Avalanche Forecast
Issued: Feb 18th, 2023 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs, Deep Persistent Slabs and Persistent Slabs.
rbuhler,
Avalanche Canada
The snowpack in this region is very complex and requires sophisticated snowpack analysis, careful terrain selection, and extremely diligent group management. The only way to minimize exposure is to select low-angle, low-consequence terrain, and avoid areas where an avalanche could propagate widely.
A weak layer at the base of the snowpack means full-depth avalanches remain possible. This layer resulted in a fatal avalanche that occurred west of Golden on Thursday. Details can be found in this report.
Summary
Confidence
Moderate
Avalanche Summary
On Friday, natural wind slabs and loose dry avalanches up to size 2 were reported as well as a few natural cornice releases. Some of these were triggered by solar and some were triggered by the wind. Skiers also triggered some small wind slabs as well as a couple of small deep persistent avalanches in small alpine features.
On Thursday, a size 3.5 avalanche failed on a deep persistent weakness and resulted in 2 fatalities west of Golden. More details regarding this avalanche can be found in this report.
On Friday, our field team observed a size 3.5 avalanche in the Bull River area (South Rockies) on an east through southeast aspect that started high and ran nearly 2000 m to the river. They estimated this avalanche to likely have occurred on or around February 15. Given its size, this avalanche likely failed on a deep persistent weakness in the snowpack.
Snowpack Summary
Any new snow that falls on Sunday will bury surface hoar which has formed in open areas and a sun crust that exists on steep south aspects. In exposed terrain, wind slabs of all ages still exist in leeward features while windward features have been scoured.
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.
Snowpack depths at treeline range between 80 and 200 cm, with the shallowest depths found on the eastern edge of the Purcells.
Weather Summary
Saturday night
Partly cloudy, possibly clearing by morning for the south of the region, light to moderate W-NW wind, treeline low around -12 ËšC.
Sunday
A mix of sun and cloud in the morning, cloudy in the afternoon with light flurries, moderate to strong SW-W wind, treeline high around -5 ËšC.
Monday
Snowfall beginning overnight 10-20 cm, moderate to strong W-NW wind, easing in the afternoon, treeline high around -6 ËšC.
Tuesday
Snowfall 5-15 cm overnight with another 5-15 cm during the day, moderate to strong SW wind switching to NE by the end of the day, treeline temperature dropping to around -16 ËšC.
More details can be found in the Mountain Weather Forecast.
Terrain and Travel Advice
- Use careful route-finding and stick to moderate slope angles with low consequences.
- Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
- Avoid rock outcroppings, convexities, and anywhere the snowpack is thin and/or variable.
- Expect slab conditions to change drastically as you move into wind exposed terrain.
Problems
Wind Slabs
Recently formed wind slabs appear to be touchy in many parts of the region. Watch for ongoing wind slab formation on Sunday, especially in more western parts of the Purcells which may see more substantial new snow accumulation.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Deep Persistent Slabs
It remains possible for riders to trigger a weak layer of facets near the base of the snowpack. The most likely area to trigger it is in shallow areas with variable snow depths. Avoid thin and rocky start zones and select routes that avoid traveling through or under large avalanche paths.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Persistent Slabs
Large avalanches have been triggered on a layer of surface hoar and facets 40 to 80 cm deep which was buried in late January. This problem seems most concerning in the western and southern Purcells, where the layer is more deeply buried and primed for human triggering. Steep open slopes should be avoided.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Feb 19th, 2023 4:00PM
