Dec 18, 2009 @ 12:00 am

December 18 Avalanche Advisory

West Central Montana Avalanche Center
Avalanche Advisory
Posted Friday December 18, 2009th at 0630

Good Morning skiers and riders, this is Steve Karkanen at the West Central Montana Avalanche Center with this first regular backcountry avalanche information advisory for the 2009-2010 season.

Current Avalanche Danger

Above 7000′ on any terrain steeper than 35 degrees that has enough snow to cover anchors the avalanche danger is HIGH. Several inches of heavy, dense snow is stressing extremely weak basal snow to the point of failure in many locations and on all aspects. At lower elevations, 5000 to 7000 feet, in areas where the snow has not yet been given the chance to bury anchors the avalanche danger is MODERATE with pockets where the danger is elevated to CONSIDERABLE particularly where wind cross-loaded a steep slope or where ground anchors are not present. Below 5000 feet, the avalanche danger is LOW.

As you can tell from the above statement, we have a complex situation developing. It is all about timing, elevation, how much snow a particular location received and if a slab has formed above the faceted snow that formed in early December.

Weather and Snowpack Analysis

Mountain temperatures warmed and the upper air mass allowed heavy precipitation to move back into the area on the heels of prolonged cold and mostly dry conditions that parked over the area for several days. SNOTEL sites picked up 2.5 to nearly 4 inches of snow water equivalent since the cold weather broke December 11th. That translates to lot of new snow and a heavy load on a very weak base.

Most of our observers reported seeing the classic signs of instability Thursday. whumpfing or collapse noise while traveling, fracture propagation, recent avalanches and a definite warm up with heavy precipitation the past few days. We have also received excellent reports from skiers and riders in the Hoodoo Pass area who saw avalanche activity and the above indicators of unstable conditions.

A word of caution. Many of the sites we like to ski and ride in are not easily accessible or just do not yet have enough snow to ride. Stability testing in some of these areas can give a false sense of security if you perform stability tests in these locations then travel to a spot not far away with a completely different snowpack. Do rely on what the snow tells you as you travel. Our first snowpit was telling us we had a moderately stable snowpack, even when the snow collapsed on approach to this particular site. We also saw evidence of recent avalanche activity on the ride up the mountain. We moved to a new site that was more representative of bigger, open, and loaded slopes to get more info. This is what we found and is truly representative of the bigger picture even though the testing shown on this clip is on flat ground.

Take a little extra time to gather as much information as possible and don’t rely on 1 set of data that proves what you set out to do. I would not want to find myself on any steep open terrain these days. Pay attention to what you see and hear. The steep and deep is dangerous right now.

Weather Forecast and Avalanche Outlook

The Missoula Office of the National Weather Service is forecasting moderate temperatures without much new snow for the next 2 days. A broad trough of low pressure moves into the Pacific Northwest later this weekend causing widespread precipitation and cooling temperatures.

Expect avalanche conditions to deteriorate if we receive heavy new snowfall. Its going to take several days for this condition to improve.

We will post the next avalanche advisory Monday December 21.

Transceiver Park Information

There are now 3 Beacon Basin avalanche transceiver parks in operation in western Montana. They are located at Lost Trail Powder Mountain, Lolo Pass Visitor Center and Montana Snowbowl. All 3 will be available for use for the entire season during operating hours at the ski areas and Lolo Pass Visitor Center. The Beacon Basin at Montana Snowbowl requires purchase of a lift ticket to access the site that is located at the backcountry access point to Point Six.


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.