Warm Weather Threatens Summer Streamflows In Montana

May 6, 2016

The recent sunny, warm weather is taking a toll on Montana’s mountain snowpack.  The Natural Resources Conservation Service says our snowpack peaked in early April. According to water supply specialist Lucas Zukiewicz, that’s one to two weeks ahead of normal.

"Which is potentially going to have impacts on us later in the season when we generally want to see a peak later and melt out more slowly. The clear, sunny skies coupled with those above normal and even record temperatures that we had through [April] really started our transition to snow melt well ahead of schedule. We’re moving water earlier than we typically do, which is going to have impacts on us as we get further in the summer and we can’t have that slow release of mountain water."

Zukiewicz says the quality of this year’s snow beat almost all expectations.

The snow water equivalent exceeded last year in all basins except one; north-central Montana’s Sun-Teton-Marias basin, which is 80 percent of average. This is the second year in a row that basin has received well below normal winter and spring snowfall.

Water users there are being warned to prepare for well-below average streamflows later this year.

Most of Montana’s river basins didn’t get as much rain and snow as normal last month.

According to the Natural Resources Conservation Service, only the headwaters main stem around Helena could muster average precipitation in April.

Montana Water Year to Date Precipitation by Percentage of Basin Normal, May, 2016.

Zukiewicz says El Niño did not stifle our winter rain and snow nearly as much as expected.

“The really big impact that we’ve had has been these above-normal temperatures. We’ve seen these persistent ridges of high pressure which bring warm air in from the south – these clear sunny days we’ve been having – and that puts a lot of energy into the snowpack, which has really started to transition towards the melt phase and our spring runoff earlier than normal.”

March’s above-normal precipitation helped buffer last month’s lower-than-normal totals.