Cool conditions are expected to improve stability this week but tricky conditions may persist on Wednesday, especially at higher elevations. Storm and persistent slabs may still be reactive to human-triggering and very large avalanches are possible.
Summary
Confidence
Fair - Freezing levels are uncertain
Weather Forecast
A ridge of high pressure builds on Wednesday and should result in mainly dry conditions for the next few days. On Wednesday, a mix of sun and cloud is expected with moderate-strong alpine winds from the NW that should ease through the day. Freezing levels are expected to fall well below 1000m Tuesday overnight and then reach around 1500m on Wednesday afternoon. On Thursday and Friday, similar conditions are expected with mainly dry conditions, a mix of sun and cloud, and light alpine winds. Freezing levels are expected to reach 1500m on Thursday afternoon, 1800m on Friday afternoon, and around 500m during each overnight period.
Avalanche Summary
On Monday, several natural size 2-3 avalanches were reported. Details are limited and 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. A natural avalanche cycle size 2-3 was reported on Friday and Saturday. These were slabs up to 100 cm deep at higher elevations and loose wet avalanches at lower elevations. Natural avalanches are generally not expected on Wednesday if there is good overnight recovery but may still be possible in isolated areas. Human-triggered storm slabs and persistent slabs are still a concern, especially on steep, unsupported slopes in the alpine. Stability is generally expected to improve with the cooling trend but this may take a few days and touchy conditions may still exist on Wednesday.
Snowpack Summary
20-40cm of heavy storm snow overlies a thick rain crust that formed last Friday when it rained into the alpine. A new surface crust is expected to be widespread on Wednesday after freezing levels drop Tuesday overnight. On Monday, moist snow was being reported to well over 2000m so the crust will likely extend well into the alpine. In the high alpine, strong winds have redistributed the new snow and wind slabs can be expected in leeward terrain features. Several persistent weak layers exist in the upper 1m of the snowpack and remain a concern. The mid-March crust/facet layer is down around 60cm and remains reactive to light triggers. Down 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
