The full day of sun following cold stormy conditions is expected to destabilize the recent storm snow. Loose wet sluffing, cornice failures, and solar triggered slab avalanches are all expected. Use extra caution during the heat of the afternoon.
Confidence
Fair - Timing or intensity of solar radiation is uncertain
Weather Forecast
A ridge of high pressure should keep the region mainly dry until Friday night. On Wednesday, mostly sunny conditions are expected with light-moderate alpine winds from the SW. Freezing levels are expected to be around 1000m in the morning and 1700m in the afternoon. On Thursday, a mix of sun and cloud is expected with moderate alpine winds from the W to NW. Freezing levels are forecast to be around 1500m in the morning and climb to around 2000m in the afternoon. Friday looks be similar with mainly sunny conditions, light alpine winds, and freezing levels reaching as high as 2500m. A weak storm system is currently forecast to reach the region Friday night.
Avalanche Summary
On Monday, isolated natural avalanches were reported as well as several skier triggered avalanches. These storm slabs were typically 30-50cm thick and were generally occurring above 2100m elevation. A couple small wet avalanches were reported from lower elevations. Several remotely triggered avalanches have been reported over the last 3 days and were triggered from up to 60m away. These remote triggers as well as reports of whumphing and wide propagations are suggesting that the weak layer below the storm snow is very reactive in some areas. Over the weekend, natural, human-triggered, and explosive-triggered storm slab avalanches up to size 2.5 were ongoing. Towards the southern parts of the region that received less recent snowfall, wind slabs in specific areas have been the primary concern. On Wednesday, lingering storm slabs are expected to be reactive to human-triggering, especially in steep alpine terrain and wind-loaded terrain features. The sun is expected to trigger natural activity on steep solar aspects including both loose wet avalanches and slab avalanches. Cornices will become weak in the afternoon and natural cornice falls have the potential to trigger large slabs.
Snowpack Summary
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. Recent snowfall amounts are highest in the north of the region and taper off to south. 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.