Windslabs will very likely be quite touchy for the next few days. These slabs are sitting over a variety of crusts buried in the upper snowpack at treeline. We are expecting natural avalanche activity and a high likelihood for human triggered slides.
Confidence
Moderate - Forecast snowfall amounts are uncertain
Weather Forecast
A low pressure system will be moving through the Rockies tonight bringing light snowfall amounts (up to 10cm) and strong southwesterly winds. Tomorrow will see partly cloudy skies, the winds will be moderate out of the southwest and gusting to 60km/h. Temperatures in the alpine around -6.0. Freezing levels will rise to 1400 meters.
Avalanche Summary
A few loose dry avalanches released out of north facing steep, rocky & unskiable faces and flushed out in the fans to size 1.0. On Mt. Buller in the northeastern corner of our forecast region, a cornice triggered wind slab scrubbed to ground and ran almost to the full run-out, size 2.5.
Snowpack Summary
10-25cm of storm snow exists over a new melt-freeze / suncrust layer that was buried on February 27th. This new soft slab over these crusts are not reactive at the moment but with additional load and winds which are forecast for tonight, we anticipate this interface will be reactive to skier traffic. The other layers of concern are the February 11th melt-freeze / suncrust (30-50cm deep) and the January 11th facets (60-100cm deep). These crusts will be most problematic at treeline elevations, snowpack tests revealed sudden collapses below these crusts on facets so exercise caution as you work through terrain and pay particular attention to the solar aspects where the crusts are strong and intact and remember that crusts are generally never trustworthy in the presence of wind slabs. The mid pack and basal layers are strengthening and generally well settled.
Problems
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.
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.