Turnagain Pass

New snow and wind have combined to create very unstable slabs, 2-3’ thick. 6-12″ of snow fell in the last 24 hrs adding to the previous storm totals. Ridgetop winds from the East (SE to NE) picked up yesterday into the 30s and 40s mph and continued with several gusts in the 70s overnight at Sunburst weather station. Sustained winds are forecasted to continue today. Fresh cornices could fall and wind slabs will be found in leeward terrain. Rain started falling at lower elevations and rain/snow line is expected to rise to 2000′ today. An additional 6” of snow is forecasted for the higher elevations today.  Slabs will likely release naturally in steep terrain and could step down into older layers in some locations. Natural avalanches could run the full length of a slope, thus it will be extra important to avoid being near any runout zones today. Human triggered avalanches are likely.  An observer yesterday reported very touchy conditions in the Tincan trees. Storm slabs in areas protected from the wind continue to be a concern. Remember that prior to the storm starting Tuesday, the snow surface was surface hoar and/or near surface facets or a sun crust, not layers that new snow bonds well with. This is not a complicated situation.  Avoidance of avalanche terrain is the only way to “manage” the avalanche hazard today. 

New snow in Summit Lake not bonding to the surface hoar buried below.  Remember the Turnagain Advisory area has 2-3′ of snow on this same set-up. Photo: Conrad Chapman

 Turnagain motorized lot yesterday, Poor visibility due to snowfall and sustained winds. Photo: Conrad Chapman

Rain falling on snow to 2,000’ will weaken the surface snow and possibly an older layer beneath. Temperatures are forecasted to rise to 40F at lower elevations today. Wet loose avalanches are likely and wet slab avalanches are possible due to a layer of buried surface hoar and/or near surface facets 2-3’ below the surface. In channeled terrain an avalanche from above will likely entrain weak snow in the lower elevations increasing overall volume. Triggering a wet avalanche in the lower elevations could have high consequences if pushed into or over terrain traps such as cliffs, gullies, or trees. Again it will be important to avoid steep terrain and maintain a conservative distance from all runout zones.  

Don’t forget that our snowpack harbors several old layers of weak snow. Avalanches releasing in the storm snow have the potential to ‘step down’ into these layers. Furthermore, as the new snow piles up and begins to stick to the old snow surface, avalanches breaking into them is possible as the load increases. Both of these situations can create a much larger avalanche – something to keep in mind as the storm cycle continues into the weekend.