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Avalanche Forecast

Archived

Feb 15th, 2019–Feb 16th, 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

Purcells.

It is possible the south of the region could see more snow than forecast. If amounts exceed 15 cm, consider this region considerable.

Confidence

Moderate - Forecast snowfall amounts are uncertain on Saturday

Weather Forecast

FRIDAY NIGHT: 5-10 cm of low density snow expected, with more likely in southern areas. Mostly light winds.SATURDAY: Around 5 cm new snow. Treeline temperatures around -8C. Light northeasterly winds.SUNDAY: Dry and cloudy. Treeline temperatures around -11C. Light northeasterly winds.MONDAY: Dry, with some clear spells. Treeline temperatures around -12C. Moderate northwesterly winds.

Avalanche Summary

Reports on Tuesday, Wednesday and Thursday include a few wind slab avalanches size 1-2 on north, south and east aspects in the alpine. There were also a few storm slab avalanches reported to size 1 at treeline. Additionally on Wednesday there was a cornice triggered size 3 deep persistent slab reported on a northeast aspect at 2800m.

Snowpack Summary

10-20 cm recent low density snow has been blown around by strong northeasterly winds, creating touchy wind slabs in exposed areas. This new snow sits above wind-affected snow and/or sugary facets. In the far south of the region (south of Cranbrook) recent storm amounts are more like 30-40 cm of new snow. Beneath this lies two weak layers of surface hoar that were buried at the end of January and mid-January. These layers are around 30 to 60 cm deep. The deeper (mid-January) layer may be associated with a melt-freeze crust on southerly aspects. These layers are most prominent at treeline and below treeline elevations.The base of the snowpack is composed of weak and sugary faceted grains that overly a melt-freeze crust. This weak layer has produced large and destructive avalanches that are sporadic in nature and very difficult to predict. It is most likely to be triggered from areas where the snowpack is shallow and weak. Rocky alpine bowls, ridge crests, and rocky outcroppings are some examples of terrain features to be wary of. See the Forecaster Blog here for more info on this 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.