An amber warning means there is an increased risk to life and property, as well as the likelihood of severe weather causing travel delays, road closures and power cuts.
A yellow warning is mainly issued when it is likely that the weather will cause some low level impacts.
Areas in Scotland and north-east England will be most affected by snow, while strong winds will be felt the most in Wales and the north and south-east of England. Heavy rainfall is expected across the UK.
The storm follows a cold snap this week, which caused some schools to close in several parts of the UK.
Higher ground in northern England and the hills of Scotland could get 20-40cm of snow, posing the risk of significant disruption on roads.
But it is affecting lower areas too. There has already been snowfall in north-east England and Scotland.
National Highways issued a severe weather alert for snow on roads in Yorkshire and north-east England as it expects blizzard conditions. It says snow is set to “accumulate quickly at all levels”.
Parts of several A-roads in England are closed due to snow, National Highways says, with traffic delays expected.
Snowfall disrupted flights out of two airports on Saturday morning.
Newcastle Airport said there was “some disruption to flights” but that it was now operating as normal after an hour of clearing the runway.
Meanwhile, Leeds Bradford Airport confirmed its runway was “fully open and continuing to operate as normal” after it expected delays due to snow on the runway.
Snow falling in wet, chunky flakes is also likely to cause power cuts as it sticks to power cables and tree branches, which may snap under the extra weight.
Across south-west England and Wales, a Met Office yellow warning for rain says that, throughout Saturday, 50-75mm (2-3in) of rain could fall widely.
The heaviest and most persistent rain will fall in south Wales and south-west England, where there could be as much as 150mm (6in) – which would be the whole of November’s average rainfall in just a day.
Incessant rain is expected to last for many hours, with some flooding likely later today and into Sunday.
