February 2, 2009 Avalanche Advisory

Posted: 07:00
Good morning. This is Dudley Improta with the West Central Montana Avalanche Center’s avalanche advisory for February 2, 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.
The advisory area includes the Bitterroot Mountains from Lost Trail to Lookout Pass, the Rattlesnake Mountains and the Southern Swan and Mission Mountains near Seeley Lake. Detailed avalanche information about the St. Regis Basin can be found on the Idaho Panhandle National Forest Avalanche Center website.

Weather and Snowpack Analysis
Some areas in West Central Montana received a bit of snow in the last 24 hours, but not very much. We did, however, get a lot of strong winds on Saturday. Gusts on Point Six in the Rattlesnakes were consistently recorded at 40-50 mph on Saturday. Generally, the snow from last week has bonded well to the melt freeze / sun crust that formed during mid-January. We did receive a report that this snow was not well-bonded in the central Bitterroots, but that snow was very loose and had not formed a slab. Another report from the St. Regis Basin area noted the heavily wind loaded areas and some shooting cracks on these areas. Reports from Lolo Pass and Lost Trail Pass indicated a stable snowpack but noted wind deposits from Saturday. We observed a very stable snowpack in the Rattlesnakes yesterday with a lot of evidence of high winds. In fact, I skied in the Rattlesnake backcountry Saturday and the wind was fierce.
Keep in mind that wind is a major architect of avalanches; so even with trace amounts of new snow do not discount any wind-loaded areas above tree-line. Ridge-tops with wind deposits or cross-loading in gullies would be hazards to look for. When the winds calmed down surface hoar did develop on many slopes Saturday night. A surface hoar layer always bears attention as a possible future weak layer.

Current Avalanche Danger
On any wind-loaded slopes above tree-line the avalanche danger is MODERATE, natural avalanches are unlikely and human triggered avalanches are possible. Elsewhere in the region the avalanche danger is LOW, natural avalanches are unlikely and human triggered avalanches are unlikely. LOW avalanche danger does not mean no avalanche danger; pockets of unstable snow may exist in some terrain features.

Weather Forecast and Avalanche Outlook
There may be some modest accumulation of snow today with a high pressure ridge moving into the Northern Rockies tonight and into Tuesday. This high pressure may allow for valley inversions to establish over the area, which means the higher elevations will see seasonably high temperatures. These high temperatures should help stabilize the snowpack and possibly break down surface hoar formation on Southerly and Westerly slopes. The high pressure should break down toward the end of the week. The next snow is predicted for Sunday night.

If you have snow observations or any snow information you’d like to share please contact us at [email protected].

The next avalanche advisory will be issued Friday February 6, 2009.

Steve Karkanen and I will be presenting an avalanche awareness class at the University of Montana. The class has two evening sessions. The first session is tomorrow night at 7pm in the North Urey Underground Lecture Hall.