Lawinenlagebericht

Lizard-Flathead

Feb 26 – 27, 2022Avalanche Canada
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Lawinengefahr

Mon
Tue
Hochgebirge
1 · Gering
Waldgrenze
2 · Mässig
Unterhalb
1 · Gering
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Kernpunkte

A persistent weak layer of surface hoar remains a concern on northerly aspects around treeline in the Flathead. 

Wind slabs are generally not expected to be a problem on Saturday but continue to watch for evidence of recent loading in steep, unsupported alpine terrain features. 

Lawinenprobleme

  • Persistent Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Unlikely - Possible
    Größe
    2–3

    Persistent slab avalanches are still possible due to a layer of buried surface hoar around 40-60 cm deep. This problem is tricky to pin down because of its spotty distribution (it isn't a problem everywhere). It has been most reactive recently in the Flathead with reports of rider triggering (see MIN post), whumpfing and propagation in snowpack tests.

    Steep, north-facing open treed features that are sheltered from the wind are the most suspect. Check out this post from the field team for the type of terrain we are avoiding.

Confidence

Moderate - Uncertainty is due to the limited number of field observations.

Weather Forecast

One more day under the influence of high pressure before the first in a series of storm systems moves inland on Sunday. 

Friday Night: Partly cloudy, light NW wind, treeline low around -15 °C. 

Saturday: Mainly sunny, light to moderate SW wind, treeline high around -5 °C. 

Sunday: Light snowfall 4-8 cm, moderate to strong SW wind, treeline high around -4 °C. 

Sunday night and Monday: Snowfall heavy at times, moderate to strong SW wind, treeline high around -1 °C. 

Avalanche Summary

No new avalanches were reported on Thursday. On Wednesday, skiers were triggering small wind slabs. The Avalanche Canada field team reported whumpfing and cracking in places where the late-January surface hoar is still preserved and reactive, but they didn't see any new avalanches (check out their MIN).

Last Saturday, there was a machine-triggered persistent slab avalanche on a surface hoar layer in an open gully feature in the Rolling Hills area.

Snowpack Summary

10-30 cm of recent snow had been redistributed by recent variable winds earlier in the week which had formed thin wind slabs. These older wind slabs appear to have stabilized and are generally not expected to be a problem on Saturday. In south-facing terrain, the recent snow sits on top of melt-freeze crusts, and in open terrain, the recent snow sits over firm, wind-affected surfaces.

A buried surface hoar layer may be found 30-60 cm deep on sheltered, north-facing treeline-type features. This distribution of this layer is spotty in nature but has recently produced avalanches, whumpfing, and snowpack test results in the Flathead. 

The lower snowpack is well consolidated, with a crust/facet layer from early-December found near the bottom of the snowpack. It is currently considered dormant but could become active later this season. Check out the forecaster blog for more information. 

Terrain and Travel

  • Be aware of the potential for large avalanches due to the presence of buried persistent weak layers.
  • Shooting cracks, whumphs and recent avalanches are strong indicators of an unstable snowpack.

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