CHEYENNE, Wyo. (AP) - Relatively minor flooding occurred in Wyoming during May from melting snow, but water experts caution residents along rivers and streams not to become complacent.
They say the mountain snowpack remains exceptionally deep in many places and the main runoff is starting and is expected to be prolonged this year.
“If you know your area is flood prone, you might want to get last-minute preparations made,” National Weather Service hydrologist Jim Fahey said.
Warm temperatures have already accelerated runoff flows in smaller streams and creeks this week and the levels of major central and western rivers are expected to rise quickly as well. The National Weather Service posted a flood watch Thursday for the Green, Shoshone, Big Wind and Little Wind rivers effective Friday morning through Sunday night.
Only eastern Wyoming appears free from any flood threat now.
While warm weather at the outset of May melted off snow at the lower elevations - below the 8,500 foot (2,591 meter) altitude - and started melting some high elevation snow above 8,500 feet, the last two full weeks of May were wet and cool and left an unusually high snowpack entering June, according to Lee Hackleman, a water supply specialist with the Natural Resources Conservation Service in Riverton.
Statewide, Wyoming’s snowpack this week was more than twice the usual amount as measured by instruments in central and western mountain ranges, according to the NRCS.
Wyoming normally sees some flooding from the spring snowmelt but this year is different in that the accumulated snowpack is high in a wide area and in multiple mountain ranges.
“The whole western side of the state is high,” Hackleman said.
Areas of Wyoming, such as Fremont County, with rivers and streams fed by the mountain runoff have been placing sandbags and other barriers to protect homes, businesses and key public infrastructure.
Fahey said the high snowpack this late in May likely will prolong the annual runoff.
“The Green especially could see moderate to high flows through July,” Fahey said.
Runoff in the Green River Basin normally peaks between June 10 and June 20, he said.
While rivers will be running high, a weather pattern of fluctuating temperatures between warm and cool would be ideal for an “efficient” runoff, Fahey said.
The wildcard is whether it rains.
“If we get enough rain on top of the melt, it really brings the rivers up high,” Fahey said.
Managers of reservoirs around the state have been draining water to make room for the high runoff.
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