meteorology LEMMY TANNER
Something
for Nothing These days it is rare for people to get something for nothing. Handouts and special offers, like ‘Free Downloads’, nearly always
A visible reminder that air carries water vapour. Cumulus cloud over the Canterbury Plains.
but in the morning most of the trees on the south coast of UK were lying on the ground. Few people have forgotten that!
have a catch to them, and in the end one has to pay or go without.
Let us be honest. Weather forecasting is guess work! One may
As glider pilots, we are particularly privileged, the air we fly in
have a very educated guess, but we do not have all of the facts
comes for free, as does the energy which keeps us up, and gravity
to make really accurate predictions, particularly with regard to the
which enables us to go fast. Air is quite remarkable. Despite being
specialist requirements of glider pilots. There was a time, not many
a melange of gases, it is invisible to our eyes. This is a good thing!
years ago, when atmospheric information was collected by observ-
It is also a good insulator, and can be compressed or expanded.
ers who recorded pressure, temperature, dew point and wind
Fortunately it has just about the right density to allow us to move
velocity every hour. This was relayed by telex to the central met
about freely whilst providing resistance if one goes fast. Fast
office and the forecasters would plot all the data on a chart and
moving air can be damaging and yet we need it to stay alive.
come up with the most likely prediction. Nowadays, the observa-
One of the common gases in air is water vapour. It is a good
tions are automated and a computer sifts through the data and the
thing this is invisible too or we wouldn’t see very far. However, if the
result is broadcast on TV, radio and other networks. Much of this
air containing the water vapour gets cooled enough, the vapour
forecasting is of a superficial nature e.g. ‘Tomorrow will be dry with
condenses into water droplets or ice crystals. A common result of
sunny intervals!’ A glider pilot might translate this as ‘There will be
this phenomenon is cloud, and one cannot see very far in cloud!
cumulus, so it will be soarable!’ What isn’t known is the height of
Again it is fortunate that cloud is not very dense, otherwise it
the cumulus base, how much cumulus, what rate of climb there
would hurt if one flew into it. For glider pilots, clouds have some
might be and whether there will be wave influence.
importance. The white fluffy cumulus clouds indicate good soaring
With the advent of the internet, a mass of data is available for
weather, as do the long, lens-like clouds that appear stationary
the average pilot to sort through. Websites such as metvuw.com;
over the ground.
metservice.co.nz; arl.noaa.gov/ready; weather.co.uk and others,
Knowing what sort of weather is required for good gliding is
provide most of what one needs to have a good guess at what is
one thing. Being able to predict that weather is another, far more
going to happen weatherwise. All of these sites are free, and glider
risky occupation. A famous occasion was when Michael Fish, a
pilots love ‘Something for nothing!’
BBC weatherman dismissed ideas of a great storm one evening,
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