Northwest Mountains

The Northwest Mountains are just two days out from an impressive loading event and subsequent natural avalanche cycle.  Yesterday, forecasters remotely triggered two avalanches on below treeline slopes.  The natural avalanche period has largely passed but many places are ripe for dangerous, human-triggered slides.  You can greatly reduce your chances of triggering a deadly avalanche by recreating on slopes less than 30 degrees that are not underneath or connected to steeper terrain.

NW Mountains Discussion

The NW Mountains bare the scars of an impressive natural avalanche cycle from this past weekend.  Take a look through the observations page to see it for yourself.  The weak layer from the January dry spell has now been buried by slabs 18 - 24" thick in sheltered areas with significantly deeper slabs on drifted leeward features that are best measured in feet.  The current Persistent Slab avalanche size is big and scary.  Two days have passed since the loading period, but the snowpack is still adjusting to the new burden; this means that natural avalanches are not expected, but human-triggered avalanches remain in the likely range.  Check out this forecaster observation and related video from the Elk Creek drainage up Kebler Pass for clear evidence that below treeline slopes are still very much suspect and the clear need to manage terrain for remotely triggered avalanches.  Big alpine terrain, where the most snow fell, offers the potential for widely propagating and deeply breaking avalanches.  With remotely triggered avalanches on the table, wandering around in basins with lots of overhead hazards could be a recipe for disaster.  Continue to use cautious route-finding and conservative decision-making to hedge your bets against triggering a deadly avalanche in the Northwest Mountains.  Place a big margin between your group and potentially dangerous slopes to prevent being surprised by a larger than expected avalanche.  Now is the time to remain vigilant about your terrain use.

SE Mountains Discussion

We haven't observed any natural persistent slabs in the Southeast Mountains (yet) from this event.  I expect a few ran on Saturday from windloading.  The Southeast mountains missed out on Saturday's bounty of snowfall (they picked up 1" to 3" from the recent storm), so persistent slab problems remain localized to wind drifted terrain, mostly near and above treeline.  The distribution rose reflects the slopes where you are most likely to find well-developed slabs over weak layers in the middle and bottom of the snowpack.  The likelihood of triggering a persistent slab is lower, and the expected size is smaller, thus the danger is lower in the Southeast Mountains.  If you're riding in the alpine and find a slope with deep and attractive snow coverage, it is probably suspect.  Below treeline, reactive persistent slab structures are rare - slabs haven't developed in most of the terrain.  Below treeline exceptions are most likely to be found where winds have drifted snow or where there are thin crusts below this week's snow to help communicate failures across slopes.