3 minute read

Meteorology

from SoaringNZ Issue 1

by mccawmedia

from SoaringNZ Issue 1, page 30

GA Airspace – going going gone

So met hin g fo r Not hin g

A visible reminder that air carries water vapour. Cumulus cloud over the Canterbury Plains.

These days it is rare for people to get something for nothing. Handouts and special offers, like ‘Free Downloads’, nearly always have a catch to them, and in the end one has to pay or go without. As glider pilots, we are particularly privileged, the air we fly in comes for free, as does the energy which keeps us up, and gravity which enables us to go fast. Air is quite remarkable. Despite being a melange of gases, it is invisible to our eyes. This is a good thing! It is also a good insulator, and can be compressed or expanded. Fortunately it has just about the right density to allow us to move about freely whilst providing resistance if one goes fast. Fast moving air can be damaging and yet we need it to stay alive.

One of the common gases in air is water vapour. It is a good thing this is invisible too or we wouldn’t see very far. However, if the air containing the water vapour gets cooled enough, the vapour condenses into water droplets or ice crystals. A common result of this phenomenon is cloud, and one cannot see very far in cloud! Again it is fortunate that cloud is not very dense, otherwise it would hurt if one flew into it. For glider pilots, clouds have some importance. The white fluffy cumulus clouds indicate good soaring weather, as do the long, lens-like clouds that appear stationary over the ground.

Knowing what sort of weather is required for good gliding is one thing. Being able to predict that weather is another, far more risky occupation. A famous occasion was when Michael Fish, a BBC weatherman dismissed ideas of a great storm one evening, but in the morning most of the trees on the south coast of UK were lying on the ground. Few people have forgotten that!

Let us be honest. Weather forecasting is guess work! One may have a very educated guess, but we do not have all of the facts to make really accurate predictions, particularly with regard to the specialist requirements of glider pilots. There was a time, not many years ago, when atmospheric information was collected by observers who recorded pressure, temperature, dew point and wind velocity every hour. This was relayed by telex to the central met office and the forecasters would plot all the data on a chart and come up with the most likely prediction. Nowadays, the observations are automated and a computer sifts through the data and the result is broadcast on TV, radio and other networks. Much of this forecasting is of a superficial nature e.g. ‘Tomorrow will be dry with sunny intervals!’ A glider pilot might translate this as ‘There will be cumulus, so it will be soarable!’ What isn’t known is the height of the cumulus base, how much cumulus, what rate of climb there might be and whether there will be wave influence.

With the advent of the internet, a mass of data is available for the average pilot to sort through. Websites such as metvuw.com; metservice.co.nz; arl.noaa.gov/ready; weather.co.uk and others, provide most of what one needs to have a good guess at what is going to happen weatherwise. All of these sites are free, and glider pilots love ‘Something for nothing!’