FAX charts show the overnight quiet weather being swept away by the circulation of a deep depression 947mb SW of Iceland, with an extra disturbance in its flow for S England on Thursday (MetO yellow warning for rain along the S Coast and as far N as Oxford). Once that's out of the way it's back to W-lies with a trough arriving from the west on Sat 20th but stalling over Britain on Sunday.
GFS Op 0z; picks up from FAX and has the trough backing towards Ireland, deepening to a defined LP and then running south to Biscay 995mb by Wed 24th with an E-ly drift for Britain, cool but not really cold air entrained. This LP bumbles around N France /SW Britain (deepest 995mb Bristol Channel Boxing Day) with higher pressure from Scotland to Norway. By Fri 2nd the HP pulls back to Norway/C Europe and the Atlantic asserts itself with mild and strong S-lies for western parts.
ECM: similar to GFS but tales the LP further south (1005mb SE Spain) and increases the HP cell over Scotland (1040mb) by Fri 26th with stronger but still not cold E-lies, sometimes more SE-ly. The pressure difference between these two declines and again the Atlantic is back with S/SW-lies by Fri 2nd
AIFS London, maxima dropping from 10C now to about 3C between Christmas and New Year, an uptick at the very end, some rain this week esp Thu/Fri 18th/19th, hints of snow flurries after Christmas. Edinburgh, similar to London until Tue 30th, then a dramatic rise in maximum to 13C with rain
GEFS: in the S, mild with rain tomorrow (Thu), then near norm with a some rain through to Boxing Day, after which a considerable spread (esp in S) of ens members, majority around 5C below norm (less in N, actually near norm in far N) but nearly all dry, back to norm for New Year. Snow rows in many places have single figure values, but not more.
Seasonably cold for Christmas but almost no sign of snow.
War is God's way of teaching Americans geography - Ambrose Bierce
Chichester 12m asl