Updated

Strong winds and heavy rains rumbled across the Southwest on Monday, causing flooding in the Lake Mead area east of Las Vegas, diverting dozens of flights in Phoenix and delaying a hot-air balloon race in New Mexico.

The storms were spawned by a low-pressure system coming in off the California coast, National Weather Service meteorologist Charlotte Dewey said. He urged people to avoid outdoor activities because of lightning.

The National Park Service closed roads in the Lake Mead area because of flooding and debris; there were no immediate reports of property damage. In Phoenix, up to 30 flights were diverted from Phoenix Sky Harbor International Airport to other airports after rain, wind and dust moved through the area. Departing flights were experiencing delays of 15 to 30 minutes.

And in Albuquerque, organizers of the annual America's Challenge gas balloon race delayed the start of the festivities by at least one day because of concerns over the weather.

The race was initially scheduled to start Tuesday evening during the Albuquerque International Balloon Fiesta before afternoon thunderstorms caused a delay.