After a 40C summer, what can we expect from the winter?
Even with the most advanced super computers, producing a weather forecast for the next day can be challenging. Real-time observations from sea, air and space are put into advanced computer modelling of the atmosphere and simulations of the future atmosphere are created.
A meteorologist looks at the output and makes a final judgement about what the computers are showing. This decision will be based on looking at as much data as possible as well as employing years of forecasting experience and knowledge.
This is a forecast for the next few days. So how do we know what the atmosphere will look like over a season? As the cost of living goes up and fuel prices rise, understanding what this winter might look like feels more important than ever.
So how is a long range forecast created?
Weather models are replaced with climate models and, instead of looking for details, the aim is to understand larger scale trends such as a ‘milder than average’ or ‘colder than average’. There are nuances to this; if the winter overall was considered mild, it doesn’t mean that there would not be periods of very cold weather.
Over the decades long range forecasting has advanced. Large weather patterns in the atmosphere are analysed and added to climate models to increase accuracy. These patterns are called teleconnections and an example of one of these is El Niño and La Niña.
La Niña is part of a larger scale weather pattern called El Niño Southern Oscillation (ENSO). This pattern of weather is measured across the central Pacific Ocean and although it is thousands of miles away it is used as a parameter to understand what weather we could experience here in the UK over winter.
Leading Chief Meteorologist at the Met Office, Paul Davies, said: “While long-rang predictions are hard to make with accuracy, we anticipate that October will bring wet and at times windy weather, the potential for colder spells is expected to be greatest in November and December. Though colder weather is still possible in the early months of 2023, it is more likely that wet, windy and mild spells will become more prevalent.”
So what could La Niña mean for the UK?
La Niña tends to bring a drier and more blocked pattern to the UK during late autumn and the start of winter. Anticyclonic or high-pressure set up suggests some colder interludes. But as it's early in the season it's less likely to be days on end of freezing temperatures as daylight hours are still relatively long, preventing temperatures from becoming persistently cold.
Previous events of La Niña in the Pacific suggest the end of winter tends to see the jet stream strength suggesting more cyclonic set up. Thus experiencing some wetter, windier and milder weather. There are other elements to the long term forecast such as the sea surface temperatures around the UK and the Atlantic hurricane season. Overall, the longer range is suggesting that lengthy cold spells are looking unlikely.
While it may not seem helpful for day to day weather, longer range forecasting has many benefits, helping not just the public plan for the winter ahead but contingency planners such as local councils and emergency services.