Avalanche Forecast
South Rockies
We're into a tricky period as a critical amount of storm snow settles (into a slab) and sits on a buried weak layer. Keep your terrain choices on the conservative side until conditions stabilize.
Avalanche Problem 1: Persistent Slabs
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
Travel and Terrain Advice
- Watch for signs of instability such as whumpfing, or cracking.
- Use caution on open slopes and convex rolls at treeline where buried surface hoar may be preserved.
- Choose well supported terrain without convexities.
Avalanche Problem 2: Wind Slabs
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
Moderate winds have created fresh wind slabs at higher elevations. In the south of the region, the winds were from the south-west. In the north of the region the winds were from the north east.
Travel and Terrain Advice
- Be careful with wind loaded pockets, especially near ridge crests and roll-overs.
- If triggered, the wind slabs may step down to deeper layers resulting in large avalanches.
- Avoid freshly wind loaded features.
Avalanche Summary
On Monday, a machine triggered Size 1.5 persistent slab avalanche was reported running on the mid December surface hoar layer, down 35 cm at that location (1700m). Even mountain goats looked like they were triggering avalanches! See the details here in the MIN post.
On Sunday a Size 2 persistent slab (stepping down to late November crust/facets) was intentionally triggered on an east aspect near 2000m in the south of the region.
On Saturday several natural and human triggered storm slab avalanches to Size 2 were reported on a wide variety of aspects and elevations. Furthermore, several persistent slab avalanches to Size 1.5 were reported (with some remote-triggered by skiers).
A week ago, a larger persistent slab (Size 2) was triggered low on a slope that propagated up and across the slope on a 50 cm deep crust. This highlights the potential for persistent slab avalanches to have wide propagations.
Snowpack Summary
Up to 45 cm of snow fell on at the end of last week. Since then, strong winds from a wide range of directions have blown snow around: In the south of the region winds were from the south west; whereas in the north the winds were from the north east.
The main question in the snowpack surrounds the mid-December layer sitting beneath the recent snow. This layer includes crusts on solar aspects and feathery surface hoar in sheltered terrain at and below treeline, and has consistently shown its reactivity, even on small features below treeline.
The lower snowpack is composed of mostly soft sugary snow and a few early season crusts that have not produced significant test results recently.
Weather Forecast
Dry with gradually warming alpine temperatures during the week. Cold in the valley bottoms.
WEDNESDAY: Cloudy with sunny breaks. Ridge wind light west. Alpine temperature -5. Freezing level surface.
THURSDAY: Mix of sun and cloud. Ridge wind light southwest. Alpine temperature -5. Freezing level surface.
FRIDAY: Cloudy with isolated flurries. Ridge wind light west. Alpine temperature -3. Freezing level surface.
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A weak layer composed of surface hoar and/or crusts is buried 35-70 cm below the surface. This layer continues to be very reactive to human triggers and may not improve anytime soon.