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.
Summary
Confidence
Fair - Timing, track, or intensity of incoming weather system is uncertain
Weather Forecast
A cold front crosses the interior on Tuesday bringing light precipitation with cooler temperatures. Models are currently showing 5-10mm of precipitation. 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, mainly dry and cloudy conditions are expected with light flurries and possible sunny breaks. 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.
Avalanche Summary
A natural avalanche cycle size 2-3 was reported on Friday and Saturday. These were slabs up to 100 cm deep and loose wet avalanches on all aspects. Observations were limited on Sunday and no new avalanches were reported. On Monday, several avalanches up to size 3 were reported. These may have occurred on Sunday or Monday. One of the size 3 avalanches released down 100cm, most likely on the mid-Feb persistent weak layer. At below-treeline elevations, avalanches are reported to be scrubbing down to ground. 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 major concern, especially on steep, unsupported slopes. At lower elevations, be cautious of sluffing from steep slopes when it is raining.
Snowpack Summary
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 2000m. In the alpine, strong winds have redistributed the new snow and wind slabs can be expected in leeward terrain features. Large cornices may be fragile due to the warm conditions. Several persistent weak layers exist in the upper 1m of the snowpack and remain a serious concern. The mid-March crust/facet layer is down around 60cm and remains reactive to light triggers. Down around 80-100cm is the mid-February crust/facet/surface hoar layer which has also been reactive to heavy loads like avalanches in motion stepping down, cornice failures, or explosives. Both layers have the potential for wide propagations and very large avalanches are possible.
rbuhler,
Avalanche Canada
