As a weather system approaches the UK late on Saturday, rain will bump into the colder air and turn to snow.
Snow will temporarily fall in parts of southern England before quickly turning back to rain on Saturday night with milder air moving in.
For Wales, the Midlands and northern England there could be as much as 5cm of snow falling to low levels and for a time, freezing rain which brings icy conditions.
As much as 20 to 30cm (8 to 12ins) of accumulating snow is possible over higher ground in parts of Wales and the Pennines. Strengthening wind blizzards and drifting snow could lead to depths of snow up to 40cm over these areas too.
There is potential for travel disruption, power cuts and some rural communities being cut off.
By Sunday and overnight into Monday, the focus of heavy snow will transfer to Scotland with an additional Met Office yellow warning in force suggesting 2-3cm of snow at low levels and as much as 20cm over higher ground.
This weather set up, where you have cold air sitting across the UK with a rain-bearing weather system from the Atlantic moving through, is a tricky one for forecasters.
How much snow and the exact locations where it will fall can be difficult to pin down more than a day ahead, leading to uncertainties in the forecast.
