February 9 Avalanche Advisory

Posted: 07:00
Good morning. This is Dudley Improta with the West Central Montana Avalanche Center’s avalanche advisory for February 9, 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, the advisory can provide valuable information for evaluating avalanche hazard for the next 48 hours.
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
West Central Montana received some snow Friday and Friday evening. The storm mainly put down snow in the Northern part of the forecast area. The Hoodoo Basin Snotel registered 8 inches, the Rattlesnake got about 5 inches, about 3 inches at Lolo Pass, a trace at Lost Trail pass; the North Fork of the Jocko and the Seeley Lake region came in the winner with 9 inches of new snow. After our brief flirtation with winter we returned to high pressure, warm temperatures at altitude and a mild inversion. There was not a lot of wind associated with the snow or with the following high pressure. Winter returned this morning and Snotel sites are showing accumulations from Sunday night; 1.5 inches in the Rattlesnake to a trace near Lost Trail Pass. Yesterday and Saturday observers reported the new snow sluffing on steep slopes. This snow is moving on steep, open slopes above 6000 feet. In some areas the snow is moving and accumulating up to a foot in depth. Generally the slopes are stable, but on large open bowls above 6000 feet on steep slopes the snow is moving when skied. These observations are related to the Northern part of the forecast area (Rattlesnakes, Seeley Lake) where we received more snow. We were sent a photo of a low elevation avalanche (below 5000 feet) near the Seeley Lake area. This slide appeared to have run this weekend during the heat of the day on surface hoar that developed during the clear nights last week. This photo can be viewed on missoulaavalanche photos .

Current Avalanche Danger
In the Northern Bitterroot, the Rattlesnakes and the Seeley Lake areas on slopes 35 degrees and steeper the avalanche danger is MODERATE. Natural avalanches are unlikely and human triggered avalanches are possible. Elsewhere in the forecast region the avalanche danger is LOW. Natural avalanches and human triggered avalanches are unlikely.

Weather Forecast and Avalanche Outlook
It looks like over the next couple of days two weak pacific systems will be passing through the Northern Rockies. Areas most likely to see moderate snow will be the mountains adjacent to the Idaho border. Some areas may receive 3 inches of new snow today and winds up to 20 mph are predicted for Tuesday. There were observations of significant surface hoar development from Saturday night; if you recreate where there is new snowfall and/or wind-blown snow keep in mind it may have fallen on this weak layer.

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

Steve Karkanen will issue the next avalanche advisory on Friday, February 13, 2009. We did not draw straws to see who would issue the advisory on Friday the 13th, Steve volunteered.