Several generations of wind slab were created on multiple aspects in the alpine this past week. In isolated areas weak snow buried 1.5 - 2 feet deep exists in the snowpack. The avalanche danger is MODERATE above 6000 feet. Human triggered avalanches are possible. Continue to evaluate recently wind loaded areas. Pay attention to signs of instability like cracking and whumfing. Also, dig into the snow to look for buried weak layers and choose simple terrain where they exist.
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Above 6500 ft.
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5000-6500 ft.
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3500-5000 ft.
Though wind speeds have not been impressive over the past few days, it won't take much to drift the latest, cold, low density snow. A few shifts in wind direction made it possible to find varying generations of wind slab on any aspect in the alpine. Continue to look for signs of recent wind-loading such as smooth, chalky pillows of snow especially in exposed terrain above 6000 feet.
Weak layers buried deeper in the snowpack 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 about 1.5 to 2 feet below the surface that formed last week. Recent stability tests indicate this layer has the ability to fracture, and this fracture can propagate across the slope (video). 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.
This early in the season we have relatively limited observations due to difficult access. So there is still some uncertainty in the distribution of these layers and reactivity with the most recent snow load.
Loose, dry avalanches (sluffs) are also possible with the recent, unconsolidated snow. Sluffs can be dangerous in steep terrain and around terrain traps. 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.
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.
Wednesday BNSF Avalanche Safety travelled above Sheds 11 and 10.7. Some wind slabs had formed in cross-loaded gullies above 5000 feet but were unreactive. No avalanche activity was observed. Winds were light to calm all day with no active wind-loading.
Skiers in the southern Whitefish range on Wednesday found a freezing rain crust in their snowpit on a southerly aspect at about 6600 feet. This layer fractured and propagated across the column in a stability test. Skiers in the Middle Fork toured up Snowshed Mountain above Essex. They noted light to moderate winds that were forming thin wind slabs on easterly aspects.
On Tuesday Erich traveled in the southern Whitefish Range. We found weak layers (facets and a freezing rain crust) about 2 feet below the surface and on some aspects these layers fractured and this fracture propagated across the column - a sign of instability (video). Whitefish Mountain Resort Ski Patrol also found wind slabs to fail on the freezing rain crust in isolated locations during their avalanche mitigation work over the past two days.
Yesterday the area saw another cold, mostly sunny day. During peak "warming" several SNOTEL sites and weather stations remained below 0º F. Currently, temperatures above 6000 feet range from -18 - 3º F, and winds are 3-7 mph with gusts to 12 mph out of the east and northeast. For today expect clouds and light snow showers to develop ahead the next weather system moving into the region. Temperatures are expected to rise to the mid-teens and winds should remain light with moderate gusts out of the east/northeast for most of the day. Tonight snow showers should become more widespread and increase in intensity.
| 0600 temperature: | -18-2 deg. F. |
| Max. temperature in the last 24 hours: | -3-6 deg. F. |
| Average wind direction during the last 24 hours: | North - East |
| Average wind speed during the last 24 hours: | 5-10 mph |
| Maximum wind gust in the last 24 hours: | 10-15 mph |
| New snowfall in the last 24 hours: | 0-1 inches |
| Total snow depth: | 31-54 inches |
| Friday | Friday Night | Saturday | |
|---|---|---|---|
| Cloud Cover: | Gradual warming with light snow showers. | Light-moderate snow. | Warmer temps and snow. |
| Temperatures: | 6-18 deg. F. | -2-14 deg. F. | 9-21 deg. F. |
| Wind Direction: | East-Northeast | South - Southwest | Southwest |
| Wind Speed: | 8-9 | 5 | 5-8 gusts 20 |
| Snowfall: | 0-1 in. | 2-6 in. | 1-4 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.
