Danger ratings reflect conditions in the northern half of the region. Storm slabs overlie a touchy weak layer and are reactive to human-triggering. Use a conservative approach to terrain selection. Avoid 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 northern parts of the region ending Tuesday afternoon. During the storm pulse, alpine winds are forecast to be moderate from the SW switching to NW and freezing levels should be between 1000 and 1500m. A ridge of high pressure builds in the wake of the storm and the sun may break though on Tuesday afternoon. On Wednesday, mostly sunny conditions are expected with light SW to W winds in the alpine. Freezing levels are forecast to be around 1000m in the morning and 2000m in the afternoon. Thursday is expected to be unsettled with a mix of sun and cloud, and the possibility of scattered flurries.
Avalanche Summary
On Sunday, skiers and explosives triggered storm slabs up to size 2.5. Typical slab depths were 40-60cm but slabs up to 80cm were reported in wind loaded areas. Multiple remotely triggered avalanches were reported with the furthest being triggered from 100m away. This suggests that the weak layer below the storm slab is very reactive in some areas. On Saturday, isolated natural avalanche activity was reported up to size 2 in the north of the region and skiers triggered avalanches up to size 1.5. 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
In the north of the region, 20-60cm 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.