The clocks generally forecast short term for the day ahead, however, this does depend on a few things.For example, if the air pressure falls really fast it would make a clock move to 'Rain' or even 'Stormy' (!) as rain is likely in the immediate hour or so. This area of low pressure might, however, be really big and/or slow moving - and so giving us all quite bad weather for several days. In such instances, the 'Rain' prediction is (although unknowingly) a longer term outlook.Similarly, in times of high pressure, a clock would be expected to display 'Fair' or occasionally 'Very Dry' meaning that the outlook is good for that day. Quite often, though, these high pressure systems (anti-cyclones) stick around for a while and so it would not be unusual for the same forecast to remain for several days. In addition, the clocks are sensitive enough to also notice smaller 'bumps' in air pressure. We occasionally see at BB HQ, single showers being picked up by the clocks. The pressure will drop slightly, it'll go dark outside as the rain cloud approaches, and then halfway through the shower, the clock will change back to fair, well in time for the end of the shower and the sky to clear! Sometimes it even just picks up single clouds that might only be on the verge of raining.