How can you tell if it is going to rain?

The British weather is unpredictable but there are ways that nature can help to give us an indication that the rain is on its way.

In the past, man relied solely on his observation of the sky and the way plants and animals behaved to predict the weather. Accumulated experience was handed down in rhyme or linked to certain dates in the calendar, and became the subject of many old wives tales. Of course, we know now that this was not a reliable way to generate a weather forecast.

There were many parts of nature that were used to foretell the weather – some more bizarre than others. Seaweed and pinecones were traditionally used due to the reactive nature of them. But while a piece of seaweed might well become slimy when humidity is high, an open pinecone , despite popular opinion, is not a reliable indicator of dry weather.

However that doesn't mean that there is nothing in that can be used to indicate changes in the weather. For example, dandelions close when it clouds over and, on the other hand, scarlet pimpernels close when humidity increases.

Highland Cow lying in field
Bee on a flower

People have also historically looked to animals to as an indicator of the weather. For example, high-flying swallows are probably chasing insects on updrafts of warm air, which is a sign of stable, fine weather. A well-known fable states that the cows will lie down in their fields when wet weather is pending. It is actually much more likely to be that they are simply chewing the cud or resting rather than waiting for rain. Bees, on the other hand, do not like the wet weather and will remain by the hive if rain is on its way – so if it is looking overcast in the summer months and you think there is a significant lack of bees around, there could well be a downpour!

storm

Almost everyone learns: ‘Red sky at night, sailor’s delight, red sky in morning, sailor’s warning’, which actually has its roots in the bible (Matthew 16:2-3). Despite sounding far fetched this often holds true. British weather usually comes from the west, so a clear evening sky heralds fine weather, while a red morning sky can be caused by high cirrus clouds at the leading edge of a front. Similarly, the high wispy clouds of ‘Mare’s tails and mackerel scales’ indicate an approaching front.

'Red sky at night, sailor’s delight, red sky in morning, sailor’s warning’

Red sky

Many ditties also refer to the moon. Cloudless night-time skies in winter allow the heat of the day to dissipate quickly and, without a breeze, ‘clear moon, frost soon’ was often a reliable predictor of a cold snap. The tiny ice crystals in thin, high cloud can refract the light of the sun or moon to create a soft surrounding radiance, and ‘Halo around the sun or moon, rain or snow soon’ foretells the possibility of an advancing front with its precipitation.

Rainbows can be striking phenomena and are caused by the refraction and reflection of sunlight through droplets of moisture in the air. They always appear in the opposite direction to the sun and in the afternoon often materialise after a heavy shower. However, ‘Rainbow in the morning gives fair warning’ indicates rain in the west and generally heading your way.

clouds

Finally, there are some weather theories that are associated with special days; Candlemas Day (2 February – a double winter), St Swithin’s Day (15 July – forty days’ rain) and Michaelmas Day (29 September – snow at Christmas). Whilst interesting, these are pure superstition and have become established because people only remember the years on which the prophesy was fulfilled.

Essentially, short-term area meteorological forecasts can be reasonably accurate, but a reliable long-range prognosis is a much greater challenge. In Wales they say ‘When you can see the hills, it’s going to rain; when you can’t see the hills, it is raining!’

why does is always rain on me?

Have you got a favourite weather saying, or a foolproof way of predicting rain? Tell us in the comments!

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