Avalanche Forecast
Issued: Mar 13th, 2021 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Cornices, Persistent Slabs and Loose Wet.
ldreier,
Avalanche Canada
We are expecting another hot day and temperatures will stay above freezing in the alpine overnight. The warmth will weaken cornices and may increase the reactivity of the persistent weak layers. Conditions may change rapidly with daytime heating and sun exposure.
Summary
Confidence
Moderate - Uncertainty is due to the fact that cornice falls are particularly difficult to forecast. Uncertainty is due to whether buried persistent weak layers become active, triggering avalanches, with the arrival of the forecast weather.
Weather Forecast
SATURDAY NIGHT: Clear, 20 km/h south wind, alpine low +1 C, freezing level 2500 m.
SUNDAY: Sunny, 20 km/h southwest wind, alpine high +4 C, freezing level 2500 m.
MONDAY: Mix of sun and cloud, 20 km/h northeast wind, alpine high +5 C, freezing level 2200 m.
TUESDAY: Mix of sun and cloud, 20 km/h northeast wind, alpine high +4 C, freezing level 2200 m.
Avalanche Summary
No new avalanches were reported on Saturday at the time of writing.
Snowpack Summary
A thick melt-freeze crust is present in many areas, with the exception being on north aspects above around 1700 m. Old wind slabs may exist on northerly aspects at alpine and treeline elevations, whereas windward slopes have been scoured to rocks or a hard crust. On solar aspects and below the freezing level, the snow will moisten during the heat of the day. Cornices will also weaken over the day.
Around 30 to 60 cm of snow sits above a persistent weak layer of sugary faceted grains that was buried in mid-February. There have been a handful of avalanches that released on this layer in the past few weeks. There is another persistent weak layer that was buried at the end of January, found around 50 to 80 cm deep. This layer consists of feathery surface hoar, facets, and/or a hard melt-freeze crust. Periodic avalanches continue to be triggered on these layers by riders, particularly where a stiff wind slab sits above them. Check out this MIN that shows the positioning of the layers in the snowpack near Crowsnest Pass.
Weak faceted snow and a decomposing melt-freeze crust can be found near the base of the snowpack.Â
Terrain and Travel
- Cornices become weak with daytime heating or solar exposure.
- Cornices often break further back than expected; give them a wide berth when traveling on ridgetops.
- Be aware of the potential for large avalanches due to the presence of a persistent slab.
- Avoid exposure to steep, sun exposed slopes, especially when the solar radiation is strong.
- Be alert to conditions that change throughout the day.
Problems
Cornices
The freezing level is forecast to stay at 2500 m overnight and during the day which will further weaken cornices and the snowpack. Cornices will become especially weak with daytime heating and sun exposure. Large cornice falls are a hazard of their own and can also trigger large persistent slab avalanches on the slopes below.
Aspects: North, North East, East, West, North West.
Elevations: Alpine.
Likelihood
Expected Size
Persistent Slabs
Two persistent weak layers exist in the snowpack that could be triggered by riders:
- The upper layer is buried 30 to 60 cm and primarily consists of weak faceted grains.
- The deeper layer is buried 60 to 100 cm and consists of surface hoar, faceted grains, and/or a hard crust.
The most likely areas to trigger these layers is where a hard wind slab exists above the layers and where the snowpack is not capped by a thick melt-freeze crust. Warm temperatures and solar input may increase the reactivity of these two layers.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Loose Wet
Solar input and warm temperatures may weaken the upper snowpack and form wet loose avalanches. These avalanches will most likely occur on steep solar slopes and around rock outcrops. The likelihood for wet loose avalanches will increase with daytime heating. Pinwheeling and a moist snow surface are signs that the stability of the upper snowpack is decreasing.
Even small avalanches can be a hazard in high consequence terrain and above terrain traps.
Aspects: South East, South, South West.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Mar 14th, 2021 4:00PM
