Low streamflows likely to follow

NATURAL RESOURCES CONSERVATION SERVICE

BOZEMAN – The transition into spring is in full swing across Montana, causing water levels to rise in rivers and streams and flowers to bloom in the valleys. During the first two weeks of June, significantly above-average temperatures transitioned Montana’s snowpack to an active snowmelt regime at all but the highest elevations, according to snow survey data from the USDA Natural Resources Conservation Service.

High daily-average temperatures and above-freezing overnight temperatures were substantial enough to cause above average snowmelt rates across the state, causing rivers and streams to rise, and in most cases, reach their snowmelt driven peaks during the middle to latter part of the month.

“There may be a few river systems that have yet to see their peak, systems where peaks are typically driven by the high elevation component of snowmelt,” said Brian Domonkos, NRCS water supply specialist.

Based on SNOTEL (SNOw TELemetry) data on June 1, basin average snow water equivalents across the state range from 44 to 64 percent of this year’s maximum. The remaining snowpack will help sustain flows through spring snowmelt and into the summer, Domonkos said.

Heavy precipitation during the second half of May helped some watersheds east of the continental divide improve their water year-to-date precipitation. Most basins across the state continue to be near normal for water year-to-date precipitation, with the Milk Basin having the highest basin average at 132 percent.

The basins in the furthest reaches of southwest Montana continue to have the lowest basin water year-to-date averages, with the Jefferson and Madison river basins both at 88 percent. Low snowpack totals in the Jefferson River basin contributed to this low precipitation average, even though the month of May was 97 percent of average for mountain precipitation.

Montana saw a large range in May precipitation – from 48 percent of May average in the Bitterroot River Basin to 112 percent in the Missouri Mainstem River Basin south of Helena. The weather patterns experienced during the last two weeks of May favored the valleys of central, northeastern and the southern Montana, dropping substantial storm totals during the events.

“The timing of precipitation is critical to the greater water system as this is the time of the year when dam tenders are filling reservoirs, while irrigators begin to draw water,” Domonkos said. “Continued precipitation during the month of June will certainly be welcome starting into the hot summer months and persistent active storm patterns become less frequent.”