St Swithun's Day Weather

  • A washout so far this summer has caused flooding across parts of the UK. Photo: Steve Parsons/PA Wire.

    An upper level chart for noon on Monday 16th July. The jet stream is clearly visible over the UK indicating unsettled weather. Wind speeds (shaded) are in metres per second.

    The upper level chart for noon on Saturday 21st July indicates a different jet stream position. Southern areas are likely to see more settled conditions.

  • St Swithun's Day Weather
    14.07.2012 14:49

    Rapidly approaching is the feast day of St Swithun, an Anglo-Saxon Bishop of Winchester. Although relatively little is known about his life, a posthumous meteorological lore exists that has garnered significant interest over the years:

    St Swithun's day if thou dost rain
    For forty days it will remain
    St Swithun's day if thou be fair
    For forty days 'twill rain nae mare

    The origin of this myth is uncertain to say the least, but one of the better known legends is that Swithun was unhappy at being moved from his outside grave to a golden shrine inside the Cathedral. The day of the move was supposedly marred by heavy showers, an apparent sign of his displeasure. The following 40 days were then said to have been deluged by outbreaks of rain.

    A better known explanation for the lore is the seasonal characteristic of the jet stream, a fast flowing ribbon of air approximately 7-12km up in the atmosphere. Around mid-July, the position of the jet stream often remains fairly steady until the end of August. If the position is to the north of the UK, generally settled conditions can be expected. However, if it is over or south of the UK, the dominance of low pressure is more likely leading to cooler and wetter weather.

    This year, residents of the UK could be forgiven for thinking that St Swithun’s day was at the start of June after the many weeks of downpours and local flooding. Indeed, the jet stream has been positioned further south than usual bringing us near-constant unsettled conditions. For the actual day itself (15th July), showers are expected across Scotland and Northern Ireland, whilst much of England and Wales will be dry with just the outside chance of a few showers.

    Looking ahead, the forecast is for further showers and longer spells of rain for the coming week, although a ridge of high pressure could bring some respite next weekend. Thereafter, there are indications that some drier conditions will build across southern parts, while the north is more likely to remain unsettled at times.

    By: Nick Prebble