The Swan Range picked up over 5 inches of snow water equivalent in the last 5 days. Dangerous avalanche conditions continue today. The avalanche danger is CONSIDERABLE at all elevations. Human triggered avalanches are likely and natural avalanches remain possible. Carefully evaluate the snowpack and make conservative decisions in the backcountry today. See advisory for other ranges here.
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Above 6500 ft.
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5000-6500 ft.
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3500-5000 ft.
We have not received recent observations from the Swan Range and there is no wind data for the area so there is some uncertainty in the conditions. Lingering wind slab and storm slab instability exists across the advisory area today. Wind speeds throughout our recent storm cycle have been relatively low. However, with abundant low density surface snow available for transport, even a light breeze can quickly transport snow, load leeward slopes and create soft slabs. Winds recently shifted to the north and east and now have returned to the southwest so be aware of atypical loading patterns. Pay attention to obvious signs of instability like cracking, collapsing, and recent avalanche activity. Substantial snow over the past few days slowed yesterday and is expected to end today. On steeper convex rollovers soft slabs were easily triggered in the past few days, and we expect these slabs to be sensitive on steep slopes today. This new snow needs time to stabilize so cautious route finding and conservative decision making remain essential.
Expect loose, dry avalanches (sluffs) today, if you are skiing or riding in steep terrain. This problem is easy to manage since they release below the trigger, but there can be severe consequences if your not paying attention. Sluffs can knock you off your feet and send you into trees, rocks, or cliffs and even bury you in terrain traps like confined gullies.
The primary persistent slab concern continues to be the weak, faceted snow above and below the Dec. 9 crust. This layer is generally found now 2.5 to 3.5 feet from the surface and exists in most locations across the advisory area. So far, we have not seen avalanche activity associated with this weak snow. The abundant recent snow has tested this layer and we will continue to evaluate the problem layer in the coming days. Continue to dig into the snow and assess this layer before committing to a slope.
In some locations in the Flathead Range, Glacier Park, and parts of the Swan Range we noted and have received observations of weak, sugary snow near the ground. In some places it breaks and propagates across a column in stability tests, and sometimes it doesn't even break. With the December 9 rain crust fairly thick in places, it makes affecting these deeper layers more difficult. Though it appears very isolated in distribution, it is worth mentioning that skiers in the southern Whitefish Range found buried surface hoar last Sunday which further illustrates the importance of digging in the snow to see what is going on below you.
On Thursday, experienced snowmobilers in the Lost Johnny area observed shooting cracks, which is an obvious sign of instability, in the recent storm snow. They reported a DEEP (3-5 feet) snowpack at lower elevations. This same party were also able to hear a large avalanche in the distance.
Whitefish Mountain Resort ski patrol reported triggering soft slab avalanches with explosives. The failure layer was the new snow/old snow interface. This layer varied between the 2 waves of precipitation received over the previous 2 days. The soft slabs did not propagate wide but, due to the low density surface/near surface snow, were able to run long distances (almost full path).
On Wednesday Erich traveled to the Ghoulie Point area in the southern Whitefish Range and found cohesionless surface snow near the ridgeline. At low elevation (below 5000 feet) he noted recent natural avalanche activity in the form of very thin soft slabs (4-5 inches thick) that failed and propagated fairly wide on steep cutbanks due to storm snow that was slightly heavier.
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
Other than a few lingering showers, the series of storms that moved over the area in the past week has ended and high pressure will begin to build. In the past 24 hours we picked up 1-5 inches of light snow (snow water equivalent range from 0.1-0.3 inches). Currently, mountain temperatures range from 9º-17º F and winds switched back to the west and southwest and are blowing at 5-9 mph with gusts from 14-16 mph. Today, lingering showers should end this morning, temperatures will reach the low 20s and light winds will continue out of the west and southwest.
| 0600 temperature: | 10-17 deg. F. |
| Max. temperature in the last 24 hours: | 16-21 deg. F. |
| Average wind direction during the last 24 hours: | N-SW |
| Average wind speed during the last 24 hours: | 3-9 mph |
| Maximum wind gust in the last 24 hours: | 12-18 mph |
| New snowfall in the last 24 hours: | 0-5 inches |
| Total snow depth: | 59-74 inches |
| Saturday | Saturday Night | Sunday | |
|---|---|---|---|
| Cloud Cover: | A few lingering showers, high pressure building. | Cold. Inversion developing. | Slight warming. |
| Temperatures: | 15-22 deg. F. | -6-13 deg. F. | 19-28 deg. F. |
| Wind Direction: | SW | SW | SW |
| Wind Speed: | 6-7 | 6-9 gusts 22 | 7-8 gusts 21 |
| 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.
