Avalanche Forecast
North Columbia
Another storm is bringing new snow, wind, and warming temperatures to the region. This is the same recipe that produced numerous very large persistent slab avalanches during the last storm.
Avalanche Problem 1: Persistent Slabs
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
Travel and Terrain Advice
- Uncertainty is best managed through conservative terrain choices at this time.
- Anticipate avalanches running full path when managing overhead hazards.
Avalanche Problem 2: Storm Slabs
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
New snow and strong west winds are expected to build fresh storm slabs over the day on Friday. Snowfall amounts are uncertain, but snow stability will be on a decreasing trend throughout the day.
Travel and Terrain Advice
- Watch for the first touchy slabs to form in the lee of exposed terrain features.
- Storm slabs may step down to deeply buried weak layers to produce very large avalanches.
Avalanche Summary
Reports from Wednesday included further observations of recent natural activity showing storm slabs releasing naturally, from Size 2-3, on all aspects and elevations. South aspects were especially active where solar warming served as a trigger. Explosives control also yielded numerous persistent slab results from Size 2-3.5 on all aspects at all elevations. All our persistent weak layers of concern were active, with the possible exception of the early January layer. The deep mid-December and even deeper late November layers were frequent failure planes. The mid-December layer is also suspected in two natural Size 4 releases in and near the Glacier National Park area.
On Tuesday, natural avalanche activity was widespread, running on all aspects and elevations. Storm and wind slabs reached Size 3 while persistent slab avalanches failing on the mid-December layer ran to Size 3.5. A Size 2.5 avalanche on a northeast facing slope at 1920 m resulted in a single fatality. More details are available here.
On Monday a widespread natural avalanche cycle was driven by warming temperatures and up to 100 cm of storm snow. Avalanches to Size 3 were reported from a variety of aspects and elevations
Snowpack Summary
60 to 120 cm of snow fell between Sunday and Tuesday night. On Monday temperatures warmed to -1 C at tree line. Winds have been strong to extreme from the south which has built cornices and formed wind slabs on lee (down wind) slopes.
The new snow sits on a complex snowpack with several active weak layers:
1) 80 to 110 cm of storm snow sits on a crust and/or surface hoar layer from mid-January. The crust is reportedly widespread, with the possible exception of high elevation north aspects. The mid-January surface hoar is 5 to 20 mm in size and was reported at tree line elevations and possibly higher.
2) Deeper in the snowpack, the early-January persistent weak layer is 110 to 140 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.
3) Another weak layer buried mid-December consisting of a facet/surface hoar/crust combination is buried 120 to 170 cm deep. It is most problematic at and below tree line. This layer has produced numerous recent very large avalanches.
A fourth crust/facet layer from late November is yet another failure plane responsible for several recent large avalanches.
Weather Forecast
Friday: Cloudy with flurries bringing 10-20 cm of new snow, increasing overnight. Strong west winds, continuing overnight. Freezing level rising to 1500 metres with alpine high temperatures around -5.
Saturday: Mainly cloudy with isolated flurries and a trace to 5 cm of new snow. Clearing over the day. Moderate northwest winds. Freezing level returning to valley bottom from 1200 metres with alpine high temperatures around -10.
Sunday: Increasing cloud with scattered flurries and 5-10 cm of new snow. Light variable winds. Freezing level remaining near valley bottom with alpine high temperatures of -6.
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Several deeply buried weak layers are persisting in the snowpack and continue to produce very large avalanches, especially with heavy triggers. This is a time to carefully measure your exposure to avalanche terrain and to avoid overhead hazards.