The avalanche danger is MODERATE above 5000 feet. Human triggered avalanches are possible. Abundant recent snow and wind formed slabs on mid to upper elevation leeward slopes. Continue to carefully evaluate wind loaded areas before committing to any slope. Also, keep in mind that the recent storm loaded variable old snow surfaces including crusts, facets, and surface hoar. Dig into the snow to assess these layers, and choose conservative terrain where they are present.
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Above 6500 ft.
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5000-6500 ft.
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3500-5000 ft.
Moderate winds with strong gusts over the past week drifted the abundant recent snow and formed slabs on leeward ridgelines and also cross-loaded mid-slope terrain features. The skier triggered avalanche reported in the Skook Chutes of the Whitefish Range on Sunday appears to have been a wind slab created by cross loading. Remember, windslabs can take as long as week to gain strength so continue to treat them with respect today. It is also important to pay attention to changing conditions in regard to fresh wind slabs. Yesterday, wind direction shifted out of the east - northeast which may load atypical slopes. Any new slabs formed on these slopes could be thick, and reactive. Pay attention to obvious signs of instability like cracking, whumphing, and hollow sounds.
Snowfall over the past week was deposited on a variety of surfaces including surface hoar, facets, sun crusts and melt freeze crusts. We have limited observations due to difficult access so there is still some uncertainty in the distribution of these layers and reactivity with the recent load. Natural and human triggered avalanches were recently reported from multiple locations. A weak faceted layer or buried surface hoar may have been the culprit in a few of these events. Dig into the snow and look for these weak layers. Where they are present and reactive choose simple terrain to ski or ride.
With all of the recent, unconsolidated snow continue to pay attention to loose, dry avalanches (sluffs) particularly in steep terrain and around terrain traps. On continuous steep slopes these sluffs can pick up a good head of steam and pack a big punch. Also, the effects of even a small loose, dry avalanche can be amplified by traveling in or near a terrain trap like cliffs, tree islands, or narrow gullies.
We really appreciate the steady flow of observations. Please continue to help us out by letting us know what you are seeing out there. Remember, that even very simple observations like recent avalanche activity, no avalanche activity, or recent snow depths are a huge help. Thank you!
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Thursday December 8, join us at the Sportsman and Ski Haus in Whitefish at 6:30 for a free 1 hour general avalanche awareness presentation.
On Wednesday December 14 join us for a free motorized avalanche awareness presentation at Penco Power Products in Kalispell at 6:30.
Yesterday, we rode into the Lost Johnny drainage in the Swan Range. We found nearly 2 feet of recent, unconsolidated snow. Wind speeds had moderated, but we were still able to see plumes of drifting snow on distant peaks. Steep slopes produced loose, dry avalanches (sluffs) early, but became a bit more stubborn as the day progressed.
On Sunday a skier triggered a soft slab avalanche in the Skook Chutes of the southern Whitefish Range. The avalanche occurred on a cross loaded slope with the bed surface being the thin crust formed during the snow event of Friday evening. The crown was 8-12" in depth, 50' wide and ran 700'. The skier was able to safely ski out of the slide.
Also on Sunday riders in the Red Meadow Pass area of the Whitefish Range noted natural avalanche activity on upper elevation wind loaded northeast aspects.
Saturday, skiers in the Marion Lake area of the Flathead Range reported moderate to strong winds along with snowfall rates of 1/2" per hour on their tour. No signs of instability were noted but they did find a buried surface hoar/facet layer 6-10" below the surface.
Also on Saturday, skiers in both the southern and northern Whitefish Range reported a thin crust 2-3" below the snow surface on all aspects above 6000'. This crust was not supportive and would break on each turn. This likely formed Friday evening as air temperatures warmed for a short duration during the storm. No other signs of instability were observed.
Yesterday, as the snow tapered arctic air moved into the region and temperatures plummeted. Currently, mountain temperatures range from -8-7º F, winds shifted and are out of the north and east at 6-8 mph with gusts to 12 mph. For today, we should see a lull in the recent wet pattern with partly cloudy skies. Temperatures will remain frigid with highs in the single digits. Winds will continue out of the north and east at 5-10 mph. It looks like the end of the week will bring a return to snow.
| 0600 temperature: | -8-7 deg. F. |
| Max. temperature in the last 24 hours: | 7-22 deg. F. |
| Average wind direction during the last 24 hours: | E-NE |
| Average wind speed during the last 24 hours: | 5-10 mph |
| Maximum wind gust in the last 24 hours: | 8-15 mph |
| New snowfall in the last 24 hours: | 1-4 inches |
| Total snow depth: | 35-63 inches |
| Tuesday | Tuesday Night | Wednesday | |
|---|---|---|---|
| Cloud Cover: | Arctic air becoming entrenched with dangerous wind chills. | Partly cloudy and very cold. | Partly cloudy, continued cold temperatures. |
| Temperatures: | -2-10 deg. F. | -18--5 deg. F. | -1-9 deg. F. |
| Wind Direction: | East - Northeast | East - Northeast | East - Northeast |
| Wind Speed: | 10-12 gusts 23-28 | 11-13 gusts 23-24 | 8-10 |
| Snowfall: | 0 in. | 0 in. | 0 in. |
| Snow Line: |
This advisory applies only to backcountry areas outside established ski area boundaries. This advisory describes general avalanche conditions and local variations always occur. This advisory expires at midnight on the posted day unless otherwise noted. The information in this advisory is provided by the USDA Forest Service who is solely responsible for its content.
