Quality of overnight freeze will play a strong factor in stability during the day on Sunday (see weather forecast tab for additiona details). Freezing level was close to 2400m on Saturday and forecast to be higher on Sunday.
Confidence
Moderate - Timing or intensity of solar radiation is uncertain on Sunday
Weather Forecast
Forecasts for the next 24hrs are calling for cloud to move in overnight, and a mix of sun and cloud throughout the day tomorrow. Cloud cover overnight on Saturday will be a key thing to note with regards to stability on Sunday. If clouds move in, it is unlikely that the snowpack will get any re-freeze overnight and stability will deteriorate earlier in the day on Sunday. If there are no clouds, the snowpack should get a good freeze overnight and stability will deteriorate as the sun comes out and temperatures warm up throughout the day much like it did on saturday. So, pay attention to the quality of the freeze overnight and cloud cover.
Avalanche Summary
Numerous loose wet avalanches up to sz 1 were observed. Field teams were down from the Spray area early in the day but we suspect that there were some solar triggered avalanches initiated later in the day.
Snowpack Summary
Strong solar radiation influence throughout the region today with temperatures at 2200m of 5C. Moist surface snow was being encountered up to ridgelines and loose wet avalanches were being observed from steeper terrain into the Alpine. Northern aspects remained dry with isolated windslabs along ridgelines and in gullies features up to 40cm thick. Field tests on Friday were showing that these slabs were failing in the moderate range with not to much propagation. Cornices are still large and failures of these features is still common. So far, pretty much every cornice failure has triggerred a substantial avalanche on the underlying slopes that failed either at or near ground.
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.
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.
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.