WX temp charts move from a position in week 1 where all of W Europe is above norm for December (bar N Scandinavia) to week 2 where the cold air has come back from the east as far as the Balkans, E France and the Scottish Highlands though probably mostly close to seasonal norm. A fairly narrow band of coldish air for Britain and W France, with only Spain and W Med anything like mild. Rain/snow on the Atlantic penetrating to Poland on week 1, retreating W-wards in week 2 with only Spain and extreme W of Ireland affected, also a patch in Turkey.
JET - well defined but narrow and weak stream across England to Tue 27th, after which fragmented with no pattern.
GFS Op - current LP moving NE past Scotland, 980mb Rockall Wed 21st, dragging a second one in its wake 985mb Sat 24th with Arctic NE-lies on their NW edge, but the said Arctic air never quite establishing over more than N Scotland. Pressure then rises with ridge from Iceland to Italy Tue 27th, mild for W and cool for E. This slowly declines SE-wards, to Italy 1030mb Wed 4th, with SW-lies for Britain. There's a large cold pool of air associated with an LP over E Russia for much of the period.
ECM - similar to GFS but the LP Sat 24th is slower to clear and brings cold air further S than GFS does. The N-ward extent of HP on Thu 29th is more limited, never reaching Iceland.
GEFS - for England with one extra dip (Wed 21st) en route, temps decline at a different rate in different ens members to a reasonably well defined minimum Wed 28th (5-8C below norm), rising irregularly to mild by Wed 4th (control on its own but otherwise fair agreement at this range). Damp to Christmas Day, drier afterwards. In Scotland, more agreement on temps dropping before Christmas with most pptn around Chritmas Day; very good chance of snow.
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Chichester 12m asl