Avalanche Forecast
Issued: Jan 10th, 2018 4:31PM
The alpine rating is Storm Slabs and Persistent Slabs.
, the treeline rating is , and the below treeline rating is Known problems includeIt appears that we've hit the tipping point, very large avalanches ran nearly full path Wednesday, and this activity will likely persist into Thursday. Don't over-think it, just avoid avalanche terrain, our snowpack needs time to adjust.
Summary
Confidence
Moderate - Freezing levels are uncertain on Saturday
Weather Forecast
Snowfall is expected to spread into the BC interior Thursday morning. With cold arctic air preconditioning, a widespread 5 to 15 cm of snow is expected with locally higher amounts throughout the region. A ridge of high pressure and rather warm air should begin to spill into the region Saturday and Sunday.THURSDAY: Overcast, freezing level at valley bottom, light to moderate south/southwest wind, 5 to 15 cm of snow expected with potential for up to 25 cm in favored locations. THURSDAY NIGHT: Overcast, freezing level at valley bottom, light west wind, 1 to 5 cm of snow possible.FRIDAY: Overcast, freezing level at valley bottom, light west wind, trace of snow possible.SATURDAY: Scattered cloud, freezing level beginning near valley bottom, rising to 800 m during the day, returning to valley bottom Saturday night. Light west wind, no precipitation expected.
Avalanche Summary
On Wednesday control work produced very large avalanches to size 3.5 on southwest, south and southeast aspects. Natural avalanches ran to size 2.5 on southeast, east and northeast aspects. These avalanches may have started as storm slabs, but quickly stepped down to the mid-December and/or late November weak layers. These very large avalanches are not to be taken lightly and this activity may persist into Thursday.On Tuesday a widespread natural avalanche cycle to size 2.5 was reported from all aspects and elevations as the upper snowpack adjusted to a new load and increasingly warm temperatures.Last Thursday a skier triggered a size 3.0 avalanche just after entering the east face of Evening Ridge near Nelson. The skier survived, but sustained significant injuries. On New Years Eve a skier triggered a size 3.0 avalanche on an east facing treeline feature at Kootenay Pass which resulted in a single fatality. Both of these avalanches are thought to have failed on the late November crust.
Snowpack Summary
40 to 60 cm of recent snow is coalescing into a slab on top of the January 5th interface which consists of a crust/surface hoar combination on steep southerly aspects and pure surface hoar on remaining aspects. The late December surface hoar remains active and is now down 50 to 70 cm below the surface. The mid-December surface hoar, facet and crust combination is now down 70 to 130 cm below the surface and remains active. This interface is most pronounced at treeline, but is present below treeline also. The overlying slab is now deep and cohesive. Two laminated crusts created by twin rain events in late November lay just below the mid-December interface, 80 to 150 cm below the surface. Facets may be found sandwiched between the two crusts and have been observed above the uppermost crust too. In shallow rocky terrain the mid-December surface hoar and the late November crust seem to be reacting together which is a volatile combination.
Problems
Storm Slabs
40 to 60 cm of recent storm snow has settled into a reactive slab that rests on the early January interface. Large natural and human triggered avalanches remain likely as the upper snowpack adjusts to the new load and recent warm temperatures.
Storm slabs in motion will likely step down and produce large destructive avalanches.Avoid all avalanche terrain during periods of loading from new snow and wind.The new snow will require several days to settle and stabilize.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Persistent Slabs
Our complex snowpack is currently producing very large avalanches on deeply buried weak layers. Expert level knowledge and significant experience is required to venture into the backcountry at this time.
Only the most simple non-avalanche terrain free of overhead hazard is appropriate at this timeAvoid exposure to overhead avalanche terrain, large avalanches may reach the end of run out zones.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Jan 11th, 2018 2:00PM