Don't let the post storm pockets of sunshine lure you into complex avalanche terrain. A reactive persistent slab exists and may be easily triggered by a skier or rider. A conservative mindset and patience is required.
Switching northwest and southwest wind will build fresh and reactive wind slabs. As the natural avalanche activity tapers off, these slabs may continue to be primed for skier and rider triggering. The slabs could be 20 to 50 cm thick, depending on how much snow fell in your riding area.
Loose-dry avalanches may be easily triggered, especially if the sun pokes out.
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.
Saturday: A mix of sun and cloud. Ridgetop wind moderate from the southwest. Alpine temperatures near -8 and freezing levels valley bottom.
Sunday: Cloudy with light snow 5 cm. Ridgetop wind moderate to strong from the southwest. Alpine temperatures near -7 and freezing levels valley bottom.
Monday: Light snow 5-10 cm with gusty strong ridgetop wind. Alpine temperatures near -3 and freezing levels 1300m.
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.
Earlier this week (Monday-Wednesday) Many large size 2 to 3 slab avalanches were triggered naturally, by skiers, and using explosives. The slabs were generally 30 to 70 cm thick, most often at treeline and alpine elevations, and occurred on all aspects but many of them on north to east aspects.
This weekend human triggering of wind, and persistent slabs will remain likely. Conditions are not easily managed right now, warranting a conservative mindset!
Up to 30 cm of new snow fell Thursday accompanied by strong ridgetop wind forming new reactive storm and wind slabs. This brings up to 50 cm of snow over 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 almost daily. Avoidance of consequential slopes is the best way to ensure a safe day right now.
There are presently no deeper concerns.
