Weather conditions that led to these abnormally early conflagrations were different for each summer, as was the impact of wildfire smoke on East Bay residents.
Last summer’s wildfires were triggered by an unusual lightning storm event in mid-August. More than 12,000 cloud-to-ground lightning strikes were recorded in Northern California in one day.
The myriad lightning strikes sparked hundreds of wildfires. By the end of September 2020, more than 2 million acres of Northern California were charred by these blazes. Three Lightning Complex Fires in the Bay Area consumed more than 200,000 acres each.
Several periods of offshore wind flow events followed last August’s lightning-generated wildfires. These dry winds pushed flames rapidly across forests and grasslands already abnormally dry due to subpar rainfall the previous winter. The offshore wind events blew dense smoke into the Concord/Clayton area, resulting in extremely unhealthy air quality for several weeks.
Last winter, fingers were crossed that plentiful rains would fill reservoirs and keep wildfire fuels moist. Unfortunately, most of Northern California received less than half the expected normal rainfall last winter – resulting in record two-year rainfall deficits.
That didn’t bode well for the 2021 fire season, and sure enough the fires began even earlier this summer. The enormous Dixie Fire near Lake Almanor started in mid-July. As of the first week of September, it had consumed more than 900,000 acres and was only 50 percent contained.
In late July, the Monument Fire began in Trinity County. So far, it has consumed more than 200,000 acres and is not yet 50 percent controlled.
The third large blaze in Northern California this summer, the Caldor Fire, began in El Dorado County on Aug. 14 and has consumed more than 200,000 acres and threatened the community of South Lake Tahoe. It also is less than 50 percent contained.
While the major wildfires of 2020 were lightning-induced, the official causes of this summer’s largest fires are currently classified as unknown – but lightning definitely was not involved. It is likely that the two-year drought and human activities will be co-blamed as culprits for these early wildfire events.
East Bay skies have been hazy on many days so far this fire season, but there have only been a few times when air quality readings have been worse than moderately unhealthy. One reason is that this season’s major fires are located in the Sierra, further away from the Bay Area than last year’s Lightning Complex Fires.
Even so, jet stream winds have managed to push smoky plumes in our direction. Fortunately, persistent onshore sea breeze winds have helped keep conditions near the surface relatively healthy compared to last summer.
We can expect more wildfires and smoke in the coming months. The best-case weather scenario for California would be an early onset to the rainy season this fall, followed by enough rain events to help make up the water deficits of the last two winter seasons.
Woody Whitlatch is a meteorologist retired from PG&E. Email your questions or comments to