Not much water fell from the sky last month and snow started melting ahead of schedule, but snowpack levels remain near normal in southwestern Montana.
The Natural Resources Conservation Service’s Water Supply Outlook Report for May 1 recorded snowpack levels near average for southwestern Montana despite paltry precipitation levels for the month of April.
Snow levels in the Gallatin and upper Yellowstone river basins were just above normal on May 1. The Jefferson and Madison river basins were just below normal.
Lucas Zukiewicz, an NRCS water supply specialist, said the numbers stayed high because cool and wet weather earlier in the year had dropped enough snow to leave some in reserve. The dry April balanced out the early boost.
“We got a significant enough January and February that we are basically right where we want to be,” Zukiewicz said.
The monthly report showed well below average precipitation for April across Montana except in two areas — the Sun-Teton-Marias basin, which got 99% of its normal April precipitation, and the Lower Clark Fork, which received 104% of normal.
The total was especially low in the state’s southwest corner. The Jefferson River basin — which includes the Big Hole, Beaverhead and Ruby watershed — recorded precipitation at 66% of normal for April. The Madison basin received 65% of normal precipitation, while the Gallatin received 62%. The upper Yellowstone fared slightly better, with 77% of normal.
But snowpack levels remain strong for those four watersheds. Snowpack in the Jefferson was at 93% of normal on May 1. The Madison was at 93%.
The Gallatin and upper Yellowstone both topped 100% — the Gallatin at 106% and the upper Yellowstone at 113%.
Zukiewicz said sunny days and nightly lows above freezing got snowmelt started in this part of the state in April, with low and mid-elevation snow melting off. Near the end of the month, high elevation snow started to melt, he said.
Runoff has slowed some, as shown by the drop in stream flow on the Gallatin River near Gallatin Gateway over the past week from near 2,000 cubic feet per second to roughly 1,300.
But continued warm and dry weather could keep runoff moving faster than normal and drain water reserves meant to last late into the summer, when demand increases.
“If we keep seeing snowmelt at an accelerated rate, that doesn’t bode well for later in the summer,” Zukiewicz said.