Regions
Kootenay Boundary.
Freezing levels are expected to rise to 3000 m for the next two days. Treeline temperatures steady near +6 accompanied by intense solar radiation and limited re-freeze. Expect danger ratings to remain elevated through the forecast period.
Confidence
Fair - Intensity of incoming weather is uncertain on Thursday
Weather Forecast
The beautiful weather we've been seeing over the past few days will start to change as a dominating upper ridge begins to break down, and turn to a warm Southerly flow. A series of systems caught in this flow will affect the region through to Friday. Tuesday: Continued sunny, cloudless skies with light ridgetop winds from the SW. Freezing levels could reach 3000 m. A temperature inversion may redevelop bringing warmer alpine temperatures through the night. Treeline temperatures steady near +6 C. Wednesday: A mix of sun and cloud with possible afternoon rain showers. Treeline temperatures near +10, with freezing levels 3000 m. Thursday: Possible 30-40 mm of precipitation (mix rain and snow) through the day, with freezing levels falling to 1500 m. Ridgetop winds moderate from the West.
Avalanche Summary
On Sunday one skier triggered slab avalanche was reported. This occurred on a North aspect @1950, running 40 m wide and 100 m in length. Other observations from he field have indicated many loose wet slides from steep solar aspects up to size 2. Last week's storm snow is now fairly well settled which has scaled avalanche activity way back. The only avalanche activity reported Saturday was from a high elevation NW facing slope that failed naturally producing a size 2.5 avalanche.
Snowpack Summary
Mild temperatures and spring-like conditions continue to drive rapid settlement of last week's storm snow. A sun crust exists on solar aspects, while Northerly slopes host dry, wintery conditions down to 1400 m. Below the surface, the upper pack seems to be settling quickly. This includes an average of 100 cm overlying the March 26th interface .The March 26 interface consists of a melt/freeze crust on all aspects except true north treeline and alpine, where small surface hoar (5mm) is present in sheltered places. The bond at this interface is gaining strength, with lingering concerns on true south aspects where the crust is thickest and where the surface hoar lurks. The snow at lower elevations has become moist and heavy during the warm sunny days, then re-freezing at night creating true spring like conditions. The persistent early February surface hoar lingers deep in the snowpack and may once again become a player mid-week when the region goes several days without a good overnight refreeze or recovery. Concern remains with heavy triggers (cornice), step down avalanches and rapid loading from intense precipitation, strong winds or sun.
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.
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.
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.