The incoming storm will likely cause a widespread avalanche cycle overnight Monday and into Tuesday. This is good time to stick to non-avalanche terrain free from overhead hazards. Avalanche paths may run into below treeline terrain.
This layer has reached a tipping point in parts of the region. 40-70 cm of snow currently sits above a weak layer from early December. Combinations of sugary facets , surface hoar and/or a crust mean persistent slabs are likely reactive, especially to human triggers.
Storm slabs will likely be reactive on Tuesday producing large and widespread avalanche activity. Open areas that are more exposed to wind have been producing more avalanches. Simple, low angle terrain away from overhead hazard is a good choice right now.
An intense Pacific frontal system will track across BC today bringing the region strong to extreme winds and heavy snowfall amounts. High pressure will start to set up Tuesday afternoon and we can expect a clearing trend.
Overnight Monday: Heavy snow 20-30 cm. Alpine temperatures near -6. Ridgetop winds strong to extreme from the southwest.
Tuesday: Cloudy with isolated flurries. Alpine temperature near -8 and freezing levels at the valley bottom. Ridgetop winds generally moderate with strong gusts from the West. Alpine temperature inversion.
Wednesday: Mix of sun and cloud. Air temperatures falling to -12 in the alpine. Ridgetop winds light from the West.
Thursday: Sunny. Alpine temperatures -6 with a strong alpine inversion and freezing levels in the valley bottom.
On Monday the South Rockies field team reported poor visibility but saw a size 2 wind slab on an East aspect. Tomorrow will likely be a different story with new snow and wind overnight. A natural widespread avalanche cycle is expected to happen overnight and/ or tomorrow.
On Sunday one of the south facing paths in Koko Claims made it to the grooming.
Also on Sunday, the South Rockies Field Team experienced lots of whumpfing and remote triggered a size 2 avalanche in a low snowpack zone. The failure plane was facets on the early December persistent weak layer, even though there was no crust at that elevation (2100m). They also saw recent natural avalanche activity up to size 2.5. Alpine and open treeline features most exposed to wind produced the most avalanche activity.
On Saturday a natural size 2.5 avalanche was spotted out of extreme, shallow, rocky, wind affected terrain in the Crowsnest Pass. It was thin, but propagated widely. The date of the event was uncertain.
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The big story is the next system arriving today and tonight bringing a lot of new snow (30-40 cm) by Tuesday. Large storm slabs will likely be reactive, especially where they sit above a weak interface.
Before the current storm there is 40-60 cm above the early December weak layer. There may be weak faceted grains and/or a crust making it susceptible to human triggering and step down avalanches from recent storm snow.
The base of the snowpack consists of a hard melt-freeze crust from early-November that may also have weak crystals around it. There has not been recent avalanche activity on this layer but it remains on our radar. The most likely spot to trigger it would be on thin and rocky slopes or, like above, from step down avalanches in the recent storm snow.
Snowpack depths vary substantially in the region with the average snowpack depth at treeline being approximately 90-140 cm.
