Keep it simple ! The warm weather and continued precipitation is beginning to subside. Uncertainty is present with the timing of when the snowpack will stabilize. Give the snowpack time to cool and heal before considering moving into challenging and complex terrain
Two concerning persistent weak layers can be found in the snowpack. The first is a surface hoar/crust layer from early December and the second is a surface hoar, facet or crust layer from mid November. These layers are most concerning on sheltered treeline features where surface hoar is most likely to be preserved.
Fresh snow and strong winds has built new and reactive slabs. Expect winds to redistribute snow at treeline and alpine elevations into deeper and more reactive slabs in wind loaded features. Where strong winds are observed slabs could be found further down slope than expected.
Expect slabs to be reactive as they sit over a variety of weak surfaces - facets, a crust and/or surface hoar.
On Tuesday numerous storm slab, wet loose and wet slab avalanches have been reported. These avalanches had been explosives triggered, skier controlled and natural. The sizing of theses avalanches varied, a few small (size 1) with many of them large to very large (size 2 to 3). The reports indicate that the avalanches gained mass as they entrained the moist snow below.
On Monday, explosive avalanche control produced a few avalanches with one very large avalanche (size 3) running up to 800 m in length. It was noted this avalanche stepped down to the the late November persistent weak layer and confirms suspicions that in specific terrain this layer of concern is reactive.
Over a week ago a natural size 2.5 persistent slab avalanche was reported. This avalanche occurred on a northeast aspect, 2000 m on a reloaded bed surface.
Monday's warm and wet weather cycle, has moistened the upper snowpack surface all the way up to 2200 m. During the past storm's precipitation amounts of 70 mm that totaled snowfall amounts of 20 to 30 cm where recorded. This new snow was redistributed by strong southerly winds. Larger deposits in east and north facing terrain can now be found and has formed new wind slabs. Slabs have formed over a variety of surfaces including; facets, surface hoar and a crust, Essentially they are moist and unconsolidated and not bonding very well.
Around 50 cm deep a layer of surface hoar at treeline and a thin crust on steep south facing slopes exists buried in early December.
The primary concern in the snowpack is the mid-November layer consisting of facets and surface hoar, buried around 80 to 120 cm deep. This layer is likely to become reactive as temperatures and the weight of snow and rain increase the load
The lower snowpack presents as primarily facetted combined with depth hoar. Ice has been reported to exist at the base in a few different locations.
The snowpack in the forecast region is quite variable with snowpack depths at treeline varying from 100 cm to 200 cm.
Tuesday Night
Cloudy with light snowfall 5 to 10 cm. Strong southwesterly winds 90 km/h . Freezing levels 1000 m. High temperatures of 1°C.
Wednesday
Cloudy with 5-10 cm of mixed precipitation expected. Moderate southwest wind 40 km/h. Freezing levels 750 m. High temperatures of -1°C.
Thursday
Cloudy with light snow 1 to 3 cm. Moderate southwesterly wind 30 km/h. Freezing levels at valley bottom with a mid day rise excepted to reach 500 m. Alpine temperatures -6°C.
Friday
Cloudy with very light snow trace amounts. Light southwesterly wind. Freezing levels at valley bottom, alpine temperatures dropping to -9°C.
More details can be found in the Mountain Weather Forecast.
