PURPOSE:  To observe the effect of the environment on snow crystals.

MATERIALS (per group):  Field -- Four glass microscope slides with blank tape labels, snowflake preservative (clear plastic in spray can OR formvar solution in dropper bottle), dissection pin or toothpick, pencil, storage area for completed slides.  Optional -- Snow shovel, wooden spring-type clothespin. Lab -- Low power microscope or hand lens.

INTRODUCTION:  Rain, hail, sleet and snow are all forms of precipitation.  In clouds containing large amounts of moisture, water droplets may join together and fall as rain.  Sleet forms when raindrops fall through a layer of cold air and freeze.  Hail forms when water droplets freeze around an ice nucleus and grow in a thunderstorm.  Snow forms in clouds when the air is cold enough so that water vapor changes directly to a solid.

In this activity, you will use a liquid plastic to make replicas of snow crystals in the air and in the snowpack. You will find out whether falling snow crystals keep their shape as they lay on the ground.

PREDICTION: You have seen snowflakes in the air and you have played in the snow on the ground.  Use what you know about snow to make a prediction:

1.  What is the usual shape of a falling snowflake?  What do you think happens to the size and shape of a snowflake which falls to the ground and is buried in the snowpack?

HOW TO COLLECT AND PRESERVE SNOWFLAKES:

Always keep slides and snowflake preservative below freezing while collecting snowflakes.  Hold slides by the edges with a clothespin or with gloved hand to prevent transfer of heat and moisture from your hand. 

To prepare slides using formvar solution:  Spread several drops of cold formvar solution on a cold slide with the eyedropper.

To prepare slides with clear plastic spray:  Spray cold slide with cold plastic.  Let excess plastic drain off one corner of the slide.

Collect snowflakes as described below. Store the completed slides in a cold sheltered place for several hours until the snowflake preservative hardens.

FIELD PROCEDURE:

A.  Collecting random falling snow crystals as follows:  Put snowflake preservative on a slide.  Hold the slide out in the falling snow until several crystals fall into the solution.  Record your name and collection method ("random") on your slide. Store the slide.

B.  Collecting selected falling snow crystals as follows:  Put snowflake preservative on a slide and on a cold pin or toothpick.  Let snow fall on the cold jacket sleeve of another student.  Transfer several snow crystals with the pin or toothpick to the preservative.  Record your name and collection method ("selected") on your slide.  Store the slide.

C. Collect snow crystals from the middle and the bottom of the snowpack as follows:  Make a hole in the snowpack down to the ground with your boots or snow shovel.  Put snowflake preservative on a slide.  Transfer several snow crystals from the middle or bottom of the snowpack to the slide using a toothpick or pin.  If the preservative does not cover the crystal, add a small drop of preservative beside each crystal to cover it by capillary action.  Record your name and collection site ("middle" or "bottom") on your slide. Store the slides.

LAB PROCEDURE:

D. Examine all snow crystals collected by your group with a low power microscope or hand lens.  Sketch the crystals on the data chart below.

E. Using the Snow Crystal Chart provided by your teacher, classify the types of falling snow crystals you found.  Label your sketches with the crystal type.

DATA:

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Random

Collection

Method

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Selected

Collection

Method

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Middle

Snowpack

Location

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Bottom

Snowpack

Location

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CONCLUSIONS:

2. How did the size and shape of snowflakes in the air compare with the snow crystals from the snowpack?  Was your prediction correct?

3. How did falling snow crystals collected randomly (step A) differ from those you selected (step B)?

DISCUSSION:

4. Give one reason why snow crystals falling in the air may not be regular in shape.

5. Explain why some falling snow crystals do not seem to fit into any of the categories in the Snow Crystal Chart.

6. The shape of falling snowflakes is different from snow granules in the snowpack.  Give at least one possible explanation for how this shape change might occur.

7. Conglomerate flakes are large masses of interlocking crystals, sometimes up to 5 cm (2 in) in diameter.  Which type of crystals on the chart are most likely to form conglomerate flakes?  Explain your ideas.

8. Use the Snow Formation Chart provided by your teacher to give the possible range of temperature and humidity in the clouds that produced the snow crystals you collected.

Figure 1. Snow Classification Chart (LaChapelle 1969)

Figure 2. Snow Formation Chart (Magono & Lee 1966)