Forecast: Salt Lake Area Mountains - Utah Avalanche Center

Forecast for the Salt Lake Area Mountains

Issued by Nikki Champion on
Sunday morning, December 20, 2020

Human triggered avalanches remain likely at the mid and upper elevations where the weak faceted snow combined with fresh wind drifts are the main avalanche problems. In these places the avalanche danger is CONSIDERABLE. Stay off of and out from underneath slopes 30° degrees and steeper at the mid and upper elevations. If you trigger an avalanche, it is likely to break down 18-30" and up to several hundred feet wide.

Low elevations generally had less wind and snow, but human triggered avalanches definitely remain possible, and the avalanche danger is MODERATE.

Low

Moderate

Considerable

High

Extreme

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Special Avalanche Bulletin

AVALANCHE CONDITIONS REMAIN DANGEROUS FOR THE MOUNTAINS OF NORTHERN AND CENTRAL UTAH, INCLUDING THE WASATCH RANGE...THE WESTERN UINTAS, AND THE BEAR RIVER RANGE. RECENT HEAVY SNOWFALL AND DRIFTING FROM STRONG WINDS HAS CREATED AREAS OF UNSTABLE SNOW. HUMAN TRIGGERED AVALANCHES ARE LIKELY. TRAVEL IN AVALANCHE TERRAIN IS NOT RECOMMENDED. STAY OFF OF AND OUT FROM UNDERNEATH SLOPES STEEPER THAN 30 DEGREES

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Weather and Snow

This morning, under mostly clear skies the temperatures range from the mid-teens to low 20s F. Winds are west northwesterly, and averaging in the teens at mid-elevations and gusting up to 30mph. At upper elevations, the winds are averaging in the 40s and gusting up to 50 mph. Yesterday morning, the winds peaked hitting speeds up to 70 mph at upper elevations.

For today, expect mostly cloudy skies as high pressure aloft to the west of Utah today will generate an increasingly strong and moist west-northwest flow across the Wasatch range through this evening. This means an increase in winds at mid and upper elevations, as well as a slim chance for trace precipitaion. Winds will be Westerly, averaging 10-20 mph at mid-elevations with gusts up to 40 mph. Howerever, the westerly winds will average 30-40 mph at upper elevations, with gusts up to 60 mph. Temperatures will be in the upper 20s to low 30s F.

Week in Review: Our first Week in Review - where we summarize snow and avalanche conditions for the past week - has been published.

Recent Avalanches

Since Friday there have been twenty six human-triggered or natural avalanches reported. Many of these avalanches were large, up to 400' wide, and triggered remotely (from a distance) failing in weak faceted snow that is now buried 18-30" deep. Overall this, in combination with the widespread cracking and collapsing being observed, is a huge indication of the sensitivity of our weak snowpack structure.

Photo: Mark White, Lower Cardiff Fork near the mine. Triggered remotely from 10 feet away. Even small slopes were sensitive to remote triggers yesterday.

Find a full list of yesterday’s avalanches here.

A video below from Observer Dave Coyne showing widespread, likely natural activity throughout Grizzly Gulch Proper.

Type

Location

Likelihood

Size

Description

Over the last two days many human triggered and natural avalanches were observed. Most of these avalanches were triggered remotely, failing on the weak faceted snow and some were quite large, up to 2' deep and a few hundred feet wide.

Weak faceted snow from storms in early and mid-November makes up the base of our snowpack on most aspects at the mid and upper elevations. This layer will eventually begin to gain strength and heal; however, over the past few days, we quickly added around a foot of snow (or more), an inch of water, and continue to add strong winds at the mid and upper elevations. With this much weight and stress on this layer, as well as obvious signs of weakness like avalanches, this layer will not be trusted for the foreseeable future.

Today, you are very likely to trigger an avalanche in terrain steeper than 30° that has the persistent weak layer of faceted snow buried underneath the storm snow. These avalanches can be triggered remotely and from below.

Type

Location

Likelihood

Size

Description

Over the last two days, the Northwesterly winds have remained strong enough to drift snow, with gusts near 70 mph at the highest of ridgelines. Today these drifts will be most widespread on the south through east-facing slopes, especially at the highest most elevations. However, sustained high winds can deposit snow around terrain features on almost any aspect, called cross-loading. For this reason, I would expect to find sensitive slabs of wind drifted snow at all upper and mid-elevation slopes, especially along with terrain features such as ridgelines, sub ridges, and gullies.

Such strong winds today will continue to form both soft and hard slab avalanches in upper elevation wind drifted terrain. As the winds continue to blow, these slabs will become more firm and cohesive. This can allow you to travel out farther onto the slope before it breaks, and can fail larger and wider than expected. Triggering an avalanche that initially fails in the wind-drifted snow will likely break down more deeply into the weak faceted snow below.

Today continue to look for slopes with any signs of wind drifted snow, such as cracking, hollow noises, and pillow-shaped snow and avoiding those slopes.

Photo of drifting snow, an obvious sign of wind loading occurring, from Solider Peak yesterday (PC: M. White)

In areas that have remained sheltered from the elevated winds, you may be able to find sensitive storm slabs up to 1’ deep. Remember, terrain traps like gullies or creeks can cause these shallow slabs to pile up much deeper and could be enough to bury a person.

Additional Information

Writing an avalanche forecast is a team process. On Friday evening, Salt Lake forecasters Nikki Champion, and Greg Gagne discussed current conditions and thoughts for putting out Saturday's forecast. While sometimes things change between the evening and the following early morning, we like to share these with the public so you have a bit better of an idea of how we communicate and the shared thinking that goes into each forecast.

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This information does not apply to developed ski areas or highways where avalanche control is normally done. This forecast is from the U.S.D.A. Forest Service, which is solely responsible for its content. This forecast describes general avalanche conditions and local variations always occur.

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