Warming and solar radiation will drive the avalanche danger in the coming days. Watch for conditions that change throughout the day, and be cautious of overhead hazards. This is our final forecast for the season and will expire Wednesday April 25.
Confidence
Moderate - Due to the number of field observations
Weather Forecast
A ridge of high pressure will develop for the forecast period bringing sunny skies and light ridgetop winds. The freezing level is expected to rise to about 3200-3600m for Tuesday, Wednesday and Thursday.
Avalanche Summary
On Sunday explosives control produced cornice releases size 2-2.5. On Saturday explosives control produced numerous wind slab avalanches mainly in the size 1.5 range in lee alpine and treeline terrain. Loose wet avalanches and cornice falls are expected to become problematic with warming and solar radiation forecast for this week. Warming also has the potential to wake-up the late March crust interface with the possibility of surprisingly large and destructive avalanches.
Snowpack Summary
New snow and wind on the weekend formed fresh wind slabs in upper elevation lee terrain. The new snow overlies settled storm snow on shaded aspects above 2000m and a melt-freeze crust in most other areas.A weak layer consisting of surface hoar, facets, and/or a melt-freeze crust from late March is now buried about 60 to 140 cm below the surface. This layer is spotty in its distribution and has recently produced large and destructive avalanches. It is most likely to be problematic on west, north, and east aspects between 1900 m and 2250 m. I'd continue to treat this layer very cautiously and would anticipate increase reactivity at this interface with warming forecast for the next few days.The mid and lower snowpack are well-settled and strong.
Problems
Loose Wet
Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.
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.