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RegisterDec 23rd, 2019–Dec 24th, 2019
South Rockies.
A huge amount of snow and rain has stressed and overloaded weak layers deep in the snowpack. Any additional load, such as a smaller avalanche, cornice failure, or person, can result in large, destructive avalanches.
Monday Night: Mostly cloudy with isolated flurries, trace to 5 cm. Alpine temperature -7 C. Southwest wind, 10-25 km/hr. Freezing level 1200 m.
Tuesday: Mainly cloudy. Alpine temperature -8 C. Southwest wind, 15-30 km/hr. Freezing level valley bottom.
Wednesday: Mix of sun and cloud. Alpine temperature -10 C. West wind, 15-25 km/hr.
Thursday: Mix of sun and cloud. Alpine temperature -6 C, possible inversion. West wind, 15-30 km/hr.
A natural avalanche cycle occurred Saturday with heavy loading from snow/rain and wind Friday night and through the day Saturday.
On Saturday and into Sunday, large storm slab, wet slab and deep persistent avalanches were reported. Explosives triggered storm slab avalanches to size 2 in upper elevations and skiers triggered wet slab avalanches to size 2 at lower elevations. More concerning are reports of both natural and explosives triggered avalanches to size 3 which failed on a deep persistent layer with avalanche crowns 40-200 cm. A complex avalanche problem has developed, read the latest forecaster blog here.
Upwards of 50-100 cm storm snow is settling around the region. At higher elevations into the alpine, wind is impacting loose, dry snow, and building wind slabs and cornices. Up to 1600 m, rain saturated the snowpack.
The bottom half of the snowpack consists of crusts from November and October and facets near the base, these weak layers are the failure plane for recent large (size 2-2.5) deep persistent slab avalanches.
Snowpack depths range between 80-200 cm around treeline and taper rapidly below.