Today you can trigger slabs up to two feet thick on steep slopes. These can break on or near recently-buried crusts and ice lenses. Fresh drifts of wind-blown snow may make these slabs more reactive to a person's weight or pose a hazard on their own. Cracks, collapses, and fresh avalanches are reliable signs of this danger. Don't be fooled by small sluffs on the snow surface into thinking there's no slab avalanche danger.
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Above 6500 ft.
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5000-6500 ft.
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3500-5000 ft.
The primary hazard today is slabs breaking in the top two feet or so of the snowpack, on interfaces between recent storms or around recently-buried ice lenses or melt-freeze crusts. The simplest way to avoid this hazard is to avoid slopes steeper than about 35 degrees. Use active tests to gather information about local conditions before dropping into steeper terrain. Hand pits can tell you how deep icy layers are buried and whether they might act as failure planes. Column tests can indicate whether a failure plane can propagate a collapse.Short slopes with runouts clear of terrain traps can tell you how sesitive slabs might be to your weight or the weight of your snowmachine. Slabs will tend to be thicker and break deeper in the Swan Range, which has received more snow in the past week. Drifted snow may make slabs more reactive to a person's weight.
Blowing snow is a clear sign that a Wind Slab avalanche problem is developing. Look for snow that feels thicker, cakier and more cohesive on the downwind side of ridges, particularly in the tops of chutes and saddles. Freshly-formed drifts will be sensitive to a person's weight today and dangerous on steep slopes above terrain traps. New cornices may be fragile, though dropping chunks of cornice may give you an idea whether slabs of drifted snow extend across start zones and can be triggered by your weight.
Observers Tuesday reported small, stubborn sluffs of loose dry snow in the Whitefish Range. These were harmless and similar slides today should be as well. Don't let these fool you into thinking there's no slab avalanche hazard, however.
The hot-cold weather pattern of the past week has created a near-surface snowpack that's a stack of crusts, ice lenses, storm snow, and graupel. With snow accumulations varying across the region, it's hard to track the layers, even when digging - is that the crust formed on the MLK holiday or on National Beer Can Appreciation Day (1/24)? The good news is that the fast parade of storms has limited the formation of persistent weak layers. We've received some reports of small slabs breaking near crusts on small facets and tests producing planar failures on interfaces between storms. Generally, though, these failure planes are within the top two feet of the snowpack, more sensitive to a person's weight on steeper slopes, and give clear feedback when unstable: cracking or small slides on test slopes, propagating results in large column tests, or sudden failures in small column tests. The Swan Range has seen significantly more snow the past week, so expect thicker slabs there.
Winds today should increase in advance of a fast-moving system tonight, and there's plenty of soft, dry snow at upper elevations for the winds to move around. Expect small slabs of drifted snow to form on steep, leeward slopes near ridges and downwind of saddles and passes that channel winds. These will be more widespread the higher you go, and they'll be the primary near-surface hazard in the Flathead Range and Glacier National Park.
The crust/facet combinations buried near the ground have been mostly quiet since the very large slides that ran during the mid-January cold snap. With no dramatic weather today, I expect them to remain quiet and well behaved. Nonetheless, I wouldn't ride upper-elevation terrain with convex, unsupported slopes that are littered with half-buried rockbands or shallow, wind-scoured patches. Too many spots where those early-season facets are close enough to the surface to be triggered by a person's weight. And those basal facets are the one layer in the snowpack that reminds me of Colorado's typically weak snowpack.
A weak, high pressure ridge today will bring mostly dry conditions. Winds will increase during the day in advance of a fast-moving system overnight. Expect gusty winds near ridges today, perhaps mixing down into mid-elevations where funneled by terrain. Snow showers tonight will bring another few inches of snow to most of the region, though the Swan Range may wring out 4 to 7 inches.
| Wednesday | Wednesday Night | Thursday | |
|---|---|---|---|
| Cloud Cover: | Mostly Cloudy | Mostly Cloudy | Mostly Clear |
| Temperatures: | 26 to 32 deg. F. | 18 to 21 deg. F. | 26 to 31 deg. F. |
| Wind Direction: | Southwest | Southwest | Southwest |
| Wind Speed: | 10 to 15, gusting to 25 | 15 to 20, gusting to 35 | 10 to 15, gusting to 20 |
| Snowfall: | 0 to 2" in. | 2 to 6" in. | 0" in. |
| Snow Line: | 3000' | 3000' | 2000' |
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.
