Feb 9, 2014 @ 9:32 am

Special information update for February 9, 2014

We are raising the avalanche danger in the Bitterroot Mountains from Lost Trail Pass to Lolo Pass to CONSIDERABLE.  Natural avalanches are possible, human triggered avalanches are likely.  Avalanche conditions are dangerous and require careful snowpack evaluation, skillful route finding and conservative decision making.

Good morning!  This is Steve Karkanen with an avalanche information update from the West Central Montana Avalanche Center for Sunday, February 9, 2014.  The avalanche danger rating expires at midnight tonight (2/9/14) and does not apply to operating ski areas.

Backcountry locations in the Bitterroot have received heavy snowfall since Friday and are currently being affected by high winds.  We’ve received reports this morning from the Lost Trail backcountry of low stability test scores, collapsing of the snowpack and recent avalanches on steeper terrain.

SNOTEL data has been unavailable this weekend so we have no hard data from northern parts of the range other than the Visitor Center at Lolo Pass reports an additional 6 inches new snow this morning. The southern mountains have been impacted the most so far.

Missoula Weather Service has issued a winter weather advisory for the Bitterroot mountains with snowfall amounts of up to 8 inches and winds gusting to 25 mph.

The avalanche danger is MODERATE at other locations in the west central Montana backcountry.

Natural avalanches are unlikely but human-triggered avalanches are possible on open terrain steeper than 35 degrees.

Recently wind loaded terrain has the most potential but all aspects must be approached carefully. A weak layer that formed during the 2 weeks of clear weather last month is now buried about 2 feet deep throughout western Montana.


Weather and Snowpack  (the information is from Friday Feb 2)

Very cold temperatures and high winds above 8000 feet made the decision on whether to take a sick day a little easier this week.

On Wednesday, east winds gusting into the mid-forties were recorded at Point Six north of Missoula, bringing the wind chill to -63 degrees at one point.  These winds have since diminished and temperatures are much more tolerable.

The wind this morning is WSW@15 mph at Point Six and SSE@4 mph at Deer Mountain east of Darby. Mountain temperatures are mostly above the zero degree mark as cloud cover moves into the area with a weather system that is pushing the cold air mass to the east.  Temperatures in the Seeley Lake area are -10F and local valleys remain below zero.

Cold temperatures allowed weak layers to persist and get weaker and high east winds moved snow around in many areas.

Because of the cold temperatures and ski area closures Thursday morning, our field data is limited but we did receive good reports from the Downing Mountain Lodge (DML) near Hamilton, a public observation from the North Fork Lost Horse area and from Carl at Yurt Ski Thursday. Our specialists toured near Lolo Pass yesterday.

John at DML reported to us that he and clients were feeling good about stability.  There was no visible avalanche activity, little wind and no other obvious evidence of instability as they ventured onto and enjoyed excellent skiing conditions on steeper terrain.

At Lolo Pass, Tim and Dave found wind affected snow and felt that wind slabs are the primary concern with the possibility of triggering a deeper slab in isolated areas. In some areas, a slab above a surface hoar/near surface facet layer that was buried last week can be easily triggered by the weight of a skier or snowmobile. A snowmobiler triggered a slide near Beaver Ridge last Sunday.

In the northern mountains near Seeley Lake, the situation is a little different.  Carl at Yurt Ski reported that the high winds earlier this week affected all aspects particularly near the ridge tops. “Backward” cornices were developing in places that are typically wind scoured and they experienced widespread whoomping and collapse noises on the ridges. They observed a small natural wind slab release in Highmarkers so they have been sticking to the trees and lower angle terrain.

The primary avalanche problem is the possibility of triggering a wind slab on steep slopes that have been recently wind loaded. Strong east winds this week have moved much of last weeks storm snow onto areas that are not usually wind loaded. A secondary avalanche problem is the facet layer that formed in late January.  It is now buried about 2 feet deep and can be triggered if you hit the right spot. Your avalanche radar needs to be attenuated for these particular problems.

You can best mitigate your risk by checking to see if these weak layers are present on the slope you want to ski or ride on. Stay away from facet factories like rock outcrops and small groups of trees, as these tend to be places where fractures can be more easily initiated.  If a slope looks like it has been heavily wind loaded, it probably is.  Trust your instincts and if you are unsure, don’t push it, and don’t let your partner(s) talk you into taking a chance you are uncomfortable with. Always practice limiting the exposure to your group by making sure only one person at a time is on or below terrain steep enough to slide.


Weather and Avalanche Forecast

Pacific moisture is starting to stream across the area and is expected to continue through the weekend.  Light snowfall and wind is expected today with gradually warming temperatures.

As temperatures begin to moderate with light snow accumulation and calm winds, I expect the snowpack to strengthen with time.  If we return to a warm/wet pattern with high winds the avalanche danger will escalate in all areas.

We appreciate hearing from you. Your observations are important for everyone who recreates in the western Montana backcountry. Send an observation from our website, send an email to [email protected] or leave a voice mail at 406-329-3752.


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.