Though avalanche occurrences are becoming less frequent, the possibility of triggering persistent slabs and wind slabs still exists. A cautious approach to backcountry travel is recommended.
Weather Forecast
FRIDAY NIGHT - Mainly cloudy with isolated flurries, up to 5 cm / southwest winds 10-15 km/h / alpine low temperature near -13SATURDAY - Cloudy with sunny periods and isolated flurries, 2-3 cm / northeast winds 10-15 km/h / alpine high temperature near -12SUNDAY - Sunny with cloudy periods and isolated flurries / northeast winds 10-15 km/h / alpine high temperature near -13MONDAY - A mix of sun and cloud / northeast winds, 10-15 km/h / alpine high temperature near -12
Avalanche Summary
On Thursday, there were three reports of human triggered persistent slab avalanches up to size 2. These were on north and northeast aspects at treeline and below treeline, and they failed on a persistent weak layer that was buried in mid January. There were also reports of several size 1 human triggered wind slab avalanches in the alpine and at treeline.On Wednesday, there were numerous reports of human triggered avalanches up to size 2, primarily on east and southeast aspects at all elevations. Four of these were persistent slab avalanches that were triggered remotely (from a distance) by people. They were on east aspects below treeline and failed on a persistent weak layer that was buried mid January. This layer is discussed in more detail in the Snowpack Summary below.Persistent slab avalanche activity on the mid January weak layer has slowed down to some degree but it has not stopped, and they continue to be triggered by humans on a regular basis. These avalanches tend to be large, potentially high consequence events.
Snowpack Summary
Up to 15 cm of new fell on Thursday night and Friday with moderate southwest winds, which has likely formed new wind slabs in lee terrain. This new is sitting on older wind slabs which may exist on all aspects due to previous variable wind directions. These older wind slabs will become more difficult to detect with the new snow on top of them.The new snow brings total recent snowfall amounts to 20-60 cm which overlies a weak layer of surface hoar (feathery crystals) and crust that was buried in early February. As this layer receives more snow on top of it, it may develop into a problem layer.Two additional weak layers of surface hoar have produced large avalanches in the region over the past month. A layer buried at the end of January is around 40 cm deep and a layer buried mid-January is between 50 and 90 cm deep. The mid-January layer may also be associated with a crust on southerly aspects. These layers are most prominent at treeline and below. The remainder of the snowpack is considered generally strong. However, there have been sporadic reports of very large avalanches that have released near the base of the snowpack. Most of these avalanches have been in the high alpine.
Problems
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.
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.