NORTH COUNTY - Temperatures below freezing have filled local homeless shelters and also have San Diego County's prolific agricultural industry counting its losses, though forecasts call for warmer nights by the weekend.

Hardest hit are the avocado groves, where more than 3,000 acres of fruit trees could be ruined in San Diego County and Southwest Riverside County. Local farm officials said statewide avocado losses could surpass record 1990 levels, when California farms lost an estimated 50 million pounds of fruit worth $40 million. Farmers said that they wouldn't know the full effects of the cold weather until at least the weekend.

"It's the coldest spell I've seen in my lifetime," said Mike Rennie, who has grown avocados and citrus in Temecula since 1972. "We don't have the facilities to combat the chill."

Some of the homeless people in coastal North County turned to the Bread of Life Rescue Mission in Oceanside for a warm spot to sleep and a plate of food from a local church.

Sam Johnson, who said he has been living on the street full-time since July, said it was simple irrigation that convinced him he should stay at the shelter.

"I saw water coming out of some sprinklers over there, and it was freezing on the sidewalk," Johnson said.

Because the coast is generally 5 to 10 degrees warmer than inland hills and valleys, homeless men and women often migrate there in winter. But last weekend had coastal temperatures dropping below freezing, a meteorological fact that mystified Johnson.

"It's some kind of record," he said.

Noel Isla, a meteorologist with the National Weather Service, said San Diego County has not seen coastal temperatures this low since 1990.

"It seldom happens but it's not unheard of to go below freezing on the coast," Isla said.

The cold snap sent North County residents searching for any way to bring a little extra warmth indoors. At Denault's True Value in Carlsbad, customers were buying space heaters of all shapes and sizes.

Manager Rich Nyberg said that because coastal cities do not see as much variation in seasonal weather, many homes and apartments are unheated.

"They don't have heaters or air conditioners, so it's fans in the summer and heaters in the winter," Nyberg said.

Most residents might expect heating bills to skyrocket as the temperature falls, but San Diego Gas & Electric Co. said that probably wouldn't happen. Although natural gas usage for SDG&E's customers is up 20 percent compared with last year, natural gas prices are down 33 percent from the same period a year ago. SDG&E officials said the lower natural gas prices should offset any price increases from higher usage.

Utility officials said that customers should see very little change in electricity costs because usage hasn't changed much compared with last year.

The Weather Service issued a "red flag" warning that ended at 6 p.m. Tuesday for most of North County - meaning that conditions were ripe for a fire - adding that much of the young vegetation covering recently burned areas had been killed by the cold and would make good kindling.

The forecast called for clouds and possible rain showers starting tonight. Stan Wasowski said Tuesday that the storm would likely be small and should depart the region by Thursday night.

"Might get a sprinkle here, a little shower there, but it's not going to do much," Wasowski said. "So don't blink, or you'll miss it."

Mostly sunny skies are expected through the weekend. Inland, daytime temperatures will warm, reaching the low 70s beginning Sunday. Overnight lows will be in the mid- to high 30s, getting into the low 40s as the weekend ends.

While energy bills are likely to be about the same as last year, the same could also be said for avocado prices, regardless of local fruit losses. Imports from Mexico and Chile should make up the difference between a normal harvest and this year's reduced harvest. Starting Feb. 1, Mexican growers will be allowed to import avocados to California, the current producer of 90 percent of the U.S. avocado crop.

Freezing temperatures actually freeze the water inside avocado leaves and branches, causing the water to burst and making leaves and branches look like they were burned, farmers said. When that happens to branches, they aren't strong enough to hold the fruit, which falls to the ground and becomes useless to farmers, they said.

Avocados weren't the only agricultural products affected by cold weather. Rennie, chief financial officer for Stage Ranch Farm Management in Temecula, said that he could lose 80 percent of his lemon and grapefruit crop because of the below-freezing temperatures. Nurseries have been working with climate-controlled greenhouses and other devices to keep flowers and plants alive.

While many homeless people turned to North County shelters to stay warm, some of them braved the weather without complaint.

A man fixing himself a yogurt snack in front of the Escondido Public Library proclaimed his independence from local social service agencies' requirements.

"I don't need their soup kitchen," said Gary, who preferred not to give his last name. "I'm a survivor. I survive out here every night."

Gary, in his early 60s, said he had worked for 30 years as a painter but now had trouble finding work.

He said he had a friend at a supermarket who gave him groceries after their expiration date. He also had found quiet places to sleep with his sleeping bag, where he would not attract the notice of the police.

"Out of sight, out of mind," he said.

- Staff writers Patrick Wright, Paul Sisson and Quinn Eastman contributed to this story.