Avalanche Forecast
Issued: Feb 19th, 2023 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs and Persistent Slabs.
jpercival,
Avalanche Canada
7 AM Update: Snow and strong wind will increase avalanche danger by continuing to add more mass to an already established wind slab problem. Seek low angle terrain that avoids steep, lee wind-loaded areas.
Summary
Confidence
Moderate
Avalanche Summary
On Saturday, numerous reports of both skier and explosive trigger small (size 1-1.5) windslabs avalanches, similarities with the reported avalanches are they failed in the lee of prevailing winds on convex roll features.
Reports of a very large (size 3) avalanche that has impacted a snowmobile access road near Brandywine. No human involvement, however very few details are currently available. Photos can be viewed at this link
On Friday, explosive control and ski cutting produced small (size 1) avalanches on lee aspects (north) terrain. Noted observations included mid-afternoon small (size 1) dry loose avalanche activity, that initiated out of very steep and thin rocky terrain.
On Thursday, ski-cutting activity produced numerous small (size 1) dry loose avalanches, these were found on steep terrain with some operators describing them as "power sluffs".
On Tuesday, A snowmobiler remote triggered a size 2 persistent avalanche in the Callaghan. The avalanche was reported to be triggered from 10 m away and was adjacent to a heavy traffic area. We suspect this avalanche slid on the mid-January persistent weak layer. See the MIN for details and photos. This is the latest human-triggered avalanche on this persistent weak layer in the region.
For more evidence of this weak layer see this MIN report from last Wednesday when a rider at Chocolate Bowl triggered a size 2.5 persistent avalanche. Find another example in this MIN from a skier accidental size 2 persistent slab avalanche that occurred on Saturday.
On Monday afternoon, search and rescue technicians responded to a fatal avalanche incident north of the Sea to Sky region. The avalanche is believed to have occurred on Saturday and was initiated in a shallow rocky area. See the MIN for more details.
Snowpack Summary
Currently, available snow amounts of between 15 and 25 cm are being redistributed via moderate variable winds over a variety of surfaces including facets, old wind slabs, and a thin breakable crust below 1650 m. In sheltered areas above 1200 m snow remains dry and unconsolidated.
Expected north through to west winds with velocities between 60 and 80 km/h are likely to strip and press north-facing terrain. New snow and available snow for transport will begin to deposit on south through to east aspects slopes and terrain features.
Two concerning crusts are found in the mid-pack at varying depths and are widespread throughout the region. A crust from late January is found at all elevations down 40-100 cm with small facets above it. In the Rhododendron and Pemberton Icefield area, this crust has been reactive to rider traffic and in test pits at treeline. In the Brandywine area, a crust found 80-200 cm deep resulted in a few surprisingly large rider-triggered avalanches last week. This layer exists to 1900 m in these areas.
Total snowpack depths are approaching 300 cm in some areas.
Weather Summary
Sunday Night
Cloudy with light snowfall, 1 to 5 cm accumulation. Winds northwest 70 km/h gusting 90 km/h. Treeline temperature -3 °C. Freezing level 1000 m.
Monday
Cloudy with moderate to heavy snowfall beginning late in the afternoon, 10 to 20 cm accumulation. Winds northwest 40 km/h. Treeline temperature -3 °C. Freezing level 1000 m.
Tuesday
Cloudy with very isolated light flurries, trace amounts of accumulation. Winds northwest 40 km/h easing to 20 km/h. Treeline temperature -8 °C. Freezing level descending to 400 m mid-day.
Wednesday
Clearing with no precipitation forecast. Winds southeast 10 km/h . Treeline temperature -9 °C. Freezing level descending to 0 m mid-day.
More details can be found in the Mountain Weather Forecast.
Terrain and Travel Advice
- Fresh wind slabs will likely form throughout the day, diligently watch for changing conditions.
- Avoid steep, rocky, and wind effected areas where triggering slabs is more likely.
- Potential for wide propagation exists, fresh slabs may rest on surface hoar, facets and/or crust.
- Be alert to conditions that change throughout the day.
- Closely monitor how the new snow is bonding to the crust.
Problems
Wind Slabs
New northerly winds are building new and reactive wind slabs in exposed alpine and upper treeline features. Continue to use caution on lee features and watch for areas that have been reverse-loaded and cross-loaded.
Southwesterly winds have previously distributed available snow into wind slabs on north and east slopes in the alpine and upper treeline. Wind slabs may be sitting on a crust making them especially reactive to light loads such as skiers.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Persistent Slabs
Two weak layers consisting of a crust with small facets found above them have been reactive to rider traffic in the last week. The first, down 40-100 cm has been reactive at treeline in the Rhododendron and Pemberton Icefields area. The second is found up to 1900 meters and is down 60-150 cm in the snowpack. It has been reactive to human triggering in the Brandywine and Callaghan area on north and west aspect between 1800 and 1600 m. Both of these layers seem like isolated problems at the moment but if triggered they will result in large consequential avalanches.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Feb 20th, 2023 4:00PM
