A forty day weather forecast?

  • A forty day weather forecast?
    14.07.2011 15:45


    July 15th is St Swithin’s Day, and it will rain in the west and north of the country.

    Winchester, where the saint is buried, should certainly see some rain later. So, does that say anything about the next 40 days? It should continue to rain, right? Or in the east, where it will be a reasonably fine day, will there be fair weather for over a month?

    Let us remind ourselves of one version the old rhyme:

    St. Swithin's day if thou dost rain,
    For 40 days it will remain;
    St. Swithin's Day if thou be fair,
    For 40 days will rain nae mair.

    Swithin was a Saxon bishop of Winchester in what was then Wessex, and a humble man who requested that when he died he be buried in a simple grave outside Winchester Cathedral, “where the rain from the eaves might fall on it.”

    However, his successor, Aethelwold, decided that his remains should be moved to a shrine inside the Minster on July 15th 971. The plan was thwarted when heavy rain fell, breaking a long drought.

    When it stayed unusually wet through the following days and weeks the plan was abandoned, not only for practical reasons but because the deluge was interpreted as a sign of heavenly pique.

    We shouldn’t be too literal and expect a continual deluge until Aug 23rd but the legend does call for an unsettled and often rainy period. Of course, it is quite often incorrect but there is a grain of truth in there, as there is with several old weather adages.

    The English naturalist John Ray drew a similar conclusion. He wrote in 1670 in his book English Proverbs that "If the first of July be rainy weather, it will rain, more of less, for four weeks together."

    So far he is in essence quite close to the truth, and there is a little sign of an upturn in the weather during the next week or possibly two.

    These predictions sometimes – not always – work out because our forebears noticed that certain weather regimes can become persistent during the summer months. Let us not forget that the St Swithin’s Day fable also suggests the possibility of forty fine days if it is sunny on July 15th.

    This year is quite a good example of one of those patterns. We have had, and will continue to have for a while longer, a ridge of high pressure in the mid-Atlantic. This has shown only occasional signs of building east and north-eastwards to bring periodic temporary warm and dry spells before disappearing back to the Atlantic. Low pressure troughs or depressions around its eastern flank across northern and western Europe ensure unsettled weather with frequent rather cool airstreams from the west and northwest.

    These patterns sometimes only start to shift when we begin the march towards autumn, beginning in August. So might we have to wait until the last month of summer and the beginning of September for something warmer and drier? Perhaps. There are few late-summer sayings that might guide us.

    By: Stephen Davenport