Avalanche Forecast
Issued: Mar 19th, 2022 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs, Persistent Slabs and Loose Wet.
zryan,
Avalanche Canada
Danger will be highest during periods of strong solar radiation, affecting sun-exposed slopes and cornices.
Watch for wind slabs at upper elevations and adjust your travel plans according to the changing conditions of elevation, aspect, and time of day.
Summary
Confidence
Moderate - Uncertainty is due to the timing or intensity of solar radiation and its effect on the snowpack. Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast.
Weather Forecast
SATURDAY NIGHT: Snowing, trace to 15 cm of accumulation. Moderate to strong westerly winds. Clearing in the early morning, 1500 m freezing level dropping to 500 m.
SUNDAY: Partially cloudy with the potential for scattered flurries. Light northwesterly winds. Freezing level rising to 1300 m in the afternoon.
MONDAY: Cloudy with light flurries. Light to moderate westerly winds. Freezing level rising to 1500 m in the afternoon.
TUESDAY: Cloudy with light flurries. Moderate to strong westerly winds. Freezing level rising to 2500 m in the afternoon.
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 week, 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
5-15 cm of new snow will add to last week's highly variable snowfall totals, with 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, last week's 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
- Minimize exposure to sun-exposed slopes when the solar radiation is strong.
- Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
- Back off if you encounter whumpfing, hollow sounds, or shooting cracks.
- Cornices become weak with daytime heating or solar exposure.
- Cornice failure may trigger large avalanches.
Problems
Wind Slabs
10-20 cm of recent snowfall and southwest winds are expected to form reactive wind slabs in lee features in the alpine and treeline.
Cornices have grown significantly in the past two weeks. Give them a wide berth when travelling on ridge-lines and minimize overhead exposure to large cornices, especially when the temperature is warm or solar radiation is strong.
Aspects: North, North East, East, South East, North West.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Persistent Slabs
Last week's 30 to 60 cm of new snow has shown evidence of forming 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
Loose Wet
If the sun comes out on Sunday, daytime warming compounded by strong solar radiation may cause the surface snow on sun-affected slopes to loose cohesion rapidly and form wet loose avalanches out of steep terrain.
If triggered, wet loose avalanches have the potential to step down to deeper weak layers creating large avalanches.
Aspects: South East, South, South West, West.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Mar 20th, 2022 4:00PM
