Avalanche Forecast

Fair - Timing or intensity of solar radiation is uncertain on Friday

A low pressure center sitting over Southern Monatana is moving North into Southern Alberta. It should remain stationary through to Friday. This low will continue to spread light- moderate amounts of precipitation to the region. Friday and Saturday the region will see a mix of sunny and cloudy skies. Solar radiation will be intense when the sun pokes through. Friday-Sunday freezing levels will rise to 2000 m during the day, then dropping to 1300 m at night. Ridgetop winds will be light-moderate from the West through the forecast period.

On Wednesday, explosive avalanche control produced numerous avalanches on SE-SW slopes up to 2200 m. Loose wet, and wet slabs ran to size 3. Most crown depths were 60-80 cm deep, entraining mass, and scrubbing to ground in many areas. Large natural triggers like cornice fall, rain, and solar induced avalanches may be able to duplicate these types of avalanches. 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.

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. With forecast snow, small wind slabs may be building at higher elevations. These may be found hiding behind terrain features, or in the immediate lee of ridgecrests. 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 mid February surface hoar layer is buried deep in the pack; this is a low probability high consequence scenario and may take a significant event to be triggered from a specific location. Concern remains with heavy triggers (cornice), step down avalanches and rapid loading from intense precipitation, strong winds or sun.