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Avalanche Forecast

Archived

Feb 5th, 2018–Feb 6th, 2018

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

Regions

Sea To Sky.

Wind slabs and cornices are the main concerns right now: Give both a wide berth and limit your exposure to overhead hazard.

Confidence

Moderate - Due to the number of field observations

Weather Forecast

Tuesday: Isolated flurries (5cm possible) / Light to moderate westerly winds / Freezing level 1000m. Wednesday: 5-10cm of snow / Moderate gusting strong west winds / Freezing level at 1600mThursday: Mainly cloudy with isolated flurries (up to 5 cm possible) / Light to moderate north westerly winds / Freezing level at 1200m

Avalanche Summary

On Monday, cornice control work with explosives resulted in a size 2.5 avalanche which ran on the early January crust/facet layer. On Sunday, ski cutting produced several size 1 to 1.5 soft slabs on immediate down wind (lee) features. Expect wind slabs to remain reactive to human triggers as winds continue to be moderate to strong with small amounts of new snow available for transport. See here for a good MIN post summarizing conditions near Whistler. On Saturday we received reports of a skier triggered size 1.5 avalanche near Whistler on a north west aspect around 2100m.

Snowpack Summary

We've had small amounts of new snow over the past several days. Temperatures had been above zero at tree line for much of the weekend, but dropped to more seasonal values on Monday. Winds, however, have been consistently strong from the south (east), creating reactive wind slabs in exposed downwind (lee) terrain. At lower treeline and below, generally light amounts of snow or rain now overlie a melt-freeze crust which formed during Monday's warm storm from a week ago.The new snow adds to the 170cm of snow that fell during the last few weeks of January. These series of storms were accompanied by strong to extreme winds which resulted in extensive scouring and impressive cornice growth in upper elevation terrain. These accumulations sit on a crust from mid-January which generally shows signs of bonding to the overlying snow; however, it has the potential to "wake-up" with a large trigger such as a cornice fall.Below this, the snowpack is thought to be generally strong and well-settled.

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.

Cornices

Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.