Red flag warnings for high fire danger are in effect for a large part of the West from Northern California and southern Oregon through the northern Rockies into the western Dakotas. Over Nevada, the danger is “critical,” according to the National Weather Service.
The situation escalated Tuesday as more potent winds, from a different direction, arrived in Northern California, under a red flag warning through Wednesday afternoon. This warning includes parts of the San Francisco Bay area.
The trouble began north of the border in British Columbia on Sunday, after high winds ahead of a passing cold front helped to blow up a number of fires in the Canadian province.
On Monday, gusty westerly winds spread over Washington, Oregon and California, driving fires to the east, as towering smoke plumes signaled that blazes were burning hot, exhibiting extreme fire behavior.
A steady stream of new evacuation orders and warnings followed as conditions deteriorated Monday afternoon and evening. The Dixie Fire continued its march through the Sierra on Monday night, destroying structures in the town of Janesville while spreading across Highway 395, which is more than 50 miles from where it first ignited. The blaze, California’s second-biggest on record, has burned 604,511 acres and destroyed 1,100 structures.
A new and dangerous fire east of Sacramento, the Caldor Fire, rapidly expanded and required new evacuations overnight. The blaze grew over 4,000 acres Monday night to 6,500 acres as of Tuesday morning.
According to Cal Fire and the Eldorado National Forest, there were immediate overnight evacuations and structure loss was observed.
“The fire continues to pose a high risk to multiple populated communities … This is a rapidly changing incident with dynamic fire behavior,” according to a Tuesday morning Cal Fire report.
The town of Grizzly Flats was hit particularly hard, where the blaze leveled homes and destroyed a school and church, the Sacramento Bee wrote.
The culprit for this latest round of dangerous weather is a strong dip or trough in the jet stream and associated cold front pushing through the Pacific Northwest and into the Northern Rockies.
According to the National Weather Service, sustained westerly winds will combine with low humidity from California to the Northern Plains through Tuesday afternoon.
A potentially more severe wind event arrives Tuesday evening and into Wednesday, when a more offshore pattern sets up, bringing persistent dry winds from the north and northeast over Northern California.
Flames are expected to spread in new directions, threatening communities to the south or southwest of any ongoing fires, especially given record-dry vegetation in the region. Smoke may also move into areas that had been relatively clear earlier in the week.
The strong offshore pattern is highly unusual for this time of year and is more typical of an October setup. Between Tuesday night and Wednesday evening, Northern California, including the San Francisco Bay area, could see winds topping 50 mph in some high-terrain locations, along with very low relative humidity, a volatile combination.
Ahead of the deteriorating weather, Pacific Gas and Electric plans to cut power to as many as 48,000 customers beginning Tuesday evening to prevent its equipment from igniting vegetation during high winds. Most of the affected customers are in Butte and Shasta counties, where some fires are burning.
Although the power shut-offs are intended to prevent new, fast-moving blazes, they could leave affected communities “in the dark” and unable to access or receive emergency information at an especially precarious time, with numerous fires already on the move.
The winds come on the heels of another intense heat wave in the West, which has further primed drought-stressed forests to burn. Last week, daily record highs were tied or broken in Oregon, Washington and parts of Canada. Redding, Calif., climbed to a record 116 degrees on Sunday, despite being shrouded by a thick layer of smoke. Much of the interior West saw its warmest June-July period since 1895 because of repeated, extreme heat waves.
The sheer amount of fire on the landscape has spewed an enormous volume of smoke into the atmosphere. In southern British Columbia on Sunday, smoke was so thick that it blocked out the sun completely. Closer to the surface, smoke is a harmful pollutant because high concentrations of fine particles, known as PM2.5, can worsen asthma and heart disease, among other health effects.
In just the past few days, a wide swath of “unhealthy” to “hazardous” air has stretched from the Western United States to the Plains states and well into Canada. The degraded air quality is also coinciding with the latest nationwide surge in coronavirus cases. A recent study has linked wildfire smoke to an increase in coronavirus cases and deaths in states affected by the 2020 wildfires, possibly because PM2.5 can make people more susceptible to lung infections.
The trough that is bringing wind to the West Coast is also ushering in some wet weather and cooler temperatures over parts of the drought-stricken interior West, including Montana, where numerous fires are burning. British Columbia also will see welcome rain this week.
However, according to the latest outlooks from the Climate Prediction Center, the Pacific Northwest and California are expected to remain mostly dry for the foreseeable future, with the most intense and windiest months of the fire season approaching.
Diana Leonard is a science writer covering natural hazards in California.
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Fire danger escalates in West as blazes emit massive smoke plumes - The Washington Post
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