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Avalanche Forecast

Archived

Feb 11th, 2019–Feb 12th, 2019

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

Regions

South Columbia.

New wind slabs, older wind slabs, and a few troublesome buried persistent weak layers. These are what we are dealing with, which can be tricky to manage. For further info on the conditions, check out the Forecaster Blog here.

Confidence

High -

Weather Forecast

MONDAY NIGHT: Cloudy with intermittent snowfall, accumulation 1 to 3 cm, moderate to strong southwest wind.TUESDAY: Cloudy with light snowfall, accumulation 5 cm, moderate to strong southwest wind, alpine temperature -14 C.WEDNESDAY: Cloudy with light snowfall and afternoon clearing, accumulation 1 to 3 cm, light north wind, alpine temperature -12 C.THURSDAY: Mostly cloudy, light east wind, alpine temperature -10 C.

Avalanche Summary

Many small and large wind slab avalanches were triggered on Sunday. They were triggered naturally and by skiers. Most of the avalanches were on west and north aspects, but there were reports of avalanches on all aspects. They occurred at all elevation bands.The mid-January persistent weak layer described in the Snowpack Summary has recently been reactive to human triggers, although activity has decreased in the past few days. The most recent activity was on Friday, as skiers triggered small avalanches on north and northeast slopes between 1650 and 1900 m.The most recent deep persistent slab was reported on Saturday, which was very large (size 3.5) and triggered naturally on a northeast aspect at 2950 m. The slab was 400 cm thick and 150 m wide.

Snowpack Summary

The top 10 to 20 cm of snow has been affected by recent strong wind from variable directions. Expect to find wind slabs in lee terrain features in exposed terrain. This snow may be particularly touchy where it sits on a weak layer of feathery surface hoar crystals, as seen here. Beneath this lies two weak layers of surface hoar, which have produced large avalanches in the region. The layer that was buried at the end of January is around 30 cm deep and the layer buried mid-January is between 40 and 90 cm deep. The mid-January layer may also be associated with a melt-freeze crust on southerly aspects. These layers are most prominent at treeline and below treeline elevations. Recent avalanches on the mid-January layer have been mostly in the northern half of the region.The remainder of the snowpack is generally well-settled. However, there have been sporadic reports of very large avalanches that have released near the base of the snowpack, suggesting that instability exists in isolated locations. Most of the avalanches have been in the high alpine. There has been about one report a week for the past month, suggesting it is a low probability but very high consequence problem.

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.