Avalanche Forecast
South Columbia
Forecast sunshine and warming will increase the likelihood of triggering in a wide range of avalanche problems on Thursday. Expect stability to deteriorate over the day.
Avalanche Problem 1: Loose Wet
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
Travel and Terrain Advice
- Avoid sun exposed slopes when the solar radiation is strong, especially if snow is moist or wet.
- Be cautious of sluffing in steep terrain, particularly where the debris flows into terrain traps.
- Manage your sluff and be extra cautious where long slopes allow for more snow entrainment.
Avalanche Problem 2: Cornices
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
Large cornice failures have been reported in the past week and cornices will weaken with forecast sun exposure on Thursday. Cornice releases may have enough force to trigger a deep weak layer and cause a very large and destructive avalanche.
Travel and Terrain Advice
- Give cornices a wide berth when travelling on or below ridges.
- Cornices become weak with daytime heating. Minimize your overhead exposure.
Avalanche Problem 3: Storm Slabs
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
The strength of storm and wind slabs formed after the last round of snowfall will be tested by warming on Wednesday. The greatest caution is needed around steep or convex terrain as well as sun-affected slopes where slabs formed over a recent crust.
Travel and Terrain Advice
- Watch for signs of instability such as shooting cracks or recent avalanches.
- Exercise increased caution around south aspects where new snow may have formed a slab over crust.
Avalanche Summary
Observations from Tuesday showed numerous small (size 1) storm slabs releasing both remotely and with ski cutting. Crown fractures were in the 35-40 cm range and activity was observed at all elevations and on all but west aspects.
Poor visibility hindered observations of avalanche activity on Monday.
On Sunday, warming and sunny breaks initiated widespread natural storm slab and loose, wet avalanche activity in the recent storm snow, up to size 2, on all aspects from 1500-2300 m.
In addition to heightened storm slab activity following regular snowfalls, observations from late last week also showed a pattern of heightened cornice failure activity. Reports of 'bus sized' blocks found in debris as well as a suspected cornice-triggered size 4 wind slab release in the adjacent North Columbias and Glacier National Park should keep these looming giants top of mind.
Looking forward, a trend toward clearing skies and warming temperatures will be increasing chances of loose wet avalanche activity as well as testing the strength of storm slabs and wind slabs formed in the wake of recent snowfall and wind events.
Snowpack Summary
About 70-100 cm of recent storm snow overlies a crust on all aspects to at least 2300 m (and possibly higher on south-facing slopes). Recent variable strong winds have pressed and redistributed the most recent accumulations into new wind slabs on a range of aspects.
Within the upper snowpack there are now a few different crusts with the shallowest of these (down 30-50 cm) remaining a concern as the uppermost layer of storm snow settles and bonds to it.
There is some lingering concern around the mid-March persistent weak layer in the alpine where it is found 80 to 120 cm below the surface. This buried crust/surface hoar interface was widely reactive but has not produced any avalanche activity in the past week. It is likely trending towards dormancy, but we need to keep it in the back of our minds as it is capable of producing large avalanches should it be triggered (think larger triggers such as; sleds, step-down from a surface avalanche or, a cornice collapse).
Deeper persistent weak layers from December and January are considered dormant at this time.
Weather Forecast
Thursday: Mainly sunny. Light southeast winds shifting southwest. Freezing level rising to 2100 metres with alpine high temperatures around -1 to 0. Weak overnight cooling.
Friday: Cloudy with light flurries beginning in the afternoon and continuing overnight. Light to moderate southwest winds. Freezing level to 2200 metres with alpine high temperatures around 0 to +1.
Saturday: Cloudy with continuing flurries bringing 10-15 cm of new snow. Moderate to strong southwest winds. Freezing level to 1800 metres with alpine high temperatures around -3.
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Rising freezing levels and increasing sunshine will destabilize surface snow and promote loose wet avalanches in steeper terrain. Loose snow releases may occur naturally or with a human trigger.