This post has been updated.

Thousands of San Antonio residents remain without power and air conditioning after severe thunderstorms struck the city Thursday, with temperatures on Friday expected to soar to nearly 100 degrees.

As of 10 a.m. Friday, CPS Energy crews were still working on restoring power to approximately 18,000 customers. Thunderstorms that brought high winds, rain, hail, and lightning most severely affected areas north of downtown, according to the utility’s outage map.

Storms gave way to blue skies and sweltering temperatures on Friday, with National Weather Service forecasters predicting temperatures to rise to 99 degrees in San Antonio.

“We’re working against the clock because as you know, we’re approaching triple-digit heat probably today and tomorrow,” Mayor Ron Nirenberg said at a Friday media briefing.

At 9:30 a.m., officials with the City, CPS Energy, and VIA Metropolitan Transit spoke about recovery efforts after the storm. They held the briefing in the Woodlawn Lake area, one of the neighborhoods most severely hit by power outages.

Fallen trees and limbs were the primary cause of loss of power, said Rudy Garza, senior vice president of distribution services and operation for CPS Energy. More than 430 downed power lines were reported across the city.

CPS Energy had 500 crew members working overnight, Garza said, adding that the utility is working with New Braunfels Utilities and the City of Austin to bring more crews to restore power.

“I can assure, anyone who is capable and available to work and is qualified to get in a bucket and restore power is out on the job this morning,” Garza said.

To help residents without air conditioning stay cool, the City is opening libraries and senior centers as cooling centers, with VIA providing free transportation to residents who need shelter from the heat, City Manager Erik Walsh said.

Walsh urged residents who need City services to call 311 to report downed lines and fallen trees. On Thursday, emergency responders logged roughly double the number of 911 calls as normal, with 27 major vehicle collisions, some of them likely the result of streetlights that lost power.

Since the storm hit, San Antonio firefighters responded to 133 calls of power lines down and three structure fires caused by lightning, San Antonio Fire Chief Charles Hood said. Firefighters also made one high-water rescue that was successful, he added.

The intense storms were the result of a clash between air masses coming from the north and south, said Melissa Huffman, National Weather Service meteorologist

“We had a combination of some deeper moisture from the Gulf of Mexico in place across the region today, as well as ample heating,” Huffman said. “We had a little disturbance moving across the Southern Plains. … The combination of these factors created an environment for strong to severe thunderstorms to develop.”