A wet and warm system thrashed the snowpack and dumped wet snow at high elevations. Reactive slabs may lurk on windloaded slopes and steep and convex features in the alpine.
20-50 cm of new snow with strong winds from the southwest formed reactive storm slabs at upper elevations. These will be more sensitive to triggering and larger in size in areas where strong winds have transported the snow into deeper slabs. Give cornices plenty of space as the grew in the storm and may be more reactive than expected.
TUESDAY Night: Isolated flurries, 5 cm / Moderate to light southwest ridgetop wind / alpine low temperature -5 / Freezing level 1100 m
WEDNESDAY: Mostly cloudy / Light southwest ridgetop wind / alpine high temperature -3 / Freezing level 1000 m
THURSDAY: Cloudy / Light southeast ridgetop wind / alpine high temperature -4 / Freezing level 800 m
FRIDAY: Cloudy with sunny breaks / Light southeast ridgetop wind / alpine high temperature -6 / Freezing level 700 m
On Tuesday, storm slab avalanches to size 2 were triggered by explosives, evidence of a natural avalanche cycle to size 2 was also reported.
On Monday afternoon, small size 1 loose and low density slab avalanches failed naturally and with skier traffic as snow began to accumulate and load ridgetops.
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Overnight Monday-Tuesday, rain and warm temperatures produced a moist snowpack up to 2000 m before freezing levels began falling. By Tuesday morning, 20-60 cm new snow accumulated above 1800m and the snow/rain line.
At upper (drier) elevations, layers of wet and dry storm snow are found due to rain reaching mountain tops during the storm. The new snow covers a melt-freeze crust and old wind slabs. A saturated snowpack is found at lower elevations, the snowpack will cool and freeze with falling temperatures.
Snowpack depths change rapidly elevation and exposure to sun and wind, average snowpack depths vary 60-100 cm around treeline to over 150 cm in the alpine.
The mid to lower snowpack contains a series of crusts, the most notable of which is also the deepest, sitting just above the ground at elevations above 1500 m. This crust may have a thin overlying layer of weak faceted grains and/or surface hoar crystals, especially in sheltered areas around treeline. Loading and observations from this storm may provide insight on if these layers will be a concern going forward.
