A SPAW has been issued for the forecast region. The concern is the Jan 6th layer and the potential for large avalanches. In addition, we are expecting some convective flurries tomorrow. The danger may rise locally if we get a significant load.
Confidence
Moderate - Intensity of incoming weather systems is uncertain
Weather Forecast
Freezing levels will remain relatively low overnight. It should hover at 1300m for this evening and rise to 1900m by tomorrow morning. Convective flurries are in the forecast for tonight and tomorrow. We can expect up to 8cm's tonight. 2500m ridge winds will remain in the light to moderate range, peaking at 35km/hr from the west. Tomorrow's alpine high will be -4.
Avalanche Summary
No new avalanches were seen today, however skies were obscured for most of the day.
Snowpack Summary
Up to 15cm of new snow has fallen in higher areas and/or areas near the divide. The winds have been light enough to prevent any major wind effect, but immediate lees are likely to have storm slabs from wind transport. Expect these on all easterly aspects in the alpine. This new snow is also adding to the load on the persistent layers. The Feb 11th layer depth varies, but expect to find it anywhere from 30-60cm down. It is a significant crust on solar aspects and a subtle density change on the polar aspects. There are also a number of other crusts present on solar aspects and low elevation non-polar aspects. The Jan 6th layer also varies in depth. In deeper areas it can be down as much as 1.8m, and in shallow areas it can be down as little as 40cm. Below treeline, heat has made for generally crusty conditions. The only exception is in shady areas, where the snowpack is weak still. Snow depths are: Burstall Pass 189cm & Mud Lake 117cm.
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.
Deep Persistent Slabs
Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.
Cornices
Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.