Persistent slabs 60-100 cm thick continue to be reactive to skier and rider triggers. These are producing large and consequential avalanches. A conservative mindset and patience are required.
Wind and more wind! Fresh wind slabs may be reactive on northeast- east slopes on Sunday.
Switching northwest and southwest wind will build fresh and reactive wind slabs. These may be easily triggered by the weight of a skier or rider.
Loose-dry avalanches may be easily triggered from steep terrain features.
Two layers of concern exist and have been reactive over the past couple of days. The upper layer being buried mid-February down 30-50 cm and has recently failed primarily on a sugary facet interface and the deeper layer of concern is found down 60-100 cm. This layer consists of surface hoar, faceted grains, and/or a melt-freeze crust. The layer has been most problematic around treeline elevations and in openings below treeline, but also reaches into the lower alpine. Avalanches have occurred on surprisingly shallow slope angles and the layer can easily be remotely triggered.
The dominating feature associated with this next frontal system will be WIND. Ridgetop wind is forecast 25-70 km/hr from the West through the forecast period. Light snowfall amounts expected.
Sunday: Cloudy with some flurries. Ridgetop wind moderate from the southwest and alpine temperatures near -5. Freezing levels valley bottom and rising to 1500m by the afternoon.
Monday: Cloudy with light snow 5-10 cm. Ridgetop wind moderate to strong from the southwest and alpine temperatures near -3. Freezing levels 1200 m.
Tuesday: Mix of sun and cloud. Ridgetop wind light to moderate from the southwest and alpine temperatures near -5. Freezing levels 1000 m.
On Saturday, a size 2 skier triggered persistent slab avalanche was reported. This was on an East aspect at 2000 m and ran on the late January interface. The person was able to ski out with no injuries.
On Friday, numerous loose-dry avalanches up to size 1.5 were triggered with the use of explosives as well as a storm and wind slab up to size 1.5.
On Thursday, numerous skier-controlled and natural slab avalanches were reported up to size 2. A significant natural explosive triggered persistent slab size 2.5 was initiated from a NE slope at 1700 m. It was 80-100 cm deep and ran 200 m in length. Loose-dry avalanches were reported up to size 1.5 and running fast and far.
On Wednesday in the South Rockies region, this MIN report highlights a critical incident of a rider-triggered persistent slab size 3. Also on Wednesday, this MIN report indicates another remotely-triggered size 2 slab avalanche. Whether it's a wind slab or a persistent slab problem, they're catching folks by surprise and will not heal quickly.
This weekend human triggering of wind, and persistent slabs will remain likely. Conditions are not easily managed right now, warranting a conservative mindset!
Strong west-southwest winds have formed deep and reactive wind slabs on leeward slopes by redistributing some of the recent storm snow that fell Thursday. Up to 50 cm of snow sits above a variety of old interfaces that formed from mid-February's cold drought. These mostly include sugary facets, possible surface hoar in wind-sheltered locations and sun crust on steep solar aspects. Recently, some reports have indicated that this weak interface has failed and caught people by surprise. This MIN report is a good example. A persistent weak layer found around 60 to 100 cm deep that was buried late-January has been prevalent in the region during February. Persistent slab avalanches remain reactive and continue to surprise skiers and riders.
There are presently no deeper concerns.
