Weather predictions

January is a time of new beginnings, when many people set – and break! – their new year resolutions. The month is named after the god Janus, who had two faces, signifying that January looks back over the past year as well as looking forward to the new year.

Despite the blustery weather, the first week of January has been mild, but this does not bode well for the spring. According to several old proverbs, “March in January, January in March” or, worse still, “If January’s calends be summerly gay, ‘twill be winterly weather till the calends of May.” Another proverb suggests that “January commits the fault and May bears the blame”, but this is thought to refer to human behaviour as much as to the weather. But “if the grass looks green in January”, as it undoubtedly does this year, “it will grow the worse all the year”.

It is interesting to consider the accuracy of these old sayings. Some are undoubtedly true, especially those that make short-term predictions. For example, the Met Office website explains the saying “Red sky at night, shepherd’s delight, red sky in the morning, shepherd’s warning”. Dust and small particles, trapped in the atmosphere by high pressure, scatter blue light leaving only red light to tint the sky. If this happens at sunset it shows that the high pressure is moving in from the west, but in the morning a red sky shows that the high pressure weather system has already moved east and the good weather has past.

A longer-term prediction is the saying “Oak before ash, we’ll have a splash, ash before oak, we’ll have a soak”. The Woodland Trust looked at the accuracy of this and found that the breaking of buds on the trees depends on spring temperatures, but records collected over 250 years suggest there is no correlation between these temperature and summer rainfall.

Another longer-term prediction is the suggestion that the weather on St Swithun’s Day (15 July) predicts the weather for the following forty days. This prediction might have some justification since around the middle of July the jet stream takes one of two paths. If it moves south it pulls in cold air from the Arctic bringing cloud and rain, while if it moves north it pulls in sub-tropical air that brings warm and sunny weather. However, while a general trend may be indicated, the Met Office reports that there hasn’t been forty days of rain since records began!


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