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Weather Home UK World Sports Coast and Sea Climate Change Features Understanding Weather Sport and Leisure Health and Culture History, Literature & Religion Science and Nature Coast and Sea Weatherwise About BBC Weather Site FAQ About the BBC	Mists in March, Frosts in May?

		Dating from the 17th Century, one well-known weather saying is thought to help you use March's weather to forecast that of May.	Key Points Radiation fog forms as the Earth and atmosphere lose their heat to space. High pressure in May can lead to frosty conditions. Sayings that attach a forecast to a date in the calendar are often doomed to failure in the UK; our weather is just not that reliable! Also in BBC Weather Nature's Forecasters Weather and Visibility Indigenious Meteorology Weather and Behaviour Disclaimer The BBC is not responsible for the content of external websites.

	For the month of March, there are several well-known weather sayings. One of these, dating from the 17th Century, is thought to help you use March's weather to forecast that of May, and goes as follows: "So many mists in March, so many frosts in May." In other words, you will see as many frosty days in May as there were foggy days in March. But is there any meteorological fact behind this saying? Inland, and not unusually in March, radiation fog can form as the Earth and atmosphere lose their heat to space on calm, clear nights under high pressure systems. Similar high pressure areas can promote calm, clear nights in May, ideal for the formation of ground frost should the air temperature fall low enough. Weather records can be examined to establish if this is true. So there is a link between mists in March and frosts in May in so much as a high pressure situation may allow both conditions to arise. But, for the lore to hold, the conditions must occur on the same number of occasions in each of the two months. Weather records can be examined to establish if this is true. The saying possibly originated in Wiltshire, a county sufficiently enough inland for radiation fog to occur. Lyneham and Boscombe Down are two villages in Wiltshire with weather stations, from which the number of 'Days of Fog' in March and 'Days of Ground Frost' in May over a 25-year period can be compared. In Lyneham, the number of fog days in March equalled the frost days in May in just one year during the period studied. In Boscombe Down, the results were only a little better; there were only two successes in 25 years. A look at seven other stations from around the UK was no more successful. Sayings like this one that attach a forecast to a date in the calendar are often doomed to failure... So the saying does not hold true. But weather lore often does have an element of truth behind it, particularly those which foretell the weather using signs in the sky. Sayings like this one that attach a forecast to a date in the calendar are often doomed to failure in the UK; our weather is just not that reliable! The 'truth' behind this one must simply have been a keen 17th Century weather enthusiast doing a spot of 'pattern matching' - noticing a correlation between the number of March mists and May frosts. Whether he spotted it correctly at the time will never be known!

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Mists in March, Frosts in May?