Whether the weather be fine
Or whether the weather be not,
Whether the weather be cold
Or whether the weather be hot,
We’ll weather the weather
Whatever the weather,
Whether we like it or not. 

[anonymous]

One of the best ways to engage a stranger in conversation in the UK is to begin talking about the weather. Because of its unpredictability in the British Isles, there is always much to discuss.

There is at least one explanation of why it is so difficult to forecast British weather reliably. I read about it in a book about chaos theory some years ago, so please forgive me if my explanation is not totally clear. As I understand it, weather forecasting is done using mathematical models involving a complex set of  interlinked equations. The forecaster feeds multiple parameters into the equations, and a result is obtained that allows the weather to be predicted reasonably accurately. This model is quite reliable in many parts of the world, but not here in the UK. The problem is that when the parameters for the region containing the British Isles, whose weather system is affected by far more complex and many more influences than in other places (I do not know why), are fed into this set of equations, instead of one solution, several appear because the parameters introduce a large degree of instability into the forecasting model. Hence, the uncertainty in British forecasting that occurs. 

Nowadays, I use a popular weather forecasting app on my mobile ‘phone. It provides several predictions of what the weather will be like during different times of the day and several days following it. Potentially useful are the rainfall predictions which are expressed as a percentage, 0% being ‘rain completely unlikely’ and 100% being ‘rain inevitable’. So far, so good.

If the app predicts rainfall of less than about 5%, I do not bother to take an umbrella or rain coat, otherwise I do. Things can go wrong. Suddenly, out of the blue, rain falls heavily. I look at my app. Suddenly, what had been a prediction of, say, 3% becomes a prediction of, say, 78%. The app appears to be responding to the weather (or recording it), rather than predicting it.

Moral of the story: take an umbrella.

Poem from: https://www.poemhunter.com/poems/weather/page-1/22212436/#content