Avalanche Forecast
Regions: Bull, Dogtooth, East Purcell, Purcells, St. Mary.
Up to 45 cm of recent snow and strong northerly winds have created dangerous storm slabs that will be reactive to human triggers at all elevations on Wednesday. The recent snow is overloading a weak snowpack and very large human triggered avalanches are especially likely in the alpine.
Make conservative terrain choices and avoid overhead hazard.
Confidence
High
Avalanche Summary
Several very large (up to size 3.5) naturally triggered deep persistent slab avalanches failing on weak facets near the bottom of the snowpack were reported on Monday. These avalanches all occurred in the alpine and were likely triggered by wind loading.
Additionally, several cornice failures triggered persistent slab avalanches around 40 cm deep on alpine features in the dogtooth range near Golden.
Last Thursday, a size 3.5 avalanche failed on a deep persistent weakness, resulting in 2 fatalities west of Golden. See MIN post.
Snowpack Summary
30-45 cm of new snow has buried a layer of surface hoar that formed in sheltered areas and a sun crust that exists on steep south aspects. Strong northwesterly winds have created wind slabs on lee features in open terrain.
A variety of persistent layers still exists in the middle snowpack and continue to see avalanches occur on them periodically. Don't let these layers surprise you.
The lower snowpack contains a widespread layer of large, weak facets that is typically 80 to 150 cm deep. This layer continues to periodically produce very large and destructive avalanches; especially during periods of rapid loading from snow and/ or wind.
Snowpack depths at treeline range between 80 and 200 cm, with the shallowest snowpacks found on the eastern edge of the Purcells.
Weather Summary
Tuesday night
Cloudy / Light, east ridgetop wind / Low temperature at treeline around -28 C.
Wednesday
Mix of sun and cloud / Light, southeast ridgetop wind / High temperature at treeline around -19 C.
Thursday
Mostly sunny / Strong, east ridgetop wind / High temperature at treeline around -21 C.
Friday
Sunny / Strong, west ridgetop wind / High temperature at treeline around -17 C.
More details can be found in the Mountain Weather Forecast.
Terrain and Travel Advice
- Use conservative route selection. Choose simple, low-angle, well-supported terrain with no overhead hazard.
- Travel in alpine terrain is not recommended.
- Storm slabs in motion may step down to deeper layers resulting in large avalanches.
- Cornice failure may trigger large avalanches.
- Avoid rock outcroppings, convexities, and anywhere the snowpack is thin and/or variable.
Avalanche Problems
Storm Slabs
Up to 45 cm of recent snow and strong northerly winds have created dangerous storm slabs that will be reactive to human triggers at all elevations on Wednesday.
Aspects: All aspects.
Elevations: All elevations.
Likelihood: Very Likely
Expected Size: 1.5 - 3
Deep Persistent Slabs
The recent snow is overloading a very weak snowpack. Very large human triggered avalanches are likely in the alpine; especially in shallow, rocky, or thin to thick snowpack areas.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood: Likely
Expected Size: 2 - 4
Persistent Slabs
A number of weak layers of surface hoar remain a concern in the mid and lower snowpack.
Aspects: All aspects.
Elevations: All elevations.
Likelihood: Possible
Expected Size: 1.5 - 3