Montana’s mountain snowpack has improved thanks to a cool, wet spring

The continued cool and wet weather this spring continues to ease the snow deficits accumulated throughout the winter and early spring. Mountain basins in central Montana typically see peak snowpack values ​​in early to mid-April.

It is important to note that the snow cover percentage values ​​become less and less reliable after the peak. Average snowfall values ​​decrease in May and early June as temperatures warm, meaning that a few centimeters above normal for a given date results in very high percentage values. These amounts of snow are far from sufficient to compensate for the lack of precipitation for several months, which are generally wetter.

To get the best gauge on the state of mountain basins, it is best to look back at the water equivalent of snowfall throughout the hydrological year (begins October 1). The black line indicates the water equivalent of the snowfall of this water year and the green line indicates the median over 30 years (1991-2020).

Areas west of the divide have maintained substantial rainfall for most of the hydrological year so far.

Water equivalent of Helena Valley Basin snowfall for the 2021-2022 hydrological year, courtesy of USDA.

Water equivalent of Musselshell Basin snowfall for the 2021-2022 hydrological year, courtesy of USDA.

While areas east of the divide, particularly in southwestern Montana, experienced well below normal precipitation and snow levels for most of the hydrological year.

Musselshell Basin reached its typical peak with about 78% of normal snowpack. It wasn’t until late April that the cool, wet weather caused snow accumulation in the basin to increase above normal levels.

Sunny, warm weather may look great as we head into the holiday weekend, but the cooler, wetter pattern that seems to be setting in through the end of the month is exactly what’s needed before the months generally drier.