Lightning isn’t usually a California thing. A meteorologist explains.

They are notable sights not just for their drama but for their rarity: lightning bolts in San Francisco, striking utility poles and prominent features of the skyline, including the Transamerica Pyramid and Sutro Tower.

The recent storms have produced much more lightning in California than the state is accustomed to seeing. In the Sacramento area, roughly 400 strikes were observed in a two-hour period early Tuesday, according to Robert Baruffaldi, a senior meteorologist at the National Weather Service in Sacramento.

Over the past seven years, the United States as a whole averaged about 17.8 lightning strikes per square kilometer per year, according to a lightning density map published by Vaisala, a company that monitors global weather and environmental conditions. Florida averaged more than 87 strikes per square kilometer per year. But the figure for California was just 1.1; only Oregon and Washington had fewer.

Why isn’t California struck more often? The main reason is humidity, or rather the lack of it. The state’s air has usually been so dry that “it’s harder to get the persistent strikes that other parts of the nation see,” Mr. Baruffaldi said.

Consecutive years of record-breaking drought, and spring and summer months without rainstorms, have kept large clouds from forming, he said. Fog often develops along the state’s coastline, but there is usually not enough wind to create the uplift needed to form the tall thunderheads, called cumulonimbus clouds, where lightning emerges, Mr. Baruffaldi said.

That changed over the past month, when a series of atmospheric rivers started to channel huge amounts of moisture into the state from the Pacific Ocean. Strong winds from those storm systems lifted the moisture high into the upper atmosphere, Mr. Baruffaldi said, adding that daytime heat and mountainous terrain also forced the warmer, wetter air upward.

Within those tall clouds, vigorous winds introduced instability, causing the ice crystals above and the water droplets below to bump together and build up static electrical charges in the clouds that are eventually discharged as lightning bolts.

As uncommon as they are in California, relative to the rest of the country, lightning bolts have ignited some of the largest wildfires ever recorded in the state.

So far, there have not been reports of significant damage caused by lightning in the recent storms, Mr. Baruffaldi said on Wednesday. Though lightning bolts can readily touch off fires in the dry season, they do not pose as great a threat now because the storms have also soaked the landscape with huge amounts of rain.

“Nothing’s going to burn this time of year,” he said.