Flood — Upr Tanana Vly Fortymile, Alaska

2023-05-12 to 2023-05-13 · near Eagle, Upr Tanana Vly Fortymile, Alaska

Event narrative

Ice jam flooding started late at night on May 12th and when the Riverwatch team landed in Eagle on May 13th (early afternoon) flood waters had receded leaving stranded ice well above the bank. The USGS river gage had a preliminary crest of 42 feet at 5 AM ADT on May 13th. Moderate flood impacts included damage to the seawall with the guardrail along the seawall was destroyed, stranded ice, and flooding on the road between Eagle and Eagle Village leaving the road impassable for a week due to stranded ice. Several structures in town were damaged by ice and floodwaters, including the Falcon Inn which had a high water mark of almost 2 feet into the finished basement. Preceding the ice jam, the river was at or above bank full, with Mission Road beginning to flood late afternoon of May 12th.

Prior to the Eagle event, there were multiple significant ice jams in Canada, including a 30-mile-long jam with the toe of the ice jam located approximately 30 miles upriver from Eagle on May 12th. This jam caused major flooding in Canada. Downstream of Eagle was a mix of intact ice sheets, open water, and an ice jam 8 miles downriver from the month of the Tatonduk River. Thus, conditions were ripe for ice jams to impact Eagle once the Canadian ice jam released, which occurred late at night on May 12th.

Wider weather episode

A prolonged period of well-below-average spring temperatures combined with an above-average winter snowpack created a dynamic breakup of the Yukon River. This resulted in numerous ice jams and snowmelt flooding on the Yukon River. Breakup flooding began on May 12th in eastern Alaska in Eagle and ended on June 3rd in the Yukon River delta at the Bering Sea coast at the community of Emmonak. The primary cause of this active flood year was a 1-2 week delay in breakup when compared to typical timing. April temperatures were well below normal, and when temperatures began to warm in early May, it melted the low-elevation snowpack quickly. Because of the relatively quick addition of snowmelt onto strong ice, the ice was more susceptible to jamming and floods. In addition to the late breakup, the snowpack this winter was 1 to 1.5 times greater than the climatological normal for interior and western Alaska. Significant ice jams and associated flooding on the Yukon River in Canada resulted in large volumes of ice and water to move down the Yukon River into Alaska.

View location on OpenStreetMap → (64.7940, -141.2075)

Source: NOAA Storm Events Database, event_id 1101977. Narrative written by the NWS forecast office that issued the report.