Snow – Reading for Meaning
What is snow?
Snow falls from the sky, but where
exactly does it come from? Is it a cloud,
breaking up into little pieces? Or is there
a giant living up there, who has made a
bunch of really cold paper confetti he
feels like throwing around?
You've probably noticed that it only
snows when it is very cold outside. If
you know about how water becomes ice
when it gets cold, then you might think
snow must be frozen rain. Generally, frozen rain is called "sleet" while snow is
actually frozen water vapour. "Water vapour" is water in the form of a gas instead of
in the form of a liquid (such as rain water) or a solid (such as ice). Even though water
vapour is invisible, it’s all around us.
When cold temperatures change the water vapour in the atmosphere directly into the
solid state of ice (without first passing through the liquid stage), it creates snow that
then showers down out of the sky! As soon as the temperature warms up again, the
snow usually melts back into liquid water – This is all part of the awesome process
of The Water Cycle that we looked at last lesson! Snow will settle when the ground
temperature is below 0C.
Why is snow often not forecast?
Forecasting snow is difficult for many reasons. The main reason is that snow does
not occur very often in the UK, and so we do not understand it as well as we do
rainfall. In addition to this a slight change in the temperature or humidity (moisture
levels) can control whether there will be snow, rain or sleet.
Wet and Dry snow.
The size and make up of a snowflake depends
on how many ice crystals group together and
this will depend on air temperatures. Snowflakes
that fall through dry, cool air will be small,
powdery snowflakes that don't stick together.
This 'dry' snow is ideal for snow sports but is
more likely to drift in windy weather.
When the temperature is slightly warmer than 0 °C, the snowflakes will melt around
the edges and stick together to become big, heavy flakes. This creates 'wet' snow
which sticks together easily and is good for making snow men.
What is a White Christmas?
For many people, a White Christmas means a complete covering of snow, ideally
falling between midnight and midday on 25 December. However, the definition used
most widely (especially by those placing and taking bets) is for a single snow flake to
be observed falling in the 24 hours of 25
December.
How does snow affect people?
The positive (good) effects of snow include
wintertime activities such as snowboarding and
skiing. These activities attract tourists and bring
in money. Snow can be good for animals as it
provides protection against very cold weather.
Can you think of any other positive effects? Do
these affect people (social effects), the
surroundings (environmental effects) or the
amount of money that is made (economic
effects)?
One of the negative (bad) effects of snow in is
that sometimes there is too much of it - so that
daily activities cannot occur. Snow can cause
natural disasters and expenses for the
community. When snow melts it can lead to
flooding. Can you think of any other negative
social, environmental or economic effects of
snow?