Forecasts are now showing 13C for Monday [t-shirt & shorts weather for Rob 
], bring it on, getting fed up with this cold spell.
Make the most of it, as there's a decent chance colder will return by next weekend.
It's a chaotic set-up at the moment, with output models flip-flopping each run. Some will show back to full-on cold by Thursday/Friday, then the next run show the opposite. And vice-versa with ones now showing mild & wet (and windy) to continue.
In simple trms, the broad set-up is persistent high pressure to our north (which has been the case for 2/3 weeks), which has been ridging southwards to impact the UK, advecting cold air over us. That has been able to happen due to pressure over mainland Europe/the Med being lower than normal. Now heights are increasing there, forcing low pressure systems to take a more northerly track - over the UK on Sun/MonTue - which in turn pushes the high pressure to our north further northwards.
The weather we get just before and over Xmas depends on the behaviour of the European high. If it contracts/shifts a little south-eastwards, that allows the lows to phase over and past the UK quickly, and this leads to the northern high ridging southwards again (into the mid-North Atlantic, putting the UK on the cold side with a brisk northerly flow). Low pressure to our east feeds some instability onto the mix, which means showers. If the air is cold enough, they would be snow.
