Persistent slab avalanches continue to be reactive to skier and rider triggers. These are producing large and consequential avalanches. A conservative mindset and patience are required.
Fresh wind slabs may be reactive on northeast and east slopes.
West to 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 are easily triggered by the weight of a person on this interface and have occurred on surprisingly shallow slope angles.
The dominating features associated with this next frontal system will be wind and slight warming. Ridgetop wind is forecast 25-70 km/hr from the southwest through the forecast period. Light snowfall amounts expected.
Monday: Cloudy with light snow 5 cm. Ridgetop wind 30-70 km/hr from the southwest. Alpine temperatures -2 and freezing levels 1300-1700 m.
Tuesday: Cloudy with light snow 3-7 cm. Ridgetop wind 25-65 km/hr from the southwest. Alpine temperatures -3 and freezing levels 1200-1500 m.
Wednesday: Trace of snow and ridgetop wind strong from the southwest. Freezing levels 1300 m.
Almost daily we're receiving reports of skier and rider-triggered persistent slab avalanches from the SoRo and Lizard forecasting regions. These avalanches have been size 2 or larger and have caught people by surprise. 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.
This problem is not healing quickly and the conditions are not easily managed. A conservative mindset and patience are crucial right now.
New wind slabs may exist on East to Northeast aspects on Monday and loose-dry avalanches may spill from steeper terrain features.
Strong west-southwest winds have formed reactive wind slabs on leeward slopes by redistributing some of the recent storm snow that fell Thursday. Solar aspects became moist on Saturday then refroze forming a 1-3mm crust. Up to 50 cm of snow sits above a variety of old interfaces that formed mid-February. These mostly include sugary facets, hard wind pressed surfaces, surface hoar in wind-sheltered locations, and sun crust on steep solar aspects. Another persistent weak layer is found down 60 to 100 cm deep and was buried late-January. This layer consists of similar weak snow crystals mentioned above and continues to be reactive by the weight of a person.
There are presently no deeper concerns.
