Montana’s snow is the best it’s been in a handful of years, so most streams should flow nicely even through August.
May’s snowpack is what sustains the state’s streams through most of the summer, and this year, it’s easily more than the 30-year average and half again what it was last year, according to measurements made by the U.S. Natural Resources Conservation Service.
The difference between this year’s snowpack and last year’s couldn’t be more striking. For example, last May 1, the Sun-Teton-Mariasbasin snowpack along the northern Rocky Mountain Front was a record-low 34 percent of normal, with eight of the 10 snow-measuring stations melted out already. This year, only one site is melted out, and the snow is at 130 percent of normal.
Unlike the two previous years, spring temperatures stayed lower longer, more like the springs of old. That allowed the snowpack to not only stick around but also grow a few more inches. So while last year’s streamflows peaked in early April, this year’s peak flows are a month or more later.
Snow on the west side of the Continental Divide is averaging about 120 percent of normal, thanks to the cool, wet weather that dominated most of April. That makes wildfires such as the Roaring Lion Fire in the Bitterroot Valley less likely.
Over on the east side of the Divide, the Missouri River basins are doing about the same except for a dry spot in the middle of the state. There, the mountain snowpack surrounding the Missouri headwaters – from Three Forks to Great Falls – and the Smith-Judith-Musselshell basins farther east was looking dire heading into April. Fortunately, April’s precipitation bumped both basins to 80-90 percent of the snowpack they normally hold.
However, this is the second year the Smith-Judith-Musselshell has received only 85 percent of its average snowpack. It would have been even less this year if the region hadn’t received 20 percent more precipitation than normal in April. The lower snow amounts are already evident to those with Smith River permits – the river is coming up a little slower than normal so early boaters have to drag their rafts in a few low spots.
April wasn't wet everywhere. The northeastern part of the state around Sidney and Wolf Point received only about 70 percent of the average precipitation for April. Fortunately, those areas receive from all the water flowing down the Missouri River from the western mountains.
The good news is the Yellowstone River basin may be spared the disease outbreaks of last year because the surrounding snowpack is more than 150 percent of normal. That means the river should flow high enough that it might not warm up as much this summer.
The other good news is that Montana and North Dakota are the only two states that aren’t predicted to be warmer than normal this summer, according to the National Weather Service three-month outlook. All other parts of the nation, especially the desert Southwest and the Atlantic Coast states are predicted to be above normal.
All the snow will also help fill the reservoirs, especially those in the West, which were running low last year. The Hungry Horse Dam is already allowing 10,000 cubic feet per second to flow into the Flathead River in anticipation of snow melt keeping the reservoir full.
However, some rivers may run a little too high, such as the rivers that feed the Bighorn River. The large volume of water from the record snowpack in the Wind and Shoshone river basins of Wyoming will work its way north into Montana during this year’s runoff. Water managers are actively managing reservoirs to try to control the situation. The Yellowtail Dam is releasing 12,000 cubic feet per second, but downstream users could still be affected over the next few months.