Watch for areas of stiffer snow, where a soft slab has formed above the buried crust/surface hoar layer. A prime combination for human triggered avalanches especially on steep, convex, or wind loaded terrain.
Summary
Confidence
Moderate - Forecast snowfall amounts are uncertain on Thursday
Weather Forecast
TUESDAY: Mix of sun and cloud. Ridge wind light from the southwest. Temperature -13. Freezing level surface.WEDNESDAY: Mostly cloudy, flurries. Accumulation trace. Ridge wind light from the west. Temperature -12. Freezing level surface.THURSDAY: Snow. Accumulation 5 - 15 cm. Ridge wind moderate from the southwest. Temperature -8. Freezing level surface.
Avalanche Summary
On the weekend, several explosives triggered slab avalanches to Size 2 and loose snow avalanches to Size 1 were reported on northwesterly to southeasterly aspects in the alpine. Sloughing in steep terrain and a skier controlled Size 1.5 wind slab avalanche on a loaded feature at 2100 m on a northeast aspect were also reported.On Friday storm storm was sloughing naturally in steep terrain with loose snow releases to Size 1, while skier traffic produced small slab releases to Size 1 in areas where the storm snow had formed into a slightly stiffer, cohesive slab above the December 15th layer.Earlier in the week numerous Size 1-2 natural, skier, remote, and explosives triggered slab avalanches were reported on all aspects, releasing both within the storm snow and on the December 15th crust/surface hoar layer; including a Size 1.5 skier accidental.Also several classic signs of instability (whumpfing, shooting cracks, small slab releases) have been reported; see the Mountain Information Network (MIN) for great recent reports
here,
here and
here. Check out the Forecasters' Blog
here for some great terrain advice.
Snowpack Summary
Last week's storm snow has now settled to 30-80 cm of soft slab overlying the "December 15th crust/surface hoar layer" - a variety of old snow surfaces depending on aspect and elevation. On solar aspects a thin melt-freeze crust has been buried. On northerly aspects, feathery, surface hoar crystals have been buried below treeline as well as protected areas at treeline. And in the alpine, the old surface of of sugary snow (facets) and hard wind-scoured snow lies below the storm snow.Recent snowpack tests have produced very easy to hard, sudden and resistant results on this December 15th crust/surface hoar layer indicating a high degree of variability in this layer. Below the December 15th layer, the late November crust is now buried 60-100 cm and has been producing hard, resistant results in recent snowpack tests. Beneath this crust the lower snowpack is well settled.
jmcbride,
Avalanche Canada
