Warm, moist, monsoonal weather swept into Southern California on Monday from the tropics of Mexico, reportedly causing two small tornadoes that touched down briefly near Lake Los Angeles in the Antelope Valley.
The twisters did no damage.
The National Weather Service issued a half-hour tornado warning at 4 p.m. after a pilot reported a funnel cloud 15 miles northeast of Palmdale. Deputies at the Antelope Valley sheriff's station said several Lake Los Angeles residents reported that there actually were two twisters, which touched down simultaneously before dissipating in a cloud of dust.
"The people were pretty excited, but it really didn't amount to much," one deputy said.
Thunderstorms pelted the mountains of Orange and San Diego counties during the day, and a few light showers were reported in Pasadena, Altadena and other foothill communities along the San Gabriel Mountains in Los Angeles County. More widespread showers were forecast for today and Wednesday.
John Sherwin, a meteorologist with WeatherData Inc., which provides forecasts for The Times, said the turbulent weather is a byproduct of a large ridge of high pressure parked over Utah and Colorado. Winds circulating clockwise around this ridge are pumping tropical air into Southern California from southern Mexico and the gulfs of Mexico and California.
"A lot of people think it's unusual, but this sort of thing happens almost every July and August," he said.
Energized by the afternoon sun, the tropical thunderstorms produce most of their lightning and rainfall before sunset, becoming dormant during the night before bursting forth again during the heat of the afternoon.
"There's a good chance of rain again on Tuesday afternoon and Wednesday afternoon," Sherwin said. "Most of it will fall in the deserts and in the mountains, but there could be some in the San Gabriel and San Fernando valleys."
Sherwin, who was surprised at the reports of twisters Monday in the Antelope Valley, said he doubted there would be any more of those in Southern California in the near future.