Tricky winter conditions exist at higher elevations. Storm slabs overlies a touchy weak layer and are reactive to human-triggering. Use a conservative approach to terrain selection. Avoid steep sun-exposed slopes in the afternoon.
Confidence
Fair - Timing, track, or intensity of incoming weather system is uncertain
Weather Forecast
A weak storm system reaches the interior Monday night. Models are currently showing 5-10mm of precipitation for parts of the region ending Tuesday morning. During the storm pulse, alpine winds are forecast to be moderate-strong from the SW and freezing levels should be between 1000 and 1500m. A ridge of high pressure builds in the wake of the storm and a mix of sun and cloud is expected for Tuesday afternoon. Alpine winds are expected to shift to the NW and remain moderate. On Wednesday, a mix of sun and cloud is expected with light-moderate SW winds in the alpine. Freezing levels are forecast to be around 1000m in the morning and around 1800m in the afternoon. Another storm pulse is expected to reach the interior on Wednesday night and should bring more light precipitation for Thursday.
Avalanche Summary
No new avalanches have been reported in the Cariboos but this is mainly due to a lack of observers. On Sunday in the North Columbia region where conditions are expected to be similar, natural storm slab activity was reported up to size 2.5 and several remotely triggered avalanches were reported with the furthest being triggered from 200m away. This suggests that the weak layer below the storm slab is very reactive in some areas. On Tuesday, lingering storm slabs are expected to be reactive to human-triggering, especially in steep alpine terrain and wind-loaded terrain features. If the sun is out in the afternoon, natural avalanche activity is expected and extra caution should be given to steep sun-exposed slopes.
Snowpack Summary
Recent observations have been limited and some of this discussion is extrapolated from the North Columbia region where conditions are expected to be similar. Around 30-40cm of recent snowfall overlies a weak layer that was buried on Friday. This weak layer typically consists of surface hoar and facets overlying a melt-freeze crust that exists everywhere except high elevation north-facing terrain. In exposed alpine terrain, strong SW winds have redistributed the recent storm snow forming thicker wind slabs in leeward features. Large cornices exist in the alpine and may become weak with daytime warming. There are three dormant persistent weak layers that we are continuing to track. The late-March crust is down 50-70cm and was reactive last week during the warm period. The mid-March and mid-February layers are typically down between 70 and 100cm and have been dormant for several weeks. These layers have the potential to wake up with sustained warming, a significant rain event, and/or a big cornice fall.
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.
Cornices
Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.
Loose Wet
Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.