Temperature from our forecast perspective are fairly well defined, they are what we would expect to measure in a standard meteorological screen (in other words, shaded and well ventilated) at 2 metres above ground level. Upper air temperatures that you will find on some pages on our site are referenced to the level above the ground stated. Measurements of temperature as opposed to forecasts, are traditionally measured in a Stevenson Screen (and these are what you will see reported under our latest tab). However, many newer electronic systems are now used that don’t require a screen although the sensors are always normally ventilated and shaded and usually at a height of 1.5-2.0 metres above the ground. This fairly strict and vital way official temperatures are measured means that we are able to compare similarly measured temperatures around the world. However, it is why sometimes our personal thermometers on a wall or under a tree don’t give reliable readings – firstly the sun shining directly on the thermometer will increase temperature considerably and nearby objects likes walls or trees can act as a buffer against the correct temperature, be it warmer or colder.
We all know that we can feel warm or cold with the same temperature, depending on what the wind speed is or the humidity. Various ways have been estimated on how to calculate what we might feel like as opposed to the traditional measured temperature. Most of this relates to how a body cools itself by moisture evaporation from our skin with is directly related to the amount of moisture already in the air and the wind speed which carries heat away from our body. Hence if it is relatively dry and windy we will tend to feel cooler and if it is humid with little wind we will feel warmer. Other factors enter into this which complicate matters such as how much exercise we are doing at the time as this expends heat and make us feel warmer. In our forecast we give an estimate of what the temperature will feel like assuming somebody walking slowly – the cooling effect of wind and dry conditions is called “wind chill” and the warming effect of humid weather with light winds is called the “heat index”. In our “myweather2” forecasts we label these both as the “ feels like” temperature when conditions are appropriate. If there is no effect then these temperatures will be the same as the normal temperature. Actually the whole science of temperature and what we are actually measuring is very interesting and worth “googling”. Thermodynamics are an area of study that cover much of the energy transfers in our physical world. The study of thermodynamics helps us to understand why warm air rises and cold sinks, how and at what rate energy transfers from one body to another or from region to region and what the impacts of this are around the world and for that matter throughout the universe.