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Flood risk substantial as warmer temps arrive

Apr 30, 2014 - From staff and wire reports

Plentiful winter snow and a slow arrival or warm weather winter means increased potential for flooding along some main river basins when the mountain snowpack starts to melt, according to the National Weather Service.

Central Fremont County is one of the highest risk areas.

Statewide, the mountain snowpack in Wyoming is 135 percent of median this week, with some areas 160 percent of median.

Jim Fahey, a Weather Service hydrologist in Riverton, said Tuesday that there was moderate to high potential for flooding from snowmelt around the Big Horn Mountains in north-central Wyoming, the Saratoga and Encampment area in south-central Wyoming, along the Wind River in central Wyoming and in the Upper Green region in southwest Wyoming.

The snow has melted in most low-lying areas, Fahey said. But the snowpack high in the mountains doesn't typically start to melt in earnest until the latter part of May.

"We still got a lot of snow at 8,500 feet, 9,000 to 10,000," he said. "That's an elevation that will create the highest water, highest floods. Stuff above 10,000 usually takes a long time to get down."

Fahey cautioned that the flood forecast only accounts for mountain runoff from the current snowpack and various other hydrological factors that now exist.

Additional precipitation and temperature fluctuations can quickly change things, he said.

"If we enter an extreme warm up, that's going to increase the flood potential," Fahey said. "Precipitation is really the wild card, though."

A heavy rain on top of the snowmelt already heading down a mountain can result in minor flooding turning into major flooding.

"Our guidance for the next two months is 50-50 either side for precipitation above or below average and temperatures above average, below average," Fahey said. "We just need to keep an eye on our temperatures and precipitation over the next six weeks."

Fahey said another flood forecast will be released on May 15.

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