Moderate to strong winds drifted the recent snow and created a fresh round of slabs yesterday. Newly formed windslabs will be variable in distribution, but where present will be sensitive to human triggers. The avalanche danger is CONSIDERABLE in windloaded terrain above 6000 feet, and MODERATE elsewhere. Carefully evaluate potential windloaded areas before committing to a slope.
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Above 6500 ft.
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5000-6500 ft.
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3500-5000 ft.
The recent cold, wet weather pattern left an abundance of low density snow for the wind to transport. Luckily, we haven't seen sustained wind speeds get too out of hand, but they have certainly been strong enough to drift the light snow and form relatively dense slabs. Wind slab formed yesterday will be somewhat variable in distribution, but where they exist expect them to be reactive to human triggers. Look for smooth, rounded features and areas that appear to have a deeper snowpack along leeward ridgelines and likely cross-loaded features. Pay attention to obvious signs of instability like cracking or collapsing.
Given the overall (slight) warming trend for the duration of the recent storm pay attention to lingering storm slab instability in sheltered terrain. These slabs are easy to identify by digging your hand or ski pole into the snow and feeling for a relatively dense layer of snow over the older light snow.
On Sunday a fatal avalanche accident occurred near Cooke City, Montana. With heavy hearts, we send our condolences to the friends and family of those involved.
Continue to pay attention to weak layers buried deeper in the snowpack that continue to show some signs of instability. A freezing rain crust exists in the Whitefish Range. Also a layer of weak snow (facets and/or surface hoar) exists 2+ feet below the surface. In multiple observations last week our stability tests indicated this layer has the ability to fracture, and this fracture can propagate across the slope (video). We have not observed avalanche activity associated with these weak layers in nearly 2 weeks which may be due to lack of overlying slab development. Dig into the snow and look for these potential weak layers. Where present, choose less complex terrain. Avoid areas where the snowpack is relatively shallow and steep, rocky areas.
Remember, the avalanche advisory is a starting point for decision making. The actual avalanche hazard could be greater or lower where you are traveling, especially due to limited early season observations.
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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Join us on Wednesday, December 14 for a free motorized avalanche awareness presentation at Penco Power Products in Kalispell at 6:30.
Seth and Guy were in Pinnacle Creek in the Flathead Range yesterday. Light winds in this area drifted the snow along the ridgeline but did not form a cohesive slab.
Sunday, skiers in the backcountry outside of WMR reported wind transport with estimated 20 mph wind speed. Snowpit stability tests resulted in propagation with moderate force on the rain crust layer. Skiers in the Apgar Range in Glacier National Park noted a shallow snowpack with a poor structure and associated signs of instability like collapsing (whumfing).
Saturday, BNSF Snow Safety reported 8-10" of low density (5%) snow overnight on the valley floor. They also noted wind loading onto easterly upper elevation aspects and small storm slabs that released on low elevation cutbanks. Skiers in the backcountry outside of WMR found a mostly cohesionless surface except in open/exposed areas where the wind was creating a more cohesive snow surface. Mark also explored the terrain east of WMR and noted 4 small storm slab avalanches that had released on the old snow/new snow interface. 1 small skier triggered wind slab avalanche was also observed.
Yesterday saw continued light snow with moderate winds and strong gusts particularly as you approached the divide. New snow accumulations in the past 24 hours only amounted to 1-2 inches. Currently, temperatures above 6000 feet range from 4-11º F , and winds shifted out of the west/southwest at 3-9 mph with gusts from 10-20mph. Today should see partly cloudy skies with light westerly winds, and cool temperatures only rising to the mid-teens.
| 0600 temperature: | 4-11 deg. F. |
| Max. temperature in the last 24 hours: | 7-20 deg. F. |
| Average wind direction during the last 24 hours: | E/NE shift W/SW |
| Average wind speed during the last 24 hours: | 5-15 mph |
| Maximum wind gust in the last 24 hours: | 14-31 mph |
| New snowfall in the last 24 hours: | 0-2 inches |
| Total snow depth: | 44-64 inches |
| Tuesday | Tuesday Night | Wednesday | |
|---|---|---|---|
| Cloud Cover: | Cold and dry with decreasing winds. | Partly cloudy and cold. | Partly cloudy, slightly warmer. |
| Temperatures: | 8-18 deg. F. | -9-1 deg. F. | 10-17 deg. F. |
| Wind Direction: | West - Northwest | Variable | South - Southeast |
| Wind Speed: | 4-5 | 4 | 3-4 |
| 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.
