Royal wedding: What's the weather forecast?

Women with umbrella in rain
Image caption Will wedding guests to Westminster Abbey need an umbrella? Hopefully not

With the royal wedding just over a week away, preparations are in full flow, with every last detail being covered. However there is one aspect of the day that no-one can control - the weather.

Prince William and Kate Middleton's decision to get married on 29 April makes it one of the earliest royal events ever to be celebrated in the calendar year. This spring-time date has meant there is a greater chance of it being cooler. There was still fresh snow falling in parts of Scotland in May 2010.

But having emerged from what felt to be a long and cold winter, the recent warm weather, and lack of traditional April showers, has raised people's hopes of a sunshine-filled day for the royal couple.

It may still be some days away but what is the forecast? Will those lining the wedding processional route be packing suncream or waterproofs?

Met Office

Image caption What April showers?

The outlook from the data provider for BBC Weather is optimistic. "We're in the midst of a pretty good spell of weather. I think there's little change from what we've got now, condition-wise - with high pressure seemingly dominating across the UK particularly across the south," says Barry Gromett from the Met Office.

"It looks reasonably promising. I wouldn't like to put any real detail on it this far away but it's looking that the chances are we'll get good conditions, light winds, temperatures in the teens. It doesn't look like a complete wash-out."

Historical look-back

Weather on April 29
2010 Cloudy weather image Dry, warm cloudy
2009 Sunny weather image Clear, dry, sunny
2008 Rainy weather image Cold, cloudy, quite wet
2007 Sunny weather image Dry, warm, sunny
2006 Cloudy weather image Cloudy, cool, sunny

Source: Met Office

In order to predict what will happen on the day it could be tempting to look back at 29 April in previous years.

However, this method cannot be relied upon, as was proved by the Queen's Coronation in 1953. The date, 2 June, was selected based on historical data for that day showed it to be mainly dry. On the day, it poured with rain. Philip Eden, former vice president of the Royal Meteorological Society, warns that this technique "must be taken with a barrel-load of salt".

He says, "It's nice to look at the statistics, but for a particular event on a particular date they don't mean anything. If you had 100 years of 29 April then it's perfectly possible to have had heavy snow, or a thunderstorm, or a heatwave, or to a gale."

Other forecasters

Image caption Back in November it was a very different temperature

Other meteorologists agree that it is likely to be a sunny spring day. Positive Weather Solutions differs from the Met Office in that its system makes long-range forecasts. These tend to look ahead for seasonal trends and patterns.

However on this occasion, senior forecaster Jonathan Powell made a prediction for the big day back in November. He says, "For this date we thought we'll put our neck on the line and go for it. Back then, it predicted a dry, warm day with sunny spells. We see no change at all from that."

Weather lore

The aternative to the scientific methodology used by professional forecasters is weather lore, making a prediction based on traditional folklore.

The old adage, "red sky at night, shepherds' delight" is one worth looking out for on the eve of the wedding, says former BBC weather forecaster Bill Giles. But he acknowledges that this has some scientific basis unlike many others. In an era of satellite imaging and computer modelling, calling the weather using pine cones or seaweed is decidely old fashioned.

Mr Giles reckons the size of the area over which a forecast is being made matters too: "The big problem with folklore is that it's been made up by people in different regions. It's really very short term. It's great fun to try but depends on what part of the country you're in. An east wind is completely different whether on the east coast or the west."

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