Avalanche Forecast
Issued: Mar 5th, 2022 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Persistent Slabs, Wind Slabs and Loose Wet.
rbuhler,
Avalanche Canada
A weak layer of facets sitting on a crust is creating a persistent slab problem which has resulted in numerous human-triggered avalanches over the past few days. The layer is most reactive on shaded aspects at 1600-2000 m. Check out the recent forecaster blog for more details.
Summary
Confidence
Weather Forecast
A ridge of high pressure brings one more day of dry and sunny conditions for Sunday before conditions change on Monday.
Saturday Night: Clear, moderate N wind, freezing levels around 1500 m.
Sunday: Sunny, light to moderate N wind, freezing levels climbing to around 2000 m.
Monday: Mainly cloudy with sunny breaks, light to moderate NW wind, freezing levels reaching around 1500 m in the afternoon.
Monday night and Tuesday: Snowfall up to 15 cm, light to moderate NW wind, freezing levels around 800 m.
Avalanche Summary
On Friday, three size 1.5-2 persistent slab avalanches were human triggered and failed on a weak crust/facet layer buried late-February. This MIN report describes one of them which was on a west aspect at around 1950 m and released down 50 cm. Another was on an east aspect at around 1800 m elevation and the third was on a steep convex feature at treeline. Some human-triggered loose dry avalanches were observed on north aspects and some solar-triggered loose wet avalanches were observed on steep sun-exposed slopes.
On Thursday, several persistent slab avalanches were reported up to size 2.5. Four of these were natural and the rest were human-triggered including one which was remotely triggered. Two of the naturals were on south aspects which were triggered by loose wet avalanches stepping down. Most of the rest of the activity was on northerly aspects. The majority of the activity appears to have occurred between 1600 and 2000 m elevation. Slab thickness was typically 30-70 cm and the failure plane was a combination of the mid-February and late-February weak layers which may be acting as more of a single thick weak layer.
In addition to the persistent slab activity on Thursday, a natural wet slab was observed on a south aspect at 1750 m and several natural wind slabs were observed. Numerous loose avalanches were observed from steep sun-exposed slopes. Explosives triggered one size 3 cornice.
Snowpack Summary
A surface melt-freeze crust is now expected on all aspects below around 1700 m and on sun-exposed slopes into the alpine. Dry surface snow is expected on shaded aspects at treeline and in the alpine, and recent periods of moderate northerly wind may be redistributing this old storm snow and forming wind slabs in exposed high elevation terrain.
A weak crust/facet layer which was buried late-February is typically down 30-60 cm and has been responsible for numerous avalanches over the past few days. The interface has been most reactive on shaded aspects between 1600 and 2000 m. There were also some avalanches on southerly aspects earlier in the week but with each subsequent day of melt-freeze conditions, the persistent problem is becoming less likely on sun-exposed slopes.
Cornices have been reported to have grown large during the recent storm, primarily on north and east aspects. These may become weak during the heat of the afternoon.
Terrain and Travel
- Be aware of the potential for large avalanches due to the presence of a persistent slab.
- Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
- Pay attention to cornices and give them a wide berth when traveling on or below ridges.
- Minimize exposure to sun-exposed slopes when the solar radiation is strong.
Problems
Persistent Slabs
A persistent weak layer of facets on a crust exists 30-60 cm below the surface and has been touchy to human triggers, especially on northerly aspects around treeline. Recent avalanche activity has primarily occurred between 1600 and 2000 m and includes some occurrences of remote triggering (from a distance away). Numerous natural and human-triggered avalanches occurred on this interface between Wednesday and Friday.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Wind Slabs
Watch for recent or ongoing wind slab formation on Sunday. Periods of moderate wind from the north may be enough to develop reactive new slabs in exposed terrain at higher elevations.
Lingering cornices may become weak during the heat of the afternoon. Cornices are most likely on north and east aspects in the alpine.
Aspects: East, South East, South, South West, West.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Loose Wet
With each subsequent day of melt-freeze conditions, loose wet avalanches will become less likely. However, extra caution is still recommended on steep sun-exposed slopes during the heat of the afternoon. Where the crust is breaking down or non-existent, loose wet avalanches will be more likely.
Aspects: East, South East, South, South West, West.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Mar 6th, 2022 4:00PM
