Episode 5 - Snowpack

“Summer streamflows saved by February storms … or were they?”

Ed Snook – Retired Hydrologist and Bitter Root Water Forum Vice President

April 2021

As a hydrologist, I understand the intense interest in water across Montana, and more specifically in the Bitterroot Valley. Water’s relative scarcity, and therefore incredible importance, was one of the reasons I followed a career path into this river-oriented community.

As a board member of the Bitter Root Water Forum, I recently had the opportunity to speak with a community member about our current efforts. I found out she was a linguist at a large university, with an ongoing interest in how people use their languages. During our discussion about the river and the evolving snowpack, she noted that people spoke differently about them in the Bitterroot than in other places she had lived and taught. People don’t say the river, they say our river, or our snowpack – in a possessive way, she said. Like people in the valley would bottle up all that water and keep it on their shelf until they needed it, if they only could. That idea reminded me why our snowpack, our “water on the shelf”, is so important in a dry valley that has little constructed water storage, or reliable summer rains. Add to that the sizeable recreation economy that has evolved around the snowpack – “ski it until it melts, then paddle it downriver”, as the adrenalin junkies say – and it’s easy to see why people can be possessive about the snowpack.

Most people with an interest in our snowpack follow the near-constant updates in the paper, or go further to research more detailed information provided by the USDA - Natural Resource Conservation Service (NRCS) Montana office personnel. These extremely useful water supply summaries can be found at https://www.nrcs.usda.gov/wps/portal/nrcs/mt/snow/products/Water+Supply/Basin+Outlook+Reports+%28Legacy%29/.

A fall 2020 prediction for a moderate to strong La Nina influence suggested we would see the vigorous, cold and moist weather normally associated with this weather phenomena – which, due to other weather influences, turned out to be only partly correct. Weather in November through January provided only glimpses of “real” winter weather that had been expected, causing more than a little anxiety amongst various snowpack fans, including one specific skiing hydrologist. Western Montana’s snowpack hovered around the mid-to-low 80% of normal range, and people wondered where La Nina (the “little girl”) had wandered off to.

Much to snow sports fans and water user’s relief, La Nina was alive and well, and throwing a tantrum throughout February. Many long-standing records for cold temperatures, wind chills and snow amounts were reset across the state, and the Bitterroot Mountain Range experienced one of its snowiest Februarys on record. Lost Horse Canyon was a particular focal point, experiencing several climax avalanches that brought down 30+ year-old trees and closing a popular, and thankfully empty at the time, snowmobile route. Almost 16” of snow water equivalent (SWE), or approximately 160” of snow was recorded at Twin Lakes SNOTEL, near the top of Lost Horse Canyon, during the month. This was an astonishing 269% of the long-term average February snowfall! Many other locations in the Bitterroot River’s watershed had terrific snowpack gains as well. The NRCS Water Supply Report for March 1 also noted that as of that date, February’s storms represented 43% of the water at the Lost Horse SNOTEL. And of course, that made me anxious again, to have one month delivering such a huge portion of the winter’s snow – what about the rest of the winter, would it “bring the goods” as well? What if that snow event was a finale, rather than the second act?

So we look to what the current snowpack, long-range predictions, climate trends and general Bitterroot River history can tell us about what to expect for this summer’s streamflows. As you can guess by that introduction, it’s still a complex situation. We have an above-average snowpack for early April and NRCS’s streamflow predictions suggest we have about an 80% chance of hitting our long-term average total streamflow for the April – September period. That estimate does not include whatever snowfall we get in April and May, which are usually good months for mountain snowfall. Long-term seasonal temperature and precipitation forecasts from NOAA suggest pretty much normal weather patterns for April and then warmer and drier than normal through July. Western Regional Climate Center maps suggest the Bitterroot has experienced a slightly cooler but much drier past 30 days than average – a win/lose situation for snowpack! And lastly, local water and river users will be quick to tell you it’s easy to have very low flows in August, even with huge spring snowpacks – how the snowpack melts out is just as important as how big it is.

How to deal with all that anxiety? Get out and enjoy the snow and the river early and often, for one. Contribute to the various non-profits that fight for water resources, fisheries and wildlife. For the long run, follow the science and support long-term drought planning and the agencies that measure and predict our snowpack and river flows. They produce invaluable products to help us plan activities and water-dependent investments. Recognize the many ways the community depends on the river and work toward mutually beneficial goals. It’s not easy – pressure on water resources tends to grow alongside the community – but it’s rewarding when puzzle pieces fit together.

Thanks for lending an ear. I feel better already!

Other Snowpack or Runoff Resources:

Montana SNOTEL Current Snow Water Equivalent (SWE) % of Normal

NRCS Interactive Map

Streamflow and Irrigation - BRWF webpage