Recent news reports claim they can tell you when the next ‘Beast from the East’ will hit the UK, including the exact date and time when snow will affect different areas. Here’s why you can’t trust ‘exact’ long-range snow forecasts.

Why is snow so hard to predict?

Snow is one of the hardest weather phenomena to predict in the UK, largely because the UK is an island surrounded by relatively warm seas. Oftentimes, snow events are what meteorologists term as ‘marginal’ – meaning the temperature is expected to be close to 0°C and a small shift up or down will mean the difference between rain and snow.

It is also difficult to predict the overall weather patterns which lead to cold air being in place over the UK, and which weather systems will bring enough moisture into that cold air to make it snow.

Chaos theory tells us that a very small error at the start of a weather model’s predictions can rapidly grow into a massive error over time. Weather models also make assumptions about how the atmosphere works, and while they are very good at simulating the atmosphere, these assumptions inject some uncertainty into the predictions.

How do meteorologists forecast snow?

Meteorologists have various tools to mitigate, to some degree, the uncertainty in weather models. One such tool is to run a model many times, with slightly different starting conditions, rather than just once. This ‘ensemble’ approach to forecasting can give some idea of the spread in possible outcomes, and if some outcomes have more support than others.

Think of it a bit like seeing the odds of all horses in a race, rather than just one. You still don’t know which is going to win, but some horses are given better odds of winning. In the weather world, meteorologists might favour one particular outcome – it doesn’t mean that’s what will happen, just that this scenario has a better chance of happening.

Thus, when you read a story showing one weather map indicating a massive snowstorm over the UK in 3 weeks’ time, it is important to use some critical thinking. Don’t believe a highly detailed snow forecast made weeks in advance and always check a reliable source of weather information.

Is another Beast stirring?

Ever since the cold and snowy weather event infamously termed the ‘Beast from the East’ impacted the UK in 2018, any hint of an easterly flow affecting the UK in winter seems to be given this moniker from some media outlets.

Image: False-colour satellite image showing snow and ice (red) over parts of the UK and Europe on February 27, 2018. Source: NASA Worldview.

Over the past week, various news articles have latched on to a few bits of weather model data and declared that the next Beast is awakening, and on its way to the UK sometime over the next few weeks. Some of these stories promise to tell the exact date and time when snow will affect different parts of the UK.

Whilst there are indications that a cold flow from the east is possible over the UK in the upcoming weeks, it’s far too soon to be able to say anything beyond this. Check Weatherzone’s latest forecasts over the coming weeks to stay up to date with conditions in your area.