risk due to moist, unstable air aloft, dry fuels, and hot temperatures near the surface.

Later that day, the Fire Weather Watch was upgraded to a Red Flag Warning,[33] noting the risk of abundant lightning already apparent as the storms moved toward the region from the south.

[34] Due to abnormal wind patterns, this plume streamed from up to 1,000 miles (1,609 km) off the coast of the Baja Peninsula into Northern California.

[35] These colliding weather systems then created excessive atmospheric instability that generated massive thunderstorms throughout much of Northern and Central California.

[36] Additionally, much of these storms were only accompanied with dry lightning and produced little to no rain, making conditions very favorable for wildfires to spark and spread rapidly.

[37] As a result of the fires, on August 19, Governors Kate Brown and Jay Inslee declared a state of emergency for Oregon and Washington respectively.

[42] The Evans Canyon Fire, a few miles north of Naches, began around August 31 and expanded to tens of thousands of acres, shut down Washington State Route 821 in the Yakima River Canyon, burned several homes and caused hundreds of families to evacuate, and caused unhealthy air quality in Yakima County.

On September 10, 2020, the August Complex became the single-largest wildfire in the recorded history of California, reaching a total area burned of 471,185 acres (1,907 km2).

[45] The North Complex increased in size as the winds fanned it westward, threatening the city of Oroville, and triggering mass evacuations.

[50] By the evening of September 8, the Cold Springs Canyon and adjacent Pearl Hill Fires had burned over 337,000 acres (136,000 ha) and neither was more than 10% contained.

[51] Smoke blanketed the Seattle area on September 8 and caused unhealthy air conditions throughout the Puget Sound region, and affected Southwest British Columbia.

[61] The first evacuations began on September 4, when almost 200 people were airlifted out of the Sierra National Forest due to the rapidly exploding Creek Fire.

[229] Climate change has led to increased heat waves and the risk of drought in California, creating the conditions for more frequent and severe wildfires.

[234] David Romps, director of the Berkeley Atmospheric Sciences Center summarizes the situation as follows: "To cut to the chase: Were the heat wave and the lightning strikes and the dryness of the vegetation affected by global warming?

A huge body of attribution literature demonstrates now that climate change is an absolute game-changer when it comes to heat waves, and California won't be the exception.

Authorities urged residents to ignore the rumors and follow evacuation orders, noting that firefighters' lives could be endangered rescuing those who remained.

[244][245][246] For example, a man allegedly set fires in Glide, Oregon, after a Douglas Forest Protection Association member refused to give him a ride to town.

[247] California relies heavily on inmate firefighters, with incarcerated people making up nearly a quarter of CAL FIRE's total workforce in 2018–2019.

[249] In Oregon, wildfires throughout the whole year, with most occurring in September, charred a record of 1,000,000 acres (4,000 km2), destroying a total of 4,800 structures, including 1,145 homes, and killing 9 people.

In California, for example, a San Francisco resident was hiking through Yosemite National Park on September 5 when suddenly the sky turned a dark, ugly color and the temperature dropped greatly, reminiscent of a thunderstorm.

[258] Due to the complex oxidative chemistry occurring during the transport of wildfire smoke in the atmosphere,[259] the toxicity of emissions was suggested to increase over time.

[264] The Cassia Crossbill may lose half its population due to the pending consequences of the wildfires, one of which engulfed a large portion of the South Hills, one of the only two strongholds for the bird.