Intense thunderstorms drenched parts of the Southwest on Tuesday, delaying flights and stranding motorists in the Las Vegas area and flooding two mobile home parks in Southern California. East of downtown Las Vegas, television news video showed yellow school buses inching slowly along swamped roads in some neighbors and muddy brown water up to the lower window sills of stucco homes in others. A Twitter photo showed dozens of cars submerged in water up to their headlights in a parking lot outside a University of Nevada, Las Vegas sports arena.