If the sun comes out on Thursday afternoon, use extra caution on steep sun-exposed slopes. The recent storm slab is expected to remain reactive to human-triggering and extra caution is required in the alpine.
Confidence
Poor - Due to the number of field observations
Weather Forecast
On Thursday morning, light precipitation spills into the region from a storm system on the north coast. Forecasts are currently showing 2-4mm for most of the region but higher amounts are possible in the north of the region. Alpine winds are forecast to be moderate-strong from the SW to W. Freezing levels are expected to be around 1000m in the morning and around 2000m in the afternoon. There is a possibility of sun breaking through in the afternoon. On Friday, mostly cloudy conditions are expected with alpine winds progressively increasing to moderate-strong from the SW. Overnight freezing levels will depend on the amount of cloud cover and by Friday afternoon freezing levels should be around 2500m. On Friday afternoon or evening, a weak frontal system is forecast to reach the region. Models are currently showing 1-3mm of precipitation. By Saturday morning, the system should have passed and mostly sunny conditions are expected by Saturday afternoon. Freezing levels are expected to stay high for the weekend.
Avalanche Summary
On Tuesday, natural storm slabs up to size 2.5 were reported around Blue River and Valemont. These slabs had depths from 20-80cm. Ski cuts triggered a couple size 2 wind slabs with 20cm thickness. A remotely triggered avalanche was triggered from 10m away. Remote triggering suggests the weak layer below the storm snow has been very reactive in some areas. On Monday, a natural cornice release triggered a size 1.5 slab avalanche on the slope below. Solar triggered slab avalanches, cornice releases, and loose wet sluffing are all expected to have occurred on Wednesday. With overcast conditions expected on Thursday and a new surface crust expected to form Wednesday night, stability should begin to improve. Human-triggering remains a major concern at higher elevations, especially north facing terrain where the storm slab is unaffected by the sun on Wednesday.
Snowpack Summary
Recent obs have been limited and some of this discussion is extrapolated from the North Columbia region where conditions are expected to be similar. The sun on Wednesday is expected to have melted the snow surface at lower elevations and on sun-exposed slopes into the alpine. A new surface crust is expected form as temperatures drop overnight. 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-Mar and mid-Feb 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.