Researchers find that nearly half of lightning down strikes in California occur with little or no rain

Researchers studied the climatology of dry lightning in California

Dry Lightning, California
(B) Total number of dry lightning flashes across three elevation zones (<1000 m, 1000–2000 m, >2000 m) within the domain for each month between 1987–2020. Text indicates the area of each elevation zone, and inset map shows the geographic distribution of the elevation zones and major mountain ranges. (D) The three elevation zones for each month (bars). Dashed lines in (D) indicate the dry lightning fraction averaged across all months for each zone. Blue dashes in (D) represent the dry lightning fraction computed from all months and elevation zones. (From the paper)

A group of six researchers who studied the occurrence and characteristics of cloud to ground lightning in Central and Northern California found that nearly half, 46 percent, was dry, accompanied by less than 0.1 inch of precipitation.

Of course dry lightning is the bane of land managers and is much more likely to ignite a wildfire than a wet thunderstorm. And on the occasions when there are thousands of down strikes, it can overwhelm the capacity to suppress what can be hundreds of fires.

The six scientists used daily gridded lightning and precipitation observations (1987–2020) in combination with atmospheric reanalyses, to characterize the climatology of dry lightning and the associated meteorological conditions during the warm season (May–October) when wildfire risk is highest.

The paper the group produced is available as open source: “Meteorological and geographical factors associated with dry lightning in central and northern California.”

Daniel Swain, a prolific user of Twitter, used the platform today to highlight some of the group’s findings. In the tweet below, click on “read reply” to see more discussion and illustrations.

The six researchers who participated in the project were Dmitri A. Kalashnikov, John T. Abatzoglou, Nicholas J. Nauslar, Daniel L. Swain, Danielle Touma, and Deepti Singh.