After 25 days of no snow in the core advisory area the spell has finally been broken and light snow started falling last night. We received 1-2″ overnight and 4-9″ is forecasted to fall today. This combined with ENE winds gusting up into the 30s may create storm slab conditions on steep slopes as it accumulates on very weak surface snow. The likelihood of triggering a loose snow avalanche (sluff) will also increase with the new snow. An observer in the upper Skookum Valley (which received 5-9″ on Thursday morning in a sneaky storm) reported natural sluffs as this current system moved in. This zone with more new snow warrants extra caution as slabs/sluffs will be larger. Today’s storm will again favor this area.
Today it will be important to pay attention to how the new snow is bonding to old snow surfaces. The snow is landing on near surface facets, surface hoar, sun crusts, and wind crusts. Watch for changing conditions, cracking, collapsing and blowing snow.
Keep in mind these additional concerns if venturing out into the mountains today and remember to practice safe travel techniques.
Wind Slabs: Small fresh wind slabs are also possible near ridgetops on leeward terrain. Old stiff wind slabs, such as the one triggered on Seattle ridge last weekend, will be stubborn to trigger. Smooth pillowed snow on steep unsupported features or in rocky areas will be the most suspect places to initiate an old wind slab.
Glide Avalanches: Glide cracks continue to slowly open above popular terrain on Seattle Ridge and in other zones across the advisory area. These may release at any time. Minimize exposure time spent under visible cracks.
Cornices: Cornices should always be given an extra wide berth if traveling along a corniced ridge. Like glide cracks, minimize your exposure time spent under these backcountry bombs.
Persistent Slabs and Deep Slabs: There are various weak layers in our thin snowpack. Buried surface hoar sits 1-3+’ below the surface and faceted snow sits in the mid and base of the pack. Due to the lack of changing weather over the past three weeks, these weak layers (with varying degrees of strength) are in a ‘dormant stage’. Although unlikely, an avalanche breaking deeper in the pack isn’t completely out of the question in areas such as Johnson Pass, Lynx Creek and on the Northern side of Girdwood Valley (near Crow Pass). Observers continue to find poor structure. The buried weak layers will require monitoring as the load on top increases incrementally or if we get a significant warm-up.
An example of surface conditions in the Girdwood Valley. Near surface facets on sun crust.
Archives 
The Bottom Line
