I think that the main factor here might just be the blocking high to our west that has been coming and going recently and which as has been said before, is largely helped by a lack of any high pressure to our south. This would result in a north to south pattern of the jet stream which could work in one or two ways since we could either be on the western side of that block with the jet stream running northwards (which would result in us getting some really mild air coming up from the south), or we could be on the eastern side of that block with the jet stream then running back southwards and resulting in us getting cold northerly winds from the Arctic. So far, we have been lucky enough to be on that eastern side of the block with the jet stream running from north to south.
Generally, weather systems upon following the route of that jet stream around that block with then be diverted northwards on the western side of the block which in this case, would probably be just off the American seaboard. Those weather systems would then move around the top of that high pressure and thus approach us from the north-west before diving southwards across the country as it continues to follow the jet stream.
Basically, these weather systems are effectively just returning to their original latitudes and whilst crossing the UK, they might bring slightly less cold air for a time with cold northerly winds then coming in behind then. If there is also some high pressure to our south though, that would stop those weather systems from being able to get back south but if that high pressure isn't there, these weather systems can return south more freely and I don't think that this would require any further blocking to our east or north-east in order for that to happen.
Originally Posted by: johncs2016