Every night billions of people around the world tune in to the weather forecast. What will tomorrow bring? Once we hear the forecast we then plan our daily activities accordingly. But how did weather forecasting develop? Let's take a look at the history of meteorology.
In Bible times the forecasting of weather conditions was based solely upon observations of the sky. This is alluded to in the Bible book of Matthew where Jesus says to the religious leaders of the 1st Century, "˜You are able to interpret the appearance of the sky but the sign of the times you cannot interpret.' This method of simple observation prevailed until 1643 when Italian physicist Evangelista Torricelli invented the barometer. This simple device was able to measure the pressure of the air. Torricelli noticed that air pressure changes in accordance with changes in the weather. In fact a drop in pressure would often signal that a storm was coming. Atmospheric humidity was also able to be measured when the hygrometer was invented in 1644. Then in 1714 German physicist Daniel Fahrenheit developed the mercury thermometer. It was now possible to accurately measure the weather.
It was in 1765 that daily measurements of air pressure, moisture content, wind speed and direction began to be made. This was first done by French scientist Laurent Lavoisier who stated,"With all of this information it is almost always possible to predict the weather one or two days ahead with reasonable accuracy." However things were not as simple as Lavoisier had thought. In 1854 a French warship and 38 merchant vessels sank in a fierce storm off the Crimean port of Balaklava. The director of the Paris Observatory was asked to investigate the disaster. On checking meteorological records it was seen that the storm had actually formed two days previous to the sinkings and had swept across Europe from the southeast. If a tracking system had been in place the ships could have been warned of the pending danger. As a result of these findings a national storm warning service was set up in France. This is recognized as the start of modern meteorology.
In the mid 1800s there was still no quick way of transferring weather data from one location to the next. Often the weather that was being warned about would arrive before the data did. That was until Samuel Morse invented his electric telegraph to allow speedy transference of information. Morse's invention now made it possible for the Paris Observatory to begin publishing the first modern weather maps. By 1872, Britain's Meteorological Office had followed suit. From then on the acquiring of weather data became more and more complex, as did the resulting meteorological maps.
New graphic devices were developed to convey more information. Isobars, for example, were invented - lines drawn to link points that have the same barometric pressure. Isotherms connect locations that have the same temperature. Other graphic devices were also developed - symbols to show wind direction and force, as well as lines that depict the meeting of warm and cold air masses.
In the 20th century much sophisticated meteorological equipment has also been developed. Today, weather stations release balloons that carry what are called radiosondes. These are instruments that can measure atmospheric conditions and then radio the information back to the station. Of course, weather stations today also use radar. In 1960 the world's first weather satellite, TIROS 1 was sent into space equipped with a TV camera. Today, weather satellites orbit the earth from pole to pole. Geostationary satellites stay in a fixed position above the earth and constantly monitor one part of the globe.
The forecasting of the weather took a leap forward when, shortly after World War One, British meteorologist Lewis Richardson stated that since the atmosphere follows the laws of physics, it is possible to use mathematical calculations to predict future weather conditions. His formulas, however, were so complicated that the weather would be upon him before he could figure out what it would be. His calculations also only allowed for weather readings taken at six hourly intervals.
However, with the advent of computers, it became possible to work out Richardson's lengthy calculations quickly. A complex numerical weather model was now established that incorporated all the known physical laws governing the weather. The equations are utilized in the following way: meteorologists divide the earth's surface into a grid with grid points spaced 80 kilometers apart. The atmosphere above each square is called a box and observations of atmospheric wind, air pressure, temperature and humidity are recorded at 20 different levels of altitude.
A computer than analyzes the data received from the more than 3,500 observation stations around the world and produces a forecast of what the world's weather will be for the next 15 minutes. Then a forecast for the next 15 minutes is produced. Repeating this process a computer can produce a six day world forecast in just 15 minutes.
To achieve even greater accuracy the British Meteorological Office has what is called the Limited Area Model which covers just the North Atlantic and European sectors. It's grid points are spaced at intervals of just 50 kilometers. However, the formulas used and the results achieved are only approximate descriptions of the behavior of the atmosphere. To achieve more accuracy the skills of the weather forecaster must come into play.
The forecaster must use his skills and experience to decide what value to place on the data he receives. As an example, when air cooled by the North Sea moves over the European land mass, a thin cloud layer often forms. Whether this cloud layer means rain is on the way in continental Europe the next day or whether it simply evaporates in the sun's heat depends on a temperature difference of only a few tenths of a degree. It is up to the forecaster to predict which will be the case.
So, how accurate is the weather forecast? Britain's Meteorlogical Office claims an 86 % accuracy for it's 24 hour forecasts. 5 day forecasts are at 80 % accuracy. Why aren't they more accurate? Well, weather systems are extremely complex. It is simply not possible to take into account all of the factors necessary to provide a foolproof forecast. And scientists still don't fully understand all of the forces of nature that shape the weather. Despite this, however, modern weather forecasting gets it right most of the time. So, it still pays to check out the forecast before heading off for a day in the sun.