Worst of Polar Vortex to fuel new pattern change, sending much-needed winter West while shielding snowy East
Although the West initially benefited from the warmth after atmospheric rivers brought catastrophic flooding to parts of Washington and California in December, many mountain ranges are facing major snow deficits.
Pattern change: Much-needed return to winter for the West ahead, while snow-weary East to see warm up
A major change in the weather pattern over North America is ahead. While much of the eastern U.S. has been frozen by rounds of Arctic air and snow, the West has remained unseasonably warm, which has left many mountain ranges in a snow drought. That is expected to change by mid-month, as a shift in the jet stream will open the door for numerous storms to bring snow and rain to the West Coast and Rockies. Additionally, this shift in the jet stream will shield the East from the worst of the polar vortex, which will retreat farther north than earlier projections.
While much of the eastern U.S. has been frozen by rounds of Arctic air and snow, the West has experienced weeks of unseasonable warmth, which has left many mountain ranges in a snow drought. A major change in the weather pattern will flip the script by mid-month, as a shift in the jet stream will open the door for numerous storms to bring snow and rain to the West Coast and Rockies.
Additionally, this shift in the jet stream will shield the East from the worst of the polar vortex, which will retreat farther north than earlier projections.
The core of the polar vortex contains some of the coldest air on the planet and typically sits over the North and South Poles.
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But by late December, the polar vortex was displaced, with a lobe of that cold air parked over Canada. This opened a freezer door over the eastern U.S. that allowed waves of Arctic air to spill south.
Simultaneously, the Pacific-North American jet stream — the steering mechanism for most of the storms over the country — dipped sharply over the East, allowing those storms to tap into the Arctic air. This has produced weeks of bone-chilling cold and snow, including January's deadly and historic cross-country winter storm.
Meanwhile, that same jet stream pattern has locked in a ridge of high pressure leading to weeks of dry and warm conditions over the Mountain West and West Coast.
High temperatures have been 15–20 degrees above average, with record highs expected later this week — San Francisco is expected to reach nearly 70 degrees Wednesday.
But a needed shake-up is expected to begin in the coming days into mid-February.
The trough of the jet stream will park over the West, ushering in rain and snow, while the ridge will move over the East, protecting that part of the country as storms are forced to ride around that area of high pressure.
This comes as new forecasts show that the main lobe of the polar vortex will move more towards northern Asia and the lobe over Canada will retreat farther north than projected earlier this year.
WHAT ARE THE ARCTIC OSCILLATION, NORTH AMERICAN OSCILLATION AND MADDEN-JULIAN OSCILLATION?
Additionally, the Arctic Oscillation — essentially a ring of wind circling the vortex that allows the coldest air to escape — will tighten, reducing the amount of freezing cold outbreaks for the East.
The upshot is a needed return to winter for the West and cold weather relief for the East.
Although the West initially benefited from the warmth after atmospheric rivers brought catastrophic flooding to parts of Washington and California in December, many mountain ranges are facing major snow deficits.
PACIFIC, WASHINGTON - DECEMBER 16: In an aerial view, a neighborhood is engulfed in floodwater on December 16, 2025 in Pacific, Washington. Evacuations have been ordered in 3 suburbs south of Seattle after recent levee failure. Atmospheric rivers are expected to continue in the coming days as northern Washington continues reeling back from historic flooding late last week. Mass flooding along the Pacific Northwest caused historic flooding, tens of thousands of evacuations, and dozens of Coast Guard rescues. ((Photo by Brandon Bell/Getty Images) / Getty Images)
These mountain snowpacks play key roles in providing water for drinking and agriculture during the summer months for a lot of communities throughout the Rockies and West Coast.
SNOWFALL IS CRUCIAL FOR LONG-TERM DROUGHT MITIGATION
The Northern Rockies in particular, are running 50–90 percent below their seasonal snow average.
The snowpack in the Central Rockies, which feeds the Upper Colorado River Basin, is at a record low.
The Wasatch Range in Utah is between 25-90 percent below its seasonal snowfall average.
According to the FOX Forecast Center, Salt Lake City is currently reporting just 0.1 inches of snow for the season, which is nearly 33 inches below its seasonal average to date.
As the weather pattern changes, many of these mountain ranges are expected to see beneficial snowfall over the next 10 days.