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Avalanche Forecast

Archived

Feb 23rd, 2014–Feb 24th, 2014

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

Regions

Sea To Sky.

Sunshine and significant warming early this week could tip off a fairly widespread natural avalanche cycle.

Confidence

Fair

Weather Forecast

Synopsis: Lingering flurries are likely on Monday in the wake of a frontal system. A ridge of high pressure begins to build in resulting in clearing and drier conditions for Tuesday and Wednesday. Monday: Flurries ending early, then cloudy with sunny breaks. The freezing level is around 300 m. Winds are generally light. Tuesday: A mix of sun and cloud. The freezing level jumps as high as 2500 m with treeline temps ranging from +3 to +6. Winds are light and variable. Wednesday: A mix of sun and cloud. The freezing level jumps remains near 2500 m with treeline temps ranging from +4 to +8. Winds are light and variable.

Avalanche Summary

There was one new report of a size 2 remotely triggered slab avalanche in the Whistler backcountry. The slab depth was reported to be approximately 1.5 m deep, likely failing on a facet/crust combo. There was also a report of a size 2 accidentally skier triggered avalanche in the Blackcomb backcountry on Friday. Check out Wayne Flann's Avalanche Blog for photos of both of these incidents. Other observers in the region reported no new natural avalanches and no results with ski testing. It's likely becoming more difficult to trigger slab avalanches, but it's certainly still possible and if triggered it will likely be a deep avalanche with real potential for wide propagation.

Snowpack Summary

20-30 cm of low density snow has fallen in the past 2 days with light winds forming fresh thin wind slabs near ridge crests. The prominent mid-February weakness, which is primarily a facet/crust combo (with surface hoar in some areas), is now 70-150 cm deep depending on wind exposure. Recent snowpack tests give variable results on this layer, but some observers are still reporting sudden "pops or drops" shears and are experiencing significant whumpfing. Previous strong winds have created wind slabs in exposed lee and cross-loaded terrain. Relatively thin wind slabs have the potential to trigger the deeper mid-Feb weakness. The mid and lower snowpack are generally strong and well-settled. Basal facets and depth hoar are likely to exist in some parts of the region; however, skier triggering has become unlikely.

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.