FARGO, N.D. (Valley News Live) –
Temperatures are getting colder, but the First Alert StormTeam says the region is about to see something that hasn’t happened at this time of year in 25 years.
La Nina has arrived for early winter, but another piece of the long-range forecasting puzzle could have major implications on weather in the coming weeks.
Historical cold snaps linked to polar vortex disruption
March and April 2023 brought 52 of 61 days with below average temperatures and a total of 31.8 inches of snow. Mid-January through February of 2019 saw 42 of 44 days below average along with nearly two feet of snow.
Both periods resulted from a weakened polar vortex due to a Sudden Stratospheric Warming, or SSW event.
The Polar Vortex is a fast-moving jet stream between 10 and 30 miles above the Earth’s surface circling the polar regions. This polar vortex is strong enough to confine the coldest temperatures to the polar regions.
However, once every two years on average, a Sudden Stratospheric Warming event slows down or even reverses the strong west to east polar vortex current. The result causes the frigid polar air to “break out” by forcing the polar jet stream closer to the Earth’s surface and dive into the United States for an extended period of time.
Rare November timing
While most of these events occur in mid to late winter, rarely a Sudden Stratospheric Warming will begin in December and even more rare, November. The last November SSW came in 2000, and before that, 1968.
Now, 25 years later, an SSW is under way and forecasted to strengthen in the coming weeks. Because there is a lag time of several weeks, the full impact of the weakened polar jet likely won’t arrive until December.
December 2000 comparison
Records from December 2000, which followed the last November Sudden Stratospheric Warming event, show that once Fargo started feeling the effects on December 5th, 17 of the following 27 days saw high temperatures only reach the single digits with lows below zero all but three days. The region received 13.4 inches of snow that month.
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