Confidence
Fair - Intensity of incoming weather is uncertain on Wednesday
Weather Forecast
A low pressure system is tracking south of the international border Wednesday which will result in about 5 -10 cm of snow which will continue through Wednesday night. Winds will be near 40 km/h at 2000m Wednesday, which is more than enough to move snow. Wed. 1500m Temp: H: -3, L: -9. Thursday looks to be more of the same as the So. Rockies receive a bit of upslope activity on the east slopes in the early morning. This activity will taper mid-morning as winds shift to the NW and diminish to light values. On Friday, the ridge of high pressure off the coast of BC flattens allowing for a more zonal pattern for the weekend, which means a few cm of snow each day both Saturday and Sunday.
Avalanche Summary
Our field team observed an avalanche failing on a steep bluff, the SH was assumed to be the weak layer. No other reports of avalanches from this region, but that doesn't mean they aren't happening. It's important to remember that this region is often quite data sparse.
Snowpack Summary
Saturday night into Sunday, moisture in the west of the region collided with cold air in the east and resulted in an intense period of heavy snowfall that was very low density. This new snow has likely settled a bit with daytime warming Monday. Now 50-60 cm of recent snow sits on a reactive weak layer of crusts, surface hoar and facets. Our field team was in the Elk Valley North sub region, operating between 2000 & 2300m. They reported weaknesses failing with moderate to hard shears down 60 cm. It will be interesting to see what kind of results they get from their field days in the next 72 hours. For the moment, we can assume that there is a slab of approx. 60 cm in depth in most of the region that is still prone to human triggering. Below this, the mid-pack is quite strong in most locations. However, lingering concern remains for basal facets, particularly in shallower snowpack areas with steep, rocky start zones.
Problems
Loose Dry
Loose Dry avalanches are the release of dry unconsolidated snow and typically occur within layers of soft snow near the surface of the snowpack. These avalanches start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-dry avalanches include point-release avalanches or sluffs.
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.
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.