Wind speeds increased overnight forming dense slabs on top of low density surface snow on exposed upper elevation leeward aspects. The arrival of the arctic air mass will result in northerly winds and atypical loading patterns. The avalanche danger is CONSIDERABLE above 6000 feet on exposed leeward aspects where human triggered avalanches will be likely. MODERATE danger exists on all other aspects. Evaluate all slopes before recreating on them.
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Above 6500 ft.
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5000-6500 ft.
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3500-5000 ft.
Continued light snowfall has provided plenty of available low density snow for wind transport. We have been fortunate in that wind speeds have been light for most of the past few days. Wind speeds increased last night and we expect that wind slab development in exposed upper elevation terrain occurred. As the arctic air mass made its way into John F. Stevens Canyon yesterday afternoon wind direction changed from southwest to northerly. Currently the majority of our area continues to have southwesterly winds. When the arctic moves into the remainder of our region today these winds will change to a northerly component and atypical loading will occur. These denser slabs will be deposited onto a weaker layer (the low density surface snow). Continue to look for signs of recent wind-loading such as shooting cracks, whumphing and smooth pillows of snow especially in exposed terrain above 6000 feet.
The snow that fell on Saturday and Sunday was "great powder" but relatively dense compared to what we saw earlier in the week. This has created a bit of an "upside down" snow surface. Small natural storm slab avalanches were observed at both upper and lower elevations on Saturday. With drying and colder air moving into our area this problem is decreasing but backcountry users should still be aware of its presence. Obvious signs will be cracking and whumphing in the near surface snow. Since this is a near surface problem it is easy to recognize and one that you can determine without even pulling your shovel out.
We are still monitoring 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 that formed last week. On three field days over the past week our stability tests indicated this layer has the ability to fracture, and this fracture can propagate across the slope (video). Recreationalists have also noted these layers and their stability tests have mirrored our results. 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.
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.
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. Resort skiers noted soft wind slab formation in exposed areas on typical leeward aspects.
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.
Friday, Mark traveled to the Skookoleel area of the southern Whitefish Range. We found a snow surface on all aspects that mostly consisted of cold low density snow. On a southerly aspect we had propagation in our stability tests that mirrored what Erich found Tuesday in Big Slide.
Also on Friday skiers in the Marion Lake area of the Flathead Range found a thick layer of low density unconsolidated snow on a southerly aspect. This layer sat on top of a crust but no results were observed in stability tests.
Yesterday, we enjoyed what felt like a balmy day with light to moderate snow showers and light to moderate winds. As of 6:00 am temperatures above 6000 feet range from -5 to 21° F, and winds are 9-14 mph with gusts to 24 mph out of the south-southwest. 24 hour snow totals are generally a couple of inches except for the eastern end of our advisory area where Pike Creek has picked up 11" of extremely low density snow. An arctic air mass moved into John F. Stevens Canyon yesterday afternoon which resulted in impressive drops in air temperature over a brief period. This air mass should eventually make its way into the remainder of our forecast area today with accompanying north winds and light snowfall. Tonight will be cold, windy and dry. Tomorrow will be cold but thankfully the winds will be on the decrease.
| 0600 temperature: | -5 to 21 deg. F. |
| Max. temperature in the last 24 hours: | 16-23 deg. F. |
| Average wind direction during the last 24 hours: | Southwest |
| Average wind speed during the last 24 hours: | 5-10 mph |
| Maximum wind gust in the last 24 hours: | 22-34 mph |
| New snowfall in the last 24 hours: | 1-11 inches |
| Total snow depth: | 45-63 inches |
| Monday | Monday Night | Tuesday | |
|---|---|---|---|
| Cloud Cover: | Arctic air arrives with light to moderate snow showers and windy. | Cold and windy with clearing. | Cold and dry with decreasing winds. |
| Temperatures: | 10-21 deg. F. | -12 to 0 deg. F. | 6-13 deg. F. |
| Wind Direction: | North - Northeast | West - Northwest | West - Northwest |
| Wind Speed: | 6-18 mph with gusts to 31 | 11-14 mph with gusts to 31 | 4-5 mph |
| Snowfall: | 1-7 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.
