Scientist explains Storm Bert and current cold snap

Storm Bert is expected to bring snow, rain and strong winds to parts of the UK over the weekend. It is the second named storm of the season, and weather warnings have been issued across the country.

We spoke to Ambrogio Volonté, Senior Research Fellow at the National Centre for Atmospheric Science and University of Reading, who explains what named storms are, and what is causing the current cold snap.

What is causing the cold snap?

Temperatures in the UK dropped this week, with many places recording temperatures below freezing, due to cold air arriving from the Arctic. 

“Temperatures have been dropping as northerly winds brought Arctic air towards the British Isles. The cold spell initially affected Scotland and northern England, then spreading south to cover the UK and bringing snow to several regions as the cold air interacted with low pressure systems arriving from the Atlantic,” explains Ambrogio. 

Ahead of Storm Bert, wintry showers have been affecting large parts of the country. But Storm Bert will actually bring about a shift to milder air, and the Met Office advises that wintry hazards will start to lessen over the course of the weekend. 

What is a storm?

"When we use the term “storm”, or more specifically “windstorm” or “winter storm”, in this part of the world and in this season, we are normally describing a deep low pressure weather system with strong winds and rainfall." - Ambrogio Volonté, Senior Research Fellow, at the National Centre for Atmospheric Science and University of Reading

Low pressure weather systems bring clouds, wind and rain to the UK, and if intense enough, they can develop into a named storm – like Storm Bert. 

“Storm Bert is forecast to deepen explosively by Saturday afternoon as its surface pressure will rapidly drop to extremely low values. This is thanks to the particularly efficient interaction between Storm Bert’s wind and moisture pattern near the surface and the jet stream higher up. The jet stream is the core of strong winds generally blowing west to east up at around 10 km above the ground and it can play a key role in directing weather systems across the Atlantic to the UK,” adds Ambrogio. 

Why are storms named?

“In the UK a storm is given a name when it has the potential to cause disruption or damage. Strong winds, heavy rainfall or snow, associated with named storms can lead to yellow, amber or red weather warnings being issued by the UK Met Office,” explains Ambrogio. 

The UK storm season begins at the end of the summer in September and ends in August the following year. 

In Europe there are three storm naming groups, and each September there is a new alphabetical list of names issued for the upcoming storm season. In Western Europe the list is created by the Met Office in collaboration with the Irish and Dutch weather services. 

Storms can impact many countries at once so to avoid confusion the UK uses the same storm name if another European weather service has already named it.