The August 2020 California lightning wildfires (also referred to as the August lightning siege or August wildfire siege) were a series of 650 wildfires that ignited across Northern California in mid-August 2020, due to a siege of dry lightning from rare, massive summer thunderstorms, which were caused by an unusual combination of very hot, dry air at the surface, dry fuels, and advection of moisture from the remains of Tropical Storm Fausto northward into the Bay Area.^[4][5] These fires burned between 1,500,000 acres (6,100 km²) to 2,100,000 acres (8,500 km²) within a 2–3 week period. The August 2020 lightning fires included three enormous wildfires: the SCU Lightning Complex, the August Complex, and the LNU Lightning Complex. On September 10, 2020, the August Complex set a record for the single-largest wildfire in the modern history of California, reaching a total area burned of 471,185 acres (1,907 km²). On September 11, the August Complex merged with the Elkhorn Fire, another massive wildfire of 255,039 acres (1,032 km²), turning the August Complex into a monster wildfire of 746,607 acres (3,021 km²).^[6]

Quick Facts Date(s), Location ...

August 2020 California lightning wildfires
NASA satellite image of the wildfires on August 24, 2020
Date(s)	August 11, 2020 (2020-08-11) – January 5, 2021 (2021-01-05)
Location	California
Statistics[1]
Total fires	650[2]
Total area	Over 2,529,000 acres (1,023,450 ha)[2]
Impacts
Deaths	23[3]
Non-fatal injuries	43
Structures destroyed	3,586+
Damage	Unknown
Ignition
Cause	Lightning

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The three major Bay Area fires, the SCU, LNU, and the CZU Lightning Complex, collectively burned about 846,000 acres (3,420 km²) by mid-September 2020, destroyed 2,723 structures, and took 6 lives.^[7]

Between August 14 and August 16, Northern California was subjected to record-breaking warm temperatures,^[8][9][10] 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^[11] 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,^[12] noting the risk of abundant lightning already apparent as the storms moved toward the region from the south.

The source of this plume of moist, unstable air was the weakening Tropical Storm Fausto. Due to abnormal winds, this plume was streaming from up to 1,000 miles (1,600 km) off the coast of the Baja Peninsula into Northern California. This moisture then interacted with a high-pressure ridge situated over Nevada that was bringing a long-track heat wave to much of California and the West.^[13] These colliding weather systems then created excessive atmospheric instability that generated massive thunderstorms throughout much of Northern and Central California. Such thunderstorms are rare for California, but were more typical of Midwest garden-variety storms, with one location near Travis Air Force Base going from around 80 °F (27 °C) to 100 °F (38 °C) in nearly 1–2 hours.^[14] 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.^[15]

Early morning on August 16, when the first thunderstorms hit, around 2,500 lightning strikes hit the Bay Area, with 200 strikes happening in 30 minutes at one point, which the National Weather Service office in Bay Area labelled as "insane".^[16] Within the next 72–96 hours, over 12,000 lightning strikes were recorded over Northern California. These lightning strikes sparked up to 585 wildfires, many of which grew to be very large at a rapid pace due to parched brush, especially in Northern California.^[13]

A second wave of thunderstorms was forecasted to hit on August 23 and 24; however, they failed to materialize over the Bay Area, which has been most impacted by these fires, and instead just produced light rain and a few lightning strikes over the Sierra Nevada, barely having any impact.^[17]

Many of the fires were started or discovered on August 16 or 17:

Moc

SQF Complex

Woodward

Carmel

W-5 Cold Springs

Salt

Sheep

Jones

North Complex

Butte Zone

LNU Complex

Rattlesnake

CZU Complex

August Complex

SCU Complex

Beach

Dome

River

Loyalton

Hills

Lake

Wolf

  

Location of August 2020 wildfires

The North Complex fire's Bear Fire had destroyed the town of Berry Creek. The SCU Lightning Complex fires have threatened the cities of Fremont, Milpitas, Patterson, and San Jose, and also threatened Lick Observatory.

Evacuations

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• 2020 California wildfires
• 2020 Western United States wildfires