Southeast Mountains

The avalanche danger will rise to CONSIDERABLE this afternoon if winds increase as forecast.   Yesterday, a skier narrowly avoided getting caught in a large persistent slab avalanche, and there were numerous remotely triggered avalanches in the Northwest Mountains. It will be easy to trigger similar avalanches today on windloaded terrain features in the Southeast Mountains.  The safest way to enjoy the powder is on slope angles less than 30 degrees or in wind sheltered terrain where recent storm totals are less than 10".   

Although we only received two observations yesterday, they both highlight a flurry of remotely triggered persistent slab avalanches in the Northwest Mountains  (Example A, Example B).   It's unclear whether the few inches of snow that fell yesterday along with continued slab settlement caused the recent snow to become a bit more reactive, or whether yesterday's terrain choices were poking harder at the dragon.  Either way, the warning message is clear:  buried persistent weak layers are alive and well.  Even where the storm snow is very soft, you can remotely trigger avalanches from below and adjacent to steep slopes. This video highlights the newest generation of persistent slabs.  It is also clear that these slabs are in their infancy, and that any further loading will only exacerbate the problem.   Thus my attention with today's weather forecast is focused on heavier snowfall in the Northwest Mountains along with increasing wind speeds this afternoon across our whole forecast area. Winds will be shifting to the northwest for the first time since our storm cycle began.  There is a bounty of soft snow on the surface available for transport; if winds reach transport speeds, expect natural avalanche activity to resume again.  We've raised the danger in the Southeast Mountains to CONSIDERABLE accordingly, and it will stay pegged at CONSIDERABLE in Northwest Mountains.   We've bumped below treeline to CONSIDERABLE in the Northwest Mountains to account for heavier snowfall today and the potential for northwest winds to crossload some lower elevation terrain.  

The avalanche danger is most pronounced in the Northwest Mountains, where storm totals from the past week are notably deeper, and thus the recently formed slabs are larger and more widespread.  Schofield Pass is showing about 2" of Snow Water Equivalent on our January 19th weak layers, which equates to more than 2 feet of snow.  Irwin is at 1.3" SWE, Gothic at 1.2" SWE, Mount Crested Butte is at 0.7" SWE, and Upper Taylor looks to be about 0.8 to 1.0" SWE.  The danger is also more pronounced at higher elevations, where winds have drifted the snow into thicker slabs.  A quick handpit digging down to our January dryspell interface will tell you the expected slab depth of an avalanche that breaks below the recent snow on buried weak layers.  This video describes what those layers looked like and where they exist.  The joker in the deck is the threat of a persistent slab that breaks deeper in the snowpack on weak layers near the ground.  It sounds like the avalanche on Schuylkill Ridge yesterday fit that description, along with this slide that was triggered on Saturday.  There are more than just a couple of these deadly jokers in the deck though: thicker slabs over weak layers near the ground are most common on the easterly quadrant of the compass near and above treeline.  That's where stiffer, thicker slabs remained intact following the dry spell and wind events of early January.  Below treeline, these larger, thicker slabs are isolated.