BETHLEHEM, Pa. — The first major blast of wintry weather in the United States happened, perhaps, in a rather predictable place.
The Chicago area was digging out last week after a band of lake-effect snow buried the Windy City, dropping up to a foot in some areas.
And while the Lehigh Valley has yet to see true measurable snow, it got a coating from lake effect showers streaming across the region early Monday.
"We are likely in for a faster start to winter than we’ve seen since the 2020-2021 season."EPAWA meteorologist Bobby Martrich
Meteorologists said it could be a sign of things to come.
“We are likely in for a faster start to winter than we’ve seen since the 2020-2021 season,” EPAWA meteorologist Bobby Martrich wrote in his most recent long-range outlook.
Keys to December snow
Martrich said he’s looking at a few key factors for possible December snowfall:
There is potential for a Sudden Stratospheric Warming Event, or SSWE — a significant disruption of the polar vortex — that could send Arctic air spilling into the United States, leading to a particularly chilly back half of December.
In fact, Martrich said it could solidify his colder-than-average temperature outlook, which had not even factored in the polar vortex when it was introduced three weeks ago.
The next thing to watch would be what Martrich calls the La Niña background state, which “suggests typically colder-than-average temperature, not to mention all of the climate models for December are suggesting colder-than-average tropical forcing,” he said Monday.
During a La Niña event, the Pacific Ocean cools down in certain areas, changing where rain falls in the tropics. Those changes affect weather patterns around the world.
In the United States, La Niña’s impact is usually strongest in the winter when the jet stream is most active, leading to colder, stormier weather than usual across northern parts of the country.
“Moving into favorable phases for colder than average temperatures is a huge contributor,” he said, pointing to chances for light-to-moderate snow, perhaps in the second week of December.
“Any bigger potential would likely be mid-month onward,” he said, emphasizing “higher than usual confidence in the December long-range forecast.”
Others on board for a snowy December
Martrich is not the only one on board with a potentially snowy December.
Noted forecasters and climatologists also are warning that a SSWE could disrupt the polar vortex much further south than normal.
Judah Cohen, a research scientist at MIT, told USA Today newspaper he’s watching to see how cold air from the north will be steered by the La Niña pattern.
He told the publication the key will be whether the warming event strongly influences the jet stream, leading to an extended period of colder and/or snowier weather in December.
Additional leading voices have echoed the same, consistently warning long-range outlooks are “dropping the Arctic hammer.”
Martrich also offered this additional warning: December could still be below average in these parts with above average snowfall irrespective of this outcome.
Get the snow shovels ready.
