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Avalanche Forecast

Archived

Dec 29th, 2013–Dec 30th, 2013

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

Regions

South Rockies.

Confidence

Poor - Wind effect is extremely variable

Weather Forecast

Synopsis: NW flow continues to dominate the pattern. A few cms may make it into the region, but no significant accumulations are expected. The big player over the next few days will be the wind. 2000m wind forecasts are provided below, 3000m winds are roughly 1.5x greater.Monday: Freezing Level: Valley Bottom; Precip: Nil Wind: Mod NW/WTuesday: Freezing Level: Valley Bottom; Precip: 1/2mm 2/5cm Wind: Mod W switching to Strong NW near sundown.Wednesday: Freezing Level: Valley Bottom; Precip: Nil; Wind: Initially Mod NW switching to Light SW by Wednesday evening.

Avalanche Summary

On Christmas Eve a backcountry skier triggered a size 2 slab avalanche on an alpine slope in the Harvey Pass area. The slab was reportedly 70cm deep and 150m wide and was thought to have slid on the late-November crust/facet interface. There were no reported injuries with the avalanche.No other avalanches have been reported.

Snowpack Summary

There appears to be a lot of snowpack variability across the region. Snowpack depths at treeline seem to vary from 60 - 130 cm with high variability in wind-exposed areas. Winds have been strong out of the SW on Sunday at all wind stations.  With 10 - 15 cm available for transport I expect wind slabs to be touchy on Monday.  In the mid pack is the late-November/early-December interface which is made up of surface hoar, a crust, and/or facets. This layer is typically down 30-70cm and has reached the tipping point for rider triggering in a few areas including the Harvey Pass area.  Check out this video of a recent snowpack test on this layer.  We're probably getting close to this layers tipping point in wind loaded terrain at treeline in much of the region. 

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.