Another data point has been added to one of Alaska’s longest and most unique climatological time series: The tripod on the Tanana river at Nenana fell over on May 8, triggering a clock that records the time of break-up. The tradition of betting on the timing of the river break-up was started in 1917 and continues to this day. The Nenana Ice Classic is organized by residents of Nenana, who install the tripod and clock system every year.

The plot below shows the day of break up for each year of the time series (1917-2023). 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. Average break-up dates for the climate reference periods 1931-1960, 1961-1990 and 1991-2020 are plotted as colored lines for reference.

Like many time series that show aspects of Alaska’s climate and weather, the Nenana break-up dates reflect the overall warming trend (leading to earlier break up on average), as well as considerable year-to-year variability. Break-up in 2023 occurred late in the season compared to the 1991-2020 average. Cold April temperatures likely contributed to the late break-up. See our monthly report for a recap of the unusual April temperatures. Compared to the previous 30-year climate normals, this year’s break-up date would have been close to average.