The storm is expected to bring strong winds and rapidly rising freezing levels. Expect avalanche danger to increase as the storm develops.
Confidence
Fair - Timing, track, or intensity of incoming weather system is uncertain
Weather Forecast
The storm system is expected to bring 5-10mm of precipitation to the Purcells region on Tuesday. Winds are expected to increase to strong from the SW and freezing levels will climb to around 2000m by Tuesday afternoon. On Wednesday and Thursday, freezing levels should remain around 2000m and winds will remain moderate or strong in the alpine. There is currently some uncertainty regarding precipitation amounts for Wednesday and Thursday with models currently showing another 10-30mm.
Avalanche Summary
Report of an isolated size 1 wind slab triggered by a ski cut in a steep gulley on Sunday.
Snowpack Summary
New snowfall sits on a layer of surface hoar. Another 15-20cm below this you may find a hard rain crust. In the Golden area this crust exists up to around 1600m, whereas in the south it is up to 2000m or higher. In total, last week's storm produced slabs up to 1m thick in the north of the region and around 60cm thick in the south. This slab sits on the mid-November weak layer (surface hoar, facets, and/or a crust). Below this you will likely find a 15-20cm thick layer of sugary facets, which is sitting on a solid rain crust from early November. The reactivity of these layers may be slowly diminishing, but they still warrant cautious consideration. Snowpack tests are getting hard pops and drops results, indicating the potential for large propagation and large avalanches.
Problems
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.
Persistent Slabs
Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.