Considerable ratings reflect conditions in the north of the region. Cooler conditions should slowly improve stability but tricky conditions are still expected up high. Use extra caution on sunny slopes during the afternoon sun.
Confidence
Fair - Due to the number of field observations
Weather Forecast
A ridge of high pressure brings a mix of sun and cloud for Thursday and Friday. Mainly dry conditions are expected with localized convective flurries possible. Freezing levels are forecast to reach around 1600m in the afternoon and drop to around valley bottom overnight. Alpine winds are expected to be light from the NW on Thursday and light from the SW on Friday. On Friday overnight and Saturday, a weak storm system should reach the interior. Light precipitation is expected with freezing levels reaching around 1500m and moderate alpine winds from the SW.
Avalanche Summary
On Tuesday, ski cutting was producing thin wind slabs in the north of the region. On Monday, a cornice triggered a size 2 storm slab was reported at 2600m on a NE aspect. Loose wet sluffing was also reported at lower elevations. Ongoing persistent slab, storm slab, and loose wet avalanches have been occurring since last Friday but this activity has tapered off recently. Natural avalanches are generally not expected on Thursday except possibly on steep sun-exposed slopes in the afternoon. Human-triggered wind slabs and persistent slabs are still a concern, especially on steep, unsupported slopes in the alpine. Stability is generally expected to improve with the cooling trend but this may take a few days at higher elevations and tricky conditions may still exist on Thursday.
Snowpack Summary
The upper snowpack likely contains multiple new crust layers. The most prominent of these new crusts is a thick rain crust down 20-30cm that formed last Friday when it rained into the alpine. Another crust likely exists near the surface but may be buried under 5-10cm of dry snow that fell on Tuesday after the temperatures dropped. These near surface crust layers likely extend well into the alpine. In the high alpine, strong winds have redistributed the new snow and wind slabs can be expected in leeward terrain features. Several persistent weak layers exist in the upper 1m of the snowpack and remain a concern. In the north of the region, the mid-March crust/facet layer is down 40-60cm and remains an isolated concern. Just below this layer is the mid-February crust/facet/surface hoar layer which may also still be reactive in isolated areas. Both layers have the potential for wide propagations and large avalanches are still possible.
Problems
Wind Slabs
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.
Persistent Slabs
Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.