As Roaring Fork Valley residents navigate this winter’s low precipitation, leaders at the Aspen Center for Environmental Studies (ACES) are warning that shifting average temperatures are also a significant concern. At the beginning of the month, Forest and Climate Director Adam McCurdy noted the asymmetric warming trend in ACES’ monthly “Wild Tracks” newsletter.
Asymmetric warming is a pattern observed by scientists in which average nighttime temperatures and average daytime temperatures change at different rates. In the early 1990s, a coalition of meteorological scientists analyzed data from over 2,000 weather stations around the world for patterns between 1951 and 1990. While the most significant finding was that average temperatures had increased over those four decades, they noted that maximum temperatures (or daytime highs) had risen by an average of 0.5 degrees Fahrenheit during that time. Minimum temperatures (nighttime lows) had warmed nearly three times as much for an average of 1.4 degrees.
Additional research has confirmed those patterns. In 2018, another study was published. It analyzed data between 1901 and 2014, concluding that the difference between daytime and nighttime temperatures (diurnal temperature range) has decreased over that time period as nighttime low temperatures rise quicker. The data pattern was more clear in certain regions, including North America. In the Fourth U.S. National Climate Assessment, also released in 2018, average minimum and maximum temperatures in the nation were observed at 1.4 degrees and 1.1 degrees warmer, respectively, compared to data between 1900 and 1950.
McCurdy’s warning for the Roaring Fork Valley is a stark one. For the winter season thus far, he said that the region’s nighttime temperatures have been 8.8 degrees warmer than the long-term average. For an area where typical winter overnight lows had been in the single digits to low teens, a nearly nine degrees swing is abnormal. However, it does follow a trend local scientists had already observed. Six years ago, Aspen Journalism published a report showing that Pitkin County’s average nighttime winter lows had increased by about 3.5 degrees from 1950 to 2017 (from below 12 degrees to over 15 degrees).
This winter, that shift influenced Aspen SkiCo’s ability to make snow on the resort mountains. Nighttime temperatures did not drop low enough for man-made snow to last until weeks later than normal. Natural snow that has fallen this winter has been a challenge to preserve between increased overnight and daytime temperatures, particularly at lower elevations.
Snowmaking is a relatively new part of the ski industry. Aspen SkiCo started making snow following the winter of 1976-77, and originally based production on filling gaps during drier winters. But the early-season production and supplementation has become standard, both for special events such as the X Games and to open in time for Thanksgiving.
Despite last week’s storm, the area remains largely in extreme or exceptional drought. As of Jan. 20, snow-water equivalent data from across Colorado shows the state’s snowpack has dropped below the measured historical minimum, dating back to 1987. As of Jan. 22, the Roaring Fork Conservancy reported that the Roaring Fork Watershed’s snowpack is at 56% of normal. Some of the lowest relative measurements are from higher elevation SNOTEL sites.
While precipitation has been low for the first four weeks of 2026, following 2025’s year-long drought, some of the low snowpack can be attributed to increased daytime and overnight temperatures. For Basalt, average January highs have historically been around 33 degrees, with nighttime lows of 4 degrees, according to U.S Climate Data. For much of the first half of the month, Basalt’s daytime highs were in the high 40s, or even low 50s, while overnight lows did not drop below 20 degrees. That trend was true for the entire Valley, though specific temperatures varied by a few degrees.
Increased nighttime cloud coverage and geography-related temperature inversions can be contributing factors to the overnight lows warming faster. Overcast nights trap heat, which prevents deep cooling that helps preserve snowpack during sunny or warmer days. Mountain valleys can also experience temperature inversions even without nighttime cloud cover. When this occurs, typically during high-pressure systems, dense cold air sinks to lower elevations, while high elevations experience warmer temperatures. This can be exacerbated by air pollution. Particulates in the air can behave similarly to clouds and trap heat, especially overnight.
Colorado State University’s Colorado Climate Center tracks temperature and other climate data throughout Colorado. The school’s data shows that statewide average temperatures increased by 2.3 degrees from 1980 to 2022.
What changes to local ecosystems and recreation should we anticipate if warming trends continue and how should we prepare? Join the discussion on Mountain Perspectives.