BOZEMAN – On Christmas Day, Southwest Montana experienced an extraordinary surge in temperatures, setting multiple daily record highs alongside several record warm minimums. The region saw numerous declarations of “The Warmest Christmas Ever” with notable warmth blanketing the area.
Among the cities celebrating these record-setting temperatures were Belgrade, Dillon, Ennis, Livingston, Helena, Townsend, and the West Gate of Yellowstone National Park. Notably, Lake Yellowstone recorded its highest average temperature for Christmas in history.
These record temperatures were predominantly concentrated in the southern half of Montana and far western regions. Noteworthy mentions include Butte and Kalispell, which experienced their fifth warmest Christmas, while Missoula recorded its fourth warmest and Anaconda its third. In the eastern part of the state, Billings noted its second warmest Christmas on record.
This warm trend extended beyond Montana, affecting the wider region from Salt Lake City, UT, to Cheyenne, WY. Much of Idaho also recorded its warmest Christmas, with places like Idaho Falls, Pocatello, and Boise achieving new average temperature records for December 25th.
So, what caused this warmth? The month of December has been heavily influenced by an Atmospheric River, bringing unseasonably warm temperatures and significant precipitation to much of the western United States. This phenomenon has also led to devastating floods in the Pacific Northwest, California, and parts of northwestern Montana.
What is an Atmospheric River? It refers to a concentrated flow of moisture in the atmosphere. When the Polar Jet Stream dips closer to the equator, it facilitates the northward movement of warm, moist air. These moisture-rich "fire hoses" often deliver an ongoing supply of deep subtropical moisture. While coastal areas of the Western U.S. absorb most of this moisture, enough occasionally reaches the central and northern Rockies.
This persistent westerly to southwesterly flow aloft has kept temperatures above normal, resulting in record daily highs. In fact, Dillon and Belgrade have each set 10 new record highs so far this December.
In the West Yellowstone area, this warm and wet pattern has been evident, with an impressive 4.10 inches of precipitation recorded to date, marking it as the fourth highest total for December. More moisture is expected to arrive this weekend.
In contrast, much of northern Montana has been significantly cooler, as colder Canadian and, at times, Arctic air has drifted across the Hi-Line. This interplay of air masses has created an interesting dynamic throughout the month. Eventually, one will prevail over the other, and as we approach January, a return to more typical cold and snow is needed to help replenish the mountain snowpack.
