Avalanche Forecast
Issued: Dec 26th, 2019 3:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Persistent Slabs and Wind Slabs.
cgarritty,
Avalanche Canada
Light new snow amounts and increasing winds are expected to form new wind slabs at higher elevations. In the north of the region, this adds a layer of complexity to a serious persistent slab problem. Danger in the south of the region is MODERATE and limited to wind slab concerns.
Summary
Confidence
High -
Weather Forecast
Thursday night: Cloudy with scattered flurries bringing up to 5 cm of new snow by morning. Moderate to strong southwest winds.
Friday: Mainly cloudy with lingering isolated flurries and a trace of new snow. Light to moderate west or northwest winds. Alpine high temperatures around -7.
Saturday: Cloudy with scattered flurries developing later in the day and bringing up to 5 cm of new snow by morning. Light to moderate south or southwest winds. Alpine high temperatures around -6 in the north of the region, closer to -3 in the south.Â
Sunday: A mix of sun and cloud. Light south winds. Alpine high temperatures around -4.
Avalanche Summary
Avalanche observations have been on a declining trend since the widespread avalanche cycle observed across the region at the end of last week. During that cycle, avalanches were reported to be running to valley-bottom in the north of the region, failing on the weak layer described in the snowpack summary below.
The possibility for large human-triggered persistent slab avalanches remains a very serious concern at higher elevations in the northern half of the region (e.g., Duffey, Hurley, etc.). See this MIN report of an avalanche involvement on Monday for an example of the issue at hand.
Given our current snowpack structure, we recommend very conservative route-finding and decision making in higher elevation avalanche terrain in the north of the region.
Snowpack Summary
Surface conditions over the region have likely evolved into a mix between newly wind-affected surfaces at exposed higher elevations and large new surface hoar in more sheltered areas.Â
Below the surface, the storm at the end of last week brought over 120 cm of snow to the south of the region and about 40 cm to the north of the region. This snow is gaining strength as the days pass but snowpack conditions found beneath this layer are variable over the region and are in some areas highly problematic.
In the north of the region, the above-mentioned storm snow brought a critical load to a now 30-70 cm-deep weak layer from late November composed of sugary faceted grains and hard melt-freeze crust. This structure is a recipe for large and destructive avalanches and a problem that may persist for weeks to months. This problematic layer is largely absent in the south of the region.
Terrain and Travel
- Don't let the desire for deep powder pull you into high consequence terrain.
- Persistent slabs have potential to pull back to lower angle terrain.
- Avoid steep convexities or areas with a thin, rocky, or variable snowpack.
- Carefully evaluate steep lines for wind slabs.
Problems
Persistent Slabs
A touchy weak layer is buried 30-70 cm deep in the snowpack in the north of the region. This layer has recently produced large and destructive avalanches that have travelled far. This problem is largely absent in the south of the region.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Wind Slabs
Light new snow amounts combined with increasing winds are expected to form small but touchy new wind slabs that will need to be managed on Friday. Expect this problem to increase with elevation and to be most pronounced in the immediate lee of wind-exposed terrain features. In the north of the region, wind slab releases currently carry a risk of triggering a deeper weak layer, especially in shallow, rocky areas.
Aspects: North, North East, East, South East, North West.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Dec 27th, 2019 5:00PM
