Terra / MODIS True Color composite image of Alaska from 2026-02-16

Frigid Arctic air mass develops during winter 2025–2026

This event occurred from December 5, 2025 to January 10, 2026

During the first half of boreal winter 2025–2026, an unusually long-duration cold snap occurred over a large area of Alaska and northern Canada. According to an analysis by Rick Thoman of the University of Alaska Fairbanks, this was “the most significant prolonged cold snap for Alaska since 2012”. Notable extremes included 32 straight days with high temperature 0 $\degree$ F or lower at the Fairbanks, Alaska airport (the second-longest streak on record).

The Thermal Infrared Spectrometer (TIRS) instruments aboard the two PREFIRE CubeSats, operating in sun-synchronous polar orbits, frequently recorded the radiation emanating from this frigid and dry air mass. These observations include unprecedented spectrally-resolved measurement of the upwelling radiation at far-infrared (> ~15 µm) wavelengths. The maps below show that mean brightness temperature (BT) measured by PREFIRE-TIRS1 over Alaska and northern Canada was much colder during 05 Dec through 10 Jan of the 2025–2026 boreal winter compared to the previous winter. Although the spatial patterns of temperature are broadly similar across the spectral bands measured by PREFIRE, there are differences in actual BT values between the far- and mid-infrared bands that result from differing effects of water vapor and clouds on the outgoing radiation at these wavelengths. Mapping the difference between the two winters helps highlight the regions where temperatures were colder during 2025–2026.

Maps of PREFIRE-SAT1 brightness temperatures over northern North America during early winter 2024–25 and 2025–26 — Maps of PREFIRE-SAT1 L1B brightness temperature (BT) averaged over four spectral bands and a 0.5 degree lat/lon grid. Data are from the early winter (05 Dec – 10 Jan) of 2024–25 (left column) and 2025–26 (center), along with the difference between the two winters (right). Rows show BT averaged over spectral bands: mid-infrared 1 (MIR-1; first row), mid-infrared 2 (MIR-2; second row), far-infrared 1 (FIR-1; third row), and far-infrared 2 (FIR-2; fourth row). The number of channels and wavelength range for each spectral band is given on the left side of the image.

Later in January, a change in the atmospheric circulation released this pent-up Arctic air mass southward into much of North America. This triggered numerous societal impacts, including widespread extreme cold warnings in the eastern United States and a devastating ice storm in the mid-South region of the US.

These PREFIRE observations also capture the extreme spatial variability in outgoing radiation that can occur during boreal winter. While much of North America shivered under a brutally cold air mass, Greenland was experiencing much warmer conditions than the previous winter, as shown by the difference maps in the right column of the image.