Archived

Avalanche Forecast

Feb 15th, 2017–Feb 16th, 2017

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

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

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

Regions: South Rockies.

Forecast snowfall amounts are highly uncertain for Wednesday night and Thursday. Pay close attention to how much snow falls in your riding area, and be prepared to back-off to simple terrain.

Confidence

Moderate - Due to the number of field observations

Weather Forecast

Wednesday night: 4-8cm of new snow / Extreme southwest winds / Freezing level at 1700mThursday: 5-12cm of new snow / Extreme southwest winds / Freezing level at 1700mFriday: Mix of sun and cloud / Moderate southwest winds / Freezing level at 1000mSaturday: Mix of sun and cloud / Light and variable winds / Freezing levels at 1000m

Avalanche Summary

Recent observations have been limited; however, a few size 2 solar-triggered persistent slab avalanches were observed at 2000m in the Elkford area on Tuesday. They were thought to be about a day old and appeared to have failed on the December facets. Gradual cooling should help to limit natural avalanche activity at this interface. However, the December facet layer will be with us for a while and should not be trusted as we enter a low-probability/ high consequence pattern with this layer. For Thursday, new snow and wind are expected to promote a round of wind slab activity in exposed higher elevation terrain. Rain at lower elevations may trigger loose wet avalanches in steep terrain below treeline.

Snowpack Summary

By Thursday morning, up to 8cm of new snow is expected with continued snowfall anticipated throughout the day. Extreme southwest winds are forecast to shift these accumulations into reactive wind slabs in exposed high elevation terrain, while rain is expected at lower elevations. Beneath the new snow, you'll find a mix of hard old wind slabs, melt-freeze crusts and moist snow from the recent warm spell. Some weaknesses may still exist within the 90cm of storm snow from last week; however, recent warming has likely helped to strengthen these layers.In deeper areas, the mid and lower snowpack appear to be well settled with only isolated concerns about the mid-December facet layer which comprises the bottom third of the snowpack. In shallow snowpack areas, this layer is weak, faceted, and has no structure. In these areas, snowpack test results and reports of whumpfing suggest large avalanches remain a concern at this interface.

Avalanche Problems

Wind Slabs

New snow and extreme winds are forecast to create reactive new wind slabs on Thursday. Conditions are expected to intensify throughout the day, so be prepared to adjust your travel plans to more conservative terrain.

Be cautious as you transition into wind affected terrain.Use ridges or ribs to avoid pockets of wind loaded snow.

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

Elevations: Alpine, Treeline.

Likelihood: Likely - Very Likely

Expected Size: 1 - 2

Deep Persistent Slabs

A weak layer at the base of the snowpack has the potential for climax avalanches. As temperatures cool over the next few days, this weakness may gain strength. I still don't trust this layer, especially in areas with minimal rider compaction.

Be aware of the potential for full depth avalanches due to weak layers at the base of the snowpack.Avoid steep convexities or areas with a thin or variable snowpack.Be aware of thin areas that may propogate to deeper instabilites.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Possible

Expected Size: 2 - 4

Loose Wet

Rain at lower elevations may promote loose wet avalanche activity. Use extra caution in steep terrain below treeline.

Be cautious of sluffing in steep terrain.Use extra caution on solar slopes or if the snow is moist or wet.

Aspects: All aspects.

Elevations: Alpine.

Likelihood: Possible

Expected Size: 1 - 2