February 6 Avalanche Advisory

Good morning! This is Steve Karkanen at the West Central Montana Avalanche Center with the avalanche advisory for February 6th, 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. Expect avalanche conditions to change as weather conditions change. Our advisory area includes the Bitterroot Mountains from Lost Trail Pass North to near Lookout Pass, the Rattlesnake Mountains and the Southern Swan and Mission Mountains near Seeley Lake. Avalanche information about the St. Regis Basin can be found on the Idaho Panhandle National Forest Avalanche Center website.

Weather and Snowpack Analysis

Mountainous locations in West Central Montana received very little precipitation the past 4 days. Afternoon temperatures reached into the 40’s and low 50’s in some locations as clear skies and sunny days ruled. Winds were SW in the 20’s and have turned more Easterly last night as a minor weather system entered into the area. Our overall snowpack continues to strengthen with the moderate temperatures however all our observers were reporting a weak layer about 6” under the surface. This weak snow is associated with a buried surface hoar layer and facet growth that is occurring above and below a crust that formed several days ago. Some areas are seeing surface hoar growth in isolated pockets. These features are not currently a problem but will need to be treated with suspicion once we receive a few inches of new snow and wind.

Our current snowpack is now excellent for travel, not so good for skiing and the top few inches a perfect avalanche bed. All we need is a big dump of snow and things will start getting tricky. Keep informed on current and expected weather conditions.

Current Avalanche Danger

At all advisory area locations the avalanche danger is LOW. Natural avalanches are very unlikely, human triggered avalanches are unlikely. In isolated areas that have been recently wind loaded, the avalanche danger is MODERATE. Natural avalanches are unlikely but human triggered avalanches are possible. Unstable slabs may be found on leeward terrain steeper than 35° above 5000′.

Weather Forecast and Avalanche Outlook

The Missoula Office of the National Weather Service is forecasting a weak upper level storm from the Southwest US to bring accumulating snow to the mountains of West Central Montana starting early Friday and continuing through Saturday. The Bitterroot Mountains and the Bob Marshall areas appear to be the most favored for accumulating snow.

Expect avalanche conditions to worsen in areas that receive significant new snow and wind. 6” to 10” of new snow with wind will bring the above mentioned weaknesses to life. Look for and pay attention to clues that shout “I’m unstable!” These are recent avalanche activity, heavy new snow, high winds, whumpf noises, shooting cracks or collapse of the snow underfoot.

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 on February 9th, 2009.