2. This assignment has been developed to instruct you
on the use of sound within a PowerPoint presentation.
Therefore, narrating a report written by someone else
does not give you the right to take credit for its
content.
Instructions:
Choose your weather topic
Type the report into a PowerPoint presentation
Select the slide you wish to record
Click on the slide show tab and begin recording your reading
Be sure to check your timing and your work before submitting
to my wiki
Add at least two pictures or clip art to your presentation
Comment on other classmates presentations
Remember to only add comments or suggestions that are
constructive and ethical in nature
3. How snowflakes are formed
A report by Sam Montana
Narrated by Kay Cremeans
4.
5. Precipitation comes in many forms such as rain, sleet,
hail and snow. A snowflake starts out as a dust
particle. Then water vapor starts to condense onto
the dust particle and if the temperature is cold
enough it freezes. Most naturally occurring ice is
shaped in a hexagonal structure. The snowflake
becomes more and more formed because water
molecules have an attraction for each other and water
is more stable in the form of ice. The water molecule
is even more stable in the form of ice when arranged
in hexagonal layers, and that gives the snowflake a
6-sided symmetry. As more and more water vapor
condenses onto this ice crystal, the snowflake grows.
6. Several factors influence the shape of any one
snowflake, the temperature, humidity and the air
currents. If there are a lot of dust and dirt
particles mixed in during this freezing process, the
shape of the snowflake is affected. As these ice
crystals move up and down in the cloud with the
updrafts and downdrafts they continue to form
and be shaped. Finally the snowflake is heavy
enough to escape the clouds updrafts and falls to
the ground.
Falling to the ground can also alter its shape. If
the snowflake spins it will probably keep its
symmetrical shape. If they aren’t spinning when
they hit the ground they will lose their shape and
be lumpy.
7. Common snowflake shapes
The shape of the ice crystals that form the snowflake is
dependent on temperature. Here is a list of their shapes and
the temperature that they formed in.
25 – 32 F: Thin 6-sided hexagonal crystals, formed in the high
clouds.
21 – 25 F: Needles or flat-sided crystals are formed in the
middle height clouds.
14 – 21 F: Hollow columns
10 – 14 F: Sector plates, which are hexagons with
indentations.
3 – 10 F: Dendrites, lacy hexagonal shapes.
Snowflakes are composed of many ice crystals that affect their
shapes. They might start out as a one shape and land as
another shape. You will probably never see two snowflakes that
look alike, it is a constant though that in the formation of one,
it is always 6-sided, or hexagonal.
Highly magnified hexagonal dendrite snowflake
8. Why is snow white?
Water is clear, so why is snow white. The
answer has to do with the fact that
snowflakes have so many light-reflecting
surfaces that they scatter the light into all of
its colors, so snow appears white. It has to
do with how the brain perceives the light
into the color.
9. There is another form of snow that some
people have never heard of or seen, it is called
graupel, also referred to as snow pellets. Some
describe it as soft fuzzy hail. It starts out as a
snowflake and then combine with super cooled
water droplets frozen together. These are small
pellets, not large like hail might be and soft.
10. A side note about updrafts and downdrafts
A snowflake can go up and down in a cloud
gathering more crystals that form its shape until it
gets heavy enough to fall to the ground. You can
actually see this updraft and downdraft action
yourself when it hails. The next time it hails and if
the hail is big enough, look for ones that have
broken in half on the ground. You can see rings
inside the hailstone. Each ring represents a trip up
and down in the cloud. The hailstone rises and
gathers another layer of ice, then it falls in the
downdraft and melts a little bit, rises up again and
refreezes picking up another layer of ice until it gets
heavy enough to fall to earth. To learn about hail,
you can read All About Hailstorms and How Hail
Forms.
11.
12. Once you have reviewed the previous
report, you are to search the internet for a
similar story and develop a narrative
presentation.
Once you are finished with your
presentation submit it to my wiki for review
by your classmates.
http://student-assistance.wikispaces.com
Place your finished assignment and
comments on the PowerPoint
narrations page
13. References
Montana, Sam (2008). How snowflakes are formed.
Retrieved March 26, 2012 from
http://weather-meteorology.knoji.com/how-snowflakes-are-
formed/
