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Forecast for the Logan Area Mountains

Toby Weed
Issued by Toby Weed on
Wednesday morning, December 16, 2020
Heightened avalanche conditions exist on upper and some mid elevation slopes where people could trigger avalanches consisting of recently drifted snow. The overall danger is MODERATE, with avalanches most likely on drifted upper elevation slopes facing north through east. Some avalanches could be triggered remotely or from a distance. You will find safer conditions in sheltered, low angle, and lower elevation terrain.
  • Evaluate snow and terrain carefully, and stay off and out from under steep drifted slopes.
A winter storm tomorrow, with potential heavy snowfall in the mountains, will overload the weak preexisting November snow and cause the avalanche danger to rise and become more widespread in the backcountry.
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Weather and Snow
A couple inches of new snow fell overnight at upper elevations in the Bear River Range, drifted by fairly strong and consistent westerly winds. Snow showers will continue this morning and taper off in the afternoon. West winds moderated a bit this morning, but will continue today, blowing 10 to 15 mph along the ridges, with mountain high temperatures pushing into the mid twenties.
The National Weather Service has issued a Winter Weather Advisory for the mountains, beginning tomorrow morning and extending through early Friday morning. Expect the avalanche danger to rise and become more widespread in the backcountry as more snow falls and is drifted onto the sugary preexisting weak snow from November.
Currently, hitting rocks or other shallowly buried obstacles presents a significant hazard. A few inches of nice light powder now obscures many hazards. Most slopes have little more than about 2' of total snow, and a steep temperature gradient is turning the shallow snow into loose sugary or faceted grains. In many places, the weak snow is easy to punch through to the rocks below.
A thick layer of very weak, sugary, or faceted snow will likely be a problematic persistent weak layer on many slopes, as future snow overloads it.
Recent Avalanches
Yesterday a local skier reported triggering a small soft slab avalanche running on the faceted snow on a very steep slope south of Tony Grove Lake. Even though the new snow is shallow and soft, and the skier was not caught, the avalanche entrained a surprising amount of snow and slammed into the trees below with a good deal of force.
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Avalanche Problem #1
Wind Drifted Snow
Type
Location
Likelihood
Size
Description
People could trigger wind slab avalanches on steep upper and mid elevation slopes where drifts formed on weak, sugary or faceted snow. In more sheltered terrain, loose sluffs and shallow soft slabs of new snow are possible for people to trigger because the older snow underneath is very weak, faceted, and loose.
  • Even a small avalanche could be very dangerous due to shallow early season snow conditions. You do not want to get caught and carried over rocks or strained through bushes and stumps, so it's best to avoid travel on all steep drifted slopes.
Avalanche Problem #2
Persistent Weak Layer
Type
Location
Likelihood
Size
Description
During the extended November dry spell, the shallow snow on the ground was subjected to a significant temperature gradient and resulting sublimation caused the snow on many slopes to become sugary, non-cohesive, faceted, and very weak. Drifted snow is a wind slab and when stiffer, more cohesive slabs develop on top of weak, sugary, faceted snow they are unstable. Many slopes in the region are now plagued by weak faceted snow, but most do not yet have a slab layer formed on top of it.
  • Avalanches failing on a persistent weak layer can be very sensitive, and they might be triggered remotely, from a distance, or worse from below!
Additional Information
Everybody should make time to examine and practice with your avalanche rescue equipment, and convince your backcountry partners to practice with you. Watch our companion rescue video HERE
My tip for avoiding avalanches in the backcountry is to keep your slope angles low. Avoid and stay out from under slopes steeper than about 30 degrees. Get a tool to measure slope angle and practice with it in the backcountry.
General Announcements
Visit this website with information about Responsible Winter Recreation by the Utah Office of Outdoor Recreation.
The Tony Grove Road is not maintained for wheeled vehicles in the winter.
EMAIL ADVISORY. If you would like to get the daily advisory by email you subscribe HERE.
Remember your information can save lives. If you see anything we should know about, please help us out by submitting snow and avalanche observations....HERE. You can also call us at 801-524-5304, email by clicking HERE, or include #utavy in your tweet or Instagram.
I will update this advisory by around 7:30 tomorrow morning.
This forecast is from the USDA Forest Service, which is solely responsible for its content. The forecast describes general avalanche conditions and local variations always occur.
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