Avalanche Forecast
Issued: Feb 27th, 2021 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Persistent Slabs and Wind Slabs.
swerner,
Avalanche Canada
Wind and more wind! Fresh wind slabs may be reactive on Easterly slopes Sunday.
A reactive persistent slab exists and can be easily triggered by a skier or rider. A conservative mindset and patience are required.
Summary
Confidence
Weather Forecast
The dominating feature associated with this next frontal system will be WIND. Ridgetop wind is forecast 50-90 km/hr from the West through the forecast period. Light snowfall amounts expected.
Sunday: Mix of sun and cloud. Ridgetop wind strong from the West and alpine temperatures near -6. Freezing levels valley bottom.
Monday: Cloudy with light snow 5-10 cm. Ridgetop wind strong to extreme from the West and alpine temperatures near -3. Freezing levels 1600 m.
Tuesday: Mix of sun and cloud. Ridgetop wind strong to extreme from the southwest and alpine temperatures near -5. Freezing levels valley bottom.
Avalanche Summary
On Saturday, a natural size 2 slab avalanche was spotted from outside the Castle Ski Hill Boundary as well as a few natural loose-dry size 1.
On Friday, isolated storm slab and loose-dry avalanches were reported up to size 1.
On Thursday, several skier controlled avalanches were reported up to size 1.
On Wednesday, this MIN report highlights a critical incident of a rider-triggered persistent slab size 3. Also on Wednesday, this MIN report indicates another remotely-triggered size 2 slab avalanche. Whether it's a wind slab or a persistent slab problem, they're catching folks by surprise and will not heal quickly.
This weekend, human triggering of storm, wind, and persistent slabs will remain likely. Conditions are not easily managed right now, warranting a conservative mindset!
Snowpack Summary
Recent snowfall amounts vary across the region with 10-20 cm accompanied by strong to extreme wind from the West. Reactive wind slabs are likely in exposed terrain at treeline and alpine elevations. 30 to 60 cm of snow now sits above sugary faceted snow that formed mid-February. This layer may be easily reactive to skier and rider triggers on slopes that have a stiffer and more cohesive slab. This recent MIN report is a prime example.
Deeper in the snowpack a persistent slab (50 to 90 cm deep) lingers above a weak layer of surface hoar and may be found in sheltered terrain or otherwise faceted grains and/or a hard melt-freeze crust. This weak layer has also been easily reactive to human triggers around the region. Check out this MIN report from yesterday in the Ruault Lake area in the western flank of the region.
Weak faceted grains and a decomposing melt-freeze crust can be found near the base of the snowpack. There have not been recent avalanche observations on this layer, but steep and rocky slopes, as well as shallow snowpack areas, should be approached with caution.
Terrain and Travel
- The trees are not the safe-haven they normally are at this time. Terrain at treeline is primed for human triggered avalanches.
- Fresh snow rests on a problematic persistent slab, don't let good riding lure you into complacency.
- Back off if you encounter whumpfing, hollow sounds, or shooting cracks.
- Choose simple, low-angle, well supported terrain without convexities.
- Pay attention to cornices and give them a wide berth when traveling on or below ridges.
Problems
Persistent Slabs
Two layers of concern exist and have been reactive over the past couple of days. The upper layer being buried mid-February down 30-60 cm and has recently failed primarily on a sugary facet interface and the deeper layer of concern is found down 50-90 cm and consists of surface hoar, faceted grains, and/or a melt-freeze crust. The layer has been most problematic around treeline elevations and in openings below treeline, but also reaches into the lower alpine. Avalanches have occurred on surprisingly shallow slope angles and the layer can easily be remotely triggered.
Aspects: All aspects.
Elevations: Treeline.
Likelihood
Expected Size
Wind Slabs
Switching northwest and southwest wind will build fresh and reactive wind slabs. These may be easily triggered by the weight of a skier or rider.
Loose-dry avalanches may be easily triggered from steep terrain features.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Feb 28th, 2021 4:00PM
