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Plenty of water should fill Montana reservoirs and keep rivers and streams flowing this spring and summer.

This month’s streamflow forecast, released Thursday by the National Resources Conservation Service, said there is enough mountain snowpack in Montana this year to keep water flowing at 119 percent of average from April through July.

On the east side of the Divide, streamflows are estimated at 118 percent of normal, while the west side could see flows at up to 124 percent of average.

The forecast for the upper Yellowstone, the stretch of river between Yellowstone National Park and Custer, calls for 117 percent of average. For the lower Yellowstone, fed by Wyoming mountains, the forecast is for 107 percent.

The Smith-Judith-Musselshell forecast is for 127 percent of average and the Missouri will run at 118 percent. The Milk, already flooding in northeast Montana, is expected to spend the summer at 164 percent of average.

The NRCS releases streamflow forecasts each month from January to July estimating how rivers will look through July 31. The estimates are based on water measured in mountain snowpack.

More than 90 percent of the season’s snowfall should be on the ground by now, but storms keep coming and temperatures remain too cold for snowmelt to begin. Usually snowmelt starts in the west by the middle of April. Yellowstone Basin mountains typically begin melting toward the end of the month.

But cooler-than-normal temperatures are predicted through June, meaning the melt could start later this year.

Snowpack across Montana was an average of 120 percent of normal on April 1 and 185 percent of last year at this time, NRCS said. March was a snowy month at high elevations, increasing the pack by 7 percent from February.

Snowpack for the upper Yellowstone was 123 percent of normal on Thursday and 111 for the lower Yellowstone. The Missouri mainstem was 125 percent of average, while the Smith-Judith-Musselshell is at 124 percent. Snowpack for the Milk is at 137 percent of average.

Reservoirs should have ample water for irrigation, electricity and recreation this summer. At the beginning of April, most were holding well above normal storage for this time of year.

Both major reservoirs on this side of the state, Bighorn Lake and Fort Peck Lake, have 107 percent of their normal storage. Tongue River Reservoir has about 191 percent.

Smaller reservoirs are doing well, too. Cooney and Deadmans Basin each have 121 percent of normal storage, while Martinsdale has 163 percent and Bair 138 percent. Nelson has 134 percent and Fresno has 114 percent. Mystic Lake is at 94 percent.

Lorna Thackeray can be reached at 657-1314 or lthackeray@billingsgazette.com.

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