Weather Forecast
The South Rockies see a bit of snow during this forecast period as a surface low develops over the southern interior and subsequently exits to the SE Monday evening. Light snow should begin Sunday around midnight delivering just a few cm overnight. Snow continues through the day Monday cooling as the day progresses. I expect 10 – 20 cm before skies clear Tuesday morning. Tuesday dawns clear and cold setting the stage for a spectacular day in the mountains.FZLVL:Mon: Starts near 2000m, lowering to the surface by Tuesday AMTue: SurfaceWed: Starting near the surface, rising as high as 1600 in the afternoon, returning to the surface overnight.Wind: Mon: 2km: Mod/Strong SW, Strong to Extreme SW at ridgetop. Diminishing overnight.Tue: L, NE at all elevations.Wed: 2km: Mod W/NW, ridgetop winds mod/str NW.
Avalanche Summary
Our field team remoted a size 2 avalanche from the flats Wednesday. It's worth checking out the details of the incident report linked to this forecast as it illustrates just how tender the persistent slab problem is in the So. Rockies. On Saturday a group of sledders remote triggered a size 1.5 avalanche which failed on the Feb.09 SH in the Coal Creek area on a North facing, 37 degree slope at 1600m.
Snowpack Summary
Strong winds and have formed wind slabs up to 20 cm deep in wind exposed terrain at and above treeline as of Sunday afternoon. The Feb. 09 surface hoar is now down between 40 & 90 cm. The depth varies throughout the region. This weak layer continue to perform, our head field technician was out for a ski and noticed a remote triggered avalanche on Saturday. See the details below. Snowpack tests continue to show sudden moderate failures on this interface. This weekend the upper snowpack is changing character as strong to extreme winds at ridge top & mild temperatures form the old storm snow into a more cohesive slab. Lingering concern remains for basal facets, particularly in shallower snowpack areas with steep, rocky start zones.Our field team was out in the Crowsnest Thursday where they observed a much stronger snowpack. The So. Rockies forecast is intended to give trends for the region as a whole, and as such, conditions will vary between the different sub regions.
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.
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.
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.