The transition into spring is in full swing across Montana, causing water levels to rise in rivers and streams. During the first two weeks of the month, significantly above-average temperatures transitioned the state’s snowpack to active snowmelt at all but the highest elevations, according to survey data released Thursday from the USDA Natural Resources Conservation Service (NRCS).
High daily average temperatures and overnight above freezing 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.
Domonkos said the remaining snowpack will help sustain flows through spring snowmelt into the summer.
The abundance of precipitation during the second half of May was a change to the first two weeks of warm and dry weather, and helped some watersheds east of the Continental Divide improve water year-to-date precipitation, according to the NRCS.
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 Flathead basin is at 102 percent of the median levels and 66 percent compared to last year. The Kootenai is at 93 percent of the median and 44 percent compared to last year.
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.
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.”