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The outlook was correct, but even the weather forecasters were astonished at how thick and fast snow fell in the south-east today.

And there is plenty more on the way this evening and tonight. With freezing temperatures during the night, there is no sign of a thaw, so any further snowfalls will simply pile up the snow even deeper, leading to more disruption to transport.

Snowfalls over 15cm deep have not been seen in southern England since 1991, although they are much more common in Scotland and the north of England. But in Kent this morning, there was added drama in the form of 'thundersnow' - lightning and thunder erupting in the snow showers - thanks to warmer air off the sea lifting up through colder layers in the atmosphere.

The trigger for this outburst of brutal weather was a depression over France dragging in bitterly cold air from central Europe. As raw easterlies swept across the Channel they loaded up with moisture from the sea and then funnelled snowstorms through the Thames Estuary into London and on through the Thames Valley. This helps explains the extraordinary depth of snowfalls that people woke up to in London and the Home Counties this morning.

But a further band of heavy snow is racing in this afternoon, as the depression from France piles through the UK, hitting the South East first and then sweeping up through East Anglia, the Midlands into North East England and East Scotland. Unfortunately those showers will be driven on by strong winds that could bring snowdrifts through the night and lead to even deeper accumulations of snow. Then, as temperatures freeze during the night, the snow freezes and turns into treacherous icy conditions by tomorrow morning, and although there will be fewer snow showers tomorrow morning there will be a bitterly cold wind chill factor in the biting wind.

How long will this appalling weather last for? Unfortunately there is no end in sight just yet. Once snow stays on the ground it acts like a refrigerator, helping to keep temperatures cold. And the weather patterns are not helping, either, as another depression drives through on Thursday, bringing the threat of another outbreak of snow and cold.

To add to the misery, the winds by then are expected to sweep down from the Arctic, bringing bone-chilling temperatures.

It will need a huge change in the weather patterns to break this freezing cold deadlock, and there are no signs of this happening until mid-February. But that sort of forecast comes with a big cautionary note, because it is too far ahead to make any confident predictions.

Quite what has made this winter so wretched is not certain, but there are signs of a sudden shift in the temperature of the stratosphere, several miles high in the atmosphere. For reasons not entirely clear, the temperature of the stratosphere has increased and this has impacted down into the lower atmosphere, where most of our weather occurs.