Confidence
Fair - Freezing levels are uncertain on Tuesday
Weather Forecast
A ridge of high pressure intensifies over the region through the forecast period culminating with a significant warm up on Tuesday. Sun interrupted by periods of convective snow flurries continue for Sunday & Monday. Sunday: Freezing level starts near the surface, climbs to around 2000 m and then returns to the surface overnight. Ridge top winds light out of the north, winds quickly diminish at lower elevations. Monday: Upper level flow switches from northerly to a more mild southerly in the AM setting the stage for a very warm Tuesday. Freezing levels start near the surface, climb to around 2000m and then return again to the surface; the classic spring diurnal temperature swing. Winds should be light to moderate with an easterly component at lower elevations, switching to a light southerly at ridge top. Tuesday: Looks to offer the most significant warm up the region has seen yet this spring. Freezing levels start near the surface and then climb to 3000 m. Winds should be light southerly at all elevations.
Avalanche Summary
Control work in the region produced avalanches to size 3 on N through E aspects in the Dogtooth Range Friday. Natural avalanches were observed in the central & southern portions of the region on both shady and sunny slopes at upper elevations to size 3. In two separate instances cornice fall triggered large avalanches on NE facing slopes in the alpine, something that I suspect will continue through the holiday weekend.
Snowpack Summary
Mild temperatures and intermittent solar radiation between breaks in convective snow flurries continue to settle out Wednesdays storm snow. Wednesday's system produced around 40 cm of new snow in the north & 25 cm in the south. The recent storms have added up to about a 125 cm of snow which rests on the March 27th interface. This layer displays itself as 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. Operators are still reporting moderate shears on this interface. Cornices are reported to be very large and exist on most ridge lines. The mid-pack is well settled and strong. There is a weak layer of facets or depth hoar in shallower snowpack areas that may fail with initial warming of the snowpack. There is also a weak layer of of facets or depth hoar above a crust at higher elevations where there was already snow in October.
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.
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.
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.