Avalanche Forecast
South Rockies
Wind slabs linger in lee features at treeline and alpine elevations. Look for signs of avalanche activity and locally unstable snow, such as whumpfing and shooting cracks.
Avalanche Problem 1: Wind Slabs
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
Travel and Terrain Advice
- If triggered, the wind slabs may step down to deeper layers, resulting in large avalanches
- Choose shallow-angled and sheltered terrain where new snow hasn't been wind-affected.
Avalanche Problem 2: Deep Persistent Slabs
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
Several weak layers are lurking in our snowpack. If triggered, they could propagate far, producing avalanches with high consequences. Watch out for thin spots in the snowpack, where it is more likely to trigger them.
Travel and Terrain Advice
- Be aware of the potential for wide propagation.
- Avalanches could run full-path if triggered: avoid runout zones of avalanche paths on solar aspects.
Avalanche Summary
On Monday, large (size 2) wind slab avalanches were triggered by skier and explosive activity, 30 to 50 cm deep. A deep persistent slab was also noted in the region, likely releasing on one of the layers described in the snowpack discussion.
On Sunday, numerous small (size 1.5) wind slabs were triggered by skiers in lee features. The slabs were generally 20 to 40 cm deep.
Avalanche activity may slow down with a period of cold, clear weather that is expected to persist this week. However, the sun is packing more of a punch as the days get longer and it will warm the snow surface on solar aspects if clear skies prevail. Watch for steep sunny slopes due to the suns influence, lee features for reactive wind slabs, and be extra cautious near thin spots and shallow snow pack areas where triggering a deeper weak layer is more likely. There is a lower probability of triggering a deeper layer than in previous weeks, but the consequence would be very high if one was triggered.
Snowpack Summary
Around 30-60 cm of storm snow with strong winds have created widespread loose dry and storm slab avalanche problems. Some of this snow has been re-distributed with strong winds, creating wind slabs on lee features. These slabs overly a layer of weak surface hoar buried mid-February that has produced very easy snowpack test results with sudden fracture characters.
The lower snowpack in this region is weak with two primary concerns:
1) a widespread weak layer from mid-December composed of facets, crusts, and surface hoar that is 100-150 cm deep.
2) a rain crust with sugary facets buried in late-November near the bottom of the snowpack.
Although the snowpack structure is variable across the region, these persistent weak layers are generally widespread.
Weather Forecast
WEDNESDAY: Mostly sunny, moderate westerly winds, alpine temperature near -17 C, freezing level below valley bottom.
THURSDAY: Partly cloudy, light easterly winds, alpine temperature -16 C, freezing level below valley bottom.
FRIDAY: Mostly sunny with increasing cloudiness, light to moderate westerly winds, alpine temperature near -15 C, freezing level below valley bottom.
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Wind slabs formed during last weekend’s storm still linger in lee features. Be cautious of overhead exposure on solar aspects if the sun is shining all day, particularly near rocky cliffs.