Watch for reactive pockets of wind slab that may be sitting on a layer of recently buried surface hoar.
Confidence
Moderate - Wind effect is extremely variable
Weather Forecast
Clear skies and valley cloud are forecast for Monday as the dry ridge of high pressure holds on for one more day. On Tuesday a Pacific front will move inland bringing trace amounts of new snow on Tuesday night and up to 5cm on Wednesday. Ridgetop winds associated with the front will be strong and southwesterly. Freezing levels will hover around valley bottom on Monday and then rise to about 1300m with the passage of the front.
Avalanche Summary
Explosives control on Saturday triggered a size 1 wind slab in the south of the region. No other recent avalanches have been reported in the South Rockies region. Several avalanches were reported in the Lizard/Flathead region on Thursday and Friday. The primary problem in that region is wind slabs failing on the early January surface hoar layer. Similar conditions may exist in some parts of the South Rockies.
Snowpack Summary
The Avalanche Canada field team has been finding variable conditions across the region this week. Up to 10cm of recent snow has fallen burying a layer of surface hoar in sheltered features. In the east of the region the snow surface is now widely wind affected with thin but stiff wind slabs in lee features at treeline and in the alpine. In areas that have seen less wind (a good indicator would be snow still hanging on the trees), these wind slabs may be softer and deeper. In either case, snow pit tests in wind loaded features show these slabs are failing under moderate loads and can propagate over wide distances. The early December crust can be found down around 60cm. It is not currently expected to pose an avalanche problem but could wake-up in the future with substantial warming or heavy snow loading.
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.