Guess where it will rain & win £10 © Walkers.

Walkers crisps are launching a new promotion at the moment highlighting the importance of the British weather for their potatoes.  The promotion allows the public, having got a voucher code from a packet of Walkers crisps, to log on to the website and have a go at guessing where across the UK or Ireland it might rain during certain three hour periods.  If you are right then you win £10 or €10.

We are using our expertise to support Walkers by providing rainfall data to validate competition entries. Walkers have decided that if it has rained 1 mm or more in your chosen grid, you will win. To reach 1 mm or more of rain, you are looking for continuous rain for three hours that you can readily feel on your face and will make the ground wet, or a slight shower that lasts for 30 minutes and causes puddles to form. It is worth remembering that a steady drizzle of three hours may not actually give 1 mm.

Walkers use home-grown potatoes to produce their crisps and weather forecasts are essential to food production. As the UK’s official weather service the Met Office plays a vital role in helping UK agriculture.

The Met Office will use the UK weather radar network, which is used to measure how much rain is falling at a given time. This records the rainfall over the Walkers map of the UK and Republic of Ireland every five minutes within each three-hour timeslot available. In order to confirm 1 mm or more of rainfall has fallen over your chosen grid-spot during your selected three-hour timeslot, several radar accumulation points are averaged together across your chosen 4 km² area. Radar observations provide the best way of observing rainfall across the whole of the UK. Radar makes an estimate of rainfall over an area that is then processed to give a total over 4 km² areas. Although the radar is very good it can not be 100% accurate.

Forecasting for the UK is very difficult as it has very changeable and varied weather. This is a daily challenge which Met Office forecasters rise to, making them amongst the best in the world. No weather forecast can ever be 100% accurate, especially when forecasting rain to 4 km², but the Met Office provides the best advice possible. Using the forecasts on our website can increase the chance of you picking the right rainfall spot.

The competition runs until the middle of next month and you can find out more about how we are helping on the Met Office website