Yes it does. As atmospheric pressure is lower at altitude, if a Weather Clock is used at a significant elevation above sea level, its forecasts will be more pessimistic. It would be more frequently forecasting 'Rain' or 'Stormy' weather than might be accurate.
We would expect a clock to start to be a little confused by elevations of over 180m (590ft), although if you're living in the UK, you are likely to be lower than that. You can easily check the elevation of your location at this website (not associated with Bramwell Brown!)
If you live in the mountains or anywhere above 180m (590ft), we can help and it's best to flag this to us before you place an order. We just need to program your clock for suitable elevation. Please contact us here to discuss.