Avalanche Forecast
Regions: Field, Little Yoho.
The weather is changing and so is the avalanche danger. An Atmospheric River over BC and AB will deliver strong winds, warming and up to 20 cm of snow (rain in the valley) = chinook conditions on the east slope and pounding snow and rain to the west. Avalanche danger rises on Thursday, again on Friday and peaks on Saturday. Expect windslab development and a reawakening of the deep persistent problem.
Confidence
Moderate
Avalanche Summary
The sun was out! Two natural avalanches reported on S aspects on Wednesday: Mt. Ball S face had a size 3 natural (observed from a distance) and Bourgeau Left-hand waterfall released a size 2 natural that started up high in the rocks. Minimal results from avalanche control at the ski areas. No new avalanches observed by our field team on the Ogden Bench.
Snowpack Summary
10-20 cm of loose snow sits over a denser mid-pack which has formed a slab over the weak facet layers below - this loose snow will get blown into windslabs starting Thursday. The December 17 weak layer is down 25-60 cm and becoming less reactive. The November 16 deep persistent layer of facets and depth hoar is near the base of the snowpack, continuing to show sudden failures. Profile from Ogden Bench on Wednesday.
Weather Summary
The weather pattern is changing as an Atmospheric River establishes itself across southern BC and AB. The coast and interior ranges will see heavy rain, snow, wind and warming. Here in the Rockies, we expect the winds to start on Thursday and reach 80 km/hr by Friday. Some snow and perhaps rain at low elevations with 5-10 cm by Friday. Expect warm and windy weather!
Terrain and Travel Advice
- Uncertainty is best managed through conservative terrain choices at this time.
Avalanche Problems
Wind Slabs
With up to 20 cm of loose snow available for wind transport, Thursday's increasing winds will create fresh, sensitive windslabs in leeward areas. Expect this to build by Thursday afternoon, growing even larger on Friday as the winds continue.
Aspects: North, North East, East, South East.
Elevations: Alpine, Treeline.
Likelihood: Possible
Expected Size: 1 - 1.5
Deep Persistent Slabs
The lower snowpack is comprised of weak facets, with a slab formed over this weakness at treeline and in the alpine. This weak basal layer is uniform across most of the region and has the potential for human triggering, long propagations and remote triggering. This problem may wake up over the next few days with warming and wind.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood: Possible
Expected Size: 1.5 - 3
Persistent Slabs
The December 17 facets that formed during the prolonged deep freeze in early December are down 30-60 cm. Although the layer is gaining strength, it is still worth monitoring this layer in the deeper snowpack areas (west) where it is still reactive in the mid-pack.
Aspects: All aspects.
Elevations: All elevations.
Likelihood: Possible
Expected Size: 1.5 - 2.5