Snowpack

A woman walks along a path at the Cherry Creek Fishing Access below the Bridger Range on Wednesday, April 7, 2021.

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Higher than normal temperatures and well below average precipitation in March caused snowpack levels to decline in all of Montana’s river basins, though some fared better than others, according to a Natural Resources Conservation Service report released Wednesday.

Despite impressive snow totals in February, warm and dry conditions in March reduced snowpack levels to below average in many areas of southwest Montana. The changes were detailed in the agency’s monthly Montana Snowpack and Water Supply Outlook Report.

Northwest flow, a weather pattern that tends to drop more precipitation in the northern Gallatin and Bridger ranges, dominated February. Record and near-record snow totals were recorded in the Gallatin and Shields river basins that month.

The pattern gave way to a westerly and southwesterly flow in March as warm air spilled in from the Pacific, said Lucas Zukiewicz, an NRCS water supply specialist. The warm and sunny days began a transition toward melt at low and mid elevations — the first week of April “finally tipped the scales.”

Daily average temperatures broke record highs at some SNOTEL sites in early April, according to Zukiewicz.

“We’re starting to see more discharge in local rivers and streams,” he said.

Though snowpack declined in March, percentages were still normal or near normal in many river basins on April 1. Zukiewicz said many regions are still on track to have near-average runoff.

On April 1, snowpack levels in the Upper Yellowstone, Gallatin, Jefferson and Madison river basins were at 101%, 96%, 92% and 87% of normal, respectively — a 4% to 8% decline from March 1.

By Wednesday, the percentages in those river basins had declined further by 1% to 4%.

On March 1, there was “an increased likelihood of near to slightly above average spring and summer stream flows across the state,” the NRCS reported. Snowpack hovered at or above normal in the Upper Yellowstone, Gallatin, Jefferson and Madison river basins at the time.

By April 1, runoff forecasts for the spring and summer months decreased. Runoff forecasts were lowest on April 1 in the Red Rock, Ruby and Madison river basins. Zukiewicz predicted below-average runoff will occur in those areas “unless the remainder of spring and summer yield above average precipitation, and more seasonal temperatures.”

Forecasts from the Climate Prediction Center indicate chances are better than normal that warm weather will persist through April, but there is an equal chance of increased precipitation, according to Zukiewicz. A dramatic shift in atmospheric patterns is necessary for conditions to change, he said.

“A return to normal temperatures and wetter weather patterns would be more than welcome at this point to slow the transition of the mountain snowpack towards melt and satisfy the existing soil moisture deficits present in many valley and plains locations,” Zukiewicz said.

Mountain snowpacks at mid and high elevations usually peak during April, so “the coming month will be critical to Montana’s water resources this summer and beyond,” according to Zukiewicz.

“This year’s silver lining has been the boost to the snowpack during February,” Zukiewicz said. “While totals right now aren’t quite as pretty as they were at the beginning of the month, many river basins continue to have near to slightly below normal snowpack on April 1.”

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Helena Dore can be reached at hdore@dailychronicle.com or at 582-2628.

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