CHEYENNE, Wyo. (AP) - The heavy snowfall so far this winter in parts of central and western Wyoming has forecasters expecting potential spring and early summer flooding in some major river basins that hasn’t been seen in decades.
National Weather Service hydrologist Jim Fahey in Riverton said Thursday that parts of the Upper Green, Sweetwater and Snake river basins are seeing unusually high snowpacks and potentially high runoffs as the snow begins to melt.
The Upper Green and Snake basins haven’t seen similar situations since the mid-1990s, Fahey said.
In anticipation of a high spring runoff, the Bureau of Reclamation has started releasing more water from the Jackson Lake Dam in Grand Teton National Park north of Jackson. The agency usually doesn’t start increasing releases from the lake until about May.
“These flows are necessary due to above-average snowpack and winter precipitation in the watershed and will help reduce the risk of flooding later this spring,” the agency said in a statement.
Statewide, the snowpack across Wyoming this week is 132 percent above the median for this time of year. The snowpack in the Sweetwater River Basin in south-central Wyoming is a whopping 219 percent of median.
Lee Hackleman, water supply specialist with the Natural Resources Conservation Service, said storms that swept through California this winter have passed on through into western and central Wyoming where they bump up against the Wind River Mountains.
“But they didn’t really jump over the Winds and go into the rest of the state,” Hackleman said. “They just kind of bumped up against the Winds right there and that’s what got the most.”
The result is the western half of Wyoming has received a lot of snow, while the eastern part has received normal, or in the case of northeast Wyoming, below normal snowfall.
Compounding the potential spring flooding in the western half of the state is that the snow that has fallen has record high water content.
Currently, rivers with the highest potential for spring and early summer flooding include the Popo Agie, Little Wind, Big Wind, Green, Bear and Sweetwater.
Spring runoff isn’t usually a problem in the Sweetwater River Basin, but it could be this year, Hackleman said.
“This is going to be quite a turnaround for that area,” he said.
More snow was falling Thursday in the western Wyoming mountains, where a winter storm warning was posted through Friday for areas around Jackson and north into Yellowstone National Park.
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