Avalanche Forecast
North Columbia
A variety of weak layers have been preserved within and below our recent storm snow. 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 caution around sheltered steep or convex slopes where buried surface hoar may be preserved.
- Minimize exposure to steep planar south-facing slopes - especially if they see sunshine.
- Choose well supported terrain without convexities.
Avalanche Problem 2: Wind Slabs
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
Strong and shifting winds have blown 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
- Be especially careful with wind loaded pockets near ridge crests and roll-overs.
- If triggered the wind slabs may step down to deeper layers resulting in large avalanches.
Avalanche Summary
Monday's reports included one observation of explosives remotely triggering a size 3 persistent slab 50 metres below the explosives placement. Numerous small (size 1-1.5) and reportedly hard wind slabs were also triggered on various aspects with both explosives and ski cutting. One large (size 2.5) natural cornice fall was reported as well.
Reports from Sunday included several more storm slab and wind slab avalanches from size 1-2. These were both skier-triggered and ski cut on north to east aspects at around 2000 metres and above. Slab depths of around 25 cm suggest the shallower weak layers identified in our snowpack discussion as failure planes. At least one larger storm slab failed at the deeper late-March layer, now labeled a 'persistent slab'.
Saturday's reports included numerous observations of storm slabs releasing naturally as well as with remote (from a distance) triggering, skier traffic and explosives control. Sizes ranged from 2-3, with crown fracture depths varying from 30-100 cm. This activity occurred on all aspects but was focused at alpine elevations.
Friday's storm caused another natural avalanche cycle with many size 1-2 avalanches in the top 20-30 cm of new snow.
Snowpack Summary
A variable 5-20 cm of new snow over Sunday night brought storm snow totals from the past week to a wide-ranging 40-90 cm. 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 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
Tuesday night: Scattered flurries bringing a trace to 5 cm of new snow. Light to moderate southwest winds.
Wednesday: Mainly cloudy with isolated flurries and a trace of new snow. Light to moderate southwest winds. Freezing level to 1200 metres with alpine high temperatures around - 8.
Thursday: Mainly cloudy with light flurries beginning in the afternoon and continuing overnight. Light northeast winds. Freezing level to 1100 metres with alpine high temperatures around -9.
Friday: Friday cloudy with isolated flurries and a trace to 5 cm of new snow, continuing overnight. Light southeast winds. Freezing level to 1500 metres with alpine high temperatures around -3.
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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.