Why are showers so hard to forecast?
Tomasz Schafernaker takes us through this quick animation explaining why showers are difficult to forecast.
It's shaping up to be a warm and humid first week at Wimbledon, and you may be forgiven for thinking that the tennis balls will travel slower through humid air. BBC Weather's Clive Mills-Hicks explains why that's not the case.
The more humid the air, the less dense it is. This is contrary to the notion that humid air is 'heavy' - that perception is probably due to the fact that there is less oxygen in humid air than in drier air, especially at higher temperatures, where it has more of an impact on a runner's lung performance.
However, these changes are barely noticeable. For atmospheric pressure of 1013 hPa (which is the average), at 10C if the humidity increases from 20% to 100% the density decreases from 1.244 to 1.241. At 30C, if the humidity increases from 20% to 100% the density decreases from 1.16 to 1.14 - again a very small 1-2% change.
The warmer the air, the less dense it is. For atmospheric pressure of 1013 hPa, if the air temperature increases from 10C to 30C the density decreases from 1.24 to 1.15 - nearly a 10% change. It might be enough to turn a Rory McIlroy 280-yard drive into a 300-yard plus monster.
In a gas, density and pressure are linked, and the lower the pressure the lower the density. I remember Bob Beamon's astonishing long jump at the 1968 Mexico Olympics. He broke the existing record by a margin of 55cm (21¾ inches) and his world record stood for almost 23 years until it was broken by Mike Powell in 1991, while his Olympic record stands to this day.
The reason was due in part to Mexico City's altitude of 7,300 feet above sea level, where the average pressure is 773 hPa compared with the 1013 hPa average at sea level. Typical air density there would be just 0.89.
Temperature, humidity and atmospheric pressure can all be changing during a sporting event. If the temperature is increasing, the humidity is increasing and the atmospheric pressure is falling, then these changes can all contribute to a fairly significant change in air density - and possibly the speed of those serves!
Tomasz Schafernaker takes us through this quick animation explaining why showers are difficult to forecast.
Ever wondered why the temperature reading on your thermometer may be different to those you see or hear on air?
Louise Lear takes a look at how our weather can influence the pollen count.
Louise Lear explains why sometimes the temperature can drop along the coast.
An explanation of the wind gusts symbol in our forecasts.
Matt Taylor explains how the body reacts to high temperatures.