Northwest Mountains

An AVALANCHE WARNING remains in effect.  It fell apart yesterday and winds are increasing today! Natural activity is expected to resume later today and overnight on wind loaded slopes, where slabs are larger and most dangerous.  You can easily trigger an avalanche on almost any aspect or elevation.  Keep it conservative and avoid the runouts of wind-loaded slopes. Be prepared for significant wind chill today.   

An extensive natural avalanche cycle occurred yesterday morning during the heavy snowfall event.  We documented over 145 avalanches that ran yesterday, including numerous remotely triggered avalanches (Ex. Mt. Baldy,  Ex. Kebler Pass).  The large slides on Baldy were triggered from up to half a mile away from the start zone!  While most of our documented avalanches were relatively small (D1-D1.5), larger terrain features and alpine slopes produced slides up to D2 in size.  We have yet to get good views of the higher elevation terrain in the deeper part of our zone, where we expect to see the largest slides, such as the Ruby Range and start zones of Axtell, Schuylkill Ridge, etc.    Also noteworthy: avalanches and signs of instability have been observed on all aspects around the compass.  Unlike some weak layers from earlier this winter, the January weak layer is widespread around the compass, consisting of very weak facets on the northern half of the compass, and faceted crusts on the southern half of the compass.  We've only excluded a couple of octants from the persistent slab distribution rose: south and southwest aspects below treeline in the Southeast Mountains because many of those slopes were too bare to have a continuous weak layer before this week's storm, and south aspects below treeline in the Northwest Mountains because our limited preliminary observations suggest the crusts are a bit stronger on low elevation, steep due south slopes.  Long story short, you should manage for the problem everywhere, unless you are on a slope that already avalanched or has sagebrush still poking out.  The biggest difference between the two zones is the average slab size: slabs are about twice as thick in the Northwest Mountains due to favored snowfall in the past week. Avalanches are equally sensitive to triggers in both zones.    

After a pause in natural activity yesterday afternoon and overnight, natural avalanches are expected to resume today as winds increase.  Significant wind transport is expected this afternoon and tonight, which should coincide with the period of highest danger, likely rising back to HIGH in areas that saw favored snowfall the last few days.  There's over a foot of snow available for transport in many fetches, especially near treeline.   If winds reach effective loading speeds, we'll see dramatic loading onto leeward slopes near and above treeline, with winds potentially mixing down into lower elevations and loading some below treeline slopes as well.  Avoid traveling on or in the runouts of windloaded slopes.