Thousands of homes in Northern California remain threatened by the nation’s largest wildfire as unstable weather creates a high danger of new blazes erupting across the West.

Weekend thunderstorms across the northern Sierra didn’t produce much rain, instead whipping up winds and unleashing lightning strikes that that bedeviled the more than 6,000 firefighters trying to contain the month-old Dixie Fire amid temperatures forecast to top 100 degrees (38 Celsius).

When Tom Larsen thinks of the Dixie Fire in Northern California, he thinks about better modeling.

Larsen, the senior director for content strategy for catastrophe modeler CoreLogic Inc., pointed to some grim facts about the ongoing Dixie blaze: It’s already the second largest wildfire in recorded state history, and over the past two years five of the state’s top seven largest fires have occurred – things he blames on forestry management, climate change, more homes being built in the wildland-urban interface and of course the massive drought plaguing the Western U.S.

“What we’re seeing now in the last few years is loss history’s insufficient,” Larsen said. “The history that we’ve seen is insufficient to look forward and understand the risk.”

California will require millions of health care workers and state employees to show proof of a COVID-19 vaccination or get tested weekly, announcing a broad measure this week to try to slow rising coronavirus infections in the nation’s most populous state, mostly among the unvaccinated.

The new rule, to take effect next month, is the latest example of California and politically progressive cities nationwide cracking down on a virus that has upended life since March 2020. New York Mayor Bill DeBlasio announced a similar plan Monday that requires 340,000 city employees, including teachers and police officers, to show proof of vaccination or undergo weekly testing.

A lightning strike likely ignited a 2020 wildfire in California’s Sierra National Forest, but the U.S. Forest Service said Friday it could not determine an official cause of the fire.

September’s Creek Fire burned 600 square miles and spread so quickly that hundreds of Labor Day holiday campers had to be rescued by a series of harrowing helicopter flights. All 214 campers were delivered safely.

Investigators did not rule out arson and lit cigarettes as the cause, but said there were no illegal marijuana grow sites nearby that could have started the fire. Forest service officials said an “undetermined” status is not uncommon with a fire this complex.

Pacific Gas & Electric reported to California utility regulators that its equipment may have been involved in the start of a fire burning in the Sierra Nevada that is threatening hundreds of homes.

PG&E said in a report Sunday to the California Public Utilities Commission that a repairman responding to a circuit outage on July 13 spotted blown fuses in a conductor atop a pole, a tree leaning into the conductor and fire at the base of the tree.

The utility said its system showed around 7 a.m. that the Cresta Dam off Highway 70 had lost power but because of the steep, rough terrain, the worker sent to check it couldn’t reach the area until nearly 5 p.m.