Sunny skies and freezing levels as high as 3500 m are continued on Wednesday. As the snowpack deteriorates, natural avalanche activity is to be expected. Solar induced wet slabs may be large and run full path.
Confidence
Fair - Timing or intensity of solar radiation is uncertain
Weather Forecast
The weather pattern will begin to change tonight as a dominating ridge of high pressure will start to break down. This will allow a strengthening, moist SW flow to enter the region. Wednesday: Freezing levels will continue to be near 3200 m, with sunny skies and light Southerly winds. Thursday: Light precipitation should begin later Wednesday night, while Thursday will bring moderate amounts. Freezing levels will fall 1500 m. Ridgetop winds will be light gusting moderate from the SW. Friday: Lingering, light precipitation in the morning. Freezing levels will rise to 2000 m, with possible sunny skies in the afternoon.
Avalanche Summary
On Monday, numerous natural slab avalanches up to size 2 were reported. These occurred on solar aspects out of steep rocky terrain. On Sunday a natural cornice fall triggered a large size 3.5 avalanche. This occurred on a North aspect at 2800 m. The width of the avalanche was 100 m, running 1100 m in length. This ran on facets to ground. This may be an indicator of more to come; especially with an increase of solar radiation and high freezing levels. One other natural cornice fall triggered a size 1.5 on the slope below. This cornice chunk triggered the March 27th layer on an East aspect around 2700 m.
Snowpack Summary
Mild temperatures and solar radiation have settled out much of the upper snowpack. Spring-like conditions prevail, with surface crusts on solar aspects and melt- freeze conditions on all aspects below 1700 m. Over the next day the region will see less of a re-freeze, and higher freezing levels promoting moist snow throughout. Up to 120 cm sits on the March 27th interface. This interface consists of a sun crust on southerly aspects and a temperature crust on more northerly slopes. A thin layer of facets and or surface hoar can be found on this crust on all aspects. Be aware of avalanches running on this layer over the next few days. There is also a weak layer of facets or depth hoar in shallower snowpack areas that is suspect once the region starts seeing warm days without overnight refreeze. Cornices are reported to be very large and exist on most ridge lines. These will become weak under the direct solar influence and warming. I would stay very clear of cornices from above and below. The mid-pack is well settled and strong.
Problems
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.
Wet Slabs
Wet Slab avalanches are the release of a cohesive layer of snow (a slab) that is generally moist or wet when the flow of liquid water weakens the bond between the slab and the surface below (snow or ground). They often occur during prolonged warming events and/or rain-on-snow events. Wet Slabs can be very unpredictable and destructive.
Deep Persistent Slabs
Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.