December 1st, 2009

Chugach, Alaska

Gale to storm force winds and up to a foot of new snow will increase the avalanche hazard today. Dangerous avalanche conditions will develop as this storm progresses. For today, the avalanche danger is rated CONSIDERABLE on all slopes steeper than 35 degrees. Cautious routefinding and conservative decision-making are essential. Today is the day to dial it back by sticking to low angle terrain and staying out from under big open steep slopes. Strong winds will easily transport this past week’s storm snow to leeward aspects where human-triggered avalanches will be likely on slopes steeper than 35 degrees, and natural avalanches will be possible on actively loading westerly slopes. Visibly drifting snow, shooting cracks, and hollow drum-like hard snow are the most obvious clues to wind slab formation.

Besides today’s danger from wind-loading, further instability is associated with a layer of weak faceted snow at the bottom of our snowpack that continues to show signs of instability. This weak layer is buried 4-5 feet deep in most locations. Keep in mind that additional load from new and wind-blown snow will further stress this layer today. A ski party on Eddies yesterday noticed collapsing of the snowpack, most likely on the facet layer. Matt, Kris, Heather, and I dug multiple snowpits on Tincan yesterday, and although we didn’t see or hear any obvious signs of instability during our tour, our compression test scores at 2000 feet elevation indicated otherwise. Check out the YouTube video I took of Matt doing a compression test by clicking on the button at the top of this page. The facets failed easily after three measly taps (CTE3Q3@160cm). This definitely got our attention. At 3000 feet elevation, the facets failed after 16 taps (CTM16Q3@126cm). What does all of this mean? It means we chose a conservative line back down because we do not trust this layer yet.

If you have observations for us please send them using the observations button at the top of the advisory page of our website. This concludes today's advisory. The next advisory will be Tuesday, December 1st. Have a great day.

For more detailed and updated conditions go to:

http://www.cnfaic.org

Here are some Chugach Snowpack analysis videos

Extended Column Test

Compression Test