Delayed snow onset leads to below-normal snowpack for Jan. 1, 2017

NATURAL RESOURCES CONSERVATION SERVICE

With La Niña forecasted to bring above average precipitation and below normal temperatures to the Treasure State this winter, conditions seemed to be looking up from the previous two winters leading into the new water year.

The water year, which began on Oct. 1, 2016, started off wet. Well above average precipitation fell in Montana’s river basins in October after a relatively dry summer in parts of the state, said Lucas Zukiewicz, water supply specialist for the U.S. Department of Agriculture’s Natural Resources Conservation Service in Bozeman.

Previous records at mountain NRCS snowpack telemetry, or SNOTEL, locations were smashed in parts of Northwest Montana. Precipitation in October largely fell in liquid form, although some higher elevation sites received snow.

As soon as the promise of a wet winter seemed to be coming true, the month of November returned the state to above average temperatures and below normal precipitation, continuing the trend from the previous summer.

Warm temperatures took a toll on the emerging snowpack, melting mid- and low-elevation snow, and leaving only the highest elevations with snow cover. Mountain snowpack was near record low in many basins on Dec. 1, but the return to a more seasonal weather pattern toward the end of the month brought snowfall and colder temperatures, which allowed the seasonal snowpack to start building.

Even though December precipitation improved the snowpack, all basins in the state—with the exception of the Yellowstone River basin—are slightly below to well below normal for Jan 1. The snowpack in northern basins is only slightly below normal, and conditions generally deteriorate to the south and east.

The higher elevation Yellowstone River basin, which experienced snowfall from the dominant storm track in December that brought snow to states south of Montana, was the only basin in the state that recorded an above normal snowpack for Jan. 1.

Zukiewicz said a weather system known as the atmospheric river or Pineapple Express has been dropping heavy precipitation to the south while cold air from Canada settled over Montana for much of January.

“Colorado, Utah, Idaho [and] Wyoming are reporting record-breaking snowfall and we’re just a little bit [north] of that flow path right now,” Zukiewicz said.

Although snowpack totals on Jan. 1 were generally below normal, there’s plenty of winter left for conditions to improve.

“Typically, only 35 to 40 percent of seasonal snowpack has accumulated in the mountains and the months we typically experience the most precipitation are yet to come,” he said. “This early in the season we are really only one or two big storms away from normal, and the storm track only needs to shift a bit north for that to happen.”

Zukiewicz said basins west of the Continental Divide typically hit their peak snowpack in April. East of the divide, that generally doesn’t happen until late April or early May. He added that the National Oceanic and Atmospheric Administration is calling for above-average precipitation over Montana for the next three-month period.

Monthly Water Supply Outlook Reports can be found at nrcs.usda.gov/wps/portal/nrcs/main/mt/snow/waterproducts/basin/