Avalanche Forecast for 2020-01-17 06:47

Westerly winds have been productive in moving snow around and lord knows there is quite a pile of new snow still available for wind transport. West/Southwest wind is forecast to blow 20-30 mi/hr above treeline today. We do not have any recent observations from above treeline due to poor visibility/access. Near treeline on Gray Butte yesterday afternoon, shooting cracks in small wind slabs was observed and very touchy cornices were easily triggered.  Expect similar conditions today. Wind slabs are confined to lee and cross-loaded terrain features and can be avoided by sticking to sheltered or wind-scoured areas. Wind slabs form in specific areas. Learn to recognize their characteristic shape and texture. They usually stabilize in less than a week, so wait several days after a big loading event. Mount Shasta sticks out 7,000 feet higher than any other piece of terrain in the area and can create very funky winds....such that the primary wind direction might be west, but you could observe wind from the opposite direction depending on your location on the mountain. Thus, we often included 'all aspects' for wind slab distribution. 

Soft, storm slabs 5-7 inches deep were easily triggered and fully propagating across small test slope convexities yesterday, as well as the east face Gray Butte whopper that stepped down and took all the storm snow with it. Storm slabs often stabilize quickly but we think it's prudent to take another day of caution. Below and near treeline on all aspects is where you'll find this avalanche problem. Storm slabs are often hard to recognize since the surface is usually soft and powdery...just how we like it! Tilt tests, ski cut results on small inconsequential slopes or natural activity on indicator slopes are often the best clues this problem exists.

You'll hear often, "Oh, we are going to just ski in the trees...". This attitude won't keep you safe from this avalanche problem. You can avoid wind slabs with such behavior, but not storm slabs. If the trees are wide enough to ski through, an avalanche is possible. Reduce your risk by waiting several days after a big loading event...like the one we just had!

Yesterday's storm slab off the east bowl of Gray Butte did not fail on the persistent weak layer we've been monitoring. That said, snowpits continue to reveal layers of weak, faceted snow, now several feet deep in the snowpack. Column tests have been widely variable. The weakest structure has been observed west of I-5. To say the least, uncertainty exists in the likelihood for triggering a large avalanche on this persistent weak layer. This layer is now buried by upwards of 2 to 4 feet of snow.  As the layer becomes more deeply buried, the weak layer often becomes harder to trigger--but the expected size of the avalanche can increase. This is that low likelihood/high-consequence situation, which is a challenge to our patience and decision making. So, we wait for the layer itself to get stronger. It will be up to you to dig in the snowpack and gauge it's strength using tools like snow profiles and snowpack tests. You can and you should do this.  It's important to mention with this avalanche problem that snowpack tests should NOT result in a "go" or "no go" decision. They are only a very small data point in a larger assessment. Overall caution is advised when dealing with persistent slab avalanches as they are difficult to forecast and often exist in isolated or specific terrain features. Continuous and wide-reaching snowpack assessment is key to determining a weak layers distribution and reactivity.