Avalanche Forecast
Issued: Feb 26th, 2021 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Storm Slabs and Persistent Slabs.
cgarritty,
Avalanche Canada
There's a lot of uncertainty in the snowpack right now, but recent persistent slab avalanches are good information to anchor your decisions to. This is a time to choose terrain based on the worst outcome the snowpack might produce.
Summary
Confidence
Weather Forecast
FRIDAY NIGHT: Increasing cloud with isolated flurries bringing a trace to 5 cm of new snow. Light to moderate northwest winds
SATURDAY: A mix of sun and cloud with cloud increasing. Flurries beginning again in the afternoon and increasing overnight. Moderate to strong west winds, peaking overnight. Alpine high temperatures around -11.
SUNDAY: Cloudy with continuing flurries bringing 5-10 cm of new snow, approaching 15-25 cm including overnight amounts, continuing overnight again. Strong to extreme southwest winds, easing only a bit overnight. Alpine high temperatures reaching about -2 as freezing levels jump to around 1700 metres.
MONDAY: Cloudy with continuing flurries bringing another 5-10 cm of new snow and 2-day snow totals to 25-40cm. Moderate to strong west winds. Alpine temperatures falling from about -7 to -12 over the day as freezing levels return to valley bottom.
Avalanche Summary
This spooky report of large remote triggered avalanches came in Wednesday.
Widespread whumphing was reported Tuesday which is a clear sign of an unstable snowpack. More details in this MIN report.
There was likely a widespread natural avalanche cycle on Sunday and Monday as a result of heavy loading from snow and wind.
There were numerous reports of touchy conditions on Sunday as evidenced here and here.
There was a fatal avalanche accident in the Hasler area on Saturday. The incident occurred on a northeast aspect between 1400 and 1600 m. The avalanche was a size 2.5. The fracture line was estimated to be 50-100 cm and is suspected to have been a persistent slab avalanche running on the weak layer of surface hoar described in our snowpack summary. Click here to link to a report on the incident.
Snowpack Summary
The north of the region has seen little snow since Monday night, but the south of the region picked up an additional 10 to 25 cm of new snow. This adds to the 40-60+cm of warm snow that fell through the weekend with strong southwest and west winds which formed reactive storm slabs and wind slabs in exposed terrain.
New snow over the last week has been increasing the load on a widespread persistent weak layer consisting of surface hoar. The layer is likely 80-120 cm deep near Renshaw and 60-100 cm deep around Torpy and further north. Reports suggest this layer is most prevalent around treeline elevations, but likely reaches into the alpine and in openings below treeline too. It may sit above a crust below 1600 m. The likelihood of triggering this layer has increased under incremental loading from new snow and the consequences of triggering it are high.
Terrain and Travel
- Use conservative route selection. Choose simple, low-angle, well-supported terrain with no overhead hazard.
- Storm slabs in motion may step down to deeper layers resulting in large avalanches.
- In times of uncertainty conservative terrain choices are our best defense.
Problems
Storm Slabs
A succession of storms over the past week has been building storm slabs over a range of weak surface grains. Although surface instabilities are likely becoming more focused toward wind-loaded areas, the storm snow interface doesn't inspire much confidence. Lingering concern for this interface outside of wind-exposed areas are multiplied when we consider the deeper, widespread persistent weak layer that has been waking up under the incremental loading pattern.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Persistent Slabs
Ongoing heavy snowfall and an overall warming trend has set up a scenario where it's possible for humans to trigger deep slabs. These slabs are failing on a layer of surface hoar that developed in late January. The layer can be found 50 to 110 cm deep across the region, being deepest in the south and shallowest in the north. This layer has been the most sensitive right at treeline, but it may extend up into the alpine and down into openings below treeline.
Aspects: All aspects.
Elevations: Treeline, Below Treeline.
Likelihood
Expected Size
Valid until: Feb 27th, 2021 4:00PM
