As a pocket of above-freezing air re-establishes in the alpine, we may see a renewal of loose wet avalanche activity especially on steep sun exposed slopes at upper elevations. Make observations as you travel and be ready to back off your line if the snow is getting cooked.
Watch for loose wet avalanche activity especially on steep sun exposed slopes in the afternoon. Pinwheeling is a great indicator of a warming snowpack.
A crust sits near the base of the snowpack. Although we haven't had any reports of avalanche activity on this layer during the ongoing warming event, there is potential for large avalanches to be triggered on this layer by:
Friday night: Clear, light southwest wind, strong temperature inversion with above freezing air 2000-3000 m.
Saturday: Sunny, light southwest wind, strong temperature inversion with above freezing air 2000-3500 m.
Sunday: Sunny, light southwest wind, freezing level 800 m.
Monday: Up to 5 cm new snow, light to moderate southwest wind, freezing level 800 m.
Loose wet avalanches up to size 1.5 were reported on steep solar aspects during the warmup on Wednesday. No new avalanches were observed on Thursday.
Our eyes and ears in the mountains are limited this winter due to fewer professional observations. If you go out in the mountains, please share your observations on the Mountain Information Network (MIN). Photos are especially helpful! Thank you so much for all the great MINs submitted so far!
A melt-freeze crust on steep solar aspects at treeline and above will soften through the day. On shadier aspects, alpine surfaces are predominantly wind affected, with soft snow still to be found in at lower elevations. Widespread growth of large surface hoar crystals and surface faceting have been reported. These types of crystals (crust, hoar, facets) that develop on the surface as it sits exposed during prolonged periods of high pressure like this often become a problem once buried by the next snowfall.
A couple of layers of feathery surface hoar crystals exist in the upper snowpack. Just 10 cm below the surface, the first of these layers has likely broken down in areas where the surface warmed up on Wednesday. Another patchier layer of smaller crystals may sit beneath 20-40 cm of old wind slab.
The lower snowpack is characterized by a couple of crusts, the most notable of which is sitting near the base of the snowpack, likely surrounded by a weak layer of sugary facets. It is most likely to be reactive to human triggers on south facing slopes and in shallow, rocky areas in the alpine.
