New and existing fires are spreading rapidly in Northern California, shrouding the region in smoke and forcing the evacuation of thousands in several counties. On Wednesday, critical fire weather descended upon the area, with high winds fanning flames that have moved into multiple communities. Dangerous conditions will continue through Thursday.

The Dixie Fire has destroyed much of the picturesque town of Greenville, Calif., about midway between Redding and Reno, Nev. The blaze, which has consumed more than 320,000 acres as of early Thursday, is the sixth-largest on record in California. Six of the state’s seven biggest fires on record have occurred since August 2020.

At least 35 to 40 structures have been lost to the River Fire in the Sierra Nevada foothills, according to Cal Fire, and 4,000 more are threatened. That blaze has charred 2,400 acres since erupting Wednesday.

The unfolding events are a devastating realization of what was widely predicted to be another severe fire season in the state. The billowing smoke plumes are the culmination of extreme summer heat waves and drought, both intensified by climate change, which has again produced an exceptionally flammable landscape.

Red-flag warnings for high fire danger were posted Wednesday from Northern California into Southern Oregon, due to a low-pressure trough moving through into the area, and were expanded Thursday. Gusty conditions will continue into Thursday night for parts of California, Oregon, Washington, Nevada, Idaho and Montana.

“Hot, dry, windy, and unstable will be the name of the game this week,” the National Weather Service in Medford, Ore., wrote in a forecast discussion.

Hannah Chandler-Cooley, a meteorologist with the National Weather Service in Sacramento, said that while the winds are not extreme, they are combining with very low humidity over existing fires.

“Fire behavior has been intense even on non-windy days, so we are definitely concerned about these fires,” she said in an interview Wednesday. In addition, steep canyons in the mountainous areas where several fires are burning can create wind tunnels and accelerate fire spread.

The Dixie Fire grew from 253,052 acres Tuesday morning to 274,139 acres Wednesday morning, breaking through containment lines, largely in the absence of organized winds. Under windier conditions Wednesday, the fire was far beyond control as it moved through the town of Greenville. By Thursday morning, it had ballooned to 322,502 acres.

To make matters even worse, several new fires and fire complexes have emerged in California and Oregon, most sparked by lightning over the past week. Although most remain small, several have grown to thousands of acres.

New California blazes are burning on national Forest Service land and include the 21,000-acre McFarland Fire and the 17,000-acre Monument Fire. The Antelope Fire, which has burned nearly 13,000 acres, closed in on Tennant, Calif., late Wednesday, about 100 miles north of Redding, having traveled many miles from where it was first ignited by lightning this weekend.

Numerous lightning fires have also been reported in Oregon, including the Middle Fork Complex southeast of Eugene, which could awaken under gusty winds this week.

Lightning has been an ongoing concern because of the record dry vegetation in the region, as well as the likelihood that any remote ignition could develop into major incidents, especially under the right conditions.

Several fires took off amid hot and dry weather this week and could spread further Thursday as unstable air combines with shifting winds from the passage of a dry cold front. In addition, thunderstorms, some severe, could bring gusty outflow winds and additional lightning.

“This pattern will cause chaotic and extreme fire behavior among ongoing fires, and could lead to new ignitions that spread rapidly,” a Predictive Services fire weather outlook for Northern California read.

Flammability is well beyond peak-season averages and pushing all-time records in many areas, with the peak of fire season still several weeks away. While the region began the summer in extreme to exceptional drought, record-breaking heat waves have doubled down on an already dire situation. Research has established a clear link between climate change and a sharp rise in the area burned in California in the past several decades, as increasing temperatures dry out vegetation.

There is also plenty of fuel to burn in drought-stressed forests. Experts say a decades-long policy of fire suppression, which has aimed to put out most fires, has resulted in overgrown forests that burn more intensely and emit more smoke as heavy fuel loads are consumed.

Amid the burning landscape, rapidly shrinking reservoirs serve as another vivid example of worsening drought — and a warming climate. Not far from the Dixie Fire, the state’s second-largest reservoir, Lake Oroville, dropped to 642.73 feet Tuesday — its lowest level on record. The California Department of Water Resources confirmed to the Capital Weather Gang that this surpasses the previous lowest level of 645 feet, reached in September 1977.

Given dwindling supplies, the State Water Resources Control Board voted Tuesday to drastically curtail allocations and will order 5,700 water rights holders, mostly farmers, to stop diverting water from the Sacramento and San Joaquin rivers.

In some good news, heavy monsoon rains have brought drought relief to Arizona, New Mexico and Colorado. However, along the West Coast and northern tier states, “conditions have been far drier, and with frequent rounds of abnormal heat, drought conditions and impacts continue to increase,” according to the latest U.S. Drought Monitor.

In just the past week, images of flooding in the interior west have stood in sharp contrast to the dramatically worsening fire situation in California. Severe mudslides have ravaged Colorado’s Glenwood Canyon, between Grand Junction and Denver, causing extensive damage along a portion of Interstate 70, which will be closed for weeks.

While fire conditions are elevated to critical in northeast California and the interior Pacific Northwest through Thursday, conditions are predicted to ease Friday in the wake of the front fanning the flames. Some beneficial rains may even drop into the Pacific Northwest, potentially ending rainless streaks of around 50 days in Seattle and Portland.

Jason Samenow contributed to this report.

Diana Leonard is a science writer covering natural hazards in California.