Lawinenlagebericht

Flathead Range & Glacier NP

Flathead Avalanche Center
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Lawinengefahr

Thu
Hochgebirge
3 · Erheblich
Waldgrenze
2 · Mässig
Unterhalb
2 · Mässig
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Kernpunkte

Intentionally triggered slides yesterday confirm that dangerous avalanche conditions exist. Weak layers buried 1-4' below the surface remain susceptible to human triggering, especially on shaded aspects at upper elevations.  Swirling winds have left slabs on most aspects and in atypical locations. Continue to enjoy the wonderful powder responsibly by sticking to planar low-angle slopes free of rollovers. Snow that looks etched or feels blocky should be bypassed in favor of higher quality snow found in sheltered terrain. The frigid weather will magnify the consequences of a small accident or equipment issue. Keep your trip short and simple.

Lawinenprobleme

  • Persistent Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Likely
    Größe
    2–3

    A widespread layer of buried surface hoar can be found 1-4' below the surface and above the 1/13 crust in shaded locations at mid and upper elevations. This layer is responsible for the recent series of intentionally, remotely, and accidentally triggered slides. Clancy was able to find this layer yesterday and deliberately triggered small slides on NE and SW aspects at mid-elevations in Canyon Creek. Generally, this layer is not providing surface clues until it is too late.  Managing a persistent slab problem is difficult, and we recommend taking the more comfortable and safer way of working the terrain instead. Slopes 30 degrees or less, and free of convexities, is key to enjoying the great surface snow safely.

    (2/9/2021) The results of collapsing buried surface hoar

  • Wind Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    1–2

    Winds continue to alternate between westerly and easterly as flow from Arctic and Pacific air dance around the Flathead Valley.  This has left slabs of varying age and thickness around the compass. The surface snow is cold smoke and easily transportable with minimum wind speeds.  Clancy noted the upper portions of south-facing chutes stripped of snow nearly down to the 1/13 crust yesterday in the southern Whitefish Range.  That is a lot of snow transported by recent relatively light wind speeds.  Channeled winds near the Continental Divide continue to drift snow at low-elevations forming slabs in unusual locations. Thankfully, wind features are recognizable by their scalloped or etched appearance. They have a distinct feel of a dense and blocky nature, especially compared to the nearby powder. It is best to steer around wind affected snow for a safer, more enjoyable experience.

    (2/2/2021) null

Avalanche Discussion

The avalanche danger remains elevated even though it has been 3.5 days since our last decent snowfall. If we were dealing with a storm slab or wind slab problem, we wouldn’t be in this boat. Both tend to heal up within a few days, depending on conditions. Persistent Slab is a whole other beast and has been our #1 avalanche problem since January 31. This problem is certainly living up to its moniker as we enter the eleventh day dealing with buried surface hoar and facets above the 1/13 crust.

We’ve scrutinized avalanche observations and field observations, trying to confirm the distribution of these buried weak layers and the avalanches associated with them. On Monday the 8th, we felt we had enough information to remove south and southwest from the Persistent Slab rose. Even though we are separating south and southwest, we need to keep this in perspective because our sample size is relatively small, and there may be southerly slopes harboring these weak layers.

We dropped the avalanche danger at mid-elevations to MODERATE for the first time since February 2. As recently as yesterday, Clancy intentionally triggered slabs in this elevation band on SW and NE aspects, so we feel pretty good that we kept the hazard elevated through yesterday.

Brrrr. An Arctic air mass has a solid grip on our region, with a forecast of even colder temperatures in the coming days. Marias Pass was the cold spot with a reading of -34F this morning! This weather allows for surface hoar growth in some areas along with a widespread weakening of the surface snowpack. Temperatures like these slow the strengthening of the weak layers and keep Persistent Slab at the forefront of our concerns. Frigid conditions dictate simple and short backcountry excursions. Even a minor injury or gear malfunction can become a severe issue in weather like this. Exposing rescuers to an extended mission is putting others needlessly at risk.

The BNSF avalanche safety team noted large avalanches in Stevens Canyon over the weekend. These photos are a good reminder of the power and magnitude of our current Persistent Slab problem.

On Saturday, a group of snowmobilers was caught, carried, and one killed. The most up to date information on this accident are found here. We will update you as more information becomes available. Our condolences go out to all of the friends and family of the victims of these tragic accidents. We thank the rescuers who accept large amounts of risk during these events.

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