I get the news I need on the weather report

He likes his eggs sunny side up and knows all the words to 'Greased Lightning' - who better to talk about all things climatical? Ladies and gentlemen... The Weather Doc:

OK, so last week we were filled with the joy of a vastly improved forecast. We at GFF spent a very jolly weekend shopping for rubber rings, flipflops & thongs, flopped back in our deckchairs & relaxed with a nice glass of advocaat, safe in the knowledge that the forecast was good. We had satisfied our legions of ardent (and increasingly aroused) fans and done great things for the sale of suncream.

Then Metcheck threw us a googly. I believe we mentioned that they were the first to really go for a nice forecast, while all others were urging caution. Sure enough, no sooner had the ink dried on our expertly crafted webmagic, they turned the hosepipe on our pale & naked pigeon chests.

60% chance of rain, 21 degrees.

The swines!

They had fallen back in line with the other generally less good forecasts out there & made it merely average. So, why the sudden change? Long range forecasting is a tricky business & it will be at least another month before they start getting anything near reliable. It relies on historic data, trend analysis, massive amounts of computing power and the office teaboy throwing a dart at a bunch of post-its to decide which of the various options is the most likely based on the current state of the weather.

Predicting exactly what will happen in a couple of months time is hugely problematic. All they can really say is that June will probably be nicer than April, & maybe the recent sunny spell threw their computer cogs into a spin & suggested a warm spell that the rest of the data didn't support.

It's obviously not just our beloved metcheck that rely on statistics - they all do & occasionally they can mislead us & be depressing. Theweatheroutlook.co.uk, for example, have a nice set of graphs that show the percentage deviation from average over 56 days of temperature, precipitation & sunshine. Their forecast for the start of the festival shows that it will have 80% more than average rainfall, below average sunshine & about average temperatures.

On the face of it, that sounds pretty disastrous, but let's look at the facts - our summers are getting warmer, & therefore the long term average temperatures are also rising. A temperature 10% below the 10 year average, for example, might be a perfectly acceptable temperature from 11 years ago. As the average rainfall for England & Wales in June is 65 mm, then 80% more than that is around the 115mm mark (roughly what you'd expect in September or October). However, this could be 4mm a day constant drizzle, in a few showers, or it could be a couple of 2005 storms. Let's not also forget that the figures quoted there are for the large chunks of England & Wales - including places where it throws it down a lot like the Lake District, the Welsh mountains, & my back garden. Averages, you see, include the extremes, & may not really tell us what we're really likely to experience.

And is if to prove just what a contrary madam the whole business of stochastic prediction is, no sooner had the wax dried on our tablet than Metcheck step in where other forecasters fear to tread, reducing the chance of rain by a whopping 16.7% to just 50% (yep, we're back to 'might rain, might not' again), and the temperature is an enormous 9% higher (50% chance of rain, 23 degrees C). See what fun statistics are?

Even with this change, our summary of all the summaries is still looking pretty non-descript at the moment, but the chances are that we will have some rain at some point & it may even be quite chilly without the sunshine. Don't throw away those wellies yet, or the shades, get something warm to cover up the bikini with of an evening, & be prepared to be a little moist in places.

For those of you rejoining this piece of precision predicting because you feared doom & gloom, it's going to be gloriously sunny & pack your thong.

Labels: Eavis, Glasto Festival Forecast, Weather