By Denise Chow -
NBC News
It's been a wild winter.
The end of February marked the end of the “meteorological winter”, which spans December, January and February and is an independent designation of the astronomical seasons, culminating a series of months in which the weather behaved in unexpected ways.
Throughout the northern hemisphere, many normally frigid places experienced dry and warmer-than-usual conditions, while others were hit with heavy snowfall and damaging ice storms.
Some cities in the southeastern US recorded temperatures above 80 degrees Fahrenheit last month.
One Texas location even hit triple digits.
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Although official figures won't be confirmed for a few weeks, experts say this winter will certainly rank among the 10 warmest ever recorded, another worrying milestone in a trend caused by the climate emergency.
“It's been a real roller coaster,” says Bob Henson, a meteorologist and staff writer for Yale Climate Connections, an online news service, referring to winter extremes.
And warmer winters have real consequences: Vegetation, including spring leaves on trees, is blooming days and weeks ahead of schedule in some parts of the country.
In Washington DC, for example, the cherry trees are blooming ahead of schedule, expected to reach full bloom in about four weeks.
“The concern is that if it is cold in the middle or end of March, it could affect the cu
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Henson pointed to the "striking" temperature contrasts in the US as an example of the strange variability of the season.
Last week temperatures dropped in California, bringing infrequent snowfall even at low elevations, while much of the Northeast enjoyed warmer-than-usual conditions with little to no snow during the winter months.
A group of people relax on a warm afternoon in New York on February 15, 2023. Spencer Platt / Getty Images
La Niña is characterized by a cooling of the eastern tropical Pacific Ocean, producing atmospheric reverberations that can strongly influence weather around the world.
The conditions of this phenomenon can also affect the movement of the jet stream, a fast-moving ribbon of air that flows from west to east and meanders around the northern hemisphere.
The jet stream is driven by temperature differences between the cooler northern polar region and the warmer southern air masses.
Jet stream ripples are what produce everyday weather, but deeper troughs and ridges can develop that contribute to extremes by forcing cold air in one region and warming others.
For most of February, the jet stream curved over North America in such a way that cool air was funneled south along the west coast, while tropical air rose to the northeast, Henson explained.
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"It's not that different from what you can see in the summer, which produces hot and humid weather," he said.
"Of course, it's not going to be hot and humid in January or February, but just like that high is usually persistent in the summer, this one has been quite persistent through the winter."
The result was snow along the West Coast, including rare blizzard warnings in Southern California, while heat records were set in February for some cities in Georgia, Florida and Tennessee, as well as North Carolina and Virginia. .
The extremes were also felt beyond North America.
Record winter temperatures were recorded in parts of Europe in January, and France went 32 days without rain in any part of the country this winter, raising fears of deepening drought across the continent.
Seasonal variations are normal, but some scientists are actively studying whether global warming is making the jet stream weaker than usual.
Some studies have established links, but more research is needed.
At the moment there is no consensus in the scientific community.
"It's still a work in progress, but something to keep in mind is that the inability to find an exact relationship doesn't mean the relationship doesn't exist," Henson said.
Two people stroll under the cherry trees at Capitol Hill in Washington, DC, on February 23, 2023. Anna Rose Layden/Bloomberg via Getty Images
What is well known, he added, is the general warming trend caused by the climate emergency.
“There is no question that the weather is warming up,” Henson said.
“When it rains, it tends to rain harder.
When it is dry, droughts tend to be more intense due to higher temperatures.
Those things are well and firmly established,” he noted.
The general shift towards warmer winters does not mean that there will not be intense storms to contend with in the coming years.
Although this winter was generally warm, a brutal winter storm ripped through Buffalo, New York, in December, a severe ice storm swept through the South in early February, and the Midwest was hit late in the month with heavy snowfall that left no electricity to hundreds of thousands of people.
“Climate warming doesn't rule out extreme winters,” Henson says, “but the trend is for less snow and less cold over time.
We know it very well."