Utah Avalanche Bulletin

This bulletin is from the UAC, which is part of the US Forest Service.

Utah Avalanche Center (UAC) Advisory

The information in this advisory is from the US Forest Service, which is solely responsible for its content. This advisory describes general avalanche conditions and local variations always occur.

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Tuesday, April 13th 2010

Each spring, avalanche conditions become more predictable and our avalanche advisories end up repeating themselves like a broken record.

So here is the usual spiel:

As my 93-year-old Czech mother-in-law reminds me, "Spring is always a fight between winter and summer." We have alternating, cold, dry powder storms followed by warm, sunny weather that quickly turns the snowpack soggy.

First for storm snow: we have to worry about the usual round of avalanche activity that occurs during storms, namely instabilities within the new snow and wind slabs. Luckily, in spring, the new snow usually falls on a very stable pre-existing snowpack, so all the monkey business is near the surface. Be sure to use your usual round of tricks like jumping on small test slopes to see how they respond and dig down with your hand to see how well the snow is bonded. Also, you should never commit yourself to a slope without first putting a good slope cut across the slope to test it. If the slope fractures, hopefully, your momentum will take you off the moving slab. And as always, avoid steep slopes with recent wind deposits.

Between storms, the new snow turns soggy in a hurry with warm temperatures and strong spring sun. Always avoid steep, sun-exposed slopes when they begin to turn wet for the first time. They will often produce roller balls or pinwheels as a precursor to producing larger, wet or damp sluffs.

Second, watch for several unusually warm days in a row because percolating melt water can lubricate and weaken deeply buried weak layers, which produce large, dangerous, wet slabs. We often see these occur during very warm weather after 3 nights of no freezes or limited freezes, especially on a layered, winter-like snowpack, which has not experienced percolating melt water before. When playing on corn snow be sure to get out early and head home early--before the snow surface gets punchy.

Third, you need to avoid steep, rock slabs, which often produce glide avalanches in which the entire snowpack moves slowly like a glacier until it releases catastrophically. These releases can occur any time of day and counter intuitively seem to release more in the early morning hours, just when you expect it the least. In the Salt Lake mountains, glide avalanches occur like clockwork in places like Stairs Gulch, Broad's Fork and Mill B South, which are always good places to avoid in spring.

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The USFS posts some additional information through the season:

• Snow Profiles
• Photos
• List of Avalanches

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