Scorching heat blamed for at least 13 deaths in Texas and another in Louisiana blanketed more of the Southeast today, stretching government warnings of dangerous, triple-digit temperatures eastward into Mississippi and Tennessee.

California, meanwhile, was facing its first major heat wave of the year. The National Weather Service warned that the dry, hot, windy conditions were ripe for dangerous fires in parts of Texas, New Mexico, Arizona, Colorado and Utah.

Mid-week temperatures were forecast to surpass 100 degrees in much of the Southeast and high humidity was expected to push heat index values above 115 degrees in some areas.

Lingering power outages after weekend storms compounded the heat-related misery in Arkansas. More than 10,000 residents were still without power in the central part of the state. In Cabot, northeast of Little Rock, a local senior center provided cool air and a place to charge cellphones and tablets for those without electricity.

“Usually I just come at noon for the meal,” Clint Hickman, still waiting for his power to come back on, said in a phone interview today. “It’s kind of nice to have a little cool air, so I came a little earlier.”

Among the casualties was a man who died late Sunday in Shreveport, Louisiana, the second heat-related death in the state in an unusually warm June. The 49-year-old from neighboring Bossier City had been found lying on a sidewalk in Shreveport, where Sunday’s temperature hit 97 degrees — 10 degrees Fahrenheit higher than the average for the date.

The death of a 62-year-old woman on June 21 in Keithville also was blamed on heat. Relatives found her after she had spent several days without electricity because of earlier severe storms, the Caddo Parish Coroner’s Office said.

In southeast Louisiana, the National Weather Service office in Slidell issued an excessive heat warning on June 16, the earliest in the year it’s ever done so for that area, a meteorologist said.

Eleven of the Texas heat-related deaths occurred in Webb County, which includes Laredo. The dead ranged in age from 60 to 80 years old and many had underlying health conditions, according to Webb County Medical Examiner Dr. Corinne Stern, who said the level of heat in the county was unprecedented.

The area has a higher poverty rate than the state average and that compounds the suffering, Stern said.

“The vast majority do not have air conditioning in their homes. They either have the fans off, or they have fans on but not proper ventilation,” Stern said. “There has been at least one or two that have air conditioning but don’t want to run it due to the bill.”

Two Florida hikers also died while hiking in extreme heat at Big Bend National Park.

The heat has prompted the U.S. Postal Service to allow earlier starting times for letter carriers, according to the National Association of Letter Carriers Lonestar Branch. This comes after the death of a letter carrier who died June 20 in near triple-digit heat. The cause of the carrier’s death was still under investigation today.

The unusually high temperatures were brought on by a heat dome that has taxed the Texas power grid and brought record highs to parts of the state, according to meteorologists.

That dome is spreading eastward and by the weekend is expected to be centered over the mid-South, said meteorologist Bryan Jackson with the National Weather Service in College Pak, Maryland.

Texas temperatures should then begin to drop from highs above 100 (38 degrees Celsius) degrees to daily temperatures in the 90s, Jackson said.

“It’s relief from the extreme heat,” Jackson said. “It’s not really an end to a heat wave; it’s just an end to the extreme part of the heat wave.”

Another dome of heat has already developed on the West Coast, and an excessive heat warning is in place in a wide swath in the central part of the state, according to Jackson.

“By this weekend there is a risk for record high temperatures exceeding 100 degrees … close to 110 degrees in the Central Valley of California,” Jackson said. “Then some of the more typical mid-summer heat of getting above 115 degrees in the hottest areas of the desert Southwest.”

Apart from the heat dome moving over the Southeast, California’s Central Valley was under an excessive heat watch from Friday through Sunday, with highs up to 110 degrees in some areas. Much of the region around San Francisco Bay will be under a heat advisory.