Northwest Mountains

An Avalanche Warning is in effect for the Northwest Mountains.  Strong westerly winds and heavy snowfall are making very dangerous avalanche conditions.  Expect large to very large natural avalanches to run.  Some natural avalanches may run from alpine terrain into below treeline elevations.  It will be very easy for you to trigger a dangerous avalanche on most steep slopes.  Travel in avalanche terrain is not recommended on Thursday.

Northwest Mountains:  An Avalanche Warning is in place for very dangerous avalanche conditions.  Storm totals range from about 10 to 14 inches of relatively dense snow (storm totals are likely deeper at upper elevations and there is a few-hour lag in weather stations reporting this morning).  Snow Water Equivalents have exceeded 1" early this morning with more snow forecasted during the day.  Strong westerly winds have been transporting snow to leeward terrain on the east half of the compass.  This round of snowfall is adding to existing slabs from this past weekend's storm.  There is a reasonable degree of confidence that large to very large avalanches are running naturally on drifted terrain features; some of these avalanches could be failing on deep weak layers near the bottom of the snowpack.  We got a small preview of the potential this past weekend with deep-breaking avalanches on Axtel, Bellview, and Mount Emmons.  When visibility improves after this stormy period ends, I expect to see that more very large avalanches have failed. 

In Sheltered areas, a widespread weak layer exists comprised of surface hoar and facets.  You can check out this video from a week ago describing it before it was buried.  This layer is now buried 2+ feet deep across the Northwest Mountains.  There was relatively little natural avalanche activity after this weekend's storm in wind-protected places, but there has been a handful of human-triggered avalanches on this interface this past week.  Yesterday, observers reported easy-to-trigger avalanches about two feet deep where the slab rests over persistent weak layers.  One backcountry traveler in the Anthracites triggered a slide and was carried into a tree resulting in minor injuries.  There is some uncertainty about a widespread natural avalanche cycle in sheltered terrain, HOWEVER, human-triggered avalanches are very likely with many avalanches big enough to bury and injure you.  The hazard is further increased by very large natural avalanches running from alpine terrain into below treeline areas.

Avoiding avalanche terrain in the Northwest Mountains is the simple travel advice.  Keep tabs of overhead hazards as some natural avalanches may run much longer than you expect and remotely triggered avalanches are on the menu.

Southeast Mountains: With less snowfall in the Southeast Mountains (storm totals might max out around 10 inches with today's additional snow), avalanche hazards are less dire.  You can still encounter dangerous avalanche conditions on drifted slopes.  Strong westerly winds have loaded the east half of the compass and natural avalanche activity is expected.  Avoid leeward terrain features to greatly reduce your risk.  In sheltered areas, the same widespread weak layer exists on west through north through east aspects, but slabs are generally soft and only about a foot thick.  You could still trigger an avalanche where you encounter 12 inches or more of recent snow above weak layers in the upper snowpack.  Look for cracking or collapsing to clue you into unstable conditions in the upper snowpack at below treeline elevations.  There is some risk of triggering a deeper avalanche in sheltered areas where the snowpack is generally less than 4 feet deep for aspects highlighted by the Persistent Slab Rose.   Lower elevation, wind-protected sunny slopes offer lower risk options as weak layers are less common in the upper snowpack, and deep weak layers are insulated by thick crusts that formed a week ago.