Archived

Avalanche Forecast

Apr 6th, 2016–Apr 7th, 2016

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

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

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

3: Considerable

The avalanche danger rating at treeline will be considerable

Below Treeline

2: Moderate

The avalanche danger rating below treeline will be moderate

Regions: Northwest Inland.

Extreme warming and solar radiation will drive the Avalanche Danger. Be alert to conditions that change throughout the day, and watch your overhead hazard. Very large avalanches may reach their run-out zones.

Confidence

Moderate - Due to the number of field observations

Weather Forecast

A dry ridge of high pressure will bring mainly clear skies for Thursday and Friday. Increased cloud and isolated flurries are forecast for Friday evening and Saturday. The freezing level will spike to about 2800m on Thursday and then hover around 2400m on Friday and Saturday. Ridgetop winds will remain mainly light and variable.

Avalanche Summary

Stormy weather has limited avalanche observations, although I'm sure there was a decent round of natural storm slab activity in response to new snow and wind on Tuesday. As the sun comes out and temperatures rise, cornice failures, loose wet, wet slab and isolated deep persistent slab avalanches should be on your radar.

Snowpack Summary

On Tuesday, 10-20cm of new snow fell. Throughout the storm, extreme westerly winds promoted continued cornice growth and created a widespread wind effect at higher elevations. About 30cm below the surface you'll find a widespread hard melt-freeze crust that formed as a result of last week's warm weather and more recent cooling. A few persistent weak layers exist in the snowpack including lingering surface hoar layer from January (down over a meter), and weak basal facets at the bottom of the snowpack. The near-surface crust has dramatically limited the reactivity of these destructive old layers; however, they have the potential for isolated yet very large avalanches with forecast warming and solar radiation.

Avalanche Problems

Loose Wet

Rising freezing levels on Thursday will promote loose wet avalanche activity, especially in steep sun-exposed terrain. Loose wet avalanches can entrain mass quickly and run long distances. Be alert to conditions that change throughout the day.

Be cautious of wet sluffing in steep terrain.>Sluffs may trigger deeper instabilities.>Avoid sun exposed slopes when the solar radiation is strong, especially if snow is moist or wet.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Very Likely

Expected Size: 1 - 4

Storm Slabs

In high elevation lee terrain hard storm slabs may remain reactive to light loads with the potential for wide propagations. In areas more affected by heat and sun, the new snow may react as a wet slab.

Stay off recent wind loaded areas until the slope has had a chance to stabilize.>Be aware of the potential for wide propagations due to the presence of hard windslabs.>Avoid sun exposed slopes when the solar radiation is strong, especially if snow is moist or wet.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Likely

Expected Size: 1 - 4

Cornices

Some cornices are the size of a bus. As temperatures rise and sunny weather makes a come-back, these monsters will become more likely to fail. A large cornice fall may be the trigger required to initiate destructive persistent slab avalanches.

Cornices become weak with daytime heating. >Give cornices a wide berth when traveling on or below ridges. >

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

Elevations: Alpine, Treeline.

Likelihood: Possible

Expected Size: 2 - 5