This year, December has started off on a chilly note, with some places seeing their first snowfall of the winter, as well as some frosty nights.

During the past week, I’ve mentioned on Twitter that the first few weeks of December are likely to be colder than average, although admittedly, there is some uncertainty as to how cold.

In recent days, the different weather computer models have started to show more agreement in the weather pattern during the next fortnight, with most of them showing signs of a notable cold spell.

snow tree g wp First notable cold snap of winter may arrive next week

The cause of this change to even colder weather is the jet stream – the fast moving ribbon of air high in the atmosphere that determines the weather that we experience at the surface.

During the past month or so, it’s been sitting to the south of the UK, steering low pressure after low pressure towards us, bringing heavy rain, strong winds and flooding.

However, during next week, the jet stream will split in two, with one branch heading northwards across Greenland, and another branch diving southwards into Iberia and northern Africa.

This means that low pressure systems, along with their unsettled weather, will be steered to these places instead, allowing a huge area of high pressure to build over much of northern Europe and western Russia.

In meteorology, this type of high pressure is known as a blocking high, because it acts as a barrier and blocks low pressure from moving in.

The real interesting point about this area of high pressure though, is its orientation. Given its forecast position, it will allow very cold air to seep gradually westwards, eventually reaching the UK by the middle of next week.

frosty leaf g wp 300x199 First notable cold snap of winter may arrive next weekThis will mean that temperatures in many places will struggle to get much above 2C by day, dropping below freezing at night, with -4C in town and cites, but even lower in rural areas.

Whilst confidence for a downward temperature trend is good, there are huge uncertainties in terms of snowfall – something that is really worth noting.

From past experience, I think that eastern parts of England and Scotland will be most prone to wintry showers, looking at the latest charts. However, there is a possibility that more organised bands of snow may develop and affect a wider area.

Another factor that will be notable next week, is the strength of the easterly wind. This, combined with low temperatures, will give a marked wind chill – accentuating the cold even more.

As ever, I’ll keep you updated here on my blog as the detail becomes clearer in the coming days. You can also follow my regular updates on Twitter – @liamdutton