This is the outlook from the JMA for January, February and March. With all long range weather forecasts and especially at this range we must take it with a large pinch of salt. You will know that I look at the JMA four week outlook every week and I give it a lot of credibility. But this is real long range so lets just see what happens.
I have added the three images together and added a red line to show you where the UK is. The images show the forecast sea air pressure locations. Blues colours are low pressures and oranges high pressure areas.
The JMA thinks low pressure is situated over the Pole stretching down over the mid Atlantic and Scandinavia with a ridge over the UK, bringing a South-westerly airflow. This would bring temperatures around average sometimes slightly above average. There could be a brief spell of colder weather if the ridge over the UK collapses allowing a short spell of a northerly airflow.
Low pressure is over the Pole and the mid Atlantic and the UK with high pressure in the mid Atlantic stretching eastwards over southern Europe. We could see a strong jet stream developing bringing some stormy weather towards the UK. So with a westerly airflow we will see above average precipitation and the temperatures around average.
A change looks like it will take place with high pressure over the UK and central Europe and Scandinavia. This setup would bring mainly drier conditions and we could see some colder spells of weather if we get a easterly airflow at times.
Remember this is just one model and things can change and do so, so it would not surprise me if it turns out to be wrong at some point. Trying to forecast beyond 5 day is difficult so an outlook for 3 month must not be taken too literally