Mountain snowpack remains healthy

Weather patterns during the first two weeks of April, while cooler than average, didn’t yield much precipitation across the state of Montana. However, the below average temperatures during this period did help to delay snowmelt at many mountain locations during the first half of the month, according to data collected by SNOTEL sites.

“Both east and west of the Divide, snowmelt was delayed by a week or two at lower elevations because of these weather patterns, which is great news as it keeps that water in the mountain snowpack and prolongs streamflow during the summer when demand is the highest,” said Lucas Zukiewicz, Natural Resources Conservation Service water supply specialist for Montana.

The last week of April brought a major weather pattern change that caused the snowpack to transition toward melt at most elevations in Montana.

“The abundant sunshine and above-average temperatures that persisted since April 20 took their toll on the snowpack in the mountains. Since then, rapid snowmelt caused rivers and streams in the state to begin the seasonal rise from snowmelt runoff,” Zukiewicz said.

In some areas the snowmelt is ahead of schedule, raising questions about available water supply later in the summer.

“High elevations continue to hold onto snowpack or have just begun to discharge water into the river systems. However, low- and mid-elevation SNOTEL sites have been melting at an accelerated pace since mid-month, and most dramatically since the last week of April and into the first week of May,” continued Zukiewicz.

Still, the Flathead Basin’s snowpack is at 117 percent of average for this time of year. The Kootenai Basin is at 112 percent of average. Snow depths currently top 109 inches in the Swan Range at a weather station in Noisy Basin at an elevation of 6,040 feet. Flattop Mountain in Glacier Park has a similar snow depth of about 111 inches.

Streamflow forecasts within Montana have generally declined since April 1 due to the lack of April precipitation and rapid decline of low- and mid-elevation snowpack in some regions. Forecasts for the May through July period remain near to slightly above average for many river systems, but some areas east of the Divide in Southwest Montana now have streamflow forecasts below average for spring and summer runoff.

“The biggest concern is within the Jefferson and Madison river basins, where snowpack is melting quickly at this time,” said Zukiewicz. “Although snowpack peaked near to above average, we are experiencing melt at a faster than normal rate this year, which moves the water through the system before we need it.”

River basins, like the Madison, may be able to make up for less than average streamflow with water stored in reservoirs, which has remained above average throughout this winter due to last year’s abundant runoff.

“Storage this winter has been above average across the state, thanks to last year, but areas where there is no storage are much more susceptible to current and future weather patterns,” Zukiewicz said.

May and June are historically two of the wettest months of the year across Montana, especially east of the Divide. Spring and early summer weather patterns will dictate not only the timing and volumes of runoff this season, but how much irrigation demand there is for water as crops begin to grow across the state.

“As always, it’s a waiting game to see what we get with regards to overall runoff volumes this year. For now, were in a good place across many parts of the western half of the state due to the snowpack that we have in place on May 1,” Zukiewicz added.

How fast the remaining snowpack melts and what occurs during May will be covered in next month’s Water Supply Outlook Report, which will be released during the first week of June.