Today's Midsummer Day, so not long now 'til July ... and the middle of July (15th) is St Swithin's Day.  The famous day where folklore says that if it rains on that day, then it'll rain for the next 40 days and nights.  Which'll be until the end of the summer, so St Swithin's is a very important day.  

Whether this is true or not is a moot point.  Perhaps it more reflects that if it's wet on 15th July perhaps then we're having a rotten summer anyway.

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

St Swithun's Day is on 15th July.  Will it rain for yet another 40 days?

The St Swithun's Day legend is an old one –the earliest surviving written reference dates back to the 14th century – although its roots are much disputed. 
St Swithun (or Swithin) was an Anglo-Saxon bishop of Winchester who died in around AD862. 
The clergyman requested that his remains be interred among the common people outside the church.  But in 971, after he had been made patron saint of Winchester Cathedral, his body was dug up and moved to a new indoor shrine. 

According to some writers, this caused sufficient displeasure in the heavens for a terrible downpour to strike the church and continue unabated for 40 days, hence the legend. 
The only problem with this theory is a complete and utter absence of any evidence, with no early account of the reburial mentioning the slightest drop of rain (http://www.rmets.org/weather-and-climate/weather/st-swithins-day, and also see: http://resources.woodlands-junior.kent.sch.uk/customs/stswithun.html).

However, here are some St Swithin's Day activities - no matter what the weather they'll still be fun: 

http://nurturestore.co.uk/st-swithins-day-activities-rainy-day-activities

http://funny-pictures.picphotos.net/20-best-indoor-kid-crafts-and-activities-for-rainy-days/itsalwaysautumn.com*wp-content*uploads*2014*01*kid-activities-crafts-rainy-day-busy-winter.jpg/

and some more are here: 

http://fimby.tougas.net/five-free-activities-rainy-summer-days 

and 

http://www.telegraph.co.uk/education/3354368/10-things-to-do-on-a-rainy-day.html