Continued snow and wind is thickening recently-formed slabs that buried a variety of weak layers and crusts. Slabs will be thickest below ridgelines and on cross-loaded slopes. Natural and skier triggered avalanches in Canyon Creek Sunday confirm instability where the recent snow buried surface hoar that formed in mid January. Evaluate new snow totals, bonding with the underlying layers and look for blowing snow.
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Above 6500 ft.
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5000-6500 ft.
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3500-5000 ft.
Several inches of new snow and northerly winds have added volume to existing slabs. Up to a foot of snow has fallen since Thursday with slabs thickest on leeward slopes below ridgelines and in cross-loaded gullies. Natural and skier triggered slides Sunday in Canyon Creek confirm that buried surface hoar is reactive at middle elevations. You may also find reactive slabs where the surface snow is upside-down (a dense slab overlies lower density snow). Evaluate new snow totals as you gain elevation. Cracking is 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 as 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. 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.
A weak weather system will produce light snow, cool temperatures, and easterly winds. Clearing tonight followed by increasing clouds and a chance of snow tomorrow afternoon.
| Monday | Monday Night | Tuesday | |
|---|---|---|---|
| Cloud Cover: | Overcast | Mostly Cloudy | Overcast |
| Temperatures: | 21 to 26 deg. F. | 8 to 13 deg. F. | 20 to 25 deg. F. |
| Wind Direction: | N | SW | SW |
| Wind Speed: | 5 to 10 mph, gusting to 25 mph | 5 to 10 mph, gusting to 25 mph | 10 to 20 mph, gusting to 30 mph |
| Snowfall: | 0 to 2 in. | 0 in. | 0 to 2 in. |
| Snow Line: | 1000 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.
