Overview

Finding great snow is sometimes about more than knowing how much snow fell. In the spring on a clear day, melting by the sun can result in dense, sticky snow that is a lot less fun to ski than dry powder. On the other hand, if it hasn't snowed in awhile, and the snow has frozen overnight, it's best to find an area where the sun will melt the snow and soften it into what is known as corn snow, which is comprised of rough granules created by repeated melting and freezing. At the conclusion of this learning activity, you will be able to identify the aspect of a slope and determine where to go to find dry snow on a spring powder day or softening snow on a spring corn day.

Instructions

Utilize the information located in the Scenario and Key Concepts to answer the questions located in this activity. You may refer to your textbook and notes to help you work through the assigned questions if desired. You will have two attempts to complete this activity. The highest grade will automatically be recorded. Once you have submitted your activity for a second time, you will be able to see the correct answers. Discuss with your instructor if you have questions about your answers or feedback.

Activity is due Sunday, by 11:59 p.m. MT

Submission and Assessment Guidelines

You will complete the quiz associated with this scenario within Canvas. For help on how to take a quiz in Canvas, review How do I take a quiz.
This learning activity is worth 7 points toward your final grade.

Scenario

Consider two ski days: one on March 15 at Kirkwood ski area in California, then one on May 1 at Arapahoe Basin in Colorado.

Your day at Kirkwood is a powder day. The lifts are opening at 9:30 a.m. due to avalanche control work. It is clear with temperatures near 32˚F, so it is essential that you chose the terrain for your first run wisely to find dry powder and avoid wet, sticky, high-density snow that has softened in the sun.

Your day at Arapahoe Basin is a corn snow day. It has been clear for several days and the snow has melted daily and refrozen at night. You arrive at 9:30 and the snow in the shade is still frozen. You need to find runs that are receiving snow and are melting.

Key Concepts

a. Aspect

Aspect is the direction that a slope faces. On a clear wintertime day in the mid-latitudes of the northern hemisphere, slopes that face north receive less sunlight than slopes that face south. Slopes that face east receive more morning sunlight, whereas slopes that face west receive more afternoon sunlight. The amount of energy received by a slope thus depends on the time of day. It also depends on the slope angle, which determines if the sun is direct or strikes at an angle. The video below examines how sunlight intensity varies with slope aspect and steepness at Snowbird and Alta Ski Areas on March 15th (images created at caltopo.com and if you would like you can learn how to do this at this web site).

As a result of these variations in sunlight, the snow conditions can differ dramatically depending on aspect. For example, in the photo below, south is to the left and north to the right. On the south aspect to the left, the snow has melted in the sun and frozen at night over the previous few days, resulting in corn snow, which comprised of rough granules created by the repeated melting and freezing. In contrast, the snow on the north aspect to the right is still dry and powdery.

Photo of hard, refrozen snow on a south aspect and dry snow on a north aspect
Figure 2. Contrast in snow type with aspect. ©Jim Steenburgh.

The snow conditions can also vary depending on time of day. If the corn snow on the left faces southeast, it will soften earlier than if it faces southwest.

Ultimately, aspect affects how well a slope holds snow and how fast water evaporates from the soil in the summer. As a result, it also affects the type of vegetation that grows.

Photo illustrating effects of aspect on vegetation Figure 3. Vegetation contrasts with aspect in southwest Idaho with trees on aspects with a more northerly aspect and sparse vegetation on aspects with a more southerly aspect. ©Thayne Tuason via Wikipedia, CC BY-SA 3.0.

b. Terrain and sunlight intensity maps

Below are topographic and sunlight intensity maps for the two ski areas. The sunlight intensity map for Kirkwood is for 10 a.m., just after the lifts open. The sunlight intensity for Arapahoe Basin is for 10 a.m., just after you load onto the chairlift.

Kirkwood, CA topographic map

Sun intensity at Kirkwood ski area at 10 AM 15 March

Google topographic map of Arapahoe Basin Ski Area in Colorado

Sun intensity at Arapahoe Basin ski area in Colorado at 10 AM May 1

Larger versions of these maps are available by clicking these links:

Citations

Images:

Key Concepts

- Figure 2. Contrast in snow type with aspect
  - Citation: Steenburgh, J. Contrast in snow type with aspect.
- Figure 3. Vegetation contrasts with aspect in southwest Idaho with trees on aspects with a more northerly aspect and sparse vegetation on aspects with a more southerly aspect
  - Citation: Thayne Tuason, Effects of aspect on vegetation - SW Idaho. CC-BY-SA-3.0.
- Kirkwood topographic map
  - Citation: Kirkwood, CA © CalTopo
- Kirkwood sunlight intensity map
  - Citation: Kirkwood, CA Sunlight Intensity Map © CalTopo
- Arapahoe Basin topographic map
  - Citation: Arapahoe Basin, CO © CalTopo
- Arapahoe Basin sunlight intensity map
  - Citation: Arapahoe Basin, CO Sunlight Intensity Map © CalTopo