The snowpack doesn't respond well to rapid change. The impact of the afternoon sun and warm temperatures could bump up the avalanche danger to HIGH. Watch for signs of instability and be conservative with your terrain selection.
A sharp rise in temperature coupled with solar radiation on will promote rapid settlement and accelerated slab development in the recent storm snow. Be especially cautious where new snow may sit over a crust (south aspects) or surface hoar (wind sheltered areas around treeline).
A rapidly warming snow surface may release loose wet avalanches. Pinwheeling is a good indicator of this type of instability.
In the north of the region (e.g., Duffey Lake), a weak layer of sugary faceted grains around a hard melt-freeze crust sits near the base of the snowpack. Avoid slopes with overhead hazards like cornices. If they fail during the warm-up they could trigger the slope below.
This problem does not exist in the south of the region.
Wednesday: Sunny with some cloudy periods. Ridgetop winds 15-25/h km from the south and alpine temperatures + 8 degrees. Freezing levels 3500 m.
Thursday: A mix of sun and cloud. Ridgetop winds 10-20 km/hr from the southwest and alpine temperatures near + 4 degrees. Freezing levels 3000 m.
Friday: A mix of sun and cloud. Ridgetop winds 15-30 km/hr from the southwest and alpine temperatures + 5 degrees. Freezing levels 3000 m.
On Tuesday, a large size 3 natural avalanche was observed on a NE aspect at 2400 m. It was reported as a cornice failure triggering the slope below and appeared to have slid on the early November crust near the base of the snowpack.
On Wednesday, we may see more of these deeper releases with the warm up as well as smaller natural avalanches becoming especially reactive where recent snow sits over a crust or surface hoar. Loose wet avalanches are also likely.
Our eyes and ears in the mountains are limited at this time of year and may continue this winter due to fewer professional observations. If you see anything (or don't) while out in the field, please consider sharing via the Mountain Information Network (MIN). Photos are especially helpful! Thank you so much for all the great MINs submitted so far!
10-20 cm of recent snow has been wind loaded into lee features in exposed areas at upper elevations and may sit over a thin melt-freeze crust on south aspects and possibly surface hoar in wind-sheltered areas around treeline. Forecast sun and rising freezing levels into the alpine will have the greatest impact on the upper snowpack, showing signs of instability.
The lower snowpack is characterized by a few crusts formed during warm periods over the last month.
