An intense storm overnight has tipped the scales and overloaded the weak layers in Little Yoho. A natural avalanche cycle to size 3 occurred Thursday. This will ease with minimal precip Friday and Sat, but will pick up again with a big storm Sunday
Weather Forecast
The SW flow continues, and we will see continued light snowfall amounts friday and saturday with a bigger looking storm coming in on Sunday. Approximately 3-5 cms per day with a drop in temperatures and winds. Sundays storm will be the one to watch and will likely trigger another avalanche cycle if it materializes.
Snowpack Summary
20 cm of new snow overnight makes 70 cm of storm snow over the last 9 days. Alpine winds have distributed this into leeward areas but only at the highest elevations. Three persistent weak layers lurk in the upper half of the snowpack: Jan 16 down 40cm; Jan 6 down 55cm; Dec15 down 70 cm giving easy-mod test results
Avalanche Summary
Last nights snow triggered a natural avalanche cycle in Little Yoho on Thursday. Avalanches up to size 3 ran on Mt Dennis including the ice climbs Carlsberg Column, Extra Lite, Super Bok and Heineken Hall. A close call with a group of climbers who were leading the crux pitch of Carlsberg when an avalanche poured over there heads.
Confidence
Due to the number of field observations
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.