BOZEMAN – Cooler temperatures and average snowfall across Montana during the first half of April continued to build snowpack in most areas, but the warming trend at the end of the month created substantial snow melt at most elevations, causing rivers and streams to rise, according to May 1 snow survey data released by the USDA Natural Resources Conservation Service.

“The majority of our SNOTEL sites reached their maximum snow water equivalent during the first two weeks of April,” said Brian Domonkos, NRCS water supply specialist for Montana.

“The southwestern region of Montana and the Lower Yellowstone River Basin felt the biggest effect from the unseasonably warm temperatures,” Domonkos said. “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.

Due to the above average snowpack melt during April, streamflow forecasts have been reduced in most watersheds. Only a select few basins have seen streamflow prospects increase as a result of above average April precipitation.