Avalanche Warning January 2, 2009

Happy New Year! This is Steve Karkanen at the West Central Montana Avalanche Center with the avalanche advisory for January 2nd, 2009. 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 you can expect avalanche conditions to remain the same through the weekend.

An avalanche warning is in effect for the mountains of West Central Montana above 5000′. Heavy snow is being deposited onto an extremely weak snowpack. The avalanche danger is HIGH. Natural and human triggered avalanches are likely. Unstable slabs exist on all aspects and slopes steeper than 30° The warning area includes the Bitterroot Range from Lost Trail Pass to Lookout Pass, the Rattlesnake Mountains (including Sheep Mountain in the Lower Blackfoot) and the Southern Mission and Swan Ranges near Seeley Lake. Backcountry travel is not recommended. Avoid travel on or underneath open slopes steeper than 30°.

Expect conditions to worsen especially in areas where snow turns to rain and where strong gusty winds load already overloaded slopes. All aspects and open slopes steeper than 30° are very dangerous and are expected to remain in this condition for an extended period of time.

Weather and Snowpack Analysis

SNOTEL sites are reporting 1.5” to nearly 3.5” of SWE (snow water equivalent) in the Bitterroot Mountains and 2” SWE in the Rattlesnake and Southern Missions the past 48 hours. This translates to 15” to 30” of new snow in some locations. Temperatures are close to 30° at many mountain locations this morning.

Stability testing in all areas is showing easy failures at the level of the faceted snow above and below the rain crust that formed in early December. This is now deeply buried with a firm cohesive slab above it. We’re also seeing easy failures with a wind slab that formed earlier this week during the high winds and warmer temperatures. Once this slab starts moving it quickly adds more weight to an already stressed weak layer that may fail at the ground. In other words, the mountains around Missoula are about to come unglued.

Current Avalanche Danger

Throughout the advisory area and on all aspects above 5000′ the avalanche danger is HIGH on all open slopes steeper than 30°. Natural and human triggered avalanches are likely. Unstable conditions exist on any open slope especially those that have been wind loaded or where anchoring vegetation such as stumps or boulders are covered by snow. Travel in avalanche terrain is not recommended.

Below 5000′, the avalanche danger is MODERATE. Natural avalanches are unlikely but human triggered avalanches are possible. The weak features we’ve been describing (weak faceted snow on a rain crust) have come into play in areas where the snow is deep enough to cover anchors. Unstable slabs can be found in isolated areas that have been wind loaded. These are typically on the leeward side of ridges or other terrain features, especially in open areas and can be found on all aspects.

Weather Forecast and Avalanche Outlook

A moist and strong winter storm system will continue to impact the area through Friday. Heavy snowfall and strong gusty winds will result especially across Northwest Montana and over mountain passes. Snow levels have risen to approximately 5000′ over portions of West Central Montana with pockets of freezing rain resulting.

Expect this high avalanche danger to continue or worsen as we continue to receive heavy precipitation at warmer temperatures. This is a very dangerous time in the mountains. Any avalanches that release may be very large and destructive. Don’t roll the dice. 19 people have died in avalanches this year in the US and Canada, most of them in the past week. Avoid travel on or under slopes steeper than 30°, never expose more than 1 person at a time to an avalanche path, carry rescue equipment and know how to use it.

SPECIAL NOTE: Many mountain ranges in Montana and Northern Idaho are not covered by avalanche advisories. Many of these areas are as popular and visited as often as the mountain ranges covered by the Avalanche Centers in this region. Backcountry recreationists seeking information about avalanche conditions in these areas should contact the local Forest Service District Office for more information. You can also interpret information provided by the Avalanche Centers, SNOTEL sites and the National Weather Service weather forecasts to determine what the snowpack conditions are like in areas that are not covered by an avalanche advisory. When avalanche danger conditions are dangerous from one avalanche advisory area to the next, chances are pretty good that mountain ranges that lie between avalanche centers have very similar conditions, particularly those ranges adjacent to covered areas.

SPECIAL NOTE #2: Foothills areas in Western Montana are beginning to accumulate respectable snow depths. While these areas are outside of our avalanche advisory area, these areas have terrain steep enough and avalanches have happened under the right conditions. In January of 1993, a young man died in an avalanche on Mt. Jumbo within sight of East Missoula. It’s worth paying attention to during unusual winter conditions and we have unusual conditions this year.

Be safe, have fun and let us know what you see out there. Your weather and snow observations are very important to us. Information about avalanche activity or weather conditions seen may save a life. If you have any information you’d like to share or have questions about anything related to snow safety, please contact us at [email protected]

The next avalanche advisory will be posted January 5th, 2009