Shifting winds will build fresh slabs on a variety of aspects. Avoid steep leeward slopes where soft slabs of drifted snow will grow throughout the day. In sheltered terrain, sluffs can entrain large amounts of snow and deep debris can pile up in terrain traps. Blowing snow, shooting cracks, and long running sluffs are signs of instability. The danger will be higher if snowfall exceeds expectations.
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Above 6500 ft.
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5000-6500 ft.
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3500-5000 ft.
New snowfall and moderate winds will increase the avalanche danger. Shifting winds will drift snow onto exposed slopes on all aspects. Slabs of drifted snow will be the primary concern. New drifts could be large in favored areas above treeline, or if snowfall is more than forecast. In sheltered terrain, soft slabs may develop. Where the surface remains unconsolidated, loose dry sluffs will run on very steep slopes. Avoid steep leeward terrain, and very steep slopes above terrain traps. Watch for blowing snow at ridgelines. Recent natural avalanches and shooting cracks in slabby snow are red flags. Steer away from slopes steeper than about 35 degrees were fresh wind slabs are developing.
Soft snow sluffed easily on crusts throughout the region yesterday, in some cases running long distances.
On Wednesday night, yet another freezing rain crust formed. Yes, another one. It is thickest in the Swan Range but observers found traces of it into the upper elevations in the Flathead and Whitefish Ranges. Even where the 2/5 crust is slight or absent from the upper snowpack, the thick, hard crust that formed just before Groundhog’s Day is widespread across the region. Several inches of low denisty snow fell with seasonably cold temperatures mid week. In some cases that newer snow has faceted above and below the crusts. On Thursday, Cam and Rob found a few patches of surface hoar and unreactive wind deposits in the northern Whitefish range. Crusts will act as slick sliding surfaces and low-cohesion snow can easily collapse under new slabs.
Winds increased yesterday afternoon and new snow began to fall overnight. Storm instabilities will run the gambit today. We can expect shifting winds to create sensitive drifts across the middle and upper elevation bands. Where the most precipitation accumulates, especially in the Swan and Flathead Ranges, storm slabs can form in more sheltered locations. Where slab formation is limited, loose dry sluffs can entrain large amounts of low density snow and run long distances.
In the Flathead range and near the Divide, deep persistent slabs are still a concern. The 2/1 crust does not extend into all alpine start zones, and it may not have shut down the potential for giant avalanches originating from up high. New loading from wind and snow will only add weight to weak layer at the bottom of the snowpack. With more snow in the tracks of large avalanche paths we have again increased the potential size of the problem. Though still unlikely, deep slab avalanches can run to lower elevations and destroy mature trees. An avalanche of that size would be unavailable. Large cornice fall is exactly the kind of trigger that could kick off another one of these monsters during a new loading event.
A few inches of snow have fallen already this morning and moderate snowfall will continue into the early afternoon. Precipitation favors the Swan Range with the Flathead Range close in second place. Gusty ridgetop winds will shift from west to northeast this afternoon after a mid day lull. The National Weather Service has issued a Winter Weather Advisory for our area through 5pm tonight. Winds and snowfall drop considerably going into tomorrow and early next week.
| Saturday | Saturday Night | Sunday | |
|---|---|---|---|
| Cloud Cover: | Overcast | Partly Cloudy | Partly Cloudy |
| Temperatures: | 23 to 27 deg. F. | 3 to 7 deg. F. | 20 to 27 deg. F. |
| Wind Direction: | Northwest | Northeast | Southwest |
| Wind Speed: | 20G44 | 18G39 | 11G25 |
| Snowfall: | 3" to 5" in. | 0" in. | 0" in. |
| Snow Line: | 2000' | 0' | 0' |
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.
