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.
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.
Two persistent weak layers exist in the snowpack that could be triggered by riders:
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.
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.
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.
No new avalanches were reported on Saturday at the time of writing.
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.
