Turnagain Pass

Because last week’s storm loaded a widespread layer of surface hoar (a persistent weak layer) we are calling this a persistent slab issue and not just a wind slab. The main concern in the advisory area is finding a slope where the snow above the January 21st buried surface hoar is acting like a slab. We are not finding evidence of this below 2500′. Cold temperatures with the inversion have been quickly degrading the snow near and below treeline. Slopes near ridgelines in the Alpine, are where the winds over the weekend affected the snow and changed it from fluffy, low density powder to stiff and consolidated wind crust or slab. There were a couple reports of people intentionally triggering small slabs on wind-loaded slopes Tuesday that failed on the buried surface hoar, one skier triggered and one snowmachine triggered. These are a good reminder that despite the cold and clear weather now slowly faceting away the slabs; there is still the possibility of finding and triggering lingering slabs in leeward terrain today.  Remember that there is surface hoar is lurking underneath the recent snow and it’s important to assess areas affected by wind. Slabs can be deeper in loaded areas. Pay attention to slopes where the snow feels stiff, looks pillowed or sounds hollow and watch for shooting cracks. A small slab in the wrong terrain could have high consequences. The easterly winds have picked up this morning blowing into the teens and 20s. Look for changing conditions today if you see snow getting moved around.

Evidence of a natural wind slab avalanche in Ragged Bowl and wind-affected snow. This was likely triggered during the higher winds around the Girdwood area Sunday into Monday morning. Photo: Mike Ausman

Snow pit from Cornbiscuit yesterday. The January 21st buried surface hoar was easy to find but not reactive in this spot. 

January 21st buried surface hoar preserved under the slab.

As the cold weather continues to loosen and facet the surface snow, loose snow avalanches (sluffs) are becoming larger and faster by the day. Watch out for and manage your sluff in steep terrain features.

Natural loose snow avalanches and skier triggered sluffs on Magnum.

Triggering a deep slab is becoming unlikely, but is still not out of the question above 3000′. In the high elevation snowpack there are a variety of weak layers in the mid pack and near the ground. Because of this poor structure, there is still a chance of triggering a deep slab if you find the wrong spot. The most likely trigger spots are in thin areas in the snow cover, often near rocks, or where the slope rolls over.