Problem Type

CB Avalanche CenterLight Box Text

Avalanche Problems are categories of avalanche activity. The Problems may not describe all avalanche activity you might observe, but they categorize the avalanches by how we manage the risk in the terrain. This approach focuses on relevant observations you can make in the field and how to treat the avalanche risk.

The forecasts list up to three current Problems, along with the spatial distribution, the likelihood of avalanches, and anticipated size. Forecasters provide specific details in a short paragraph.

Below Treeline

CB Avalanche CenterLight Box Text

Below Treeline

Below Treeline is the lowest of three elevation bands used in the CBAC’s forecasts. It extends from valley floors or snowline to Near Treeline. Open areas and sparse trees are possible. Snowfall tends to be less than the other elevation bands. Tree cover shelters the snow from wind effects.

Near Treeline

CB Avalanche CenterLight Box Text

Near Treeline

Near Treeline is the middle of the three elevation bands used in the CBAC’s forecasts. It is a transition zone between dense forests and treeless alpine areas. It is the narrowest of the three elevation bands, extending only a few hundred feet above and below the treeline. It varies locally, and is not a constant elevation or width.

Above Treeline

CB Avalanche CenterLight Box Text

Above Treeline

Above Treeline is the highest of the three elevation bands used in the CBAC’s forecasts. It includes alpine areas where the most snow falls and the winds are the strongest. It is not an exact elevation, but a characteristic of the terrain, beginning as the treeline transitions into open slopes extending to ridges and the tops of the highest peaks.

Baldy

CB Avalanche Center2014-15 Observations

Name: Brandon Clifford
Title: Baldy
Location: Paradise Divide Area
Date of Observation: 11/19/2014
Aspect: South
Elevation: 12,805′

Avalanches: None.

Weather: Sunny with 0-5 (mph) wind.

Snowpack: Thin on top with better snow on leeward slopes.

Great skiing on Baldy Peak in November.

November 19th – Sunny

CB Avalanche CenterWeather

24 Hour Weather Outlook

Weather Discussion: Nunc ac ipsum vel nulla dignissim auctor. Nulla gravida fermentum tempus. Phasellus ut mollis lorem, a auctor mi. In rutrum turpis sit amet feugiat tincidunt. Fusce sollicitudin mi tellus, non tincidunt nulla sodales in. Nam eu suscipit enim. Nullam eu massa ultrices, lobortis orci vel, scelerisque metus.
Temperature:10Ëš
Wind Speed (mph):10 – 20 mph
Wind Direction:S
Sky Cover:Clear
Snow (in):0″

48 Hour Weather Outlook

Weather Outlook: Nunc ac ipsum vel nulla dignissim auctor. Nulla gravida fermentum tempus. Phasellus ut mollis lorem, a auctor mi. In rutrum turpis sit amet feugiat tincidunt. Fusce sollicitudin mi tellus, non tincidunt nulla sodales in. Nam eu suscipit enim. Nullam eu massa ultrices, lobortis orci vel, scelerisque metus.
Tomorrows Temperatures:10-15
Tomorrows Wind Speeds (mph):10-20 mph
Tomorrows Wind Directions:SW
Tomorrows Sky Cover:Mostly Clear,Few Clouds
Tomorrows Snow (in):0″

Todays Forecast

CB Avalanche CenterWeather

Weather Discussion: Nunc ac ipsum vel nulla dignissim auctor. Nulla gravida fermentum tempus. Phasellus ut mollis lorem, a auctor mi. In rutrum turpis sit amet feugiat tincidunt. Fusce sollicitudin mi tellus, non tincidunt nulla sodales in. Nam eu suscipit enim. Nullam eu massa ultrices, lobortis orci vel, scelerisque metus.
Temperature:10Ëš
Wind Speed (mph):10-20 mph
Wind Direction:N
Sky Cover:Clear
Snow (in):0″

Mount Owen Jenga Chute Avalanche

CB Avalanche Center2014-15 Observations, Avi-map

The CBAC got up to Mount Owen today to investigate yesterday’s slide that caught and carried two skiers as they boot packed up Jenga Chute. The slide broke above the pair near the top of the couloir as they were about halfway up the chute. The area received 10-12″ of snow on the night of November 2nd which fell on a variety of surfaces ranging from bare ground to up to 2ft residual of snow from the few storms that rolled through the Elk Mountains in October.

The avalanche should be classified SS-AF-R2-D1.5-O/G. The slope angle ranged from 37-41º on an ENE facing slope (61º). It ran ~400 vertical feet from ~12,600ft to 12,200ft. Debris width spread about 60ft wide, ranging in depth from 40-150cm deep.

The snow structure of the slab in the couloir consisted of two distinct graupel layers that fell in our most recent storm, capped by a thin windslab generally 3-6″ deep created by light winds during and after the storm; however, the new snow has drifted into 1-2ft deep isolated pockets. The slab failed and ran on a 4cm “pencil+” hard melt freeze crust from the October 12th storm, although it did scour down to rock within parts of slide path. Up to 50cm of 1-2mm faceted grains remained below the bed surface, which will continue to mature/grow in size as the season progresses, likely causing more concerning instabilities in the months to come, in this location and surrounding slopes.

The CBAC would like to genuinely and humbly thank those involved for sharing their experience for the greater awareness of our Crested Butte backcountry community as we plunge into another winter.

Get ready for winter!!

CB Avalanche CenterAvi-Off-Season

The gold leaves and some snow in next week’s forecast are both good reminders that winter is just around the corner!  Before the flakes start piling up, fall is a great time to freshen up on your avalanche education, or set aside some money and time to take an avalanche course.  I’ve put together a list of a few educational opportunities below.

Avalanche Training/Lectures

WMRT Avalanche Seminar.  7 pm, November 20th, 2014.  Western State Colorado University 

CBAC Avalanche Awareness Night.  December 6th, 2014. CB Center for the Arts
A night of avalanche talks, beer drinking, silent auction, raffle, and winter stoke, all  to support your local avalanche center

CBAC Beacon Brushup.  December 7th, 2014.  CB Town Park.
Learn how to conduct an avalanche search or tune-up your beacon skills.

AIARE Avalanche Courses 
Level 1, Level 2, and refresher courses offered locally through Crested Butte Mountain Guides or check AIARE’s schedule for courses around the country.    

Colorado Snow and Avalanche Workshop. October 17th, 2014. Breckenridge, CO
A one-day seminar aimed at avalanche professionals, but with plenty of material for motivated recreationists.

 

Weather Forecasting Courses

Sick of your local weather experts blowing the forecast? 
Mountain Weather Workshop.  October 31st – November 2nd, 2014.  Silverton, CO
Winter Weather Forecasting.  October 10th-12th, 2014.  Jackson, WY

Recommended Readings

I put together a list of some of the classic avalanche literature out there. I’ve ordered this list from easiest to digest to most technical reading. Grab a book for the next rainy or snowy day!

Snow Sense: A Guide to Evaluating Snow Avalanche Hazard – 5th Edition.  By Doug Fesler and Jill Fredston.  

A great book for starters or if you need a refresher

 Staying Alive in Avalanche Terrain – 2nd Edition.  By Bruce Tremper

My favorite. Bruce does a great job of describing challenging concepts using analogies and examples

The Avalanche Handbook – 3rd Edition. By David McClung and Pete Schaerer

If you want to dive into the science behind basic concepts, this is a good one.

Snow, Weather, and Avalanches: Observation Guidelines – 2nd Edition. 

Learn how to make observations at a professional standard

International Snow Science Workshop Proceedings.  Free online here.

Science nerds rejoice! All of the proceedings from this bi-annual conference are now online. Heavy on science.

Have a great fall!

Zach Guy
Forecaster, CBAC

Oh no! Dust on snow

CB Avalanche CenterAvi-Off-Season

Yesterday, we got a brief and silty taste of the Dirty Thirties when a major dust storm blew over Crested Butte.  Scarp Ridge recorded wind speeds of 110 mph (the highest of the season), and these winds brought with them a sizeable chunk of Moab.

Dust-ageddon in Crested Butte on March 30, 2014.  Photo credit: Matt Hogan

How will this dust on snow event affect snow stability and avalanches?   Lets start with a key concept: albedo.   Albedo is how reflective a surface is.  White colors have a high albedo — they reflect a high amount of radiation energy rather than absorb it. That is why you reach for a light colored T-shirt if you’re going outside on a hot sunny day instead of a black T-shirt.  Fresh snow has a very high albedo and it reflects most incoming solar energy. (So thats why my mom always made me double up on sunscreen when I went skiing!)  On the other hand, the dark-colored dust more readily absorbs solar energy and heat, and also retains that heat longer.

Pristine snow reflects radiation more effectively than dusty snow.  Courtesy of Jeff Deems.

Dusty snow can absorb two or three times the solar energy of a clean snowpack.  Whenever dust is near the surface of the snow (even when its buried up to a foot deep), it amplifies the rate of surface warming, increasing the amount of snowmelt and weakening the snow around it.   This leads to more frequent loose wet avalanches.  Intense melt rates send freewater deeper into the snowpack, which can also compromise the strength of deeply buried weak layers, causing an increased likelihood of wet slab avalanches.  Both of these problems, with or without dust, can be avoided by monitoring how well the snowpack refreezes at night and getting off of slopes before they thaw too much.  Dust on the snow simply shortens that window of stable snow and may prevent good overnight refreezes in some situations.

Snirt.  Snow+Dirt.   Photo taken March 31, 2014 near Crested Butte.

The second avalanche concern is that dust can do weird things when its buried by a slab of snow, and it can behave like a persistent weak layer.  Because they absorb and retain heat longer, dust layers can cause wet grains above or below them to remain unfrozen and unstable longer. Dust can also cause tremendous temperature gradients in the surrounding layers, which causes the bordering snow around it to decay and facet. This is not always the case, but it is worth checking on how reactive dust layers are after they get buried by spring storms.  It will be the easiest layer you will ever identify in a snowpit!

The crown of a large slab avalanche that was remotely triggered from hundreds of yards away last spring.  It failed on a dust layer.

Sadly, dust on snow has negative impacts on the timing of spring runoff and water resources in the West.  The Center for Snow and Avalanche Studies in Silverton, CO tracks and studies the effects of dust-on-snow events, and is a great resource for more information on this topic.  On the bright side of things, your favorite mountain bike trails will melt out sooner now, and business is booming if you own a car-wash business.

Zach Guy
CBAC Forecaster