This Christmas outlook is based on the latest ensemble runs of the GFS, GME, UKMO, ECMWF and GEM models. More here

General situation: Mild first, but a deepening low pressure system north west of Iceland will send some very cold and wet polar maritime air right across the British Isles. Very cold upper level air masses might even trigger a wintery thunder over the far north.

Confidence for this forecast is moderately good. Models agree on the main parameters. Confidence is almost 90% for wintry conditions over the northwest and still some good 60% for at least a wet flake or sleet in south-east lowlands. Note: This is so far the most promising White Christmas outlook since 2001.

It will start with a wet mild spell on the 23rd, but it will slowly be turning wintry over the far north during the early hours of the 24th.

Christmas Eve: Confidence is moderately good that higher grounds in Scotland and much of NW Ireland will see wintry showers, wet first, but more and more turning to sleet and snow by noon. Later in the day these wintry hill showers might reach the S Pennines and wintry conditions will affect most of N Ireland and Scotland. The wet cold temperatures will even feel colder in chilly breezes over North. Much of the snow on grounds higher than 400m (1,200ft) asl will still be lying the next day.

Christmas Day: Chances for a "Bookie-Christmas", i.e. wintry with sleet and wet snow showers for many are pretty good as it will be turning even colder and wintry for possibly most of Britain. Snow might rest on hills over 300m (900ft) asl. There might even be an isolated thundery snow shower over the far north during the early hours of Boxing Day.

Issued Monday, 20th Dec 2004, 4:30 pm. Updated regularly.