If the rain-soaked snow freezes as expected through the weekend, avalanche hazard will follow a decreasing trend until the next storm on Sunday. Please treat this forecast as an initial assessment, as we have little information at this time.
Confidence
Low - Due to the number of field observations
Weather Forecast
We're looking at relatively benign weather until Sunday afternoon, when a brief but intense cold front will bring rain and then 10-15cm snow by Sunday night. Saturday: Dry. Freezing levels initially around 1500 m, but increasing later in the day. Light southwesterly winds, increasing in the afternoon.Sunday: Rain early afternoon changing to flurries (10-15 cm possible). Freezing levels 2200m decreasing to surface by the evening. Winds moderate southerly. Monday: Scattered flurries. Freezing level around 1200 m. Moderate westerly winds.
Avalanche Summary
There are few observers right now. Several loose wet avalanches to Size 1 were reported at the tail end of the rains (Thursday). Some persistent slab activity to Size 2.5 was reported to the north in Kananaskis country. Elevations ranged from 2400 to 2600m on Northeast through Northwest aspects. I suspect avalanche activity will taper off with cooling temperatures on the weekend.
Snowpack Summary
Rain and warm weather have resulted in a widespread wet upper snowpack. The freezing level rose to approximately 2700 m on Wednesday and Thursday meaning very few places, if any, will have escaped the melt. The last three days have seen the snowpack diminish by approximately 20-30 cm.Some areas saw 5-15 cm of snow at the tail end of the storm and the possibility of thin windslabs exists. Expect treeline snow depths of around 45 cm in the Elk Valley and more like 80 cm further south in the Flathead in sheltered areas. A crust that formed around Halloween has been reported within the snowpack that may lie around 40-50 cm below the surface.
Problems
Persistent Slabs
Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.
Wind Slabs
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.