Weather Service monitors heavy snow buildup for flooding potential
'We are sitting on a very large snowpack" hydrologist says
It’s been a heck of a snowy winter, so it shouldn’t come as a surprise that there’s above-normal potential for flooding in several river basins around the state. The National Weather Service’s Alaska-Pacific River Forecast Center says the Yukon, Tanana, Koyukuk, Kuskokwim and Susitna basins all have more snowpack than usual — some, well above normal.
“We are having some of these basins with record snowfalls being reported,” says Karen Endres, a senior hydrologist with the weather service’s Fairbanks office.
Endres said in an interview Friday that it’s too early to say whether data from sensors up in higher elevations accurately reflect the entire snowpack in those basins. That’ll have to be confirmed by overflights and other analyses to be conducted next month.
“We aren’t sure exactly what we’ve got up there,” she said, “but that’s our best guess right now – that we are sitting on a very large snowpack.”
The River Forecast Center says the Tanana Basin, which includes Fairbanks and Delta Junction, registered the greatest above-normal snowpack – about 220 percent more than usual. The Upper Yukon, in Canada, had about 160 percent of median; the Middle Yukon, which includes Eagle and Circle, 190 percent of normal; and the Lower Yukon, including Ruby and Galena, at 150 percent of normal.
“We are concerned with pretty much all of the forecast area,” Endres said.
But snowpack isn’t the only indicator of flooding potential. She says river-ice thickness is another, although so far the data show that’s about normal.
Another indicator is the onset of warmer-than-normal temperatures in late breakup that could trigger rapid melting of snowpack. But Endres says long-term forecasts are inconclusive on whether that might happen.
“Until we get those April numbers that confirm how much snow is up there, and better numbers for what the temperatures might do, we don’t make any real predictions,” she said.
Climate expert Rick Thoman agrees it’s too soon to draw conclusions from data available so far.
“I think the short answer is that at this point, we’re just going to have to wait and see,” says Thoman, a climate specialist with the University of Alaska Fairbanks’s Alaska Center for Climate Assessment and Policy.
He says the weather service’s Alaska Climate Prediction Center forecasts a small chance of cooler-than-normal temperatures in April around the eastern Interior. But he said in Friday’s ACCAP climate outlook webinar that conditions could change by mid-month.
“So if it’s really cold the first two weeks of the month and then temperatures pop up in the second half of April to slightly above normal,” he said, “we could still have a rapid transition to thawing weather in late April and early May.”
Thoman says cooler weather throughout April would help slow the melting of all that snow up in the mountains – and the release of meltoff into areas downslope.