Regions
Kootenay Boundary.
Confidence is poor due to disagreeing weather models, track and timing of the low in Southern Alberta. The region may receive heavier amounts of precipitation than forecast. If this occurs, expect the danger ratings to be elevated.
Confidence
Poor - Timing, track, or intensity of incoming weather is uncertain
Weather Forecast
A low pressure center sitting SW of Montana will continue to move SE, this should be arriving in Southern Alberta by Thursday afternoon. Depending on timing and track, this low is expected to spread moderate amounts of precipitation to the BC interior Wednesday night into Thursday. Ridgetop winds will start light-moderate from the South, switching moderate SW through Thursday. Freezing levels will fall to 1800 m. Some lingering flurries may exist into Friday with freezing levels near 1500 m. The weekend will see a fairly inactive ridge of high pressure dominating the interior, bringing sunny skies and freezing levels up to2500 m. Confidence is poor for Thursday/Friday due to the uncertainty of the lows location in Alberta. This could potentially bring more than anticipated (heavy) precipitation amounts to the regions.
Avalanche Summary
On Tuesday reports indicated widespread snowballing up to 2200 m with some natural loose wet avalanches up to size 1.5. On Monday a skier triggered slab avalanche (size 1.5) was reported. This occurred on a North aspect @1900, running 40 m wide and 80 m in length. Other observations from he field have indicated many loose wet slides from steep solar aspects up to size 2. I suspect loose wet, and wet slab avalanches to become a problem through Thursday. The danger ratings will remain elevated as we get hit by moderate-heavy precipitation on Thurs/Fri.
Snowpack Summary
Spring-like weather has transformed the snowpack significantly in the last 5 days. Melt-freeze conditions have existed, promoting crusts on solar aspects at all elevations. Melt-freeze crusts also exist on all aspects up to 1500 m. Below treeline elevations have seen more of the melt than the freeze, and the upper snowpack has become quite moist. Northerly aspects at upper elevations still host dry, wintery snow. Below the surface, the upper pack seems to be settling quickly with up to 100 cm of snow overlying the March 26th interface. This interface consists of a melt/freeze crust on all aspects except true north in the alpine, where small surface hoar (5mm) is present in sheltered places. This interface is a concern on true south aspects where the crust is thickest and where the surface hoar lurks. The persistent early February surface hoar lingers deep in the snowpack and may re-awaken with forecast skyrocketing freezing levels and mod-heavy precipitation on Thursday. 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.
Wind Slabs
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.