Continued snow and wind are forming fresh slabs on a variety of weak layers and crusts. Slabs will be thickest below ridgelines and on cross-loaded slopes. Natural and skier triggered avalanches in the Jewel Basin Friday confirm that recently-formed slabs can be reactive to a person's weight. Evaluate new snow totals and look for blowing snow; avoid steep slopes where you find about 8 inches of new and drifted snow.
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Above 6500 ft.
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5000-6500 ft.
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3500-5000 ft.
Up to 16" of snow has accumulated since Thursday on weak layers capping a rain crust. These layers exist at all elevations but are most prevalent and weakest at middle elevations. Natural and skier triggered storm slab activity Friday in the Jewel Basin and Sunday in the Whitefish Range failed on buried surface hoar at middle elevations. Utilize hand pits to evaluate bonding with the underlying crust. Shooting cracks are an obvious red flag.
Weak faceted snow buried deeply in our snowpack remains a concern, especially during loading events. These layers can awaken naturally by loading from snowfall or wind, small slides, and cornice falls. They can also still be triggered by a rider hitting the "Not-So-Sweet" spot on a slope where the slab thins. Deep slabs surprise us with their ability to propagate above a rider and across multiple slopes. Avoidance of steep rocky areas is the answer to this complex problem. Well supported, concave slopes with a uniform snowpack are preferred.
We have issued a separate avalanche forecast for each range in our area for the past 4 days. This can be confusing but it is the only way to accurately depict the avalanche problems and danger ratings given our recent weather. We hope to trim back to one or two forecasts as we enter a short period of dry weather.
Yesterday, we replaced storm slabs with wind slabs are our #1 problem in the Whitefish Range based on weather station data and limited observations. Zach traveled to Canyon Creek Sunday where he was able to intentionally trigger 8-10" deep storm slabs at mid-elevations failing on buried surface hoar. He noted numerous signs of skier triggered slides and shooting cracks from previous days. If these signs of instability were reported to FAC we would have been able to provide a more accurate forecast. Due to the reactivity of the buried surface hoar layer, we are listing storm slabs as our #1 problem in the Whitefish Range.
In the Flathead Range and GNP moderate winds earlier in the weekend formed reactive slabs in southern Glacier Park. Due to their proximity to the Continental Divide, these areas experience the effects of east winds and we are keeping wind slabs as the #1 problem.
The Swan Range has received the most snow since Thursday and we are keeping Storm Slabs as our #1 problem. Natural and skier triggered slides occurred in the Jewel Basin on Friday.
| Monday | Monday Night | Tuesday | |
|---|---|---|---|
| Cloud Cover: | Mostly Cloudy | Partly Cloudy | Mostly Cloudy |
| Temperatures: | 20 to 25 deg. F. | 10 to 15 deg. F. | 22 to 27 deg. F. |
| Wind Direction: | N | SW | SW |
| Wind Speed: | 5 to 10 mph, gusting to 20 mph | 5 to 15 mph, gusting to 25 mph | 10 to 15 mph, gusting to 25 mph |
| Snowfall: | 1 to 2 in. | 0 in. | 1 to 3 in. |
| Snow Line: | 1500 FT | 1000 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.
