Archived

Avalanche Forecast

Dec 17th, 2015–Dec 18th, 2015

Alpine

3: Considerable

The avalanche danger rating in the alpine will be considerable

Treeline

3: Considerable

The avalanche danger rating at treeline will be considerable

Below Treeline

2: Moderate

The avalanche danger rating below treeline will be moderate

Alpine

2: Moderate

The avalanche danger rating in the alpine will be moderate

Treeline

2: Moderate

The avalanche danger rating at treeline will be moderate

Below Treeline

1: Low

The avalanche danger rating below treeline will be low

Alpine

3: Considerable

The avalanche danger rating in the alpine will be considerable

Treeline

2: Moderate

The avalanche danger rating at treeline will be moderate

Below Treeline

1: Low

The avalanche danger rating below treeline will be low

Regions: South Rockies.

Strong winds and new snow are likely to promote avalanche activity on Friday, especially in steep, wind affected terrain.

Confidence

Moderate - Intensity of incoming weather systems is uncertain

Weather Forecast

Friday: Around 10 cm new snow expected, ridgetop winds 60-90 km/h from the southwest, treeline temperatures rising to around -5C. Low elevation winds are expected to also be strong. Saturday: mostly dry with some good sunshine. Winds westerly. Treeline temperature dropping to around -16C. Sunday: light snowfall starting late in the day, strong southwest winds, temperatures around -8C.

Avalanche Summary

On Monday, a couple of size 2 avalanches were reportedly triggered by skiers in steep north and northeast facing slopes. Since then no further avalanches have been noted in this region. I anticipate the chance of both natural and human triggered avalanches will increase during the expected storm on Friday.

Snowpack Summary

The series of recent storms has left us with around 40-60 cm new snow sitting on a firm rain crust. For the most part, the new snow has bonded well to this rain crust, although potentially unstable wind slabs could exist where wind-pressed snow rests directly on a slippery crust below. A previous weak layer from early December consists of crust, surface hoar, and/or facets and is typically down 70-90cm. Around 20-30cm below this interface is a rain crust from mid-Nov with a thick layer of facets below it. Both the early-Dec and mid-Nov layers have become dormant and are likely being capped at treeline and below by the more recent rain crust layer. However, these layers may still be reactive to heavy triggers such as cornices, explosives, or smaller avalanches stepping down.

Avalanche Problems

Wind Slabs

As snow accumulates during the storm, steep terrain will become susceptible to avalanche activity, especially where the wind has drifted snow into dense pillows.

Stay off recent wind loaded areas until the slope has had a chance to stabilize.>Use conservative route selection, stick to moderate angled terrain with low consequence.>Note recent avalanche activity.>

Aspects: North, North East, East, South East, South, South West.

Elevations: Alpine, Treeline.

Likelihood: Likely - Very Likely

Expected Size: 1 - 3