Utah Avalanche Bulletin
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This bulletin is from the UAC, which is part of the US Forest Service.
Utah Avalanche Center (UAC) Advisory 
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Wednesday, April 29, 2009
Forecaster: bruce tremper
We have ended our avalanche advisories for the season.
General Spring Avalanche Advice:
My darling, little, 92-year-old mother-in-law from the Czech Republic lives with us and she said the other day, "Spring is always a fight between winter and summer." Each spring, we see a series of cold, winter storms with cold powder and the requisite dry, slab avalanches.
In between storms, warm temperature and strong sun instantly turns all the new snow into wet, mashed potatoes, which can come slurping down the steep mountainsides in a hurry as wet sluffs and sometimes wet slabs. Because of these rapidly alternating extremes, it can make avalanche stability assessment especially tricky. Even if we continued our avalanche advisories through May it wouldn't help much because spring conditions vary dramatically not only from one place to another but from one minute to the next. So your only choice is to carefully evaluate snow stability as you travel. Here are some general tips:
Dry snow:
With each snowstorm, we need to worry about the usual round of storm-snow instabilities, namely wind slabs and instabilities within the new snow. Wind slabs are especially easy to recognize because they are smooth, rounded, hollow-sounding and often feel "slabby", meaning that you can feel strong snow on top with weaker, softer snow underneath. You should always avoid these recent deposits of wind drifted snow on slopes approaching 35 degrees or steeper.
Even out of wind-affected areas, new snow can have buried weak layers deposited by rapidly-changing storm conditions. These weak layers most commonly include graupel, or a lower density layer in the new snow. Finally, high precipitation rates during the storm can cause instant soft slabs within the new snow because it is being loaded up with weight faster than it can adjust to its load. You can easily test for these instabilities by jumping on small, test slopes or quickly digging down with your hand and pull on small blocks that you isolate.
Wet snow:
We live in a desert, after all. So between storms we almost always get sun and this time of year, we also get very warm temperatures, which mean nearly instant damp or wet avalanches. Everyone knows that if you want powder snow in spring, you need to get it quick, because it has a very short shelf life. Once the sun and warm temperatures start to cook everything down, new snow can loose its internal strength very quickly and it starts to produce point-release, damp or wet sluffs, which can fan out to very large areas and pile concrete-like debris into very deep piles. Occasionally, wet slabs occur, which can produce very large and dangerous avalanches. Also, each spring we always see "glide" avalanches, which occur when the entire season's snowpack slides slowly on steep rock slabs or grassy slopes like a glacier until they catastrophically release as a very large avalanche. These occur during especially warm weather and they can release any time, day or night. So you should always avoid traveling on or below steep rock slabs, especially in notorious glide avalanche areas such Stairs Gulch, Broad's Fork and the steep slabs in Cardiff Fork.
Once we get a few days of warm weather with freezing each night, the snow turns into much more stable corn snow, which many backcountry skiers and boarders love because it's flat and grippy, like a groomer at a ski area. The key with corn is to get on it just after the sun softens it up enough to get an edge into it and get off of it before it gets too mushy. If you're punching through, leaving deep ruts or sinking in past your ankles when walking on foot, it's time to change to a shadier aspect or head home. Besides, it's considered to be bad form to leave deep ruts in the snow, which ruins it for others who will be there the next morning. The name of the game is to get out early and get home early.
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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.
The USFS posts some additional information through the season:
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