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Forecasters fret about flooding potential on Yukon, Kuskokwim rivers

Alaska Dispatch

Alaskans living along the state’s rivers should considering stocking up survival gear -- the flood potential throughout Alaska is rated as moderate, according to the National Weather Service. Alaskans endured the coldest April in decades, and spring’s lazy approach has exhausted residents. But a sudden rise in temperatures would only exacerbate flood fears.

April temperatures began in sync with most previous springs, but the weather shifted, and a cold spell lingered much of the month, slowing the melt. Alaskans should keep their fleeces within reach, as colder temperatures are forecasted for mainland Alaska through next week.

This year, April temperatures across Alaska were among the coldest in decades, the weather service reported Wednesday. The eastern Interior hasn’t experienced such lows since 1974. In central and northern Southeast, it was the coolest April since 1972; Southcentral residents may remember enduring similar temperatures back in 1984.

Anchorage, located in Southcentral Alaska and the state’s largest city, had an average April temperature of 29.6 degrees. Generally, the city starts to see temperatures raise to the 30s at the start of the month. Bettles, a tiny community in the Interior, saw an average April temperature of 11.8 degrees. It was the town’s third coldest April since 1940, the weather service reported.

Although the current flooding forecast only raises slight alarms, the ingredients have been set for an eventful breakup, when warmer temperatures, longer days and melting snows causes ice to break apart and float down Alaska rivers. Typically, ice jam floods require cooler than average temperatures for most of April followed by an abrupt transition to summer-like weather in late April to early May. Alaskans will have to wait and see how May unfolds.

Thus far, Alaskans in Southwest, Southeast and Kodiak Island have shivered through the most colder-than-normal days. Snow remains on the ground, even at many low elevations.  A sudden warm-up could unleash a surge of snowmelt into Alaska rivers, boosting the chance of flooding and severe ice jams, the weather service reported.

Colder temperatures expected for the first week of May have pushed back the expected beginning of breakup five to seven days.

Those conditions are extending an Alaska pastime, the Nenana Ice Classic, in which people guess when the Tanana River will break up in an effort to win a hefty cash prize. The Tanana River usually freezes over during October and November, and the ice thickens throughout winter. The river’s average ice thickness on April 1was 42 inches.

As of April 29, the ice thickness was measured at 47 inches. Last year, on April 19, the last measured day, the thickness was 28.7 inches.

But if cool temperatures persist through May, the flood risk will diminish as ice melts slowly and snowpack enters rivers gradually, the weather service reported. Only a few sites in Alaska report ice thickness measurements, which generally falls between normal and 25 percent above it. 

The Natural Resources Conservation Service analyzed snowpack across the state in early April. The service found normal and above normal snowpack. Significant snowfall during April caused higher than normal snowpack for Anchorage, Alaska’s largest city, and the Kenai Peninsula, a borough consisting of smaller hamlets in Southcentral. There’s also more snowpack in the Interior and southern Yukon Territory.

Prospective flooding has the residents of Eagle, population 86, taking precautions. Eagle hugs the U.S.-Canada border on the southern bank of the Yukon River, a nearly 2,000-mile waterway that runs from British Columbia to the Bering Sea. The community endured a severe flood four years ago, APRN reported, when Eagle’s historic river front was wiped out after a massive ice jam broke free.

Eagle resident Andy Bassich told APRN there’s still a foot of snow in the woods near his homestead, roughly 12 miles downriver from the town site. The ice is thick, too, he said. He worried it adds up to a strong flooding potential -- bad news for Bassich, as his home rests at an “apex of a turn” on the river. He and his partner had to be rescued by helicopter off the top of their house in 2009.

Eagle City Mayor Don Woodruff is visiting residents along the river, warning them of this year’s conditions, APRN reported. 

Last fall, areas in Southcentral Alaska absorbed heavy rainfall, and subsequent flooding led to a disaster declaration for the Matanuska-Susitna Borough and the Kenai Peninsula Borough by Gov. Sean Parnell. Those areas likely will have higher-than-normal groundwater levels this spring, leading to minor flooding and drainage issues if it warms up rapidly.

Contact Jerzy Shedlock at jerzy(at)alaskadispatch.com