SOUTH LAKE TAHOE, Calif. — Spik­ing tem­per­a­tures and increas­ing winds on Sun­day added to the chal­lenges faced by fire­fight­ers bat­tling blazes across North­ern Cal­i­for­nia, includ­ing one that con­tin­ued its march toward the Lake Tahoe resort region.

“It is going to be the hottest day so far since the fire began, and unfor­tu­nate­ly, prob­a­bly the dri­est,” said Isaac Lake, a spokesman for the two-week-old Cal­dor Fire.

Flames churned through moun­tains just a few miles south­west of the Tahoe Basin, where thick smoke sent tourists pack­ing at a time when sum­mer vaca­tions would be in full swing ahead of the Labor Day weekend.

Triple-dig­it tem­per­a­tures were pos­si­ble and the extreme heat was expect­ed to last sev­er­al days, Lake said. A red flag warn­ing for crit­i­cal fire con­di­tions was issued for Mon­day and Tues­day across the North­ern Sierra.

Crews work­ing in rugged ter­rain scram­bled to douse spot fires caused by errat­ic winds.

“It’s so dry out there that when embers blow out into the unburned fuel beds, the prob­a­bil­i­ty of igni­tion is 90 per­cent,” Lake said.

The blaze that broke out August 14 was 19% con­tained after burn­ing near­ly 245 square miles (635 square kilo­me­ters) — an area larg­er than Chica­go. More than 600 struc­tures have been destroyed and at least 18,000 more were under threat.

The Cal­dor Fire has proved so dif­fi­cult to fight that fire man­agers pushed back the pro­ject­ed date for full con­tain­ment from ear­ly this week to Sept. 8. But even that esti­mate was tenuous.

In South­ern Cal­i­for­nia, a sec­tion Inter­state 15 was closed Sun­day after­noon after winds pushed a new blaze, dubbed the Rail­road Fire, across lanes in the Cajon Pass north­east of Los Angeles.

Fur­ther south, evac­u­a­tion orders and warn­ings were still in place for remote com­mu­ni­ties after a wild­fire broke out and spread quick­ly through the Cleve­land Nation­al For­est on Sat­ur­day. A fire­fight­er received minor injuries and two struc­tures were destroyed in the 2.3‑square-mile (5.9‑square-kilometer) Chap­ar­ral Fire burn­ing along the bor­der of San Diego and River­side coun­ties, accord­ing to the Cal­i­for­nia Depart­ment of Forestry and Fire Pro­tec­tion. It was 10% con­tained Sunday.

Mean­while, California’s Dix­ie Fire, the sec­ond-largest in state his­to­ry at 1,193 square miles (3,089 square kilo­me­ters) was 48% con­tained in the Sier­ra-Cas­cades region about 65 miles (105 kilo­me­ters) north of the Cal­dor Fire. Near­ly 700 homes were among almost 1,300 build­ings that have been destroyed since the fire began in ear­ly July.

Con­tain­ment increased to 22% on the 12-day-old French Fire, which cov­ered more than 38 square miles (98 square kilo­me­ters) in the south­ern Sier­ra Neva­da. Crews pro­tect­ed for­est homes on the west side of Lake Isabel­la, a pop­u­lar recre­ation area north­east of Bakersfield.

More than a dozen large fires are being fought by more than 15,200 fire­fight­ers across Cal­i­for­nia. Flames have destroyed around 2,000 struc­tures and forced thou­sands to evac­u­ate this year while blan­ket­ing large swaths of the West in unhealthy smoke.

The Cal­i­for­nia fires are among near­ly 90 large blazes in the U.S. Many are in the West, burn­ing trees and brush des­ic­cat­ed by drought. Cli­mate change has made the region warmer and dri­er in the past 30 years and will con­tin­ue to make the weath­er more extreme and wild­fires more destruc­tive, accord­ing to scientists.

The Depart­ment of Defense is send­ing 200 U.S. Army sol­diers from Wash­ing­ton state and equip­ment includ­ing eight U.S. Air Force C‑130 air­craft to help fire­fight­ers in North­ern Cal­i­for­nia, the U.S. Army North said in a state­ment Sat­ur­day. The sol­diers are expect­ed to arrive in Cal­i­for­nia in ear­ly Sep­tem­ber after a week-long train­ing. The C‑130s have been con­vert­ed into air­tankers that can dump thou­sands of gal­lons of water on the flames.

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