Avalanche Forecast
Issued: Jan 22nd, 2018 4:42PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Storm Slabs and Persistent Slabs.
mconlan,
Avalanche Canada
We have a highly complex snowpack: touchy storm and wind slabs sit above three weak layers that are reactive to human triggers at all elevations. Perform cautious route-finding without overhead exposure as the snowpack adjusts to the recent load.
Summary
Confidence
Moderate - Timing, track, or intensity of incoming weather system is uncertain
Weather Forecast
TUESDAY: Mostly cloudy with intermittent snowfall, accumulation 1-3 cm, moderate to strong southerly winds, alpine temperature near -10 C, freezing level near 500 m.WEDNESDAY: Mostly cloudy with intermittent snowfall, accumulation 1-3 cm, moderate southerly winds, alpine temperature -7 C, freezing level near 600 m.THURSDAY: Mostly cloudy with light snowfall, accumulation 5-10 cm, moderate to strong southerly winds, alpine temperature near -10 C, freezing level below valley bottom.
Avalanche Summary
On Sunday, a large (size 2) storm slab was remotely triggered by a skier on a southeast aspect, 50 cm deep, at treeline. Other avalanches likely released, but there were limited observations in the region because of the stormy conditions.Many avalanches were reported on Saturday (with conditions indicated as Spicy). Small to large (size 1 to 3) storm slabs and wind slabs were observed, being triggered naturally, by skiers, snowmobiles, and explosives. The avalanches generally released on lee slopes (northerly to easterly) at all elevation bands, ranging from 30 to 90 cm deep. Many of the avalanches released on the persistent weak layers described in the Snowpack Summary. Similar avalanches were observed on Thursday and Friday.
Snowpack Summary
The current snowpack is complex, with three active weak layers that we are monitoring. 30-60 cm of storm snow sits on a crust and/or surface hoar layer (mid-January). The crust was reportedly widespread; high elevation north is likely one of the few crust-free zones. The mid-January surface hoar is up to 10 mm and reported at all elevation bands. The recent storm snow fell with strong south winds, producing wind slabs in lee features at treeline and alpine elevations and in open areas below treeline. Deeper in the snowpack, the early-January persistent weak layer is 30 to 70 cm below the surface. It is composed of surface hoar on sheltered slopes and sun crust on steep solar aspects and found at all elevation bands. Snowpack tests show sudden fracture characters with easy to moderate loads and high propagation potential, as well as whumpfs and cracking. Another weak layer buried mid-December consisting of a facet/surface hoar/crust combination is buried 40 to 100 cm deep. It is most problematic at and below tree line.A rain crust buried in November is 100 to 150 cm deep and is likely dormant for the time being.
Problems
Storm Slabs
Up to 60 cm of recent snow has formed a slab that sits on a reactive weak layer composed of feathery surface hoar and/or a crust. Expect the storm to have produced wind slabs in lee features due to strong south winds.
Avoid exposure to terrain traps where the consequence of a small avalanche could be serious.Be very cautious as you transition into wind affected terrain, wind slabs may be deep and touchy.If triggered, the storm/wind slabs may step down to deeper layers, resulting in large avalanches.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Persistent Slabs
Three persistent weak layers are lurking in our snowpack, which are capable of producing very large and destructive avalanches at all elevations. Below treeline, be cautious in cutblocks and gullies. The snowpack needs time to adjust to recent load.
Good day to make conservative terrain choices and watch for clues of instability.Avoid open slopes and convex rolls where buried surface hoar may be preserved.Be very cautious below treeline in open areas where surface hoar may be preserved.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Jan 23rd, 2018 2:00PM
