Hertfordshire could face extreme weather in the coming weeks as the Met Office warns that a one-in-250-year event is underway.

It comes as the forecasters share that they've recorded three Sudden Stratospheric Warming (SSW) events over winter.

As the Met Office added the "likelihood of having three SSW events in one winter period is just a one in 250-year chance."

Records of SSW events go back to the 1950s, with records showing that there are typically just one SSW every two extended winters.

But, now the Met Office is suggesting that for the first time on record, a three SSW event could take place in the coming weeks.

Hertfordshire weather could face SSW event, Met Office warns

Professor Adam Scaife, Head of Long-Range Forecasting at the Met Office, said: “Although we have not seen it before, we recently documented the chances of an unprecedented three SSW events happening in one winter. 

"Our research work, using multiple computer simulations, showed that this could occur about once in every 250 winters.”

The Met Office also shared how rare an SSW event is during an El Niño which takes place when there is an unusual amount of warming of surface waters in the east Pacific Ocean.

Professor Scaife added, “Although this is very rare, we also found that the chance of multiple SSW events is increased during El Niño and so the chance of multiple events this winter is raised.”

What is a Sudden Stratospheric Warming (SSW) event?

According to the Met Office, an SSW event is a "disruption of the normal westerly airflow 10 to 50 km above the earth."

Adding: "This often makes the jet stream meander more, which can lead to the development of a large area of high pressure over northern Europe at the Earth’s surface.

"This can ‘block’ the Atlantic low-pressure systems which are responsible for the relatively mild, wet and windy weather that often occurs in UK winters.

"This blocking pattern increases the chance of cold, dry weather in the UK and mild, wet and windy conditions for southern Europe."

The Met Office does add that an SSW may not mean bad or cold weather, explaining: "However, the impacts of an SSW do not always equate to cold weather, for example, we have only seen intermittent drops in temperature around the two SSW events early this winter and typically around 70% of events are associated with a cold snap."