Archived

Avalanche Forecast

Mar 4th, 2013–Mar 5th, 2013

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

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

Regions: Glacier.

Watch for periods of strong sun today. Thin cloud should reduce solar inputs, but if it gets clear solar triggered avalanches are possible. The sun may also cause cornices to fail and trigger deeper slabs.

Weather Forecast

Expect thin broken cloud, light winds and a chance of flurries today. Cool temps (-10 in the alpine) and the thin clouds should help to reduce solar effects, but periods of strong solar are possible. Late tuesday/early wed a low pressure system will bring light precip before another ridge forms bringing clear and dry conditions.

Snowpack Summary

20cm of dry snow has refreshed the surface, and cool temps are tightening the snowpack. 60cm of heavy, moist snow from the weekend appears to be bonding. The Feb 12 surface hoar/crust layer, down ~1m, has been reactive to large loads (see below). In the alpine, S'ly winds are transporting snow rapidly loading slopes and forming new windslabs.

Avalanche Summary

A large avalanche cycle occurred over the weekend. Most avalanche paths along the highway (and likely the backcountry) ran, with size 2-3.5 avalanches running into fans. These were failing on the storm interface and Feb 12 layer. None appear to have stepped down to deeper layers. Several large cornice failures, size 2-2.5, were observed yesterday.

Confidence

Timing, track, or intensity of incoming weather system is uncertain

Avalanche Problems

Storm Slabs

Over 80cm of snow has fallen since Friday. Weak interfaces within the storm slab exist. The snowpack needs time to adjust to the new load. It will still be touchy to human triggering, and may step down to surface hoar below.

Choose conservative lines and watch for clues of instability.Ski short pitches and regroup in safe spots.

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Possible - Likely

Expected Size: 2 - 3

Persistent Slabs

A weak surface hoar layer is now down ~1m. This layer has caused widespread avalanches: natural's up to size 4, and size 2.5 human triggered avalanches. In areas where it hasn't already avalanched it is very reactive, and has been remotely triggered.

Avoid open slopes and convex rolls at and below treeline where buried surface hoar may be preserved.Avoid paths that have not avalanched recently.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Possible

Expected Size: 2 - 4

Wind Slabs

Moderate to strong southerly winds shifted to NE overnight. Winds have loaded lee slopes, triggered avalanches, built large cornices and formed fat pockets and windslabs on exposed slopes. These areas will take even more time to stabilize.

Use caution in lee areas in the alpine. Recent wind loading have created wind slabs.Pay attention to overhead hazards like cornices.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Possible - Likely

Expected Size: 1 - 3