Observers across the region have been reporting on our talkative snowpack, especially in the higher terrain near the Divide. Wind drifted snow has been whumpfing on top of persistent weak layers. Terrain selection is the best way to avoid triggering persistent slab avalanches. Sheltered slopes are a safer bet than steep, leeward areas.
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Above 6500 ft.
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5000-6500 ft.
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3500-5000 ft.
Persistent slabs are tricky. Sometimes there's inconsistent or conflicting evidence about how reactive or widespread they are. That seems to be the case now. Observers in the Swan Range urged caution after their snowpack tests showed failures on Sunday. Travelers in the Whitefish Range experienced several collapses on Christmas Eve. Reports of whumpfing and failures in snow profiles have been frequent nearer to the Divide. Picking and choosing your terrain carefully is best to manage the problem. Steep wind-loaded and cross-loaded slopes are most reactive. Mellow, gladed slopes are a safer option.
The relatively quiet pattern continues for the Northern Rockies. There have been no reports of avalanches since last Tuesday's storm. Feedback from persistent weak layers can be spotty and inconsistent. On Christmas Eve, however, we received reports of several sudden collapses in the Whitefish Range and Glacier Park. Audible whumpfs and shooting cracks are direct signs that buried weak layers can fail under your weight. Stability tests have shown the propagation potential of these layers across the forecast zone (Example 1, Example 2, Example 3).
Persistent slabs require careful terrain selection. This problem is most pronounced on steep wind-drifted and crossloaded features, and in the bigger terrain near the Divide. Triggering persistent slabs is also possible from rocky areas with variable coverage. Slopes sheltered from the effects of the wind remain a safer bet.
We are offering an Avalanche Awareness talk Thursday, December 27 at Stumptown Snowboards at 7:00 p.m.! We are offering a Motorized Level 1- Avalanche Fundamentals course January 11-13!
Expect a mix of clouds and occasional sun today. Trace amounts of snow may accumulate by tomorrow as low pressure spreads over eastern Washington and Idaho. Any showers will be light.
| Wednesday | Wednesday Night | Thursday | |
|---|---|---|---|
| Cloud Cover: | Mostly Cloudy | Overcast | Mostly Cloudy |
| Temperatures: | 16 to 26 deg. F. | 8 to 13 deg. F. | 16 to 26 deg. F. |
| Wind Direction: | Southwest | South | North |
| Wind Speed: | 5 to 10 mph, Gusting to 20 mph | 4 to 8 mph, Gusting to 20 mph | 7 to 10 mph, gusting to 20 mph |
| Snowfall: | 0 in. | 0 in. | Trace to 1 in. |
| Snow Line: | 500 ft | 500 ft | 0 ft |
This forecast applies only to backcountry areas outside established ski area boundaries. The forecast describes general avalanche conditions and local variations always occur. This forecast expires at midnight on the posted day unless otherwise noted. The information in this forecast is provided by the USDA Forest Service who is solely responsible for its content.
