Northwest Mountains

Dangerous avalanche conditions have developed as 24hr snow totals have stacked up. Storm slab avalanches are going to become reactive to human triggers like flipping on a light switch as they are building on a weak old snow surface. In some terrain that switch has already flipped, and in other areas that avalanche problem is just waiting for a little more snow to accumulate. Either way, you don't want to be in the wrong terrain when you find out how reactive this avalanche problem is. Start your day with lower consequence terrain and small test slopes, while further planning to set a limit on how aggressive you plan to get with your terrain selection. 

On Tuesday we are in a lull between storms before the avalanche danger continues to ramp up this afternoon and through Wednesday. This is our 3rd atmospheric river event this month and avalanche conditions are going to develop differently than during the previous two storms. During this round, the storm snow is accumulating on a weak old snow surface. More like what we would see in December for example. Given the low density of the current storm snow, you may observe more sluffing than slab activity in lower-elevation wind-sheltered terrain. However, at some point, the light switch will flip and storm slabs will become reactive on that old snow surface. That switch will get flipped at different times across the forecast area and you don't want to get caught in the wrong terrain when that happens. 

Accumulating snow starts picking up around mid-day or this afternoon. Avalanche conditions will continue to change during that time and the avalanche danger will continue to rise. On Wednesday, an extreme wind event combines with high precipitation rates, and the avalanche danger is expected to rise to HIGH (4 of 5).

It's been a rough weekend for our backcountry community. Persistent slab issues have caught numerous groups by surprise this week in the Elk Mountains, and unfortunately, two of the accidents resulted in fatal outcomes. One accident was near Marble and the other near Aspen Highlands.  In the deeper zone, the issues appear to be tied to a near-crust faceted layer at the base of our two recent storms (March 10th interface), about 2 to 3 feet deep on average.  Our forecast team checked out the impressive crown on Mt. Baldy,  which was notably thicker due to extensive wind drifting.  This issue has been particularly challenging to forecast for because the layer was not obvious on the snow surface prior to its burial, so we don't have a clear map of its distribution.  Furthermore, it has provided very limited feedback in the way of collapses or unstable pit results.  Our best tool right now for plotting the problem is observing avalanche activity patterns, which have been most common on east-to-south aspects.  With significant loading over the next few days, we are in a stepping-back mindset, with more uncertainty on where and when this problem will act up again.  In our shallower zone, we are painting a broader distribution because we are also concerned about issues on northerly terrain where the snowpack is shallow and/or variable in depth.  Sunday's accident in Maroon Bowl is a good example of that.