Avalanche safety tip of the week
As longer days bring more spring-like conditions to the Sierra, wet snow avalanches will become an increasing occurrence. A general pattern of increasing avalanche danger in response to daytime warming of the snowpack is common during periods of warm weather.
The greatest effects of warming are observed first on east- through south-facing aspects, and then on west-facing aspects as the sun arcs across the southern sky. Above treeline, bowls receive increased solar radiation due to parabolic reflection that leads to more rapid heating of the snow surface. Avalanche danger tends to decrease overnight as the wet snowpack refreezes. Follow the sun and change aspects as significant roller ball activity is observed or boot penetration reaches boot top height in wet snow. These are both signs of wet snow instability.
Out of respect for others, time your travel early enough in the day so as not to leave ruts in the slope. These ruts will refreeze overnight and ruin the slope for other travelers. It is critical to watch for periods of overnight cloud cover that keep air temperatures warm and do not allow for the strong radiational cooling of the snowpack that occurs under clear skies. If the snowpack does not refreeze, avalanche danger will not decrease overnight and avalanche danger will rise to a higher level the following day with continued warming.
Brandon Schwartz is the Avalanche Forecaster for the Sierra Avalanche Center and U.S. Forest Service in the Tahoe Region. Look for a new avalanche safety tip of the week each week here in the action. For more information and daily updates, please see http://www.SierraAvalancheCenter.org or call the Avalanche Hotline at 530-587-2158.
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