Cold air incoming: When exactly snow will arrive

There is growing certainty that colder and snowy conditions are on the cards, but is it possible to say exactly when?

Through the week of March 6th, it looks as though our winds will become more northerly orientated, importing colder air and bringing more unsettled, potentially snowy conditions.

At this stage, though rather far out to say, snow showers look to blow in from the north from early next week, with the potential for more persistent spells of snow for parts of central southern England and Wales at times.

This could happen if milder air moving in interacts with the drier, colder air ahead, which weather models are currently hinting at. However, as we know, you can't trust a snow forecast too many days out, particularly in the detail.

The temperature of the air is perhaps the most crucial aspect when looking at a snow forecast. Generally, when temperatures are below 2C, snow is possible with temperatures less than zero bringing more dry and powdery snow due to the lower moisture content.

While this sounds simple, whether the precipitation actually hits the ground as snow depends on the temperature of the air it's falling through. If the air temperature is low enough throughout the snowflakes fall it is likely to stay as snow.

However, if the snow travels through a warmer patch of air, it will melt and turn into rain or sleet. So while the air on the ground might be cold enough, temperatures further up could be slightly different meaning it won't hit the ground as snow.

Altitude is another important aspect. For every 100 metres in altitude, temperatures generally fall by 1C. This explains why mountaintops often see more in the way of snow during autumn and winter compared to areas at lower levels.

Thirdly, location is important. If you live in a city or on the coast, it’s likely to be warmer than the surrounding area, so the snow could be just a few miles up the road.

Finally, it isn't just temperature, altitude or location that influences whether it will snow or not, but wind is also a factor. A sudden change in wind direction can mean you will see either heavy snow or rain depending on where the wind has come from.

If the temperatures are very low, below freezing, 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, making forecasting especially tricky.

When there is the chance of snow in the weather models, up to three days ahead, you can have a look for yourself on our WeatherRadar. We show snow using the colour pink, where the darker the colour, the heavier the snow.