Archived

Avalanche Forecast

Mar 16th, 2014–Mar 17th, 2014

Alpine

4: High

The avalanche danger rating in the alpine will be high

Treeline

3: Considerable

The avalanche danger rating at treeline will be considerable

Below Treeline

3: Considerable

The avalanche danger rating below treeline will be considerable

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

2: Moderate

The avalanche danger rating below treeline will be moderate

Regions: South Rockies.

Fresh snow, forecast solar radiation and a complex snowpack means this is no time to be pushing into steep terrain. Conservative slope selection is critical to safe mountain travel.

Confidence

Fair - Timing or intensity of solar radiation is uncertain on Monday

Weather Forecast

Overview: A generally dry ridge of high pressure will develop on Monday and Tuesday with the passing of Sunday's frontal system. Another pulse will bring moisture to the region on Wednesday.Overnight Sunday: Up to 20cm of snow / Moderate to strong westerly winds / Freezing level at about 1500mMonday: Light flurries with a mix of sun and clouds / Light to moderate westerly winds with strong gusts / Freezing level at 1500mTuesday: Mix of sun and cloud / Light northwesterly winds with strong gusts / Freezing level at 1500mWednesday: Flurries / Moderate westerly winds / Freezing level at 1500m

Avalanche Summary

Avalanche observations were extremely limited on Sunday due to inclement weather. With Sunday's storm, I expect avalanche activity to include a significant round of storm slab activity as well as the possibility of destructive persistent slab activity. Persistent weaknesses still have the potential to react as wet slab avalanches at lower elevations where rain fell.

Snowpack Summary

As of Sunday morning up to 30cm of new snow had fallen and was blown by strong winds into much deeper deposits in lee terrain. Rain below about 1700m continued to saturate the snowpack. The recent accumulations overlie hard rain crusts which exist on all aspects below 2000m and on solar aspects in the alpine. North of Sparwood and in the Crow's Nest Pass areas the crust seems more specific to previously sun-exposed slopes. More precipitation and wind forecast for Sunday night will add to this developing storm slab. The deep facet/crust persistent weakness buried at the beginning of February, now down up to 150cm, is still producing sudden results in snowpack tests. I would be very leery of any slopes that have not already avalanched as any activity at this interface would be large and destructive. Triggering will become more likely with forecast clearing and solar radiation.Cornices have also become large and potentially unstable.

Avalanche Problems

Storm Slabs

Sunday's wind and snow has created a punchy storm slab which overlies a smooth crust in many areas. Forecast sunny breaks over the next few days will likely add to the reactivity of the new snow.

Be cautious as you transition into wind affected terrain.>Choose conservative lines and watch for clues of instability.>The new snow will require several days to settle and stabilize.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Likely - Very Likely

Expected Size: 1 - 4

Deep Persistent Slabs

In some areas the deeply buried weak layers that formed in early February are still showing significant reactivity in snowpack tests. Avalanches at this interface would be large and destructive and are possible at all elevation bands.

Use conservative route selection, resist venturing out into complex terrain even if you observe no obvious signs of unstable snow.>Consider the consequences of the terrain if an avalanche steps down to a persistent weakness.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Possible

Expected Size: 3 - 6

Wet Slabs

Continued precipitation on Sunday night is expected to fall as rain at lower elevations with the potential to trigger deep and pushy wet slab or loose wet avalanches. Be cautious of slopes that did not avalanche during the last big cycle.

Be alert to conditions that change with elevation.>Avoid paths that have not avalanched recently.>Avoid steep unsupported terrain below treeline especially if the snow is moist or wet.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Possible

Expected Size: 1 - 4