The weekend warm up is over and cooler temperatures now prevail. Our #1 concern remains the January 6th facet layer interface, it is a tough layer to trigger but will produce big avalanches out of steep rocky, shallow snowpack areas in the alpine.
Confidence
Moderate - Forecast snowfall amounts are uncertain on Thursday
Weather Forecast
Cloudy with sunny periods and isolated flurries with trace snow accumulation. Alpine temperature -6.0. Winds will be westerly 25km/h with gusts to 60km/h in advance of a front that is due to arrive overnight Wednesday. Freezing level will be valley bottom (1400 meters).
Avalanche Summary
As alluded to there were several avalanches on the January 6th facet interface. One size 2.5 by some skiers heading up to the brand new Des Poilus Hut over in the Yoho Park. Another size 2.5 near the Bow Summit area and today Parks Canada reported a solid size 2.5 out of Eagle 3 path at the Sunshine Ski Area. The common thread with all of these avalanche events is that the start zones were in shallow snowpack areas.
Snowpack Summary
The snowpack had taken on some significant warming over the weekend with high freezing levels in addition to rain at lower treeline elevations. This moist snow has transformed into yet another melt freeze crust that was buried yesterday evening March 8th. The storm ended last night and deposited anywhere from 4-15cm of low density snow over this newly buried crust - the bond on this new snow to the crust appears to be pretty strong from what we saw. The new crust ends at about 2250 meters and the ski quality improves profoundly above this elevation. The crusts from Feb 27th are buried 35-45cm deep and the Feb 11th layer is down anywhere from 50-80cm deep. The January 6th layer is the one that concerns us the most - it is approximately 80-100cm deep in the alpine and it is still producing anywhere from moderate to hard sudden collapses and also no results in some test pits indicating high variability. There has been steady avalanche activity on this layer in the Rockies and although it is a hard layer to trigger - it is regularly producing monster avalanches size 2.5-3.0.
Problems
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.