2024 Tanana River at Nenana Break-up
Pretty much as expected nowadays
Ice on the Tanana River at Nenana went out early in the morning on Saturday, April 27th, 11 days earlier than last year. This is very close to the recent average and the earliest since 2019. The Nenana Ice Classic reported the official break-up as occurring at 5:18am AKST. Curiously, this was only the sixth time since 1917 that the ice went out between 1am and 9am. Figure 1 show images from the Nenana Ice Classic website from Friday early afternoon (left), showing the tripod standing on water-covered ice, and Saturday morning shortly after the tripod floated out of sight.
The 108 year time series of break-up dates at Nenana is one of the very best climate records in Alaska. The Tanana River at Nenana is a single channel. The population of Nenana has not changed much in the past century. The funky configuration of a tripod connected to a clock has been used since the beginning. For more details on the break-up observations at Nenana and the observational history, see my post from May 2023, here. Figure 2 plots the date/time of break-up each year since 1917 along with an estimate of the time varying average.
The trend toward an earlier break-up is clear, with the average break-up date nowadays a bit over eight days earlier than it was in the early and mid-20th century. While eight days does not sound like much, that’s actually larger than the typical year-to-year variability1 and so the change is significant from the climate perspective.
In 2011, Peter Bieniek at the University of Alaska Fairbanks led a research effort (published in the Journal of Climate, here) looking at some of the regional and climate scale influences on the timing of river break-up around Alaska. Unsurprisingly, April and May temperatures in Alaska are very important. At the larger scale, El Niño Southern Oscillation (ENSO) was shown to be significantly correlated to the timing of break-up, with El Niño (La Niña) winters favoring earlier (later) break-up the following Spring. Figure 3 builds on Peter’s work: I plot the 1950 to 2024 date of break-up relative to the trend shown in Fig. 2. Each year is colored by whether the January through March Oceanic Niño Index (ONI) was classified as El Niño, La Niña or Neutral. In effect, this shows (possible) ENSO influence after the substantial trend is accounted for. A quick glance at Fig. 3 does not suggest that El Niño/La Niña has much correlation with the timing of break-up relative to the trend.
However, when we parse out breaks-up dates in the El Niño and La Niña years, an interesting pattern emerges, as shown in Fig. 4. For both ENSO phases, the “opposite of expected” break-up date is strongly disfavored. For example, with La Niña in place in the late winter season, only about 20 percent of the time was break-up the following Spring more than two days earlier than that expected from trend alone. Conversely, during El Niño, break-up was more than two days later than the trend only about 20 percent of the time.
So the next time you’re thinking of buying Nenana Ice Classic tickets, remember that the trend is your friend, and El Niño/La Niña can help you narrow down the widow for most likely dates of break-up. As for the hour and minute, well, for that, you’ll need different tools.
Technical details:
The Nenana Ice Classic reports all date/times in Alaska Standard Time. However, no adjustment has been made in the historical observations to reflect the time zone change of October 1983. For purposes here this is inconsequential. Real-time Nenana Ice Classic webcam images are here.
The full period of record mean of 15-year running standard deviation of break-up dates is 5.8 days.