Avalanche Forecast
Issued: Mar 18th, 2022 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Persistent Slabs and Wind Slabs.
zryan,
Avalanche Canada
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.
Summary
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.Â
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
Last week's 30 to 60 cm of new snow has the potential to form a persistent slab above weak layers. There have been reports of a poor bond to underlying sun crust layers on south slopes and surface hoar crystals on north slopes.
At this point, we are uncertain about how long this problem will take to heal and suggest a more conservative approach to terrain to handle this uncertainty.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Wind Slabs
Expect to find freshly wind-loaded features that are reactive to human triggers as snowfall and southwest winds create wind slab in lee features in the alpine and treeline.
Aspects: North, North East, East, South East, North West.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Mar 19th, 2022 4:00PM
