One for a rainy day...

Like today...

Walkers crisps have added a competition to bags of crisps: WALKERS RAINY DAYS

Thanks to Chris Green for pointing out the possibility of using this for an activity..

The basic idea is that having registered your bag code, if you are lucky you can choose a location by grid square and you get a time slot to choose.
Each time it rains a certain amount, you could win £10...

If it has rained 1mm or more in your 3-hour timeslot on your chosen 4km² grid-spot, you will win £10 (€10 in ROI).

To reach 1mm 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.

The winning grid-spots will be verified against data provided on a daily basis by the Met Office, and all such rainfall results provided by the Met Office will be final for the purposes of the prize allocations. No correspondence will be entered into with consumers in relation to any disputed rainfall or rainfall data.

So which are the wettest grid squares in the country ?
What would be the best ones to select if you wanted to increase your chances of winning ?

Students could be asked to choose from a list of places or postcodes, or rank them in order of their "rain-potential" ??