Spring river ice break-up is underway south of the Brooks Range in Alaska and the Yukon Territory. In most areas break-up is a little bit later than normal but not dramatically so. So far, there hasn’t been any major flooding, but ice jam flooding can and does develop quickly, so the story could be different tomorrow.

Snowpack at the end of the 2025-26 snow accumulation season (Fig. 1) was significantly above normal across much of the Tanana and Yukon River drainages. Combined with near to below normal temperatures in April and early May, this raised concerns for significant ice jam flooding as water levels could rapidly increase. Snowpack in mid-April was near normal in the Porcupine drainage and below normal in the Koyukon drainage. The Kuskokwim valley presented a mixed snowpack picture, with above normal snow water equivalent along the lower river but generally near to below normal above Kalskag.

Break-up on tributaries of the Tanana River and southern tributaries of the Yukon River started the last week of April and first days of May. The Fortymile River, south of Eagle, was reported to be breaking up on May 1 and break-up on the Chena River near Fairbanks (above Ft. Wainwright Power Plant) occurred on May 2. Unlike some recent years, ice was reasonably intact on the Tanana river at Nenana just prior to moving out as waters rose in the river (Fig. 2).

Break-up on the Tanana River at Nenana (below Fairbanks) clocked in at 6:58pm AKST May 4, a week later than last year, though not unusually late for the 21st century (Fig. 3). However, a May 4th break-up would have been earlier than normal prior to the 1970s. For the back story on the unique Alaska climate record we have in the break-up dates on the Tanana River at Nenana, see my May 2023 post, here.

On the Yukon River, Dawson, Yukon Territory, with annual observations since 1896, has the longest time series of river break-up dates in northwest North America. This year the ice broke mid-afternoon on May 5th, a little later than the modern average but nothing unusual at all (Fig. 4). Unlike at Nenana, there hasn’t been a “top ten” latest break-up at Dawson in more than 40 years, and nine of the ten earliest break-ups have occurred since that time.

Ice went out at Nikolai on April 25, a couple days later than usual. Nikolai, on the South Fork Kuskokwim, is the farthest upriver community and is often the first place for ice to break due to the comparatively steep slope of the river there. Since then, break-up along the middle and upper Kuskokwim has proceeded. Break-up was reported on May 5 or 6 at Sleetmute, Crooked Creek and Chuathbaluk and shifting ice was reported at McGrath. On May 7th ice was moving at Aniak. This entry from the Alaska-Pacific River Forecast Center’s River Notes is interesting:

In spite of the high end-of-season snowpack in the Tanana and upper Yukon River Valley, there has been comparatively minor flooding so far (through 11am AKDT May 8 ). Significant flooding was reported May 6th at Chalkyitsik, east of Fort Yukon, due to an ice jam on the Draanjik River just below town. At Eagle, the road to Eagle Village was covered with water for a few hours on May 5th before receding. There was also ice jam flooding on the Chatanika River north of Fairbanks impacting (mostly) recreational cabins along the river. This May 7th Alaska Public Media article provides more details on flooding and high water issues around the Interior.