Before you ski any slope you must first determine if it is stable and safe to ski. When trying to determine if a slope is safe there are many factors you must consider: weather, terrain and snowpack are the three most important.
As far as weather be concerned with wind, temperature and new snowfall. Wind transports snow, loading certain slopes and creating sensitive and dangerous wind slabs. Heat can warm and weaken the snow pack so be aware of warming temperature as a slope can quickly become unstable with the temperature rising just a few degrees. New snowfall adds weight on top of possible weak layers below and also builds new slabs that can be sensitive.
In regards to terrain one needs to look at slope angle, aspect, and what will happen if the slope does slide. Even a small sluff can have bad consequences if it pulls the skier over a cliff or into some rocks. Pay attention to the slope angle, aspect and elevation of any avalanche activity you see while in the backcountry. Also your local forecast center should have records of any reported avy activity. This info is priceless, use it! Trees are anchors and add stability to slope but remember everything short of a 30 degree christmas farm can slide. Ski avalanche terrain wisely. Ski from safe spot to safe spot and use ski cuts often.
Learning to read a snowpack takes years of experience to master. I will touch on the basics. Digging a pit is the best way we can take a look at the actual snowpack on the slope we are going to ski. When choosing where to dig a pit you want to find an area similar to the slope you are concerned about. Same aspect, elevation, slope angle and snow conditions. It is a good idea to probe the area to find a spot as representative possible. Be smart, do not ever dig a pit in a location where you might trigger a slide that could injure yourself or others. Once you choose a location dig a pit roughly five feet wide by five feet deep. Since most human trigger slabs release 4-5 feet deep or less it is not always necessary to dig to the ground. If there was a recent storm of 5 feet or more, especially if you are worried about weak layers below, dig deeper. When digging your pit always make sure the uphill wall is vertical and that the snow above is not disturbed.
Once your pit is dug identify the different layers in the snowpack. The harder, stronger layers may be possible slabs or bed surface for the snow to slide on. The soft layers are possible weak layers. Once your have identified the layers begin your tests. There are many types of tests to used to determine stability. One of the most common and my favorite is the compression test. To perform a compression test you must isolate a column of snow out of the uphill wall of your pit by making cuts with your snow saw behind and to the side of the column(see video). Pay close attention to make sure all cuts are vertical and plumb. Once you have a nice plumb, free-standing column place your shovel blade on top of the column. Start with 10 taps on the shovel blade using only your wrist. Then 10 hits on the shovel blade using your elbow and wrist. Then 10 hits on the shovel blade using your whole arm from the shoulder. Always count as you hit 1-2-3-4...10. If you have a slab release on the eighth tap from the wrist you have a CT score of 8. If it releases on the first hit from the elbow you have a CT 11 and if releases on the eighth hit from the shoulder you have a CT 28 and so on. Each time you have a failure reset the shovel blade in place and continue counting from where you left off. Through this test we are able to gain a feel for the shear strength and bonding of the layers within the test area. A limitation to this test is the fact that you are testing a very small column and trying to apply the results to a whole slope. Consistency is critical. The more consistent and skilled you can get at performing this test the more confidence you can have in the results. These test takes years of experience in the field to master, even "experts" have misinterpreted their results. Take this info and practice on your own but actual field training from an avalanche class is absolutely critical to performing these tests properly.
This test is just one of many. Learn as many as possible and practice. Any test in snow pit, compression test or otherwise, is just one part of the puzzle. A compression test may tell you that a slope is unstable, but it should not tell you a slope is stable unless it is substantially backed up by good observations of data pointing to stability. I can't over emphasize that any snow pit test is just one piece of information helping you determine if a slope is stable or not. You must put all of the data you have about weather, terrain and the snowpack to make a decision about the stability of a given slope. Get out there. Take this information, get out there and practice, practice, practice. Take avalanche classes when available. Training in the field is the only way to fully understand these concepts. Keep it safe and keep it real. Respek.
Contributed by Andy Jacobsen