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.
