Avalanche Forecast
Issued: Jan 29th, 2021 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs and Persistent Slabs.
shorton,
Avalanche Canada
Triggering avalanches will gradually become more likely as new snow and wind builds reactive slabs. Closely watch for whumpfing, cracking and natural avalanches.
Summary
Confidence
Moderate - Uncertainty is due to the limited number of field observations.
Weather Forecast
A weak storm will cross the region on Sunday night.
FRIDAY NIGHT: Partly cloudy, moderate southwest wind, treeline temperatures around -18 C.
SATURDAY: Mix of sun and cloud, moderate southwest wind, treeline temperatures around -10 C.
SUNDAY: Cloudy with some isolated flurries and trace accumulations of snow, moderate south wind, treeline temperatures around -10 C.
MONDAY: Scattered flurries with 5-10 cm of snow, light west wind, treeline temperatures around -10 C.
Avalanche Summary
No avalanches have been reported in the past week, however some notable shooting cracks and whumpfs were reported around Pine Pass on Thursday. They were both linked to buried surface hoar layers, one 30 cm deep underneath a fresh wind slab (here) and the other 65 cm deep underneath old snow (here).Â
Wind slabs developing above surface hoar is a good example of the primary problem we expect to see over the weekend. The deeper surface hoar layer appears to be a very isolated problem on specific slopes in the north of the region.
Snowpack Summary
Open terrain is likely being impacted by moderate wind, with wind slabs forming on lee terrain features. Sheltered areas have 10-20 cm of soft faceted snow. Underneath the soft snow and new wind slabs, you will likely find a hard melt-freeze crust up to roughly 1600 m, perhaps weak and feathery surface hoar crystals, and otherwise wind packed snow. Wind slabs developing above surface hoar could be particularly reactive.
There is a spotty weak layer of surface hoar 30 to 65 cm deep in sheltered treeline terrain. This layer has not produced any avalanches to date, but our field team reported some large whumpfs on this layer at Pine Pass on Thursday.
There are presently no deeper concerns in the snowpack.
Terrain and Travel
- Closely monitor how the new snow is bonding to the old surface.
- Back off if you encounter whumpfing, hollow sounds, or shooting cracks.
- Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
- Exercise caution on steep, unsupported slopes.
Problems
Wind Slabs
As wind picks up over the weekend there is potential for new wind slabs in lee terrain features. These wind slabs may be sitting on top of weak surface hoar crystals, which would make them more easy to trigger.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Persistent Slabs
There is a spotty surface hoar layer 30-65 cm deep that appears to be unreactive in most areas, however, there have been some isolated whumpfs on this layer around Pine Pass. With such an isolated distribution, triggering an avalanche on this layer is unlikely, but the potential size means some extra caution should be taken with steep open slopes.
Aspects: All aspects.
Elevations: Treeline.
Likelihood
Expected Size
Valid until: Jan 30th, 2021 4:00PM
