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Avalanche Forecast

Archived

Feb 21st, 2015–Feb 22nd, 2015

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

Regions

South Rockies.

Watch for fresh isolated pockets of windslab on reverse loaded features.

Confidence

Good - The weather pattern is stable

Weather Forecast

Were looking at a couple of nice days. Freezing levels will climb during the day but are forecast to return to valley bottom overnight. Sunday will see high of -5C in the Alpine with light westerly winds. Monday will have a high of 0C and light northwesterly winds with increasing clouds in the afternoon. Tuesday will be much the same. No new precipitation is expected through the forecast period.

Avalanche Summary

No new avalanches have been reported recently

Snowpack Summary

Up to 10 cm of new snow may now cover a thick, solid crust that extents up to 2100m and firm wind pressed surface higher than that. The recent winds have been light to moderate from the northeast and I suspect that you may find isolated fresh windslabs forming in reverse loaded lee features on southern aspects. Below 2100m the crust is effectively capping the snowpack and protecting a couple of buried persistent week layers. Two layers of surface hoar can be found between around 50 and 80cm down. Recent snow pack test indicate that these layers are unlikely to fail but could propagate widely if they do. I suspect that at upper elevations where these layers are not protected by the surface crust it could still be possible to trigger an avalanche from a thin or rocky spot. The mid-December crust is becoming harder to find but where it does exist (mainly at treeline elevations) it is over a meter down.

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.