Northwest Mountains

An AVALANCHE WARNING is in effect.  The storm has ended, but very dangerous conditions persist.  Large natural avalanches are possible on slopes with active wind loading from northwest winds.  It will be very easy for you to trigger a dangerous avalanche.  Avalanches can be remotely triggered from below or adjacent slopes.  Travel in or below avalanche terrain is not recommended. 

Snowfall ended yesterday evening and skis began to clear but very dangerous conditions continue.  HIGH danger does not commonly last beyond loading events but each storm cycle and slab/weak layer is unique.  A significant decrease in natural avalanche activity is expected on Tuesday, but gusty northwest winds will continue to load some leeward terrain leaving open the possibility for very large natural avalanches at upper elevations.  Human-triggered avalanches could be very likely in sheltered areas making it easy for you to trigger a dangerous avalanche.  These two factors create very dangerous avalanche conditions even though the sunny skies may try to persuade you otherwise.

Our friends at Irwin Guides and CBMR shared data yesterday evening about the recent stormy period that helps illustrate the size of the recently formed slabs.  CBMR patrol recorded 42" (3.75" SWE) between 1/10 - 1/15 with 29 inches in the past 48 hours.  Irwin Guides cat-skiing tenure recorded a staggering 83" (6" SWE) of snow between 1/5 - 1/15.  Those numbers are hard to ignore.  To be clear, slabs are not historic in size, but plenty large to bury and hurt you on many slopes.  Slabs have gained enough strength to propagate widely across the landscape with this avalanche from Schuylkill Ridge illustrating the point well.

Persistent weak layers exist beneath this pile of recent storm snow on all aspects and elevation due to a cold, dry period in late December and early January.  Persistent Slab avalanche problems are notoriously tricky and behave in unpredictable ways.  The best way to deal with the current conditions is to select low-angled terrain not directly below steep slopes.  Consider the possibility of remote triggering slopes from a great distance.

Clear skies today will allow observers to make better sense of recent avalanche activity as we have been largely in the 'dark' for a week.  Documented avalanches in the Observations tab are skewed towards small terrain features below treeline due to poor visibility thus documented avalanches size have been on the small side even though we fully expect there were many more large avalanches yet to be observed.