Heightened avalanche conditions exist at upper elevations from the combination of low density snow and moderate, westerly winds forming wind slabs on leeward slopes and gullies. Some slopes could harbor new snow depths greater than 6”, so evaluate snow depths before committing to bigger terrain. Fresh instabilities overlap with stubborn, but high consequence persistent slab problems.
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Above 6500 ft.
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5000-6500 ft.
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3500-5000 ft.
Moderate westerly winds have accompanied the 2 to 14” of low density snow that fell over the past 24-hours. Drifting snow has formed shallow but tender wind slabs on leeward terrain features and cross-loaded gullies at higher elevations. Evaluate the depth of new snow and extent of recent wind loading while looking for cracking below ridgelines, rollovers, and in gullies traveling into consequential terrain.
Persistent weak layers such as surface hoar and faceted crust are found 2 to 4 feet deep on a few slopes. Several destructive avalanches occurred last week in the Flathead Range providing confirmation this stubborn problem still exist. Stability test producing propagating results have been observed in all 3 ranges, but feedback from the snowpack is limited and distribution is spotty. This problem is becoming isolated and more difficult to trigger as our snowpack settles and overlying slab stiffens. Avoid an encounter with this lurking monster by avoiding steep, un-supported slopes with convexities while sticking to lower angle, well-supported slopes.
Basal facets and our Thanksgiving facet/ crust layer is buried under a 5 foot dense, hard slab. A skier on Tuesday intentionally triggered a deep slab avalanche in the Flathead Range from kicking a cornice. This is an obvious sign that our deep persistent slab problem has not gone to bed and is still found on some slopes. Conservative terrain selection at upper elevations is the best way to manage this unpredictable, deadly problem. Slopes with deep, uniform snow cover are your best options while avoiding potential trigger locations found in shallow and rocky terrain.
Primarily light snowfall occurred over the last 24-hours throughout our forecast area: 4”/ 0.2” SWE in the Whitefish Range, 2”/ 0.1” SWE at Noisy Basin, and 3-4”/ 0.2” SWE in the Flathead Range. However, Flattop in southern GNP received 8”/0.4” SWE yesterday and 14”/0.7” SWE in the last 48 hours. Evaluate new snow totals exceeding 6” before committing to bigger terrain as some slopes could harbor isolated storm slabs not found in other parts of our forecast area.
Low density snowfall combined with moderate westerly winds and strong gusts could easily form wind slabs at mid and upper elevations. Observations from yesterday point at these slabs being thin and stubborn, but pay close attention to cracking in the snow surface while keeping an eye out for lens shaped pillows of dense, hard snow. Riding conditions will be better where more snow has drifted covering old hard snow surfaces. However, these slopes will contain thicker slabs and likely more reactive to the weight of a skier or rider.
The likelihood of triggering a persistent or deep persistent slab is lower since we are several days out from a major loading event and the warmup from earlier in the week is over. A skier triggered deep slab avalanche in steep, rocky terrain in the Flathead Range confirms this spotty, scary, and deadly problem still exist in our forecast area. This problem continues to plague neighboring mountain locations and doesn’t appear to show signs of going to bed anytime soon. Don’t be lured into complacency and treat all slopes as if they could avalanche until proven otherwise. Good habits save lives so make a plan, expose only one at a time on the slope, and get out of the way at the bottom.
Light northwest flow continues today with intermittent snow showers, overall light accumulations, and 1-3" of snowfall can be expected. Anticipate areas of convective snow squalls with moderate winds, strong gusts, and temperatures ranging from low to mid 20's. A warmer and wetter system is still forecasted to impact northwest Montana Thursday night through Saturday mid-day, so stay tuned for details.
| Thursday | Thursday Night | Friday | |
|---|---|---|---|
| Cloud Cover: | Snow showers | Snow | Snow |
| Temperatures: | 22 to 28 deg. F. | 19 to 24 deg. F. | 30 to 35 deg. F. |
| Wind Direction: | W | W | SW |
| Wind Speed: | 10 to 15 mph, gusting to 20 mph | 10 to 15 mph, gusting to 25 mph | 15 to 20 mph, gusting to 30 mph |
| Snowfall: | 1 to 2 in. | 2 to 4 in. | 3 to 5 in. |
| Snow Line: |
This advisory applies only to backcountry areas outside established ski area boundaries. This advisory describes general avalanche conditions and local variations always occur. This advisory expires at midnight on the posted day unless otherwise noted. The information in this advisory is provided by the USDA Forest Service who is solely responsible for its content.
