This morning I looked at the BBC website's 24-hour forecast for Cambridge in order to judge how wet I was going to get walking out to Tesco at lunchtime; it said it was raining a bit at 11:00, would be raining a lot by 13:00, and would become an outright thunderstorm by 16:00.

Trouble was, it was already after 11:00 and there wasn't a drop of rain in sight. So, on the basis that it might just be late, I went to Tesco as early as reasonably possible, and it was still bone dry.

But it's now past 13:00 and still not raining, and the BBC website still thinks it's pouring down out there. It's very much like the motion-tracker scene in Aliens, where the guy with the detector keeps insisting that the aliens are already inside the room and the guy in the room keeps saying no they're not. Only it would be rather hard for the weather to turn out to be hidden where the aliens were…