Avalanche Forecast
North 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
- Choose well supported terrain without convexities.
- Minimize exposure to steep planar south-facing slopes - especially if they see sunshine.
- 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 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
- 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 remote triggered a size 2 avalanche on an east facing slope at 1700 m. The avalanche had a crown depth of 50 m running on the March 29th crust. A natural size 2 wind slab from a northwest facing slope at 2500 m was also reported.
On Monday a size 3 persistent slab avalanche was remotely triggered by explosive control work. 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 storm/wind slab avalanches from size 1-2. These were skier-triggered on north to east aspects above 2000 m. 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'.
On Saturday numerous storm slabs failed naturally and were triggered by both skiers and control work. 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.
Snowpack Summary
The region picked up a few centimeters Tuesday night with very little wind.
A variable 5-20 cm of new snow 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
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: Scattered cloud cover, freezing level beginning near valley bottom rising to 1000 m, light variable wind, trace of snow possible.
FRIDAY: Broken cloud cover, freezing level beginning near valley bottom rising to 600 m, light southerly wind, 1 to 3 cm of snow possible.
SATURDAY: Broken cloud cover, freezing level beginning near valley bottom rising to 700 m, light southerly wind, 1 to 2 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.