Firefighters battle California fires in conditions so harsh some water evaporates before it hits the ground

Firefighters struggled to contain an exploding Northern California wildfire under blazing temperatures as another heat wave hits the U.S. West this weekend, prompting an excessive heat warning for inland and desert areas.

On Friday, Death Valley National Park in California recorded a staggering high of 54 C and could reach the same high on Saturday. If verified, the reading would be the hottest high recorded there since July 1913, when the same Furnace Creek desert area hit 57 C, considered the highest reliably measured temperature on Earth.

The Beckwourth Complex — two lightning-caused fires burning 72 kilometers north of Lake Tahoe — showed no sign of slowing its rush northeast from the Sierra Nevada forest region after doubling in size between Friday and Saturday.

California's northern mountain areas already have seen several large fires that have destroyed more than a dozen homes. Although there are no confirmed reports of building damage, the fire prompted evacuation orders or warnings for roughly 2,800 people along with the closure of nearly 518 square kilometres of Plumas National Forest.

On Friday, hot rising air formed a gigantic, smoky pyrocumulus cloud that created its own lightning, fire information officer Lisa Cox said.

Spot fires caused by embers leapt up to 1.6 kilometres ahead of the northeastern flank — too far for firefighters to safely battle — and winds funnelled the fire up draws and canyons full of dry fuel, where "it can actually pick up speed," Cox said. The flames rose up to 31 metres in places, forcing firefighters to focus instead on building dozer lines to protect homes.

Heat never lets up

Firefighters usually take advantage of cooler, more humid nights to advance on a fire, Cox said, but the heat and low humidity never let up. The more than 1,200 firefighters were aided by aircraft. But the blaze was expected to continue forging ahead.

The air was so dry that some of the water dropped by aircraft evaporated before reaching the ground, she added.

"We're expecting more of the same the day after and the day after and the day after," Cox said.

The blaze, which was only eight per cent contained, increased dramatically to 222 square kilometres after fire officials made better observations.

It was one of several threatening homes across Western states that are expected to see triple-digit heat through the weekend as a high-pressure zone blankets the region.

The U.S. National Weather Service warned the dangerous conditions could cause heat-related illnesses, while California's power grid operator issued a statewide Flex Alert from 4 p.m. to 9 p.m. PT Saturday to avoid disruptions and rolling blackouts.

Oregon fire threatens transmission lines

The California Independent System Operator warned of potential power shortage, not only because of mounting heat, but because a wildfire in southern Oregon was threatening transmission lines that carry imported power to California. Gov. Gavin Newsom issued an emergency proclamation on Friday suspending rules to allow for more power capacity, and the ISO requested emergency assistance from other states. On Saturday, Newsom issued another proclamation allowing the emergency use of auxiliary ship engines to relieve pressure on the electric grid.

Pushed by strong winds, the Oregon fire doubled in size to 311 square kilometres Saturday as it raced through heavy timber in the Fremont-Winema National Forest near the Klamath County town of Sprague River.

Las Vegas late Saturday afternoon tied the all-time record high of 47 C, the weather service said. The city has recorded that record-high temperature four other times, most recently in June 2017.

NV Energy, Nevada's largest power provider, also urged customers to conserve electricity Saturday and Sunday evenings because of the heat wave and wildfires affecting transmission lines throughout the region.

Fire sparked by burning big-rig

In Southern California, a brush fire sparked by a burning big-rig in eastern San Diego County forced evacuations of two Native American reservations Saturday.

In north-central Arizona, Yavapai County on Saturday lifted an evacuation warning for Black Canyon City, an unincorporated town 66 kilometres north of Phoenix, after a fire in nearby mountains no longer posed a threat.

A wildfire in southeast Washington grew to almost 155 square kilometres as it blackened grass and timber while it moved into the Umatilla National Forest.

In Idaho, Gov. Brad Little declared a wildfire emergency Friday and mobilized the state's National Guard to help fight fires sparked after lightning storms swept across the drought-stricken region.

Fire crews in north-central Idaho were fighting three lightning-sparked wildfires covering a combined 160 square kilometres. The blazes threatened homes and forced evacuations in the tiny, remote community of Dixie about 64 kilometres southeast of Grangeville.