Purcells

Winter is returning to the alpine and with it comes new storm instabilities. Storm slabs may be touchy, especially in wind loaded areas. Buried persistent weak layers remain reactive and still have the potential to produce very large avalanches.

Fair - Timing, track, or intensity of incoming weather system is uncertain

A cold front crosses the interior on Tuesday bringing light precipitation with cooler temperatures. Models are currently showing 5-15mm of precipitation with the highest amounts to the north. Freezing levels are expected to stay high Monday overnight and progressively fall to around 1500m by Tuesday afternoon. Alpine winds are forecast to be moderate-strong from the SW switching to the NW. On Wednesday, a mix of sun and cloud is expected with light flurries. Freezing levels are expected to drop below 1000m Tuesday overnight and reach around 1500m on Wednesday afternoon. Alpine winds are forecast to be moderate from the NW. Similar conditions are expected for Thursday with a mix of sun and cloud, light scattered flurries, and freezing levels around 1500m.

On Sunday, several natural avalanches up to size 2 were reported but no details were provided.  These could be new storm slabs or could be failing on deeper layers resulting in persistent slab avalanches. A couple of small skier-triggered soft slabs were triggered on Saturday, most likely from wind loaded features. On Thursday and Friday, wind and warming were responsible for several natural slab avalanches up to size 3, mainly on east and north aspects above 2100 m. There was also a report of a close call, skier triggered size 2.5 slab avalanche in the Dogtooth range.  Natural avalanches are possible on Tuesday as new snow falls at higher elevations and rain falls down low. Human-triggered storm slabs and persistent slabs are a concern, especially on steep, unsupported slopes. At lower elevations, be cautious of sluffing from steep slopes when it is raining.

10-20cm of recent snow overlies a wet layer or a crust that formed on Friday when it rained into the alpine. This new snow is moist to around 2300m. In the alpine, strong winds have redistributed the new snow and wind slabs can be expected in leeward terrain features. Several persistent weak layers may exist in the upper 1m of the snowpack. The mid-March crust/facet layer is down around 60cm is the biggest concern. Just below this layer is the mid-February crust/facet/surface hoar layer which may also still be reactive in isolated areas. These layers have the potential for wide propagations and very large avalanches remain possible.