Last month’s second-half warming trend substantially melted snow in the mountains at most elevations, causing rivers and streams to rise, according to the latest snow survey data released by the USDA Natural Resources Conservation Service this week.
Although snowpack is actively melting, Brian Domonkos, NRCS water supply specialist, said a few northwestern basins continue to be above average. The Flathead, Kootenai, St. Mary’s, Milk and Lower Clark Fork River basins continue to be at or slightly above average. Most other river basins have seen a decrease in average over the month and were slightly below average on May 1, according to the NRCS.
The Flathead saw a 5 percent decline in snowpack last month but remains at 101 percent of average snowpack. The Kootenai increased by 2 percent in April and is at 129 percent of average snowpack.
“The southwestern region of Montana and the Lower Yellowstone River Basin felt the biggest effect from the unseasonably warm temperatures,” Domonkos said in a statement. “These basins experienced substantial melt during the second half of April, decreasing the basin averages to well below average and lowering stream flow prospects into spring and summer.”
Domonkos said Montana rivers typically peak during May and weather patterns over the next month will dictate the timing of river flows.
“A return to warmer temperatures over the coming weeks could move our peak flows ahead of average, while cooler weather could help prolong river flows across the state into the summer,” he said.
For average river basin streamflow forecasts, Flathead is expected to be at 109 percent from May through July. These forecasts assume near normal moisture and runoff conditions in that period. Last year the forecasted percentage for the Flathead was 173. The Kootenai is expected to be at 118 percent this year compared to 145 percent last year.
For detailed snowpack information visit the NRCS website.
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