Unusual persistent slabs continue to produce very large human triggered avalanches. See the latest forecaster blog for a more in depth look at this situation: http://bit.ly/1HHQrK2
Confidence
Fair - Intensity of incoming weather systems is uncertain on Sunday
Weather Forecast
Warm but dry weather is expected to continue for Friday with freezing levels as high as 2600 m, before more organized precipitation arrives in the afternoon. Expect up to 5 cm cm of fresh snow by Saturday morning falling under moderate to strong southwesterly winds with freezing levels back down to 1700 m. Continued light snow flurries and moderate winds are expected Saturday morning before a stronger system brings another 2-5 cm overnight and 5-10 cm throughout the day on Sunday. Freezing levels hovering around 1700 m and moderate to strong southwesterly winds expected during the height of the storm on Sunday.
Avalanche Summary
Over the past week, there have been a number of avalanches to size 2.5 occurring on the mid-March persistent weak layer. Some avalanches have occurred naturally and many have been remote triggered from up to 100m away.
Snowpack Summary
Warm temperatures and light rain have promoted settlement within the most recent recent storm snow, but the region has a very serious persistent slab problem just under the surface. A touchy crust/facet interface known as the mid-March persistent weak layer is down 40 to 120 cm. This persistent weak layer continues to produce sudden test results at upper treeline and alpine elevations, especially in the north of the region. Below this, the snowpack is reported to be generally well-settled and strong.
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.