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Avalanche Forecast

Archived

Feb 28th, 2021–Mar 1st, 2021

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

Regions

Lizard-Flathead.

Persistent slab avalanches continue to be reactive to skier and rider triggers. These are producing large and consequential avalanches. A conservative mindset and patience are required.

Fresh wind slabs may be reactive on northeast and east slopes.

Confidence

Moderate - Uncertainty is due to how quickly the snowpack will recover and gain strength.

Weather Forecast

The dominating features associated with this next frontal system will be wind and slight warming. Ridgetop wind is forecast 25-70 km/hr from the southwest through the forecast period. Light snowfall amounts expected.

Monday: Cloudy with light snow 5 cm. Ridgetop wind 30-70 km/hr from the southwest. Alpine temperatures -2 and freezing levels 1300-1700 m.

Tuesday: Cloudy with light snow 3-7 cm. Ridgetop wind 25-65 km/hr from the southwest. Alpine temperatures -3 and freezing levels 1200-1500 m. 

Wednesday: Trace of snow and ridgetop wind strong from the southwest. Freezing levels 1300 m.

Avalanche Summary

Almost daily we're receiving reports of skier and rider-triggered persistent slab avalanches from the SoRo and Lizard forecasting regions. These avalanches have been size 2 or larger and have caught people by surprise. On Saturday, a size 2 skier triggered persistent slab avalanche was reported. This was on an East aspect at 2000 m and ran on the late January interface. The person was able to ski out with no injuries. 

This problem is not healing quickly and the conditions are not easily managed. A conservative mindset and patience are crucial right now.  

New wind slabs may exist on East to Northeast aspects on Monday and loose-dry avalanches may spill from steeper terrain features.

Snowpack Summary

Strong west-southwest winds have formed reactive wind slabs on leeward slopes by redistributing some of the recent storm snow that fell Thursday. Solar aspects became moist on Saturday then refroze forming a 1-3mm crust. Up to 50 cm of snow sits above a variety of old interfaces that formed mid-February. These mostly include sugary facets, hard wind pressed surfaces, surface hoar in wind-sheltered locations, and sun crust on steep solar aspects. Another persistent weak layer is found down 60 to 100 cm deep and was buried late-January. This layer consists of similar weak snow crystals mentioned above and continues to be reactive by the weight of a person.

There are presently no deeper concerns.

Terrain and Travel

  • The trees are not the safe-haven they normally are at this time. Terrain at treeline is primed for human triggered avalanches.
  • Fresh snow rests on a problematic persistent slab, don't let good riding lure you into complacency.
  • Back off if you encounter whumpfing, hollow sounds, or shooting cracks.
  • In times of uncertainty conservative terrain choices are our best defense.
  • Pay attention to cornices and give them a wide berth when traveling on or below ridges.

Problems

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.

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.