First, you will read the avalanche case study, which is an accident report of an avalanche related accident that occurred in Colorado. After reading this report you will fill out the avalanche worksheet assuming the role as an accident investigator who is seeking clues to causes of the accident.

AvalancheCaseStudy

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AvalancheWorksheet
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Second, you will look at a few surface maps and forecast upslope mountain snow.

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Last, you will look at and label a figure showing a downslope windstorm.

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ACTIVITY:
Discuss the case study and the accident summary with your group. Assume the role of an accident

investigator. Using both the case study story and the accident summary, seek clues to causes of the accident.
List the clues in the appropriate categories below.

Choose Terrain

Travel Wisely

Observe

Avalanche Activity

Snowpack

Weather

Plan Teamwork

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1.2 – Case Study

Case studies are accident accounts that can provide valuable insight into how people make decisions that lead to
accidents. Read the following case study (or one supplied by the instructor) and consider how the components of the
AIARE DMF apply to the decisions that were made. These are not “Darwin Award” candidates. They are regular
backcountry recreationists who’s decisions led to unwanted consequences. Note that while this incident affected
recreational backcountry users, professionals have made similar mistakes. This story underscores the fact that all
humans are capable of making poor decisions. Following the case study there is an exercise to complete. While reading,
make a note of any factors outlined in the DMF that in retrospect could have alerted the group about the risk to which they
were exposing themselves. How could the team have created and chosen better options for the day? How could they
have increased their margin of safety and still accomplished their goals?

ACCIDENT REPORT: OHIO PASS, COLORADO

Date: February 25, 2001
Location: East Bowl in the Anthracite Range, 7 miles west of Crested Butte, CO.
The account below is condensed from a report written by Dale Atkins, who investigated the accident for the CAIC:

The day dawned clear and cold after a 10” snowfall the day before. A group of 5 friends – two men and three women – met
at the Kebler Pass trailhead and snowmobiled into the Anthracite Range, approximately 7 miles from Crested Butte, for a
day of powder skiing in the backcountry. All of the group were experienced backcountry travellers familiar with the terrain,
most having lived and skied in the area for 15 plus years. One member of the party was former ski patroller. Everyone
had formal avalanche training and carried a transceiver, shovel and probe.

The public avalanche bulletin that day reported a danger level of
“moderate with pockets of considerable at or near treeline.” The
bulletin also noted that backcountry skiers in the Crested Butte
area had reported triggering avalanches recently but had no
information about where or when the avalanches had occurred.
That day, the group left early and did not access the bulletin.
The day was going well as the group skied laps on 30+ degree
slopes in treed and open runs generally on northern facing
aspects. The snow was perfect and they experienced no
cracking and saw no avalanches. There were two other groups
skiing in the same area.

On their last run they decided to ski “East Bowl” one of the
available routes down to the snowmobiles. East Bowl, as the
name implies, faces east and is a mix of treed and open slopes
with a variety of terrain features such as convexities, wind rolls,
small cliffs and many small trees. In general it is steeper than
the terrain the group had been skiing that day with slope angles between 25-45 degrees. At the top, the group saw two
ski tracks leading into the bowl. All was progressing fine when part way down the group split up into one group of 2 and
one group of 3 with the plan to meet on a shelf in the trees above the last pitch. The group of 2 (Mitch and Sue) split up
with Mitch skiing to the bottom beyond the meeting point and the other, Sue, meeting the group of 3, above the last pitch,
insight of the snowmobiles at the bottom. The group had voice contact with Mitch at the bottom of the run a short distance
away and Sue decided to traverse over to where he had skied down. On the traverse to the slope that Mitch had
descended she intersected with a steep rollover, triggered and was caught in an avalanche. Sue remained on the surface
but sustained a fatal head injury and died at the scene. Crested Butte lost a cherished member of the community that
day.

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Name: ________________________________  Class: ____________Date: __________ 

Severe & Hazardous Weather    Active Learning Exercises – Ed 4 

Exercise 16.2  Pressure Patterns, Wind Flow, and Mountain Snows 
 
The four surface maps below each show the sea  level pressure distribution across the western 
United States on different days in January.  
 
1.   Draw arrows around the pressure systems to  indicate wind direction. (The first one  is done 

for you.) 
 
2. Shade in the regions on each map where the wind direction is favorable for the development 

of snow in the mountains of the western United States.  
 
3.  If the snow would fall on the east slope of the Rockies, label it “upslope snow.” 
 
 
 
 

1. Name:
2. Class:
3. Date:
4. Text 1:
5. Text 2:
6. Text 3:

Name:

________________________________  Class: ____________Date: __________ 

Severe & Hazardous Weather    Active Learning Exercises – Ed 4 

Exercise 17.3  Features of a Downslope Windstorm 
 

 
 
 
The diagram above is a cross section through a mountain range looking west to east. The 
contours shown are streamlines of wind flow. A downslope windstorm is occurring. The gray 
shaded region indicates the location of clouds. On the diagram, place letters where the features 
listed below are located: 
 

A.   Chinook Wall 

B.   Rotor 

C.   Hydraulic Jump 

D.   Breaking waves 

E.   Inversion 

F.   Most severe winds at surface 

G.   Shooting flow 

H.   Snowstorm 

1. Name:
2. Class:
3. Date: