Farm leaders are holding their breath as a Canadian arctic blast passes Portland, Ore., today, charging toward the San Joaquin Valley's $1.5 billion citrus crop. About 85% of the fruit is still on the trees.
By Friday, overnight temperatures in Valley citrus groves could drop as low as 21 degrees -- a killing frost for mandarins and navel oranges if the exposure lasts more than a few hours.
December freezes are notorious here. In 1990 and 1998, December cold blasts left damage exceeding $500 million and thousands of people out of work. The east Valley economy was devastated.
Citrus industry leaders are taking this early freeze seriously.
"The concern is real," said Joel Nelsen, president of the Exeter-based California Citrus Mutual, representing more than 70% of citrus growers in this region. "We're sending out notices right now to make sure everyone knows."
The cold core of the arctic blast was minus 33 degrees at 18,000 feet over the Columbia River in Oregon this morning, says private meteorologist Steve Johnson, who is tracking the cold for many growers.
Wind speeds within the core were recorded at more than 100 miles per hour, he said.
"Growers are asking me for forecasts every six hours," Johnson said. "They've speeded up their picking and other operations to get as much of the fruit as possible."
Johnson said the big chill is the result of high pressure or a big mound of air forming above Alaska and bumping the high-elevation jet stream into the Arctic Circle.
The jet stream then roars down through the Yukon, British Columbia, the Pacific Northwest and California, heading into the Valley.
"The trajectory keeps it over land and it dries out," Johnson said. "This kind of thing doesn't happen very often. The pattern is very similar to what we saw in December 1998 and 1990."
Johnson said he has been tracking the arctic blast since Nov. 25. He didn't immediately announce his suspicions about it, hoping the forecast would shift. But it has not changed much, he said.
In cities, such as Fresno, the temperature will not drop as low as the outlying areas due to the heat island effect -- buildings and pavement tend to hold heat and keep temperatures higher.
The National Weather Service says Fresno can expect near-record lows. On Thursday, Friday and Saturday, the lows will be 30, 29 and 32, said meteorologist Paul Iniguez. The record low for Thursday and Friday is 28. The record for Saturday is 25.
Out in farm country, growers will be saturating the ground before Wednesday with water to raise temperatures in the groves, said Nelsen.
By Thursday and Friday, wind machines probably will be switched on to keep warm air from rising, perhaps elevating the grove temperature by three or four degrees, Nelsen said.
"Growers are out there right now making sure their equipment is working," he said. "We will be ready."