Presidents’ Day Avalanche Advisory
West Central Montana Avalanche Center
Avalanche Advisory
Posted Monday February 16th, 2009 at 0600.
Good morning! This is Steve Karkanen at the West Central Montana Avalanche Center with the avalanche advisory for Presidents’ Day, February 16th, 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 Forest Avalanche Center website.
Weather and Snowpack Analysis
This report will be mostly a repeat of what we said last Thursday. Mountain locations have not received any significant weather the past 3 days and temperatures have remained cool and consistent even during the sunny days. I was touring in the Rattlesnake Sunday and saw that people are skiing steep lines with abandon with only minor surface sloughing occurring.
The buried surface hoar and facets that formed on a sun crust several days ago is persisting with the cooler weather but there really isn’t a slab above it to worry about. The main thing to watch for now will be wind slabs forming on the steeper terrain. As soon as we start receiving significant snow expect the surface to start moving as the buried facets fail to support a heavy new load.
Current Avalanche Danger
At all advisory area locations above 6000′ on wind loaded terrain steeper than 35°, the avalanche danger is MODERATE. Natural avalanches are unlikely but human triggered avalanches are possible. All other slopes have a LOW avalanche danger where natural avalanches are very unlikely and human triggered avalanches are unlikely. You can almost always find isolated pockets where there are dangerous avalanche conditions on some terrain features.
Weather Forecast and Avalanche Outlook
A series of weak Northerly storm systems will bring a chance of snow to the Mountains of Western Montana Sunday night and then again Tuesday. No significant snow accumulation is expected during any of these events.
Expect avalanche conditions to continue to improve for the next few days. A significant new load on steep slopes from wind or storm snow will quickly raise the avalanche danger to considerable or high in areas where the above described weakness exists. Also keep in mind that many of the sheltered lower elevations that were in the fog during the inversion 2-3 weeks ago have an obvious buried surface hoar layer that will become reactive with a new load. This is most pronounced in the Lolo Creek drainage at elevations below 5000′.
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 Friday, February 20th, 2009.
