A reactive persistent slab exists and can be easily triggered by a skier or rider. A conservative mindset and patience are required.
Fresh wind slabs may be reactive on east to northeast slopes on Monday.
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 30-60 cm and has recently failed primarily on a sugary facet interface and the deeper layer of concern is found down 50-90 cm and 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 features associated with this next frontal system will be wind and slight warming. Ridgetop wind is forecast 50-90 km/hr from the southwest through the forecast period. Light snowfall amounts expected.
Monday: Cloudy with a trace of snow. Ridgetop wind 55-70 km/hr from the southwest. Alpine temperatures -2 and freezing levels 1300-1700 m.
Tuesday: Mix of sun and cloud with flurries. Ridgetop wind 50-90 km/hr from the southwest. Alpine temperatures -3 and freezing levels 1000-1500 m.
Wednesday: Trace of snow and ridgetop wind 35-60 km/hr from the southwest. Freezing levels 1600 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. 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, especially when the sun is out.
Extreme ridgetop wind from the West has formed reactive wind slabs in exposed terrain at treeline and alpine elevations. Loose-dry surface sluffing may occur from steep terrain features. 30 to 60 cm of snow now sits above sugary faceted snow that formed mid-February. Snowpack testing done on this layer Saturday in the Mear Lake area showed a relatively easy to moderate failure which propagated across the whole column (ECTP 13 down 40 cm). This indicates that the persistent slab can be triggered by the weight of a person and produce a consequential avalanche. This test was on a south-facing slope at treeline.
Deeper in the snowpack (50 to 90 cm deep) is yet another weak layer that was buried at the end of January. This layer consists of surface hoar, faceted grains, and/or a hard melt-freeze crust and continues to be reactive to skier and rider triggers. Check out this MIN report from Ruault Lake area in the western flank of the region.
Weak faceted grains and a decomposing melt-freeze crust can be found near the base of the snowpack.
