Strong solar radiation and high freezing levels may elevate hazard and could trigger natural avalanche activity on south facing slopes during the day.
Confidence
Fair - Timing or intensity of solar radiation is uncertain
Weather Forecast
High pressure conditions will remain for Wednesday and Thursday but a pulse of moisture may cross the region late Wednesday. A more organized system is expected for Friday and will likely result in light flurries or rain. Wx models are currently uncertain regarding precipitation amounts and timing for Friday.Wednesday: A mix of sun and cloud, scattered flurries in the evening 0-3cm, freezing level 600-800m overnight, ~2000m afternoon, ridgetop wind 15-30 km/h SWThursday: A mix of sun and cloud, freezing level 800-1200m overnight, ~1700m afternoon, ridgetop wind light SWFriday: Snow or rain 3-10mm, freezing level 1000-1200m overnight, ~2000m afternoon, ridgetop wind 15-30 km/h SW
Avalanche Summary
During the storm on the weekend, we saw widespread natural slab avalanche activity. Most of this activity involved the storm snow itself but there were numerous avalanches which stepped down to the early-March weak layer or possibly even the February weak layer. Now that the storm is over, natural activity is tapering off but large avalanches are still possible. On Monday, we received reports of slab avalanches up to size 2.5, both natural and human-triggered. At lower elevations, loose wet sluffing from steep solar aspects is being reported.
Snowpack Summary
The weekend storm produced 30-50 cm of dense snow with strong southerly ridgetop winds. Freezing levels have been cycling between valley bottom and roughly 1700m, and low elevation terrain saw significant rain on the weekend. Expect to find a crust at or near the surface below treeline. The early March melt-freeze crust is now down roughly 90-150 cm. This layer was found on all aspects at treeline and below, and on all but North aspects in the alpine. The early-Feb weak layer is down over 1.5m and is generally not a concern for human-triggering but avalanches or cornice falls have the potential to trigger it.
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.
Persistent Slabs
Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.
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.