Snowpack Summary

October storms deposited the season’s first snowfall in the high peaks, which lingered into November on the high, shady slopes of our northern mountains. From November 7th-19th, a series of storms dropped several feet of snow in the mountains. Mountain temperatures warmed to near 40F towards the end of the cycle, providing a dense base for early -season backcountry skiing—and even snowmobiling. Folks were talking about the possibility of a record-setting La Niña season!

But wait—not so fast! These storms were followed by 3 weeks of dry conditions, clear skies, and relatively cold temperatures. This drought produced an especially weak and widespread persistent facet layer that plagued us for most of the season. Daily Backcountry Avalanche Forecasts began on December 13th, and then 1-2’ of new snow falling from December 15th through Christmas finally loaded the weak layer. Avalanche Danger increased to CONSIDERABLE and HIGH on December 21st, and we issued our first Avalanche Warning of the winter for the Sawtooths & Western Smoky and the Banner Summit zones. Small avalanche cycles in our northern zones occurred on December 17th, and December 26th, and a widespread cycle occurred December 20th-21st.

The New Year rang in with a multi-day storm that ramped up on January 4th, dropping 1-2’ of snow. January 4th brought HIGH avalanche danger and an Avalanche Warning for all four zones. During this storm, 51 avalanches larger than D2 (big enough to bury or injure a

person) were recorded in our new avalanche occurrence database. Six to 12” of dense snowfall and warm temperatures January 12th-13th once again prompted HIGH danger in all zones, and another Avalanche Warning for the Sawtooths & Western Smokys and Galena Summit & Eastern Mtns zones. This storm produced 63 avalanches D2 and larger.

Avalanche conditions calmed down until late January, although the danger remained MODERATE to CONSIDERABLE due to the December persistent weak layer. On January 26th, the largest storm of the winter smashed into our area, with a bullseye squarely on the Southern Mountains. The Sun Valley Ski Resort recorded over 4 feet of uncharacteristically low-density snowfall from the 26th-29th, with nearly as much falling in the town of Ketchum. The Soldiers picked up over 3 feet, and the rest of the forecast area received 2 feet. This storm broke the camel’s back, especially in the Southern Mountains that had yet to receive a significant load on the December weak layer. The avalanche danger was HIGH for 5 straight days (excluding the Banner Summit zone), and we issued an Avalanche Warning that lasted for 3 days. Once the skies cleared, over 50 avalanches D2 and larger were observed; many more likely occurred during the storm. Most of these avalanches ran on December facet layers, although some ran on the weak snowpack surfaces (facets, crusts, and surface hoar) that existed prior to the storm.

The snowy pattern continued through February. Small storms rolled through early in the month, and measurable precipitation occurred each day from February 11th- 26th. This nearly constant trickle of snowfall heavily favored our Northern and Western Mountains, where more than 4 feet of snow accumulated over this period. While visibility was a challenge during the storm cycle, we saw a few avalanches that failed on the mid-pack weak layer that was buried in late January. Avalanches were most prevalent where the layer consisted of surface hoar (primarily around Banner Summit) and a facet/crust combination (mainly in the Sawtooths & Western Smokys). Tragically, a snowmobiler was killed in an avalanche in the Smiley Creek drainage on February 19th. The avalanche broke about 3 feet thick on the mid-pack facet/crust layer. During the month of February, the Sawtooths & Western Smoky zone was rated as CONSIDERABLE for 25 days, HIGH on one day, and MODERATE the remaining 2 days.

Tragically, a snowmobiler was killed in this avalanche in the Smiley Creek drainage on February 19th.

In contrast to February, March was exceptionally dry. Only 18-24” of snowfall was recorded during the month, spread out over several small storms. Our first major warm-up of the winter occurred in early March, producing many wet loose avalanches and one very large wet slab in the Sawtooths. When the temperatures cooled on March 7th, the danger across the forecast area dropped to LOW for the first time since mid-December. A few of the small storms were accompanied by wind, resulting in the threat of wind slab avalanches. A major wind event occurred late in the month, but by that point, firm snowpack surfaces left little snow to blow around. By and large, conditions were fairly stable during March—quite a juxtaposition to the winter up to that point.

The first half of April proved drier yet, with only a few inches of snow recorded as of April 15th. A major warming event during the first week produced one day of CONSIDERABLE danger, otherwise, conditions were rated as MODERATE or LOW. We produced our last Avalanche Forecast of the season on April 11th. As of mid-April, the snowpack in the forecast area is just 55-80% of normal. With the December facet layer still lurking near the base of the snowpack, the threat of wet slab avalanches still exists if we experience a major warming event later in the spring.