Southland braces for winter wave

After starting the week with hot winds and temperatures in the 80s, Southern California will end it with an extreme cold spell, raising concerns about crop damage, road conditions and the health of the frail and elderly.

Overnight temperatures are expected to dip into the 20s in local valleys, and snow levels in the mountains could drop to 1,000 feet, said Jamie Meier, a meteorologist with the National Weather Service in Oxnard.

“In terms of overnight lows, that is where it’s going to be very dramatic,” Meier said Thursday.

Cold wind from the north combined with clear skies over the weekend will cause overnight temperatures to drop precipitously, she said.

“Make sure you’ve got all the blankets out and the pets indoors,” she said.

William Patzert, a meteorologist at the Jet Propulsion Laboratory in La Canada Flintridge, had some more advice.

“Now is also a good time to bring in some of your potted plants,” he said. “We’re definitely in for it here. This is the big Friday-night freeze.”

Patzert said that a blast of Arctic air was cascading like a huge U-shape across the Canadian border from Seattle to San Diego and much of the country, bringing stinging cold with it.

“We’ve had jet streams on steroids coming out of the Gulf of Alaska, but this is much colder air. This is a massive mountain of zero to sub-zero cold air,” he said. “This is a huge mass of air, not just a jet stream. This is the big breakout that really is the signal for the beginning of winter.”

State officials, who last summer struggled to deal with the deaths of more than 100 mostly elderly people during a record-setting heat wave, said Thursday they were gearing up to deal with this round of extreme weather.

Gov. Arnold Schwarzenegger ordered officials to place 16 additional “warming centers” on standby to provide shelter for those left out in the cold.

Officials said low-income residents, the very young and the elderly and disabled were especially vulnerable to the effects of hypothermia, and they urged residents to seek help in heating their homes and finding shelter.

“Our community providers are prepared with a number of programs to help those suffering from the cold,” said Lloyd Throne, director of the California Department of Community Services and Development.

Across the state, farmers were preparing for sub-freezing conditions that could kill crops and other vegetation, and towns along the Sierra foothills were bracing for the formation of slippery black ice, which can cause vehicles to skid out of control.

In the Southland, snow could fall along the Grapevine, which connects Los Angeles County with the Central Valley, and on California 2 from La Crescenta to the lower foothills of the San Gabriel Mountains, according to National Weather Service meteorologists.

The lows were expected to affect Northern and Central California, and the coldest valleys in the Bay Area could reach temperatures in the teens, officials said.

Daytime temperatures on Thursday reached 64 degrees. That was downright chilly compared with Monday’s high of 88 degrees and Tuesday’s of 85. The hot, dry weather sparked a red flag fire danger warning in Los Angeles County earlier this week, and the conditions contributed to a fast-moving blaze Monday night in Malibu that destroyed or damaged several homes.

A series of two back-to-back cold fronts is causing the winter chill. The first passed through the region Thursday morning, and the second was expected to make its way through the Southland on Thursday night.

Weather officials said there is a chance of showers today into this evening, with snow levels between 1,500 and 2,000 feet late tonight.

There could be up to an inch of snow in the Antelope and Cuyama valleys, with an inch or two possible in the mountains.

Frost advisories will be in place along the Ventura County coast and in the Santa Monica Mountains and may even be issued for the coastal areas of Los Angeles County, said National Weather Service officials.

The combination of low temperatures and gusty winds will create wind chills of between 10 below zero and 5 above zero through Saturday morning.

The chilly conditions will hit Orange County as well.

The National Weather Service forecasts lows in the mid-30s along the coast and in the central county tonight and Saturday night. In the Inland Empire, lows could dip into the 20s Saturday night.

amanda.covarrubias @latimes.com

hector.becerra@latimes.com

Times staff writer Rong-Gong Lin II contributed to this report.