Archived

Avalanche Forecast

Dec 30th, 2019–Dec 31st, 2019

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

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

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

Regions: South Rockies.

Avoid terrain where triggering large deep persistent slab avalanches is most likely, such as shallow rocky areas and steep convexities.

Confidence

Moderate - Uncertainty is due to the timing, track, & intensity of the incoming weather system.

Weather Forecast

MONDAY NIGHT: Cloudy, moderate wind from the west, alpine temperatures around -10 C.

TUESDAY: Light flurries in the afternoon with trace amounts of snow, strong wind from the southwest, alpine high temperatures around -8 C.

WEDNESDAY: 10-20 cm of snow by Wednesday morning then cloudy in the afternoon, moderate wind from the southwest, alpine high temperatures around -3 C.

THURSDAY: Another system brings 5-10 cm of snow, light wind from the west, alpine temperatures drop to -12 C.

Avalanche Summary

New avalanche problems will develop with the arrival of new snow and strong wind on Tuesday evening. Small (size 1) wind slab avalanches have been reactive to human triggering the past few days, including a size 2 avalanche that had impressive propagation on Friday.

A widespread cycle of very large deep persistent slab avalanches occurred prior to Christmas (up to size 3), and while the likelihood of triggering deep persistent slab avalanches has declined, the consequences are severe. The most recent report of a deep persistent slab avalanche was on Friday near Summer Lake (see this MIN report). This avalanche was triggered by a snowmobile in adjacent terrain and shows the possibility of triggering large avalanches from thin spots in rocky alpine terrain.

Snowpack Summary

Wind has blown around surface snow into unstable wind slabs at higher elevations. The snowpack is gradually recovering from a major storm that delivered 50-100 cm of snow just before Christmas. The bottom 30-50 cm of the snowpack consists of weak facets and crusts, which resulted in large deep persistent slab avalanches during and immediately after the storm. These layers are gradually adjusting to the weight of the new snow, and so the likelihood of triggering deep persistent slab avalanches is declining.

Terrain and Travel

Fresh wind slabs will likely form throughout the day, diligently watch for changing conditions.
Avoid convexities, steep unsupported terrain and rocky outcroppings.
Be aware of the potential for large avalanches due to the presence of a deep persistent slab.