Break up is underway on the Tanana River at Nenana. The tripod of the Nenana Ice Classic fell over on April 27 at 3:56 PM AK Standard Time. This was preceded by much anticipation in the previous few days as ice conditions visibly deteriorated.

Since 1917, Alaskans have places betts on the exact date and time of break up on the Tanana at Nenana. A tripod is placed on the ice and connected to a clock. When the tripod falls over, a mechanism to stop the clock is triggered and defines the winning time.

This unique tradition has produced an equally unique climatological time series tracking break up dates through more than a century. Below is a graph of the Nenana Ice Classic break up dates through 2025. Data is plotted as decimal days of year to avoid a shift in leap years. The axis labels are given as dates for easier interpretation. May first is the 121st day of the year in regular years and the 122nd day of the year in leap years. This year’s break up date (April 27) was the same as last year (also April 27). However, as can be seen in the plot, April 27 2024 was the 118th day of the year, while April 27 2025 was the 117th day of the year. Average break-up dates for the climate reference periods 1931-1960, 1961-1990 and 1991-2020 are plotted as colored lines for reference.

This year’s break up date (April 27) is about two days earlier than average when compared to the 1991-2020 reference period and  a week ahead of the 1931-1960 and 1961-1990 reference periods. The earliest break up date of the time series occurred on April 14, 2019. The latest break up occurred on May 20, 1964.