Avalanche Forecast
North Columbia
We have a complex snowpack: touchy storm and wind slabs sit above three weak layers that are reactive to natural and human triggers at all elevations. Perform cautious route-finding without overhead exposure as the snowpack adjusts to the load.
Avalanche Problem 1: Storm Slabs
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
Travel and Terrain Advice
- Be very cautious as you transition into wind affected terrain, wind slabs may be deep and touchy.
- Avoid exposure to terrain traps where the consequence of a small avalanche could be serious.
- If triggered, the storm/wind slabs may step down to deeper layers, resulting in large avalanches.
Avalanche Problem 2: Persistent Slabs
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
Three persistent weak layers are lurking in our snowpack, which remain capable of producing very large and destructive avalanches at all elevations. Below treeline, be cautious in open features, such as cutblocks and gullies.
Travel and Terrain Advice
- 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.
Avalanche Summary
On Sunday, numerous small to large (size 1 to 2) storm slabs and loose dry avalanches were triggered naturally and by skiers, generally failing on the mid-January weak layer. Three persistent slabs between size 1 and 3.5 were observed, being triggered naturally and by skiers in treeline and alpine terrain on all aspects.
These sorts of avalanches have been a consistent trend since last Wednesday, with small to large storm slabs observed at all elevations and large persistent slabs most often observed at treeline and alpine elevation bands. Being triggered naturally and by skiers and snowmobilers. These avalanches have been releasing on all three persistent weak layers described in the Snowpack Discussion. Expect similar avalanches to release, as our snowpack adjusts to the recent load.
Snowpack Summary
The current snowpack is complex, with three active weak layers that we are monitoring.
50-80 cm of storm snow sits on a crust and/or surface hoar layer (mid-January). The crust is reportedly widespread, except for possibly at high elevations on north aspects. The mid-January surface hoar is 5 to 20 mm in size and was reported at treeline elevations and possibly higher. 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 80 to 100 cm below the surface. It is composed of surface hoar on sheltered slopes as well as sun crust on steep solar aspects and is found at all elevation bands. Snowpack tests show sudden fracture characters with moderate loads and high propagation potential, and signs of instability such as whumpfs and cracking. Another weak layer buried mid-December consisting of a facet/surface hoar/crust combination is buried 100 to 150 cm deep. It is most problematic at and below tree line.
A rain crust buried in November is generally 150 to 200 cm deep and is likely dormant for the time being.
Weather Forecast
TUESDAY: Mostly cloudy with intermittent snowfall, accumulation 3-7 cm, moderate to strong southerly winds, alpine temperature near -10 C, freezing level near 500 m.
WEDNESDAY: Mostly cloudy with intermittent snowfall, accumulation 10-15 cm, light to moderate southerly winds, alpine temperature -7 C, freezing level near 700 m.
THURSDAY: Mostly cloudy with light snowfall, accumulation 5-10 cm, moderate to strong southerly winds, alpine temperature near -10 C, freezing level near 500 m.
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Up to 80 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.