New snowfall and winds formed fresh slabs across our advisory area. The recent storm brought us warmer temperatures and dense, heavy snow. This accumulated onto a layer of lighter, less dense snow, creating dangerous avalanche conditions. It is also possible for avalanches to step down to weak layers that exist deeper in the snowpack. The avalanche danger is CONSIDERABLE above 5000 feet. Human triggered avalanches are likely and conservative decision-making is essential today.
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Above 6500 ft.
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5000-6500 ft.
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3500-5000 ft.
Several inches of warm, dense snow has fallen over the past 24 hours and another 3-4 inches is expected today. This new snow was deposited onto a colder and less dense snow surface resulting in a classic "upside down" snowpack. This is an unstable scenario and it is likely you could trigger an avalanche in the recent storm snow. Obvious signs of instability are shooting cracks in the snow surface from under your skis or sled and whumpfing sounds resulting from the collapse of the heavier storm slab into the underlying weaker snow.
Light to moderate winds over the past 24 hours have been drifting our new snow onto lee aspects. The wind does a great job of making dense, cohesive slabs. Again, in many locations these fresh wind slabs have been deposited on a low density snow surface that was in place before the recent storm. Winds have predominantly been blowing from the west and southwest, but observations from yesterday indicate there was variability in wind direction. Look for signs of recent wind-loading such as smooth rounded pillows on all aspects today, especially above 6000 feet. It is likely that you could trigger a wind slab avalanche today and all wind loaded terrain should be viewed with suspicion.
Our snowpack is not the strong northwest Montana snowpack that we are typically accustomed to seeing. There are a variety of weak layers lurking under the snow surface. We have seen only a limited number of avalanches failing on deeper weak layers in the pack this season. This makes these layers a low probability but high consequence scenario. The recent heavy snow load will be a good test of the strength of these layers. We do not yet know the load that these deeper weak layers can handle, so again conservative decision making is essential. Take a little extra time and dig in the snow to look for these buried weak layers. Choose safer terrain where these layers exist.
We are deeply saddened to report that a skier sustained fatal injuries in an avalanche accident on Stanton Mountain in Glacier National Park Thursday, 01/05/2017. We extend our most sincere condolences to the family and friends. FAC staff, along with Glacier National Park Rangers, vistited the site on Friday. We will provide a complete report of their findings within a few days.
Join us on Friday, January 13 at The Stonefly Lounge, in Coram, at 7:00 pm for a free, engaging, and entertaining 1 hour avalanche awareness presentation.
Monday: BNSF Avalanche Safety toured in John F. Stevens Canyon. They observed an upside down snowpack as a result of the recent snowfall and wind-loading occuring on easterly aspects. In a snow pit at 6000 feet on a southeastern aspect they found a weak snowpack structure with multiple buried weak layers, including depth hoar at the ground. No avalanche activity was observed, but visibility was limited. Skiers in the Wahoo drainage in the Flathead Range found about 12 inches of new snow near 6000 feet and noted the shifting wind directions over the course of the day. They also did not observe any avalanches, but the storm snow was reactive in a snow pit, with propagation in an extended column test with easy force (one tap).
Sunday: Riders in South Canyon of the southern Whitefish Range observed firm snow at low elevations but a soft snow surface at mid and upper elevations.
Friday: Mark and 2 Glacier National Park Rangers visited Mt. Stanton in GNP. They found a relatively shallow snowpack with weak snow at the ground at mid and upper elevations. Wind slabs formed during the New Year's Day arctic intrusion were also noted. BNSF Avalanche Safety toured in John F. Stevens Canyon and observed a variety of wind slabs at mid and upper elevations. Shooting cracks in the surface slab were noted in isolated locations. Depth hoar was found at the bottom of the pack and had developed into larger grains than what was last viewed in this location 2 weeks ago.
See below for all observations this season.
4 to 12 inches of new snow accumulated over the past 24 hours across the advisory area. As of 6:00 a.m., mountain temperatures above 6000 feet are -10 to 21 °F with winds out of the southwest at 5-15 mph with gusts to 30 mph. A frontal passage today will bring about another round of snowfall, but with only light accumulations expected. On the backside of the front will be an arctic airmass seeping through the Divide and entering northwest Montana. This will generate winds out of the east and northeast. Temperatures are already dropping rapidly in the eastern parts of our advisory area near Marias Pass. Sub-zero temperatures can be expected again tonight as snowfall tapers.
| 0600 temperature: | -10 to 21 deg. F. |
| Max. temperature in the last 24 hours: | 23 to 32 deg. F. |
| Average wind direction during the last 24 hours: | SW |
| Average wind speed during the last 24 hours: | 4 to 18 mph |
| Maximum wind gust in the last 24 hours: | 10 to 37 mph |
| New snowfall in the last 24 hours: | 4 to 12 inches |
| Total snow depth: | 21 to 77 inches |
| Tuesday | Tuesday Night | Wednesday | |
|---|---|---|---|
| Cloud Cover: | Light snow and cooling temperatures | Temperatures dropping N-NE winds increasing | Cold with N-NE winds |
| Temperatures: | -10 to 23 deg. F. | -15 to 0 deg. F. | 4 to 10 deg. F. |
| Wind Direction: | West to Northwest | East to Northeast | North-Northeast |
| Wind Speed: | 7 to 9 mph with gusts to 23 mph | 8 to 9 mph with gusts to 21 mph | 9 to 10 mph |
| Snowfall: | 1 to 3 in. | 0 to 1 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.
