In reply to Slackboot:
It depends on what exactly you mean by long range, but you're right, most forecasts have some climatological built into them to try and keep the forecast within plausible limits. This helps to filter out the more extreme forecast outputs, but it does have the down side that more extreme outputs are very occasionally right!
Depending what your looking at most medium to long range forecasts will be model driven, but can have some skill applied, such as looking at things called teleconnects, basically global weather that can have an influence on our weather a few weeks down the line. A couple of the more commonly known of these are the Northern Atlantic Oscillation (negative phase gives a higher chance of cold dry weather) and sudden stratospheric warming which can increase the chance of cold easterlies across the UK two or three weeks later.
That said, they still come with large amounts of uncertainty.
Post edited at 12:00