Warm/Dry March Weather Cause Decreases in Forecasts
April 14, 2021
Just when it seemed like the snowpack was on the right track to rebound from the dry December and January, March yielded substantially different weather patterns than the cold and wet conditions experienced during February.
Snowpack percentages on March 1 were at a high point for the year, boosted by well above normal snowfall leading to near to above normal snowpack for almost all Montana river basins. “Unfortunately, March weather started off on the opposite trajectory. Warm, dry air spilled into the state during the first week of the month and many mountain SNOTEL sites matched record daily average temperatures on March 5,” said Lucas Zukiewicz, USDA Natural Resources Conservation Service (NRCS) water supply specialist for Montana. The weather patterns of the first week foreshadowed the weather patterns for the month. While seasonal temperatures returned for brief periods, monthly temperatures recorded at most mountain locations were above normal for March.
During March, precipitation at both mountain and valley locations was well below average. “For the most part, only the last week of March saw widespread accumulation of mountain snowpack, and after a three-week hiatus it did little to salvage monthly snow totals,” said Zukiewicz. Snowpack percentages on April 1 have declined in all river basins in Montana since March 1. “This year’s silver lining has been the boost to the snowpack during February. 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,” continued Zukiewicz. However, this is not the case for all river basins in the state. Snowpack in some of the river sub-basins located in northwestern Montana have declined from near normal to below normal on April 1. Southwestern river basins, which have been below normal throughout the snow season, have snowpack which has further declined through March.
Streamflow forecasts issued by the NRCS on April 1 for spring and summer runoff have also decreased since last month, and the decreases are notable in some river basins. “Forecasts for spring and summer runoff in Montana are the lowest in the Red Rock, Ruby, and Madison River basins. In these areas, well below average flows can be anticipated unless the remainder of spring and summer yield above average precipitation, and more seasonal temperatures,” said Zukiewicz. Not all areas of the state are expected to be below normal for runoff this year, and many regions of the state still have chances of near average flows for the coming runoff season.
“As always, our runoff prospects and timing are directly tied to the weather experienced in the coming two to three months,” said Zukiewicz. Mountain snowpack historically peaks at mid and high elevations during April, so the coming month will be critical to Montana’s water resources this summer and beyond. “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,” said Zukiewicz.