The month of April saw a dramatic change from the warm and dry weather experienced during the latter half of March, with cool, wet weather dominating the month across most of Montana. Snow melt at low to mid elevations slowed in April, even adding snow water to seasonal snowpack, according to snow survey data from the USDA Natural Resources Conservation Service (NRCS).
All but one major basin across the state experienced a gain in snowpack, most notably the Sun-Teton-Marias River basin, which saw an increase from 88 to 110 percent of median. The Lower Yellowstone River basin increased from below median to 107 percent. The Jefferson River basin in southwestern Montana saw the least amount of snowfall, with no improvement from last month and remaining at 89 percent of median, the lowest basin average in the state.
According to NRCS data, statewide snowpack percentages rose 14 percent from 91 percent on April 1 to 105 percent on May 1. Overall the increased snowfall during the month of April helped streamflow prospects, increasing from 2 to 21 percent.
Across the northwestern part of the state, late April into May is typically the time when snowmelt and streamflows peak.
“The cool weather has added additional water to the snowpack and has delayed the slow release and melt of snow water into the systems,” said Brian Domonkos, NRCS water supply specialist. “Because of the delay in our seasonal melt, the weather during the month of May will certainly be a major driver in the timing and volume of water in our river systems through June.”
The Flathead basin increased 16 percent and is currently 115 percent of median. This time last year it was at 98 percent. The Kootenai is also at 115 percent of media, compared to 81 percent last year.
Domonkos said that given the current snowpack in place and near normal future precipitation and temperatures, streamflows are predicted to be near average in most basins this runoff season.
“Each basin’s forecasts vary greatly so be sure to have a closer look at particular basins of interest.”
The NRCS projections provide normalized streamflow forecasts for each basin. These forecasts assume near normal moisture and runoff conditions April through July.
The streamflow forecast for the Flathead basin is 115 percent of average between May and July, compared to 87 percent last year. The Kootenai is at 102 percent, compared to 64 percent last year.
For detailed snowpack information, visit here.
For detailed basin streamflow forecast information, visit here.