Archived

Avalanche Forecast

Mar 23rd, 2016–Mar 24th, 2016

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

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

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

Regions: Northwest Inland.

Forecast snowfall amounts are uncertain for Wednesday night and Thursday. If more than 10cm falls, the avalanche danger may be higher than posted.

Confidence

Moderate - Intensity of incoming weather systems is uncertain on Thursday

Weather Forecast

Generally light snowfall (5-10cm) is expected on Thursday. A dry ridge should develop on Friday bringing mainly clear skies while overcast conditions are forecast for Saturday. Ridgetop winds should be moderate from the southwest on Thursday and then become light for Friday and Saturday. Daytime freezing levels are forecast to hover between 1100 and 1200m for the forecast period.

Avalanche Summary

In recent days a natural cornice fall triggered a size 3 slab avalanche in the southwest corner of the region. The avalanche occurred on an east aspect in high alpine terrain and stepped down to a few persistent weak layers from January and December. This avalanche demonstrates how a cornice fall can trigger layers that may otherwise be difficult to trigger. New wind slab activity is expected in response to new snow and strong winds on Wednesday and Thursday morning.

Snowpack Summary

As of Wednesday morning, up to 5cm of new snow had fallen with moderate to strong southerly winds. At treeline and in the alpine small wind slabs are expected to have formed. These wind slabs overlie a variety of surfaces which include a hard crust on solar aspects above 1300, moist or refrozen snow on all aspects below 1300, and settled wind slabs in exposed high elevation terrain. A layer of surface hoar from early March can be found down 50-70cm but only seems to be a problem for the northern half of the region. Professional operators are still tracking two deep weak layers from early-January and early-February which can be found down about 1m or more. These layers are generally dormant but could wake up with substantial warming or a heavy trigger (like a cornice fall). Basal facets exist in most areas and have recently been reactive in the north of the region

Avalanche Problems

Wind Slabs

Continued light snowfall and strong southwest wind are forecast to form new wind slabs at treeline and in the alpine. Wind slabs may be especially reactive due to underlying hard surfaces.

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

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

Elevations: Alpine, Treeline.

Likelihood: Likely

Expected Size: 1 - 2

Cornices

Some cornices are the size of a bus, and will continue to grow with forecast snow and wind. Cornice collapses in the region continue to trigger large avalanches on the slope below.

Extra caution needed around cornices with current conditions.>Pay attention to overhead hazards like cornices.>

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

Elevations: Alpine.

Likelihood: Possible

Expected Size: 2 - 5

Deep Persistent Slabs

A few persistent weaknesses exist in the mid snowpack (see snowpack description). These potentially destructive layers may become reactive with spring warming or with a large trigger such as a cornice fall.

Be aware of the potential for full depth avalanches due to deeply buried weak layers. >Be aware of thin areas that may propagate to deeper instabilities. >

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Unlikely - Possible

Expected Size: 3 - 6