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Avalanche Forecast

Archived

Mar 18th, 2022–Mar 19th, 2022

Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.

Regions

Purcells.

Uncertainty surrounding buried weak layers in the western part of the region is best managed with conservative terrain choices and good travel habits.

Reactive wind slabs may exist at upper elevations. Be cautious as you transition into wind-affected terrain.

Confidence

Moderate - Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast.

Weather Forecast

Active weather continues, with a series of frontal systems moving inland bringing light to moderate amounts of new snow.

FRIDAY NIGHT: Cloudy with snowfall, up to 5 cm of accumulation. Light to moderate southwesterly winds. Freezing level 700 m. 

SATURDAY: Snowing, trace to 5 cm of accumulation. Moderate to strong southwesterly winds. Freezing level rising to 1500 m, dropping to 500 m overnight.

SUNDAY: Partially cloudy, light flurries. Moderate to strong westerly winds easing in the afternoon. Freezing level rising to 1500 m, dropping to 500 m overnight.

MONDAY: Snowing, up to 5 cm of accumulation. Light to moderate southwesterly winds. Freezing level rising to 1500 m.

Avalanche Summary

We have heightened concern about a developing persistent slab problem in some parts of the Purcells (read more in this blog).

Several notable human-triggered slab avalanches occurred in the past 3 days, suggesting that the recent snow is bonding poorly to the underlying layers. These occurred on a range of aspects above 2000 m. Most slabs were small in the top 20 to 30 cm of snow (size 1), but one larger 70 cm thick slab was remotely triggered from below by a group of skiers (size 2). This avalanche occurred on a south aspect at 2250 m.

Snowpack Summary

The upper snowpack is highly variable as snowfall totals over the past week have ranged from 20 cm in the eastern Purcells to 60 cm in the western Purcells. Snow depths also taper significantly with elevation, with moist and crusty surfaces below 1800 m and on south aspects into the alpine.

In some areas, this snow is well bonded to old crust layers, while in other areas the snow has settled into a reactive slab above weak layers around the crusts. At this point, it appears persistent slab problems could be developing in the deeper snowpack areas along the western side of the range, while the eastern side more likely has thinner wind slabs. The lower snowpack is generally well bonded.

Terrain and Travel

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Uncertainty is best managed through conservative terrain choices at this time.
  • Choose slopes that are well supported and have limited consequence.
  • Back off if you encounter whumpfing, hollow sounds, or shooting cracks.
  • Be carefull around freshly wind loaded features.

Problems

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.