Mar 11, 2011 @ 6:33 am

March 11, 2011 Avalanche Advisory

Pockets of CONSIDERABLE avalanche danger exist on recently wind-loaded terrain above 6000 feet.

Dangerous avalanche conditions exist on recently wind-loaded terrain steeper than 35 degrees. Though this is not currently a widespread condition, careful snowpack evaluation, cautious route-finding and conservative decision-making is essential.

On other terrain above 5000 feet, the avalanche danger is MODERATE. Heightened avalanche conditions exist on specific terrain features. Natural avalanches are unlikely and human-triggered avalanches are still possible. Under these conditions it is important to identify where these areas exist and travel accordingly. Small to moderate size avalanches can easily be triggered on steep wind-loaded terrain.

Below 5000 feet the avalanche danger is LOW. Natural and human-triggered avalanches are unlikely. Watch for unstable snow on isolated terrain features.

Good morning backcountry skiers and riders! This is Steve Karkanen at the West Central Montana Avalanche Center with backcountry avalanche safety information for Friday, March 11, 2011.

Weather and Snowpack Analysis

The past few days have been relatively mild with lighter winds and warmer temperatures.  Most areas received a few inches of snow since Monday which settled out quickly under the warmer temperatures.  A robust storm system entered the area Thursday afternoon with high winds, snow and cooler temperatures. SNOTEL sites are reporting a range of new snow this morning with the Hoodoo and Lookout Pass sites receiving the bulk of the precipitation. This new snow is heavy and dense and may form sensitive slabs at the higher elevations. 

We received a report from a skiing party in the Mill Point area in the Bitterroot Wednesday who triggered several small avalanches on steep cross-loaded terrain on south to north aspects above 7000 feet. They saw major wind-slab development and settling as well as easy failures of these slabs on steep terrain. This is a good example of the variability of the conditions we’re seeing this year in many places and a good reminder that yes, even under a moderate rating for the general area, it is still possible to trigger small avalanches in specific areas or conditions.

Further south near Lost Trail, observers felt that conditions were mostly stable but that there was high wind moving a lot of snow onto leeward terrain. There are older layers of buried surface hoar still present in their pits but they are very strong. This is something to be looking for if the area receives a heavy load of new snow.

The Rattlesnake also received high winds with snow. Although stability was good, dense wind-slabs were forming throughout the storm and these will be sensitive for a couple of days.

Weather Forecast and Avalanche Outlook

A vigorous Pacific cold front is moving across the area this morning with cooler temperatures, strong west to southwest winds and significant snow in the higher terrain. Lookout, Lolo and Lost Trail passes are expected to receive the heaviest amount of snow. Weak high pressure builds over the area Friday afternoon with lighter wind and drier conditions expected through Saturday. Weak weather systems may brush the area Saturday night into Monday bringing only light precipitation..

Depending on the amount of new snow and wind, the avalanche danger may increase over the next 24-48 hours. There is plenty of snow already on the ground that will be easily moved during high winds. Pay close attention to what the winds have done in the area you want to play in. Wind-loaded slopes and wind-slabs formed lower down a slope due to cross-loading have been our biggest stability concern recently and that concern is elevated this weekend.

A good thing is that this storm started out warm then gradually cooled overnight giving us a right-side-up snowpack. This new snow also bonded well to the older snow surface.

If you get out and see any avalanche activity or see something you think is important to pass along, 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.

Dudley Improta will issue the next advisory Monday, March 14, 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.