Purcells

Poor - Due to limited field observations

A warm wet and windy storm is forecast to move into the interior mountain ranges on Saturday afternoon. The storm is tracking down out of the northwest and will affect the Cariboos and North Monashees a little earlier than the South Monashees and Selkirks. The storm is not forecast to push very far to the East, so the Purcells may not see as much snow, or as much wind. Southwest winds early in the storm are forecast to be in the 100-120 km/hr. range. The freezing level should rise early in the storm to about 2000 metres and then fall back to about 700 metres as a trailing cold front follows the storm track. Heavier snowfall, up to 30 cms is expected on Sunday as the colder air meets the moist air. Upslope areas in the Cariboos and West Monashees may see more snow than forecast. Most of the interior should get a few more cms of snow on Monday morning before the storm moves off to the east. The rest of the day Monday should be cooler and drier. On Tuesday the next wave is forecast to move into the interior, but it is a little too early to be very specific about the track or intensity.

Avalanche control in Glacier National Park produced many size 2.0-2.5 slab avalanches on north and south aspects in the alpine. The park also reported many size 1.5-2.5 natural avalanches releasing in the recent storm snow from steep gullies. Earlier in the week we had reports of large avalanches with wide propagations from explosive control work in the Purcells. Today we heard that results were limited in the same area. The snowpack may be a bit less reactive due to cold overnight temperatures. I expect that the new load forecast in the storm combined with warmer temperatures may make things more reactive by Sunday.

There is a lot of variation in this region. There is about 150 cms of snow in the alpine in the north, and only 70-80 cms in the southeast. Shallow areas are more likely to have a weak facetted layer near the ground. The wind has come from various directions during the past week, creating wind-slabs on several aspects. Areas that have a deeper snowpack are more likely to have developed a cohesive slab above a basal weakness. The new storm is likely to add a significant load to the snowpack above any deeply buried weak layers. Wind-slab releases in the alpine may step down and propagate very large avalanches on these deeply buried weak layers.