The danger will begin as MODERATE and rise to CONSIDERABLE above 6000 feet today. New snow with increasing wind will cause the danger to rise as the day progresses. Temperatures are increasing and this new snow is falling on lighter snow from the past week. Human triggered storm and wind slab avalanches will become more likely as the storm continues. Also pay close attention to deeper weak layers around the Dec. 9 rain crust and the ground.
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Above 6500 ft.
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5000-6500 ft.
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3500-5000 ft.
This new snow and increasing winds will begin to form both storm and wind slabs. With rising temperatures accompanying this storm, new storm slabs will be more cohesive and fall on lighter unconsolidated snow from this past week creating an upside-down snowpack. This older snow will probably have a hard time supporting the weight of the new snow as it begins to pile up. Storm slab depth will increase as the day progresses, and the avalanche hazard will rise. Storm avalanches could fail on either the new/old snow interace or deeper along the December 9 rain crust.
Previous wind slabs weren't as prevalent and widespread as expected based on recent observations, however, I expect to see more wind slab development with this storm as winds increase. Look for convex pillows of wind drifted snow, particularly near ridges and in cross-loaded gullies.
There are two major parts of the snowpack that can be considered a persistent slab problem:
1. The Dec. 9 rain crust (about 2 feet down in most locations). Weak snow below this layer has fractured and propagated in our stability tests in some but not all areas. The snow sitting above the crust is rather light and fluffy, and we could also see avalanches on top of the crust with heavier snow today into tomorrow.
2. Probably a lesser problem at this point, but still a concern is the presence of weak, sugary snow (facets) near the ground in parts of our advisory area. This layer is not present everywhere. We've noticed it in the Flathead Range, Glacier Park, and parts of the Swan Range. In some places it breaks and propagates across a column in stability tests (video), and sometimes it doesn't even break. These faceted grains near the ground are generally found in areas of thin snowpack and around rocks. With the December 9 rain crust fairly thick in places, it makes affecting these deeper layers more difficult, but still possible.
With this variability, you'll need to carefully evaluate each slope before committing to it. This could be the storm that is just enough to tip the balance and awaken these deeper layers. Pay attention to obvious signs of instability like cracking, collapsing, "whumpfing", and, of course, recent avalanche activity. If you observe these signs, it's wise to stick to low angled slopes and away from avalanche terrain.
Dangerous avalanche conditions could develop more quickly than expected this morning if snowfall intensifies and more snow accumulates than expected. Pay close attention to how the snowpack behaves with this warmer storm.
Yesterday, Todd and I skied into the backcountry east of the boundary of Whitefish Mountain Resort to the Chicken Bones area. We found a relatively strong snowpack with no facets near the ground, but weak snow below the December 9 rain crust made us think about how the incoming storm will interact with it (video, observation).
Skiers on Elk Mt. (observation) and another party on False Shields (Peak 7798) in southern Glacier Park yesterday found mostly unconsolidated surface snow (read: powder) with thin wind slab development just near ridgetops. Stability tests showed mixed results with deeper instabilities.
Other skiers in Canyon Creek in the southern Whitefish Range observed loose sluffing on steep slopes with some wind slab formation.
On Tuesday, Mark and his partners rode into Noisy Basin where he observed a relatively shallow snowpack with weak, sugary snow near the ground. The December 9 rain crust on an east aspect was nearly 8 inches thick in one of their pits. BNSF Snow Safety found moist, weak snow near the ground in a very shallow snowpack on Tuesday as well, but it did not propagate in their stability tests (observation).
Visit our Observations page and our You Tube channel for more information from the entire season.
Please let us know what you are seeing out there. Your observations are important and valued.
HOW TO SUBMIT OBSERVATIONS:
Email: [email protected]
Call and leave a message: 406.387.3821
You can also submit quick observations via text: 406.241.4571 (FAC mobile)
OR
Submit Snowpack Observations: http://www.flatheadavalanche.org/node/add/snowobs
Submit Avalanche Observations: http://www.flatheadavalanche.org/node/add/avyobs
As of 5:00 a.m. 0-3 inches of snow has fallen across the advisory area. Once again, the Swan Range seems favored for this storm. Mountain temperatures currently range from 13-24º F with southwest winds at 6-10 mph gusting to 14 mph. Today, temperatures will rise to the mid- to upper-20s F above 6000 feet with lower elevations reaching into the low 30s F. Winds will continue out of the southwest at 5-15 mph with gusts to 35 mph. We should see 4-7 inches of new snow across the advisory area today and more tonight.
| 0600 temperature: | 13-24 deg. F. |
| Max. temperature in the last 24 hours: | 15-26 deg. F. |
| Average wind direction during the last 24 hours: | South-Southwest |
| Average wind speed during the last 24 hours: | 3-14 mph |
| Maximum wind gust in the last 24 hours: | 16-19 mph |
| New snowfall in the last 24 hours: | 0-3 inches |
| Total snow depth: | 31-50 inches |
| Friday | Friday Night | Saturday | |
|---|---|---|---|
| Cloud Cover: | Snow. Increasing temperatures and wind. | Snow and a cold front passes through region. | Snow tapering and decreasing winds. |
| Temperatures: | 28 to 36 deg. F. | 20 to 26 deg. F. | 25 to 33 deg. F. |
| Wind Direction: | Southwest | Southwest | Southwest |
| Wind Speed: | 10-15 mph with gusts to 35 mph. | 9-13 mph with gusts to 35 mph. | 5-10 mph. |
| Snowfall: | 3-7 in. | 1-4 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.
