The Crested Butte Avalanche Center is now open for the 2012-2013 season! While the first year the CBAC was in operation was 2001, this is our 10^thanniversary of becoming “officially” incorporated as a non-profit entity.  Since we opened ten years ago the CBAC had grown into a professional forecasting office with a staff of 4 forecasters and a board of directors of 10 local professionals and backcountry enthusiasts with diverse backgrounds. New this year we will be introducing CBAC Ambassadors who will be the extended face of the CBAC out in the backcountry and here in town as well.

Look for the CBAC to be making some changes to our website product this year. The avalanche forecasting community is making a move to become more consistent with what the avalanche danger means and how to determine what the avalanche problem of the day is. Once the main avalanche problem is determined, it is a bit easier to figure out how to manage the risk for that particular day. Not all avalanche problems are created equal, and not all problems should be dealt with in the same way. Hopefully our new format will make it more evident to backcountry users as to what their considerations for the day should be. Of course we will still have days when our complex snowpack dictates that there is more than just one avalanche problem out there!

While things are slow to get rolling with snowfall in the backcountry so far this year it is important to remember that if there is enough snow to play in, there is also enough to create an avalanche.  While the current avalanche danger is limited to specific areas (where there is actually accumulated snow!) we have already seen some large and impressive slides earlier this month. In your quest to get your season on track, remember to take the time to pay attention to the snowpack. Not just for today’s avalanche conditions, but for what might evolve for the rest of the season. When we get early season snow, and then long dry periods, the snow tends to “rot” or facet. This faceted snow will create a weak layer near the ground, which will be the supporting snow layer for additional snows to (hopefully) come. With a weak supporting structure we can expect to have an active avalanche season! The good news is that with a lot of bare ground showing out there right now, there is no weak base structure yet in some areas. These might be the best places to play in the coming winter.

With not much quality skiing or riding out there just yet, this is a great time to brush up on your avalanche knowledge. The CBAC, in conjunction with Crested Butte Mountain Guides and the Alpineer will be hosting a “Beacon Brush Up” day on Saturday December 1^st. Come on out from 11-3 in the Town Park to learn or practice your beacon skills, demo new avalanche beacons and airbags and get tips from the pros. The Alpineer will host a gathering afterwards from 3-6pm with food and beer as well as special discounts on avalanche gear.

For more information on avalanche danger ratings or avalanche problems, to get the daily avalanche bulletin in the Crested Butte area, to submit your backcountry observations, or to become a sponsor of the Crested Butte Avalanche Center, check out our website www.cbavalanchecenter.org.

Figure 1

First off, let’s get some defintions out there: According to SWAG, avalanche danger, or avalanche hazard, is defined as “the potential for an avalanche to cause damage to something of value [people or property].” A leading authority on avalanche forecasting describes an avalanche danger rating as “a ranking of avalanche danger for a period of time over a specific region.” (Stratham et al 2010) 

The CBAC issues an avalanche danger rating of LOW, MODERATE, CONSIDERABLE, HIGH or EXTREME for specific aspects and elevations within our forecast area–the greater Crested Butte backcountry which roughly covers 100 square miles centered around the town of Crested Butte. This creates the Avalanche Danger Rose (Fig. 2):

Figure 2

So what goes into the danger rating? It all starts with the forecasters assessment of snow stability and how the current and future backcountry conditions fit with the avalanche danger definitions. The forecaster looks at the likelihood of both human-triggered and natural avalanches as well as the size and distribution of avalanches. Each level of avalanche danger has a specific definition for those categories (Fig. 1). 

Easy enough, right? If it could only be so simple! It has been very challenging here at the CBAC to attach an avalanche danger rating to our snowpack since the first major storm of 2012 arrived on January 16th. We have been reading (and re-reading) all the qualifying and defining traits of each danger level and assigning danger based on those definitions. Each morning, we look at the probability of both natural and human triggered avalanches and then think about how big avalanches will be and where they will be occurring in the terrain. The resulting product has been a strict interpretation of MODERATE or CONSIDERALE danger that appropriately sums up the avalanche conditions but does not necessarily connote how “dangerous” it is out there. This is where the “SCARY” modifiers have been coming into play this season. 

While not an official danger rating, forecasters often attach or imply the “SCARY” pre-fix during times when the danger is at the upper end of either MODERATE or CONSIDERABLE. Often times during SCARY MODERATE, there is a lower probability of human-triggering an avalanche but the resulting avalanche has the potential to be very large, and deadly. 

We dealt with SCARY CONSIDERABLE after the January 16th storm. 1.3″ of water fell on a mostly shallow and weak snowpack. The danger did not spike all the way to HIGH because the size and distribution of avalanche activity did not fully meet the HIGH requirements. We did not see “large avalanches in many areas”– a clause that helps define HIGH danger. Instead we observed “small avalanches in many areas and large avalanches in specific areas”–two of the defining traits of CONSIDERABLE danger. It was SCARY CONSIDERABLE because we were pushing the limits of the definition, but the way the storm and subsequent avalanche cycle played out fit into CONSIDERABLE danger. During the peak of the storm–the night of 1/16–the probability of human triggered avalanches may have jumped to “Very Likely”–a defining trait of HIGH–but the natural activity observed over the next several days all pointed to the fact it was CONSIDERABLE danger. 

The storm that arrived the following week–the January 22nd storm–dropped over 2″ of water onto our weak, top-heavy snowpack. The danger jumped to HIGH post storm due to the combination of a larger load of snow, winds, and our increasingly unstable snowpack. The result of that storm was a spike in danger to HIGH for 24 hours. More larger avalanches were observed after the 1/22 storm than the 1/16 storm and HIGH danger was warranted. 

The danger then hung out at CONSIDERABLE for the next 2 weeks on many aspects. Why? Naturals weren’t occurring, but human triggered avalanches were “LIKELY” on most slopes. Going back to the definitions (Fig. 1), “likely” triggers are enough to keep the danger at CONSIDERABLE. Also, all the reports of cracking and collapsing hinted that remote triggered avalanches were a real possibility as were “large avalanches in specific areas and very large avalanches in isolated areas.” 

Currently we are at SCARY MODERATE. Human-triggered avalanches are no longer “likely,” but they are “possible” and even very possible on certain slopes. Why is the “Scary” pre-fix still being tossed around the forecasting community? We use the term SCARY MODERATE during times when the probability for triggering an avalanche is slowly decreasing, but the consequences remain severe and even deadly. 

The Bottom Line: Our snowpack remains dangerous despite the fact it is getting harder to trigger an avalanche. Don’t let decreasing signs of instability lure you into exposed and consequential terrain. Many fatal avalanches or close calls (think Lucky Boy Slide on Whetstone) occur during SCARY MODERATE danger. Do not let your guard down and treat all slopes over 35 degrees with extra caution. 

John MacKinnon

Forecaster