March 30, 2012 Avalanche Advisory
On terrain that is wind loaded or steeper than 35 degrees, there is MODERATE avalanche danger in the west central Montana backcountry. Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
Good Morning! This is Tim Laroche at the West Central Montana Avalanche Center with your backcountry avalanche advisory for Friday, March 30th, 2012.
Weather and Snowpack Analysis
The snowpack has been experiencing a melt-freeze cycle this past week. Daytime temperatures have been in the mid forties and nighttime temperatures have been in the mid twenties. Most locations received 1-2 inches of new snow and the wind has been blowing mostly out of the south at 8-10 mph and gusting into the low thirties. Currently, mountain temperatures are in the mid thirties, winds are blowing out of the south and west at 12-14mph gusting to 26mph with light snow above 7000 feet and light rain below.
We are now in a classic Spring like pattern of weather and snow. Most advisory locations have a thick and supportable crust on all aspects. Watch for this crust to break down and become wet if it gets rain or sun. This condition will increase the avalanche danger and produce wet loose slides on steep slopes. Once initiated, these slides could step down to deeply buried weak layers in the snowpack.
Observers in the northern Bitterroots reported deeply buried weak layers that were failing cleanly in stability tests. It took a lot of force for these layers to fail, but they did fail with a lot of energy. If this area receives heavy rain or snow, it will increase the avalanche danger. Observers in other locations are not reporting these deeper instabilities and the snowpack is generally more stable.
Where precipitation is falling as snow, it is falling on a variety of surface crusts. Watch for fresh wind drifts to fail easily on leeward ridgelines and cross-loaded gullies at the highest elevations. In the Rattlesnake area, we observed a thick layer of graupel on all aspects above 6500 feet yesterday. This condition will provide a slick sliding surface for any new snow deposited on top of it.
When the sun comes out this week, pay attention to how the snow is changing. It will warm the surface snow quickly and begin to produce wet loose snow slides in steep, rocky terrain first. This is a good indicator of changing conditions and decreasing stability. Stay off and out from underneath any steep exposed slopes, especially those with cornices or glide cracks.
Weather Forecast and Avalanche Outlook
A warm, moist weather system is entering our area and will affect the Northern Rockies through Saturday. We could see 6-10 inches of heavy, wet snow in the upper elevations and rain is likely below 7000 feet. Winds will be blowing out of the south and west with speeds in the 20mph range. Temperatures will be warm and the snow level should hover around 7000 feet until Saturday night, when a cold front arrives. The cold front will lower snow levels and could deliver another 6-10 inches of snow above 3000 feet.
In areas that experience heavy rain or snow, I expect the avalanche danger to rise through the storm period. Otherwise, I expect the avalanche danger to remain the same.
Steve will issue the last advisory of the season on Friday, April 6th.
If you get out and have the time to send us some information about what you are seeing, please use our “submit observation” link on our website or send us a quick note at [email protected]. This information is invaluable to us and in turn comes back to you in the form of a better forecast.