FRESNO, Calif. (AP) -- A cold snap that has California farmers struggling to protect the $1.5 billion citrus crop has slowly started to ease, though freeze warnings remained in effect Tuesday morning throughout the state.

For a fifth night, temperatures in the San Joaquin Valley, the state's agricultural heart, dipped as low as 21 degrees.

"It was still a critical night" even though the temperatures were a degree or 2 warmer than previously, said Bob Blakely, director of industry relations for Exeter-based California Citrus Mutual, an association representing 2,200 growers who have roughly 65 percent of the state's citrus acreage.

Growers needed wind machines and irrigation to offset the cold, mainly with success. However, damage was predicted to the mandarin crop, a growing segment of the industry.

"We still think the navel oranges have come through in good shape," Blakely said.

Growers are used to such cold snaps coming at least once each winter, he said.

Protection didn't come cheap.

Lindsey-based Robert LoBue -- who grows 1,000 acres of citrus, including mandarins -- said he runs one wind machine for every 10 acres and has to employ a crew to operate them.

"We're very diligent, we run the wind and water all night," LoBue said, "but we're spending thousands of dollars to protect these crops."

In urban centers, it was 39 degrees in downtown Los Angeles early Tuesday, while San Francisco had 37 and San Diego, 36.

Motorists were urged to use caution because of icy conditions in some places. On Monday, black ice was blamed for a seven-car pileup in Oakland and other crashes elsewhere. No serious injuries were reported.

Highs Tuesday were generally expected to be in the 50s to mid-60s, some 10 to 15 degrees below normal in some areas. And there could be wind gusts to 45 mph in the valleys and mountains.

The National Weather Service predicted another night of frosty weather, but forecasters said temperatures would begin to warm gradually as the week progressed. High pressure was building and temperatures could hit 70 again in Southern California by Thursday, forecasters said.

Copyright 2013 The AP.