Today's post is brought to you using data from nw3weather.co.uk, an automatic weather station located on the southern edge of Hampstead Heath. It's a fantastic amateur site, if you like meteorological statistics, with real time and archive data available in graphical and tabular form. The site owner admits that the data isn't necessarily 100% accurate, but it's a lot more accessible than anything the Met Office might churn out. With this summer's rain showers being especially hit and miss, there's also no guarantee that the rainfall data from Hampstead matches the rest of London. But I needed to pick one location and stick to it, so Hampstead's as good as anywhere.
Each graphic below shows the weather for one month in calendar form. Weeks start on Sunday and end on Saturday. I've used one symbol per day, with the raincloud meaning it rained at some point during the 24 hours from midnight to midnight. The sunshine symbol simply means it didn't rain, not that it was necessarily sunny.
Today is StSwithun'sDay - the 1150th anniversary of the day Bishop Swithun of Winchester was buried in 862AD. Legend has it that if it rains on July 15th it will continue to rain for the next forty days. It's a rubbish legend, obviously, based on zero observational evidence and a series of apocryphal stories. But with the jet stream locked into a persistent meander to the south of the British Isles, maybe this summer there might be something to St Swithun's rhyme after all.
Remember March? March was glorious, at least relative to other Marches, with a succession of unbroken dry days throughout the month. Only three days were wet, with half the month's rainfall falling on Sunday 4th. It was the the UK's driest March since 1953, contributing to that long-term drought which - you remember - everyone was oh so worried about. March seems such a long time ago now.
Then came April. A hosepipe ban kicked in during the first week of April, and the weather turned almost immediately. It rained and rained and rained, a total of 20 days altogether, with almost all of the second half of the month being wet. At Hampstead there were nearly four inches of rain in April, 75% more than usual, and across the UK it was the wettest April on record. It feels like it hasn't stopped since.
But May got better. The first half of May continued wet, then bang in the middle of the month the weather switched back to warm and dry with blue skies. This balancing act meant that, overall, May turned out pretty much average. The only rain in the entire second half of the month was a trace on Wednesday 30th. It would have been a glorious bank holiday weekend, if only this hadn't been held back for the Jubilee.
June wasn't good. Every single day of the extended Jubilee weekend was wet, with Pageant day (June 3rd) the third wettest day of 2012 so far. By the end of the month there had been 18 wet days, almost as many as in April, although rainfall totals were actually higher. Hampstead got double its usual June rainfall, peaking with more than an inch on Monday 11th. Across the UK it was the wettest June on record... although the last week of the month was warm and dry - you've probably forgotten that already.
And here's July so far. July so far has been foul. We've already had twelve wet days, more than in the whole of May, and we're not yet even halfway through the month. Only Sunday 1st and Thursday 5th have been dry, and in just the last week we've had more than the average monthly rainfall. Sure,this sort of thing happens sometimes - the English summer is notoriously fickle. But it's rare for so many records to be be broken, and rare for decent sunny weather to be so persistently absent.
Which brings us to St Swithun's Day. Saturday's heavy showers all passed through before midnight, so it's just possible that Sunday 15th might be an atypical dry day. If the legend is correct this means 40 dry days, right up to the August Bank Holiday. But more likely the jet stream will fire yet more showers across the UK and we'll get nearer 40 days of rain.
Olympic officials are praying for dry, because nothing will dampen the public's spirits quicker than a fortnight of relentless rain. Having attended the BMX test event last summer where it chucked it down, I know that the organisers are well prepared for prolonged downpours. But as a spectator it's hard to enjoy an outdoor event when you're forever running for cover, or when the selfish witch sat in front of you sticks her umbrella up.
St Swithun's day if thou be fair, for forty days 'twill rain nae mare. We can but hope.