With snow starting to fall across all parts of the UK and Ireland, you might be wondering how and why your snow forecast could change.

In recent weather models, snow has now snuck into south-east England for Sunday evening, just two days before the event is due to occur.

You might be wondering why the snow wasn't in the forecast until now, and it is because snow can be hard to predict. For starters, in this case, the weather models changed from a dry scenario, to having a frontal system push up from the Channel.

There is also such a fine line between rain and snow, so even though it is now in the weather models, and on the WeatherRadar as snow, it doesn't necessarily mean that is what will be falling out the sky. Let us explain what this means:

Most precipitation first falls as snow from clouds, even sometimes in the summer months because it is so much colder higher up in the atmosphere.

Whether it then hits the ground as rain or snow depends on the temperature of the air that it’s falling through. The level at which the precipitation falls as rain rather than snow is known as the ‘freezing level’.

This is where the problems begin, because that can change over very short times and distances. When forecasting snow, elevation and surroundings are very important.

If the freezing level is higher than where you live but only by a fraction, you may be able to see snow on nearby hills. If you live in a city, it’s likely to be warmer than the countryside, so the snow could be just a few metres up the road.

The freezing level can change suddenly if the wind direction changes, altering where the air has come from or how long it has spent over the sea. If precipitation is falling heavily, it can drag down the freezing level down, turning heavy rain to snow.

If the temperatures are very low, around -8C, then snow obviously becomes easier to predict. But in the UK our temperatures are usually nearer freezing and a fraction of a degree is all that separates rain and snow.

This makes snow one of the most tricky parts of a forecast. Stay in the know on our WeatherRadar, so you can see the most up-to-date data yourself!