Unscheduled Avalanche Update - New snow and wind through today will cause the avalanche hazard to rise to Considerable above 5000 feet by the end of the day. Weak snow exists near the top of our snowpack. Human triggered avalanches are likely particularly on wind loaded slopes due to increasing wind and new snow load on top of these weak layers. Conservative decision making and cautious route-finding are essential now particularly after a prolonged period of lower avalanche hazard.
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Above 6500 ft.
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5000-6500 ft.
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3500-5000 ft.
A couple of skier parties reported isolated, thin wind slabs this week. New snow with enough wind on top of surface hoar and facets near the surface could be enough to make both wind slabs and storm slabs a problem later today. The melt-freeze crust from last week also provides a great bed surface for future slabs to slide on. New snow was easily sluffing on slopes steeper than 35 degrees, and even more new snow will begin to form storm slabs today. Identifying wind loaded slopes and avoiding convex rollovers where wind slabs exist is a good way to mitigate this problem. Just digging down a foot or so into the snowpack and performing stability tests will help you assess the sensitivity of these wind slabs.
The weak snow near the ground throughout our advisory area continues to show signs of strengthening. However, in some locations, particularly areas with a shallow snowpack (typically three feet or less), this layer still shows signs of instability by propagating fractures in stability tests. Getting this layer to fracture and propagate in extended column tests is becoming increasingly more difficult, but the results cannot be ignored. Managing this problem is best done by avoiding steep slopes with a shallow snowpack. It's important to assess this layer on slopes you want to ski or ride. While obvious signs of instabilty (like cracking and collapsing) are lacking, this layer could become an issue again as new snow loads the snowpack in the coming days.
We are currently moving into a period of increased avalanche hazard. The hazard the past few weeks has been Low to Moderate without much new snow to enjoy. It's important to change your mindset and don't let powder fever cloud your judgement. With new snow falling on a a surface consiting of weak layers and crusts it will be critical to ease into terrain and carefully assess each slope. Buried surface hoar has the potential to be a very sensitive weak layer that can propagate far and wide. So, let's see what happens in the coming days, but conservative decision making and careful terrain selection will be very important.
The next scheduled advisory will be issued Saturday, December 20, 2014.
Flathead Nordic Backcountry Patrol installed the beacon checkers at three locations near the Whitefish Mountain Resort ski area boundary. Thanks! This is a valuable resource and a great reminder to all who venture into the backcountry to carry your avalanche gear (beacon, shovel, and probe). Look for beacon checkers within the next week or so at other trailheads like Canyon Creek, Hungry Horse Dam, and Essex.
Beacon checker outside the ski area boundary near Flower Point.
We know that when we send the advisory via email that some folks are unable to see the hyperlinks in some email clients. We are working on our end to try and remedy this. Thanks for being patient.
Cold, clear nights with just a touch of wind earlier this week caused the development of surface hoar on most slopes. We found this surface hoar to be fairly large in the southern Whitefish Range on Wednesday (image). This layer was preserved overnight and is now buried by a few inches from yesterday. Since it's still close to the surface it would be wise to dig and investigate to see if this surface hoar layer exists on the slope you intend to ride or ski. A couple of other parties found this surface hoar layer on in Glacier National Park as well (observations).
The top 8-12 inches of the snowpack consists of a mix of this surface hoar, facets, and melt-freeze crusts from earlier this week (snow profile and image). It's important to monitor how these layers change and react with new snow over the next few days. Skiers in southern Glacier National Park found facets beneath the most recent melt-freeze crust (just 2-3 inches below the surface) to already propagate fractures in extended column tests.
Once again, the layer of weak snow (facets) near the ground continues to display variability across the advisory area. On some slopes this layer propagates fractures in our stability tests, and on other slopes it does not (video).
Currently, the SNOTEL server is down. We are unable to retrieve current air temperatures and snow data for those locations. The current weather is from a limited number of other area mountain stations. Yesterday saw about 3-5 inches of new snow fall across the advisory area. A series of progressively stronger storms through at least Sunday replaces the mild weather from earlier in the week. Currently, mountain temperatures are in the upper 20º F range with winds out of the southwest at 5-15 mph. As of 6:00 a.m. mountain weather stations report around 3 inches of new snow in the past 24 hours. Today, expect snow to continue with winds out of the southwest at 10-15 mph with gusts into the 30 mph range near ridgetops. Snow amounts will vary across the ranges, but we could see up to an additional 4-8 inches above 6000 feet. An even stronger system will impact the area this weekend.
| 0600 temperature: | 25-31 deg. F. |
| Max. temperature in the last 24 hours: | 25-31 deg. F. |
| Average wind direction during the last 24 hours: | Southwest |
| Average wind speed during the last 24 hours: | 5-15 mph |
| Maximum wind gust in the last 24 hours: | 20 mph |
| New snowfall in the last 24 hours: | 3-5 inches |
| Total snow depth: | 37-45 inches |
| Friday | Friday Night | Saturday | |
|---|---|---|---|
| Cloud Cover: | Cloudy with snow showers. | Cloudy with snow showers. | Cloudy with snow showers. |
| Temperatures: | 31-37 deg. F. | 22-27 deg. F. | 27-34 deg. F. |
| Wind Direction: | Southwest | Southwest | Southwest |
| Wind Speed: | 7-15 mph with gusts to 25 mph. | 7-15 mph with gusts to 25 mph. | 8-20 mph with gusts to 25 mph. |
| Snowfall: | 2-5 in. | 1-3 in. | 1-2 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.
