Alaska Interior Ripe For Rapid Breakup, Flooding - NWS

[hatrack]

FAIRBANKS -- "The National Weather Service is warning that conditions are right this spring for a dynamic breakup in Alaska's Interior. Computers are telling meteorologists and hydrologists that breakup this year could involve flooding, ice jams and significant erosion in fire-ravaged areas.

Record-setting snow depths and water-content measurements have hydrologists warning of the potential for spring floods along several major Interior rivers. "They should be getting prepared," said Scott Lindsey, a hydrologist with the National Weather Service's Alaska-Pacific River Forecast Center. "There is a potential for what the villages call 'spring flooding,' when the snowmelt ends up causing flooding after the actual breakup." A significant amount of water, most of it locked away in ice and snow, sits in the drainages of several Interior rivers, including the Yukon, the Koyukuk and the Chena. The same is true for much of the huge Susitna River drainage in Southcentral.

Scientists describe the two kinds of breakups as "thermal" and "dynamic." A thermal breakup, as described by Larry Hinzman of the University of Alaska Fairbanks, occurs when temperatures rise gradually over several weeks, allowing the river to thaw slowly as the ice rots. The Interior this spring is more likely to undergo a dynamic breakup. That occurs when the weather is relatively cool -- which is what the Interior experienced over the last month -- and then becomes very warm.

Conditions such as those on Friday, with the temperature hovering at or above freezing at night, then soaring as high as 60 under increasingly sunny skies, are just right for a dynamic breakup. String together a week of conditions like that and water will stream over frozen ground into rivers that are still locked in ice."

EDIT

http://www.adn.com/news/alaska/story/6418920p-6297758c.html