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Avalanche Forecast

Archived

Feb 26th, 2022–Feb 27th, 2022

Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural avalanches possible, human triggered probable.
Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural and human triggered avalanches likely.

Regions

Lizard-Flathead.

Watch for ongoing wind loading and wind slab formation in exposed terrain at higher elevations. 

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

Confidence

Moderate - Uncertainty is due to the speed, direction, or duration of the wind and its effect on the snowpack. Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast.

Weather Forecast

The first in a series of storm systems is forecast to reach the region on Sunday afternoon. 

Saturday Night: Mainly clear, moderate SW wind, treeline low around -12 °C. 

Sunday: Increasing cloud cover with light snow in the afternoon up to 5 cm, moderate SW wind, treeline high around -4 °C. 

Sunday night: Snowfall 10-20 cm, moderate SW wind, treeline low around -5 °C.

Monday: Snowfall 15-30 cm, moderate to strong SW wind, treeline high around -1 °C.

Monday night and Tuesday: Periods of heavy snowfall continuing overnight and then easing during the day, moderate to strong SW wind, freezing levels reaching near 2000 m. 

Avalanche Summary

No new avalanches were reported on Thursday or Friday. 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.

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 old storm snow has been redistributed by recent variable winds earlier in the week which has formed thin wind slabs. Reports from Saturday suggest wind transport continues but wind slabs are expected to be relatively small and isolated. In south-facing terrain, the recent snow sits on top of melt-freeze crusts, and in exposed 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. While it does not appear to be as widespread or reactive in the Lizard, it has been found in some locations. 

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

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • 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.

Problems

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.