High avalanche danger prompts warning across northern Utah mountains

Fresh avalanche debris fills the runout zone beneath a steep slope in the Salt Lake area mountains as the Utah Avalanche Center warns of high avalanche danger Wednesday. Forecasters said recent heavy rain, snow and wind have created conditions where large natural and human-triggered avalanches are likely, and urged people to avoid slopes steeper than 30 degrees and areas below them. Photo: Utah Avalanche Center

SALT LAKE CITY, UT — Utah Avalanche Center forecaster Drew Hardesty warned Wednesday that high avalanche danger exists across the Salt Lake area mountains, with recent heavy rain, snowfall, and moderate to strong west winds creating conditions in which large, destructive avalanches are “very likely.”

In a forecast issued Wednesday morning, Feb. 25, the Utah Avalanche Center said both natural and human-triggered avalanches are likely and advised people to avoid travel on or beneath steep terrain, defined as slopes steeper than 30 degrees, as well as avalanche runout zones. The center also warned that large avalanches can be triggered from below, even by people standing in lower-angle terrain.

An avalanche warning remains in effect from 6 a.m. MST Wednesday, Feb. 25, to 6 a.m. MST Thursday, Feb. 26, for the mountains of Northern Utah and Southeast Idaho, including the Wasatch and Bear River ranges, according to the Utah Avalanche Center.

“Very dangerous avalanche conditions exist,” the center said, adding that recent heavy snow combined with wind has overloaded slopes with poor snow structure and created widespread instability.

Hardesty said the Wasatch Range was engulfed by heavy rain early Wednesday, with the rain-snow line fluctuating around 8,500 to 9,000 feet. Temperatures were in the low- to mid-30s, with moderate to strong west winds. Reported overnight totals as of 3 a.m. included 4 inches of snow and 1.38 inches of water in Little Cottonwood Canyon, 4 inches and 1.15 inches in Big Cottonwood Canyon, 5 inches and 0.80 to 1.27 inches in Park City, 4 to 6 inches and 1.0 to 1.60 inches in the Ogden area, and 1.30 to 1.72 inches of water in the Provo area, where snowfall totals were unknown, according to the Utah Avalanche Center.

Additional rain and snow were expected through Wednesday morning, with the rain-snow line dropping to about 8,000 feet and another 0.5 inches of water possible. Hardesty said clearing is expected later Thursday, followed by warming through the weekend, with another storm system forecast for late weekend into early next week.

The warning comes after a deadly week in Utah’s backcountry. Three people were killed in separate avalanche accidents in the past week, and a fourth person was left in critical condition.

The incidents included:

• Wednesday, Feb. 18, at Ant Knolls in the Wasatch Back, where a snowmobiler was killed.
• Thursday, Feb. 19, at Rock Garden in Big Cottonwood Canyon, where an 11-year-old skier was killed.
• Saturday, Feb. 21, in Butler Basin in Big Cottonwood Canyon, where one backcountry skier was injured, and another was left in critical condition.
• Sunday, Feb. 22, in Caribou Basin in the Wasatch Back, where a snowbiker was killed.

The Utah Avalanche Center said all four accidents involved slab avalanches 2 to 3 feet deep and up to 500 feet wide that failed on weak faceted snow known as the January Dry Layer, or JDL.

Hardesty said nearly all of the recent fatal accidents — along with many other close calls — involved avalanches triggered from below while people were in gentler terrain, underscoring that low-angle slopes alone do not eliminate risk if steeper connected terrain is overhead.

The center identified a persistent weak layer as the primary avalanche problem. According to the Utah Avalanche Center, that layer has been involved in about 70% of all avalanche fatalities in Utah and was responsible for the three deaths reported in the past week. Hardesty said nearly 60 avalanches failing on that layer were reported in the past week alone, with many more likely unreported. Some avalanche paths at and below 8,000 feet are also considered dangerous, which Hardesty described as unusual.

A second concern is wet snow. Hardesty said forecasting wet avalanches on Wednesday carried significant uncertainty, but areas up to about 8,500 feet had received 1 to 1.5 inches or more of rain on top of an existing snowpack. He said both wet loose and wet slab avalanches were likely in some areas, with wet slabs potentially more likely on west-, north-, and east-facing slopes and possibly releasing naturally.

Above the rain-snow line, the Utah Avalanche Center also warned of wind-drifted snow, with the potential for dense, fresh wind slabs on north-, east-, and south-facing terrain.

No avalanche reports were received on Tuesday, aside from storm snow sliding off mountain roofs, according to the Utah Avalanche Center. The center noted that roof avalanches have also been deadly in Utah, including fatalities in spring 2023 in upper Big Cottonwood Canyon.

The Utah Avalanche Center advised that travel on or beneath avalanche terrain is not recommended and urged people in the mountains to understand avalanche runout zones and alpha angles, which help define how far avalanche debris can travel.