Over the past week, winter has walloped North America hard. In much of the U.S. and Canada, temperatures were below freezing. In some cases, the mercury was higher at the North Pole.
Temperatures in the early morning hours dropped below zero throughout much of the Midwest and northeastern United States overnight on Wednesday and Thursday. Illinois may have broken a state record when Mt. Carroll recorded a temperature of 38 below zero on Thursday morning. In Cotton, Minnesota, the low was -56.
But in Lodi, trees along Church Street have already burst into bloom and temperatures have been spring-like in the mid-60s.
“It’s not incredibly above normal, it looks like, but generally 5 to 10 degrees above normal” over the past four or five days, said meteorologist Max Vido of Accuweather, a private forecasting firm.
Part of the answer is the jetstream.
“It’s this flow of air that dictates storm systems and air masses,” Vido said.
During the recent frigid spell, the jetstream was rising sharply north over the Pacific. Then, east of the Rockies, it dropped sharply southward over Canada toward the Gulf Coast, bringing freezing Arctic air with it.
“It’s a very amplified jetstream,” Vido said.
Adding to the freezing air is an unstable Polar Vortex. Usually at this time of year, there is an area of low pressure over the North Pole.
“It’s always there during the winter months,” Vido said.
Icy winds rotate counter-clockwise tightly around it, keeping the pole cold.
Or at least, that’s how it’s supposed to work.
“In recent years we’ve seen disruptions to this strong vortex,” Vido said.
But in years when temperatures at the North Pole are warmer than usual, the vortex can collapse and the chilly air flows south.
“When that happens, we usually see a ripple effect,” Vido said. “That’s something we’re seeing right now over the U.S.”
So why is the West Coast spared from the cold? It isn’t always.
“The main response to the Polar Vortex disruption is you get a wavier pattern, larger rises and dips in the jetstream,” Vido said — like the large rise over the Pacific and the large dip past the Rockies. In other years, it could be California freezing while the Midwest is warm.
Regardless of the reason for Lodi’s unseasonable weather, the area does need to return to its normal January and February weather soon, for the sake of the local agricultural industry.
“We need the cold weather. It’s extremely important for crops like cherries,” said Bruce Blodgett, the executive director of the San Joaquin Farm Bureau.
Lodi saw spring-like weather in late January three years ago, in 2016. Highs hit the low to mid-60s at the end of January, and lows rarely dropped below the mid-40s, according to records kept by Lodi dentist Patrick Sweeney, who maintains a weather station at Lodi Lake.
The weather was cooler in 2017, but last January, highs were in the 60s again — though nights cooled off to the high 30s and low 40s, according to Sweeney’s website.
The unusual weather did affect a few local growers a couple of years ago, though the ag industry in general still had a decent year, Blodgett said.
“The biggest issue we’ve had is that the cherries have been annihilated a couple of times in the past few years,” he said.
A few factors have played into that, not just the early warmth, Blodgett said. But while cherries had a great year in 2017, they had a bad 2016. The jury’s still out on last year, he said, but it doesn’t look great.
Luckily, winter is on the way.
“We do expect some cooler weather to arrive,” Vido said.
Temperatures are likely to stay mild today, but rain is likely to roll in this afternoon. The weather’s expected to start cooling on Saturday, dropping down into the low to mid-50s during the day with lows hovering around freezing next week, Vido said.
The shift in the weather will be welcome for local farmers.
“We need the rain. We need to get the reservoirs filled, we need the snow in the mountains,” Blodgett said.