Jan 18, 2013 @ 6:27 am

January 18, 2013 Avalanche Advisory

The avalanche danger in the west central Montana backcountry is MODERATE. It is possible to trigger avalanches on slopes steeper than 35 degrees; particularly on steep slopes with aspects from west to northeast and steep wind-loaded slopes. Avoid cornices and sun-baked slopes in the heat of the afternoon.

Good Morning! This is Dudley Improta with the West Central Montana Avalanche Center’s avalanche advisory for Tuesday, January 18, 2013.

Weather and Snowpack Analysis

We’re well into an inversion cycle this morning (cold temps in the valleys, getting quite warm at higher elevations).  Winds are strong (30 to 40 mph) from the south/southeast at 8000 feet. The bright side is we have had beautiful sunny weather in the mountains and the colder aspects are still offering good skiing and riding; but those colder aspects are still harboring some isolated weak layers in the snowpack.

We have a couple of surface hoar layers that are still showing up in our stability tests.  Although I found mostly stable conditions in the Rattlesnakes yesterday; I could still identify the layer responsible for Monday’s skier – triggered avalanche on colder exposures (more info about this avalanche below).

Tim and Dave found a surface hoar layer much deeper into the snowpack near Lolo Pass.  That layer was breaking cleanly; although with a bit of force. Check out their video.  Tim pretty well sums it up; you won’t find it everywhere, but it pays to look for it before committing to steep terrain.

Observers near Lost Trail Pass are finding this layer about 12 inches from the surface; reacting much the same way, moderate scores but breaking cleanly. They also noted a cornice failure, certainly something to keep in mind in the heat of the afternoon.

The surface hoar layer is about 17 inches from the surface near Lookout Pass. Observers had overall moderate results in their pit tests but felt there was CONSIDERABLE danger on very steep, exposed, wind-loaded slopes in this area.

So, as we’ve been saying; there are not necessarily obvious clues out there that the snow in a particular area may release. You need to take a few moments and look for weak snow before riding and skiing steep slopes (steeper than 35 degrees).

Skier – triggered avalanche in the Rattlesnakes

On Monday a skier triggered an avalanche in the Rattlesnakes near the Snowbowl Ski Area. All parties came out on their own power. They were skiing the right way and affected a textbook rescue. Steve posted this incident report on our document/accident page.  There is also a video and photos about this incident.

Weather Forecast and Avalanche Outlook

The high pressure pattern is expected to continue through the weekend with the next chance of snow by mid-week.  I would expect the snowpack to strengthen; but I would continue to look for weak layers on colder aspects and be wary of the warm aspects during the afternoon heat.

More Info

If you’re out and about and would like to send us some info uses this link:  Public Observations.

Thanks to everyone who showed up for the Kettlehouse Pint night!

Steve will post the next advisory January 22.


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.