THE BLOG

Weather Lore

19/09/2014 12:50 BST | Updated 17/11/2014 10:59 GMT

Cows lying down, red skies in the morning and a feeling in your bones. Must be rain on the way. But hang on, what happens if only half the cows in a field are lying down - are they giving a 50 per cent chance of rain? Who taught the cows to predict the weather in the first place? Hmm, is there actually any truth in weather lore?

Back in the dark old days before weather forecasts, people would use proverbs and sayings to provide an indication of what tomorrow's weather would bring. Growing up on the west coast of Scotland we had our own saying, "If you can see Arran it's going to rain and if you can't see Arran it already is".

Joking aside, a lot of old weather phrases and sayings are based on human experience, so you would expect some statistical merit. That certainly seems to be the case when you look at the sky to make your prediction.

Red skies

One of my favourite weather sayings is "Red sky at night, shepherd's delight. Red sky in morning, shepherd's warning". You might know the version with a sailor rather than a shepherd but either way, this phrase apparently first appeared in the Bible in the Gospel of Matthew and was used to help shepherds prepare for the next day's weather.

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The saying is most reliable in the UK when weather systems come in from the west, which they often do. A red sky appears when dust and small particles are trapped in the atmosphere by high pressure. This scatters blue light and leaves only red to give the sky its notable appearance.

A red sky at sunset means high pressure is moving in from the west so the next day will be dry and pleasant - shepherd's delight.

A red sky at sunrise means the high pressure system has already moved east meaning the good weather has passed and more likely than not, a wet and windy low pressure system is heading our way.

Another reason the sky may light up red in the morning could be due to an approaching weather front. As the sun rises at a low angle in the east it may light up the impending clouds associated with a weather front coming in from the west that is likely to bring in rain later that day - shepherd's warning.

And likewise red clouds in the evening will be those in the east that have already passed us by, giving us a good chance of clear skies and fine weather ahead.

Round and round

Have you ever spotted a ring or arc around the moon or sun? This is a good indication that the weather is changing, as summed up by "If a circle forms round the moon, twill rain or snow soon".

The cloud layers that make up a weather front are topped by cirrostratus clouds containing ice crystals. Due to the structure and angle of an approaching warm front, this thin wispy or hazy layer of cloud can sometimes be seen in the distant horizon or high in the sky, well before the rain arrives.

The ice crystals within this cloud can create an optical phenomenon known as a halo. When sunlight passes through the randomly oriented hexagonal ice crystals the light is spread in every direction and thus appears as a circle a fixed distance from the sun.

Easterly winds

A classic weather rhyme that sends a shiver down my spine is "When the wind is out the east, tis no good for man nor beast". The reason for the shiver? An easterly wind blowing across eastern parts of the UK during the winter is bone-chillingly cold, dragging air all the way from eastern Europe and Russia.

Farmers hundreds of years ago would have known a strengthening easterly wind meant harsh winter weather was on its way. Cold easterlies often bring spells of heavy snow to eastern parts of the UK but the wind chill from a Siberian blast is felt right across the country.

It's not just a "bad" wind in winter, as easterly winds often pick up pollutants as they pass over the factories of Europe before reaching the UK. During the summer months they bring poor quality air from the near continent, giving us hazy skies and even summer smog.

Wet wet wet

So far so good with our weather lore. But what about those rain-loving saints, shadow-fearing groundhogs and the amazing weather cows?

You've probably heard that if it rains on St Swithun's day (15th July) then we're in for forty days of rain. The good news is that this just isn't true. In fact, since weather records began in 1861 there has never been a record of 40 dry or 40 wet days in a row following St Swithun's Day.

Shadow forecaster

Next up is Punxsutawney Phil, a groundhog who likes to give his weather predictions on 2 February each year, immortalised in the film Groundhog Day. According to tradition, if Phil sees his shadow and returns to his hole he has predicted another six weeks of winter weather. If he doesn't see his shadow then he's opting for an early spring.

The logic behind this is that clear skies, and therefore a visible shadow, at that time of year are said to herald cold weather ahead. Unfortunately Phil's predictions have only been correct 39 per cent of the time. Still, it is quite a big task for an animal fresh from hibernation to forecast the next six weeks of weather for one town, let alone the whole of the northern hemisphere.

Herd mentality

Some people remain convinced that cows lie down when rain is on the way. The problem with this is that cows spend a lot of time lying down, about 14 hours a day for a dairy cow. Add in the fact that in this country the heavens do tend to open rather more frequently than we'd like, and it comes as no surprise that it will often rain at some point while a cow is lying down.

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Proving that the cows knew the rain was coming and decided to lie down in advance is pretty much impossible. As is working out why they would want to lie down in the rain - do they like to keep an area of grass dry for future munching?

Best way to predict the weather? I tend not to ask a field of cows but instead utilise the power of supercomputers, improved forecasting models and better data collection from weather observations along with radar and satellite imagery. I also have a nice app on my phone from the Weather Channel.