Mountain snowpack slow to melt, flooding possible

Snowfall this April didn’t keep up with the above-average snowfall in February and March, according to data from the U.S. Natural Resources Conservation Service, but lingering winter-like weather has delayed melting of Montana’s snowpack.

The Flathead River at Columbia Falls should reach flood stage or higher this spring, the National Weather Service said last week. Just how high the water will get remains to be seen. The snowpack currently is high, but below the snowpack of 2011, when there was some flooding in the Flathead and some severe flooding in the Bitterroot River in Missoula. The final flood outlook will depend on the timeliness of spring rains, according to NWS meteorologist Ray Nickless.

This week should see temperatures at or above normal, which will start spring runoff in earnest, Nickless noted. The Flathead snowpack, particularly in Glacier National Park, is just below what is was in 2011 and bears watching, he said.

NRCS data shows snow-water equivalent peaking in most Montana basins during the beginning and middle part of April, while peaking along the Continental Divide at the end of the month.

Some snowmelt has occurred at lower to mid elevations, but higher elevations have seen little melting during April, according to hydrologist Lucas Zukiewicz.

“Assuming normal climatic conditions in the upcoming weeks, more advanced melt rates should begin to occur, as days get longer with more solar influence and temperatures get warmer,” Zukiewicz said.

Snow-water content in the Flathead River basin by May 1 was 156 percent of median and 138 percent of last year. Statewide, snow-water content was 155 percent of median and 149 percent of last year.

If melting of mountain snowpack continues to be delayed, basin percentages of normal will continue to increase, Zukiewicz said.

While April precipitation varied across the state, the statewide precipitation for April was slightly below average at 93 percent. But the overall water year-to-date precipitation totals since Oct. 1 still reflect above average precipitation in most basins.

The statewide precipitation is currently 116 percent of average, and 115 percent of last year at this time.

Streamflow forecasts continue to be well above average in most parts of Montana. Statewide streamflow forecasts indicate 146 percent of the average May-July flows, and 152 percent of what was experienced last year.

Assuming near normal moisture and runoff conditions for January through July, the forecast for May-July streamflow in the Flathead River is 129 percent of average and 117 percent of last year’s streamflow.