Avalanche Forecast
South Columbia
A variety of weak layers continue to produce large human triggered avalanches. We're still managing a midwinter snowpack that requires thoughtful terrain selection.
Avalanche Problem 1: Persistent Slabs
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
Travel and Terrain Advice
- Use conservative route selection, choose moderate angled and supported terrain with low consequence.
- Minimize exposure to steep south-facing slopes where recent storm snow overlies a crust.
- Use caution around sheltered steep or convex slopes where buried surface hoar may be preserved.
Avalanche Problem 2: Wind Slabs
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
Strong and shifting winds have been blowing loose snow into wind slabs on a wide range of aspects in wind-affected areas. The most recent strong winds came from the north, so be especially cautious around recently loaded south aspects.
Travel and Terrain Advice
- If triggered the wind slabs may step down to deeper layers resulting in large avalanches.
- Be especially careful with wind loaded pockets near ridge crests and roll-overs.
Avalanche Summary
On Tuesday a skier accidently triggered a size 1.5 persistent slab avalanche on an east facing slope at 2200 m with a crown 50 cm in depth. Two more avalanches to size 2 were remote triggered on a south/southeast facing slope between 2050 and 2150 m, likely running on the mid-March interface. A cornice fall on a southeast facing feature around 2500 m produced a size 3 persistent slab that likely ran the night of April 1st.
Reports from Monday include several storm slab avalanches from a variety of triggers ranging from size 1-2. Fracture depths of 20-40 cm indicate some of the shallower weak layers identified in our snowpack discussion as failure planes. More sporadic reactivity at the deeper mid-March layer was observed in adjacent regions. Numerous small (size 1-1.5) and reportedly hard wind slabs were also triggered on various aspects with both explosives and ski cutting.
On Saturday numerous storm slabs failed naturally as well as with skier traffic and control work producing size 2-3 avalanches, with crowns 30-100 cm in depth. This activity occurred on all aspects but was focused at alpine elevations and this problem is now being identified as a 'persistent slab'.
Snowpack Summary
Tuesday night's storm produced 10 cm of cold snow with very little wind.
A variable 5-20 cm Sunday night brought storm totals from the past week to a wide-ranging 50-90 cm, with amounts that taper with elevation. The snowfall was initially accompanied by strong south winds and then followed by strong north winds, so a mix of old and stubborn and newer, more reactive wind slabs can now likely be found on a range of aspects at higher elevations.
Below the wind-affected surface, a few regionally variable weak layers exist within the depth of the recent storm snow, formed during breaks in storms that allowed for the formation of sun crusts on sun exposed slopes as well as surface hoar on shaded aspects. These shallower layers (20-50 cm deep) remain a concern, as does the similar mid-March persistent weak layer, now buried up to a metre deep. The reactivity of these layers appears to decrease with depth, however the mid-March layer still features in daily reports and the potential for deep 'step down' types of releases can't yet be dismissed.
Deeper persistent weak layers from January and December are still being reported by professional observers, but are generally considered dormant.
Weather Forecast
A seasonably cool weather pattern is expected to stick around for the foreseeable future and it looks like we will pick up a few centimeters of snow every day through the weekend too.
THURSDAY: Broken cloud cover, freezing level beginning near valley bottom rising to 1000 m, light variable wind, 1 to 3 cm of snow possible.
FRIDAY: Broken cloud cover, freezing level beginning near valley bottom rising to 1000 m, light southerly wind, 1 to 2 cm of snow possible.
SATURDAY: Broken cloud cover, freezing level beginning near valley bottom rising to 1000 m, light southerly wind, 1 to 4 cm of snow possible.
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Weak layers of crust and surface hoar from last month are now buried up to 90 cm deep and have shown prolonged reactivity since the last storm. Manage the uncertainty around triggering these layers by sticking to lower angle, supported slopes.