This year’s risk of river breakup flooding is above average for much of the state, according to a report released March 13 by the Alaska-Pacific River Forecast Center.
The heightened risks apply broadly to the Interior, much of the Yukon River, the Tanana River, and the lower Kuskokwim River.
Factors for the increased flooding risk include above-average snowpack, average to above-average river ice thickness, high water when freeze-up occurred, and rough ice conditions or freeze-up ice jams reported at multiple Interior locations.
Snowpack for the Upper Yukon River and Tanana River basins, as well as across much of the Yukon-Kuskokwim Delta, has been as much as one and half times above the average this winter.
Rivers in the interior part of the state have seen above-average ice thicknesses following the coldest winter in the region in 30 to 50 years, according to the report. Ice thickness in early March on the Tanana River at Nenana tied the thickest ever recorded for that time of year, reaching 51 inches.
High water levels and jumbled ice conditions for Interior waterways during the fall freeze-up have increased the chance of ice jam flooding along the lower Yukon River and portions of the Kuskokwim River. The average date of breakup on the lower Kuskokwim River at Bethel is May 9. The average date for communities at the mouth of the Yukon River is May 20.
The report says that it is still early to tell how all the melting ice and snow will play out. Near normal temperatures predicted through May for Western Alaska could lead to a dynamic breakup and ice jam-related flood risks on much of the Yukon River. But the report says there is also a potential for above-normal temperatures during the same period, which would significantly reduce flooding risk along both the lower Yukon River and Kuskokwim River.
The exceptions are the Koyukuk River basin in the Western Interior, and the Southcentral part of the state, which face a lower threat of breakup flooding due to below-average snowpack, according to the report.
The forecast center plans to release its next spring breakup report on April 10.
