ANCHORAGE — Alaska’s largest city should be spared major problems from the melting of near-record snowfall, but the potential for flooding continues along Interior rivers, a National Weather Service expert told U.S. Sen. Lisa Murkowski on Thursday.
The Alaska Republican organized a forum to discuss the 2012 flooding outlook. Anchorage averages 69 inches of snow but is just over 3 inches shy of the record 132.6 inches set in 1954-55.
“Many Alaskans are growing concerned that record-breaking snow could lead to record-breaking floods,” Murkowski said.
Hydrologist Scott Lindsey, however, said Anchorage residents should not have to worry unless the temperature suddenly zooms upward. Anchorage so far has seen an orderly thaw with warm daytime temperatures and freezing at night, he said. Also, all the snow insulated the ground and prevented deep freezing.
“A lot of that soil is starting to thaw already,” Lindsey said. Much of the melt water will simply percolate into the soil if the ground is not frozen, he said.
The potential for serious damage, Lindsey said, is higher in communities along major rivers, where six months of snow can fill channels, break up thick river ice and cause it to dam, creating high water behind it.
In 2009, ice jammed below three villages on the Yukon River, causing millions of dollars in damage at Eagle, Tanana and Stevens Village. At 37 other villages, life was disrupted by high water or precautionary evacuations.
The Yukon River begins in British Columbia, Canada, and flows north and west through Yukon Territory before spanning more than 1,260 miles through Alaska to the Bering Sea. Temperatures in the region fall below minus 40 degrees, making for thick river ice.
The snowpack in Canada this year was 100 to 150 percent of normal depths. In Alaska’s Interior, it was about 100 to 130 percent of normal, Lindsey said.
Extreme cold led some people to suspect ice thickness on rivers would be greater than usual, but the snow acted as an insulator.
“Because we’ve had a pretty consistent deep snowpack, the ice growth hasn’t proceeded like we would normally expect for some of the temperatures Fairbanks and some of the other Interior areas we’ve seen,” he said.
The main trigger for flooding is always temperature, Lindsey said.
At Bethel last year, when bad flooding on the Kuskokwim River hit the village of Crooked Creek, and at Fairbanks three years ago, when Yukon River communities had high water, late April and early May saw low temperatures stay above freezing and record highs during the day.
“That’s the pattern that can cause problems,” Lindsey said.
The long-term climate outlook for April is for cooler-than-usual temperatures, leading to worries that there could be a temperature surge in early May, Lindsey said.
Lindsey in early May will start flying the Yukon on daily trips to look for trouble spots. During a dynamic breakup, the river generally opens up east to west.