Mar 21, 2011 @ 3:38 am

March 21, 2011 Avalanche Advisory

At all advisory area locations above 5000 feet on wind-loaded terrain steeper than 35 degrees, the avalanche danger is MODERATE. Heightened avalanche conditions exist on wind-loaded terrain steeper than 35 degrees. Natural avalanche are unlikely but human-triggered avalanches are possible. Small to moderate size avalanches can be triggered on steep wind-loaded slopes.

The avalanche danger is LOW at all other mountain locations above and below 5000 feet.

Hello!  This is Steve Karkanen from the West Central Montana Avalanche Center with backcountry avalanche safety information for Monday, March 21, 2011.

Weather and Snowpack Analysis

Since Friday mountain locations have remained mild with little snow accumulation. Daytime high temperatures have been in the high 30’s and 40’s with nighttime temperatures dropping into the teens. Light snowfall moved through the area Saturday with no appreciable accumulation. On Sunday, the wind increased from the east as low pressure moved onshore in northern California.

We’re beginning to see consecutive melt-freeze cycles that are affecting the snow surface and helping with the overall settling and bonding of the snowpack. Northerly aspects are holding colder snow and do not have the obvious crusts seen on all other aspects below 8000 feet. These colder aspects are also preserving some of the earlier weaknesses we were concerned with earlier this winter but they are now buried deeply and take a heavy amount of force to produce any failure in our stability testing.

An east wind materialized Sunday and was strong enough to start scouring open slopes at the ridgelines. This should be a short-lived event so I don’t expect a lot of snow to be transported while the low pressure moves east.

Travel conditions are excellent now and the overall stability is good. Wind-loaded pockets remain the primary concern.

Weather Forecast and Avalanche Outlook

The Missoula Office of the National Weather Service is forecasting an offshore trough to move inland Monday bringing heavier precipitation than what we’ve seen over the weekend. The best chance for precipitation to occur with this system appears to be early Tuesday. Snow levels will start out high Monday then drop by early Tuesday. Moderate snow accumulation is expected at higher elevations through Tuesday.

A few inches of snow spread out over time usually is good for stability. This next storm starts out warm then cools, also good for stability. This time of year the conditions can easily strengthen ones confidence in their ability to ski anything safely. It can also make you complacent enough to forget about the hidden devils in the details such as sensitive wind slabs and weak cornices.

The wind continues to be a major factor in where the weak spots are so pay close attention to what slopes are loaded near the ridgelines and what slopes are cross-loaded further downhill.

Expect avalanche conditions to remain similar until we receive significant new snow. If sky conditions clear during high pressure, expect conditions to quickly worsen on steep slope exposed to the sun.

During warm sunny days or when it is raining, expect the wet snow avalanche danger to rapidly rise to CONSIDERABLE on any slope exposed to the sun. If it rains all aspects will become dangerous.

A considerable avalanche danger means that natural avalanches are possible and human-triggered avalanches are likely. There can be many small avalanches over a large area or large avalanches on the more heavily loaded steeper slopes. Careful snow evaluation, cautious route-finding and conservative decision-making is essential. Move off of and out from underneath potential avalanche paths when you start seeing evidence of weakened conditions such as pinwheels or roller-balls, small point release avalanches, or sinking in or punching through the snow surface as you travel.

If you get out and see avalanche activity or anything that would be important to pass along, please send us a quick note at [email protected] or fill out the form on our public observations page. The information you send is valuable to us and could keep someone from getting hurt.

The next advisory will be issued on Friday, March 25, 2011.


This information is the sole responsibility of the Forest Service and does not apply to operating ski areas. The avalanche danger rating expires at midnight tonight but the information can help you make a more informed decision regarding travel in avalanche terrain for the next few days.

Our advisory area includes National Forest System lands in the Bitterroot Mountains from Lost Trail Pass north to Granite Pass, the Rattlesnake Mountains north of Missoula and the Southern Swan and Mission Mountains near Seeley Lake, MT. Avalanche information for the Lookout Pass/St. Regis Basin area is available from the Idaho Panhandle Avalanche Center.