The 15th of July in any year is known as St. Swithin's (or Swithun's as the original is supposed to have been) Day after the 9th century Bishop of Winchester. It is said that the Bishop asked to be buried, whilst uttering a last request on his death bed, outside of the cathedral in a simple tomb not within the cathedral - "where the sweet rain of heaven may fall upon my grave". This was done when he died in 862 AD (CE). But Bishop Aethelwold decided to rebury Bishop Swithun, after his canonistaion, within the cathedral and whilst his remains were about to be transferred with great pomp and ceremony on the 15h of July 971 AD (CE) - a great storm that continued for about 40 days broke the previous weeks of drought and ruined the ceremony. His remains were left outside.
It is from this account that led to the rhyme that follows:
"St. Swithin's day, if ye do rain,
For forty days it will remain;
St. Swithin's day, if ye be fair,
For forty days 'twill rain nae mair."
Unfortunately, this piece of history can neither be backed up by historical data or by weather statistics so says the Meteorological Office in this posting. Since the start of records in 1861, there have been no periods of either forty dry or wet days following the 14th of July.
The Met Office has recently published a post that describes the reason for the wet weather that has delayed or cancelled many of the summer's outside events - "Our weather here in the UK is complex and determined by many different factors, including the position of the jet stream (a narrow band of fast moving winds which runs from west to east across the Atlantic high up in the atmosphere)." The post continues to state that the "low pressure systems bearing rain and unsettled conditions move across the Atlantic on a regular basis" that are guided by the jet stream that would normally be north of the UK giving us relatively settled weather. But "this year it has been to the south of the UK, guiding those systems straight to us. This is the position we’d normally expect the jet stream to be in during winter, when we are more accustomed to these wet conditions." The Met Office gives a few reasons as to why there has been this persistence on the jet stream being south of the UK, so have a look at their blog post.
The Met Office has also published a list of locations in the UK that have had over 100% of their average July rainfall, the Isle of Portland has had over 250% already.
If you are unlucky to live in an area that has had flooding or is about to flood (you can check on an interactive flood map by Shooter Hill and the EA), the Environment Agency has prepared notes on how to prepare your property for a flood from either river or groundwater, both these leaflets can be found here.
