Sun hitting slopes for the first time after a storm may increase the probability of natural and human triggered avalanches.
Confidence
Fair - Timing, track, or intensity of incoming weather system is uncertain
Weather Forecast
The pacific frontal system produced significant moisture Saturday night and into Sunday over the south of the region. There is a chance of moderate precipitation overnight Sunday into Monday in the extreme south corner of the South Rockies. The exact track of the storm is tough to pin down so there could be significant amounts of precipitation or nothing at all. Less eventful weather for Monday and Tuesday with slightly lower freezing levels is expected.Sun Ovn: 70% chance of snow or rain, moderate accumulations possible (Flathead and Elk Valley South) if the storm makes it above the 49th parallel. Light to moderate wind out of the West. Freezing levels 1300-1600mMonday: Trace possible. Light to moderate winds from the west, freezing levels around 1400-1600m.Tuesday: Cloudy with sunny periods, light west winds with moderate gusts. Freezing levels 1400-1600m.
Avalanche Summary
There was a report that the Morrisey slidepaths near Fernie ran to nearly full path on Sunday. Also on Sunday, near neighbors in the Lizard Range report storm slabs and loose wet avalanches to size 2.5.There is concern for an ongoing natural and human triggered avalanche cycle on Monday with more snow in the south, and solar radiation hitting the slopes where we get some blue skies. Cornices have gotten large and tender and may trigger slabs if they fail.Avalanches in the region have the potential to run full path as dryer storm slabs from the alpine entrain moist snow as the descend. Avalanches in clearcuts, road banks, lower angle terrain and non obvious avalanche paths continue to surprise backcountry enthusiasts throughout the region, so consider them carefully in your travel plans through the forecast period.
Snowpack Summary
Various storm slabs continue to build on top of the March 2nd weak layer made up of facets, surface hoar or crusts, depending on your elevation and aspect. There is now 70-100cm of snow on this layer in the bigger snow zones in the south of our region (Flathead and around Fernie).The mid pack contains the February 10th persistent weak layer. In the deeper snowpack areas it could be up to 2 meters deep now, but in the shallower snowpack zones, it is likely about a meter deep. It is becoming a more isolated problem and likely only trigger-able by large loads like cornices or storm slabs in motion in areas that have not previously run on the February 10th layer... and those areas are getting harder to find.In the lower elevations (below 1600m) in the south of the region, expect the snowpack to be rain soaked and loosing cohesion. Below treeline terrain is likely close to isothermal in the high rain affected zones, and at least moist everywhere else.
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.
Wet Slabs
Wet Slab avalanches are the release of a cohesive layer of snow (a slab) that is generally moist or wet when the flow of liquid water weakens the bond between the slab and the surface below (snow or ground). They often occur during prolonged warming events and/or rain-on-snow events. Wet Slabs can be very unpredictable and destructive.
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.