Avalanche Forecast
Issued: Jan 23rd, 2023 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Deep Persistent Slabs, Wind Slabs and Persistent Slabs.
trettie,
Avalanche Canada
At the risk of sounding like a broken record, it is still the time for conservative terrain choices. Several concerning layers exist in the snowpack that are producing large human triggered avalanches.
Summary
Confidence
Moderate
Avalanche Summary
On Sunday a few skier triggered wind slabs were reported to have occurred on west through east aspects at treeline and above. Explosives and cornice falls produced more large/very large avalanches running on the November facets.
On Saturday in the neighbouring region to the north, a serious avalanche, resulting in a fatality , occurred in the Oasis riding area south of Valemont. The avalanche was on a north-northwest aspect at 2100 m. It was remotely triggered and ran on the November facets near the bottom of the snowpack. This large avalanche (size 2.5) had a depth of 80 to 120 cm. There were several other reports of human-triggered avalanches from nearby areas.
A few concerning avalanches occurred last Thursday. The first took place in the far north of the region on a southwest-facing alpine slope. It was a natural size 3 running on the November facets.
The second was a size 3.5 vehicle remote in the Central Monashees. This avalanche was remotely triggered by a snowcat travelling across a rocky west-facing ridgeline. This avalanche also failed on the November facets. The crown was up to 3.5m deep.
The third was another vehicle remote also running on the November facets. This one was in the Selkirks on a south-through west-facing piece of terrain.
All of these very large avalanches occurred at upper treeline/lower alpine. Avalanches like these are most likely to be triggered on steep, shallow and previously undisturbed slopes.
Snowpack Summary
New snow continues to gradually accumulate. A layer of surface hoar may be found below 5-15cm of recent snowfall as well as a sun crust on steep solar aspects. Westerly winds will continue to affect exposed terrain and form wind slabs near ridge tops. At lower elevations, a rain crust exists down 10 to 40cm, with reported elevations extending up to 2000 m around Nelson, 1700 m around Revelstoke.
Two persistent weak layers in the middle of the snowpack may remain reactive to human triggering. They are both surface hoar layers that formed in early January and are typically found 40 to 90 cm deep throughout the region. There are also some deeper facet and surface hoar layers that formed in December, but recent snowpack observations suggest they are strengthening.
The bottom of the snowpack is made up of large weak facets buried in late November, which has caused an atypical deep persistent slab problem for this region.
Weather Summary
Monday Night
Cloudy with up to 5cm of new snow expected. Strong northwest wind and a low of -10 at 1800m.
Tuesday
Cloudy with up to 10cm of new snow expected. Moderate to strong northwest winds and a high of -7 at 1800m.
Wednesday
A mix of sun and cloud with the possibility of flurries bringing up to 5cm of new snow. Moderate to strong northwest winds and a high of -4 at 1800m.
Thursday
Cloudy with around 5cm of new snow expected. Moderate to strong northwest winds and a high of -5 at 1800m.
More details can be found in the Mountain Weather Forecast.
Terrain and Travel Advice
- Be mindful that deep instabilities are still present and have produced recent large avalanches.
- Avoid thin areas like rock outcroppings where you're most likely to trigger avalanches failing on deep weak layers.
- Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
- Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.
Problems
Deep Persistent Slabs
A layer of large and weak facets sits near the base of the snowpack. This layer has most recently been problematic in upper treeline/lower alpine elevations.
Avoid thin and rocky start zones where weak layers sit closer to the surface, riders are most likely to trigger an avalanche on this layer in steep, shallow previously undisturbed terrain or by first triggering a layer further up in the snowpack.
Remote triggering is a concern for this layer, avoid traveling below steep slopes.
The likelihood of avalanches will increase on slopes with active wind-loading.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Wind Slabs
Increasing northwesterly winds are expected to form fresh wind slabs in the alpine and exposed areas at treeline. Winds have varied in direction over the past few days. wind slabs could be found on all aspects with the largest and most reactive likely on easterly aspects.
Be aware that wind slabs could step down to deeper layers.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Persistent Slabs
Numerous problematic weak layers exist in the top meter of the snowpack, with recent observations suggesting the most likely of these to trigger are surface hoar layers found 40 to 90cm deep. Be especially cautious around steep convex openings at treeline and below.
Remote triggering is a concern for this layer, avoid traveling below steep slopes.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Jan 24th, 2023 4:00PM
