Turnagain Pass

A sunny Saturday combined with a new load of snow and recent wind loading is a perfect recipe for a human triggered avalanche. A storm that ended Thursday night dumped around 20+” of cold low-density snow and loaded several weak layers (buried surface hoar and near surface facets.)  Several groups reported “whumpfing” yesterday and one human triggered avalanche occurred in the Alpine of Sunburst where a person breaking trail triggered a soft slab that propagated about 30’ wide without incident. A period of elevated winds (15-50mph) last night has been moving loose snow around and loading leeward features and increasing the strength of the slab. Triggering a storm slab today could be big enough to bury a person, and will depend on the steepness and the size of the terrain you are exposing yourself to. Obvious clues like collapsing and shooting cracks will be evidence the snowpack still needs more time to adjust before venturing into bigger and steeper terrain. Hand pits are a good tool to evaluate the slab and weak layers as you travel. Be aware that you may encounter two types of storm snow problems. 

Wind Slab: Fresh wind slabs formed overnight may be shallow or propagate 2-3’ deep on a widespread layer of buried surface and near surface facets. This problem will be more likely on wind loaded features below ridge lines or in cross loaded gullies. This includes the starting zone of the back bowls of Seattle Ridge and the popular SW facing terrain along on the East side of the road.  Pay attention to places where the snow is becoming stiffer and more supportable and avoid steep wind loaded features and unsupported slopes with the classic wind-pillowed shape.   

Storm Slab: Yesterday’s storm snow was loose and poorly bonded and didn’t want to stick together or act as a slab except where it was more consolidated.  Overnight the slab has settled around 5” at Center Ridge Weather Station. This could be enough cohesion to allow the new snow to act more as a slab, even where the slab is very soft. Triggering a storm slab could run farther and faster than expected, which is the nature of cold snow.   Be aware of other groups of people in the same area and practice safe travel protocols. 

Photo on left by Kathy Still of a small slab triggered Sunburst near 3600′ and a close-up photo by Chad Saetre of the crown (~24″ deep). Your observations are welcomed and apprecated!!!

Note the very large buried surface hoar in a pit at 2700′. This layer was buried with a few inches of snow a few days before the storm is widespread at all elevations. 

Loose snow avalanches ‘sluffing’ is possible on steep terrain features protected from wind. Similar to a storm slab, this dry loose snow could run faster and farther than expected. 

Triggering a deep slab is becoming difficult, but is still possible above 3000′ where a hard slab (3-8 feet thick) is sitting on a variety of weak layers in the mid pack (including buried surface hoar) and old November facets near the ground. The most likely trigger spots are in thin areas in the snow cover, often near rocks, or where the slope rolls over. The Southern end of Turnagain Pass to Johnson Pass is more suspect due to a thinner snowpack where there is a potential for more trigger spots. Remember, this is a ‘low probability, high consequence’ situation. This issue can simply be avoided by sticking to terrain below 3000’ and is secondary to triggering a storm slab avalanche today. Choosing low-consequence terrain in the Alpine is recommended. 

*** There is very little info in the Johnson Pass and Lynx Creek zone. If you’re headed to either of these areas and you observe any signs of instability: recent avalanches, shooting cracks, or whumpfing please send us an observations HERE.