Up to 8 inches of snow is set to fall on parts of England this week - but London is expected to remain wet and mild.
Temperatures will drop as the week goes on, with a yellow snow warning issued which covers much of Wales as well as northern and central England, the Met Office said.
Although temperatures are also set to be slightly cooler in London from Wednesday, according to the Met Office, highs of 8C are still expected.
A cold start is predicted on Wednesday with a good deal of sunshine while Thursday and Friday are set to bring heavy rain and strong breezes.
While the capital experiences rain, one to two centimetres of snow is possible in other areas of the country, while some high areas could see as much as 20cm (8 inches).
The snow warning runs from 3am on Thursday to 3am on Friday and stretches from Cumbria and the Scottish border down to Cambridgeshire and the Midlands in England.
All of northern and central Wales, including the isle of Anglesey, is included in the warning.
There is a risk of power cuts, travel delays and some rural communities becoming cut off, the forecaster said.
The snow will ease later in the day, and may turn back to rain or drizzle, especially in the south and east.
There is uncertainty with respect to the rain-snow boundary, and the northern limit of the snow, the Met Office said.
Met Office deputy chief meteorologist Chris Almond said: “While the early part of this week will see some rain, at times heavy, gradually sinking southwards, there’s an increased signal for wintry hazards as we move through the week as cold air from the north moves over the UK.
“It’s from Thursday that the snow risk becomes more potentially impactful, as mild air attempts to move back in from the south, bumping into the cold air and increasing the chance of snow developing on the leading edge.
“While there are still lots of details to work out, the initial snow risk looks highest in northern England and Wales from Thursday.”
The snow will turn into sleet and rain towards the end of the warning period from the south.
Further warnings for ice could also be issued later in the week as temperatures drop below average for this time of year, the forecaster said.
