July 15th is Saint Swithin's Day

St. Swithin's Day is 15 July, a day on which people watch the weather for tradition says that whatever the weather is like on St. Swithin's Day, it will continue so for the next forty days.

There is a weather-rhyme is well known throughout the British Isles since Elizabethan times. copied from projectbritain.com

'St. Swithin's day if thou dost rain 

For forty days it will remain 

St. Swithin's day if thou be fair 

For forty days 'twill rain nae mair.'

dost = does

thou = you

nae mair = no more.