When will it snow? How many days ahead the Met Office can give accurate forecast

You may see forecasts of snowfall days or even weeks in advance. But how accurate are these reports?

Pedestrians struggle through a heavy snowstorm in Windermere, in the English Lake District
The Met Office has predicted a cold snap in the UK next week, but how accurate are forecasts? (Getty Images)

Up to 20cm of snow could hit the UK over the coming days in the country’s “first taste of winter”, the Met Office has said.

The weather agency is usually cautious about snow forecasts, and regularly plays down "exaggerated headlines". It's because predicting Britain's weather – particularly snow – is rarely a straightforward affair.

Here, Yahoo News UK tries to make sense of things.

Snow forecasting for anyone, even the Met Office, can be pretty tricky – just one degree warmer or colder can be the difference between a washout and a winter wonderland.

Location can also make a difference. The same type of weather front might lead to snow somewhere in a higher altitude, but cause rain in low-lying areas.

The Met Office says that the UK's specific location makes it particularly difficult to accurately predict snow too far ahead, especially compared to some other countries where snow can be quite reliably forecast "days or weeks in advance". Part of this is down to the fact the UK is surrounded by water.

Some media reports forecasting snow weeks or months ahead will often be based on a single predictive model. However, official forecasts will compare several models before giving a judgement – and even that will be couched in terms referring to the relative likelihood of a given weather event.

“It only takes very small temperature changes to determine whether it’s impactful snow that reaches the ground or just brushes the tops of the mountains," Met Office spokesman Stephen Dixon says.

“What meteorologists look for includes where the air is coming from – is it from a colder region that could mean a chance of snow generation?

“Where warm air meets colder air in the winter months – these fronts meeting can introduce moisture, which can allow snow to fall. But it’s often a fine line between who can see snow and who can see rain more than a few days' ahead.”

London, UK. 11th November 2024. UK Weather: Morning mist and fog over the city, seen from Richmond Park, brings a continual period of dreary “anticyclonic gloom” with overcast conditions of fog, drizzle and low cloud, according to the Met Office. The mist has been under way since the start of November, with some regions of England recording just a few minutes of sunshine this month. Credit: Guy Corbishley/Alamy Live News
The UK has had a relatively dry November so far. (Alamy Live News)

There's a reason the Met Office presents its long-range forecasts for the UK as a whole – there's not much point trying to be any more precise.

Even short-term daily predictions for the next five days can change at short notice due to small fluctuations in air pressure, temperature or wind direction.

“Forecasts are quite tricky to do in the UK, where we have competing air masses," says Dixon.

“What those excitable headlines don’t quite capture is the uncertainty forecasts get the further ahead you look. When you’re looking a week or two ahead, a date for a particular set of conditions is not really how it works.

“Meteorologists will talk about the degree of certainty they have in competing scenarios that could happen - or not.”

The Met Office is becoming less shy about criticising some of the more "excitable" weather headlines which appear in some media.

In September, it even went so far as to label one story claiming the UK was due to be "pummelled by rain" as "utter rubbish".

While not strictly averse to some favoured media labels, the forecaster says its priority is that they should accurately reflect the expected conditions.

So while a 'Beast from the East' or 'Arctic blast' could reasonably refer to a particular weather front originating from a specific region, terms like 'snow bomb' should probably be avoided (unless it genuinely does possess explosive qualities).

Dixon says: “It’s not for me to dictate how some of those headlines are written, but what’s important for us as an organisation is that the language reflects the forecast.

“‘Beast from the East’ could refer to the conditions, but if it’s not reflective of the current outlook [it should be avoided] and that rings true for other terms.

“It’s important people understand the forecast they’re getting and we need to reflect the uncertainty they’re getting - particularly when forecasting snow at longer ranges. It can be a communications challenge.”

Heavy snowfall disrupts travel in the midlands region of the A14 near kettering. Road closures and heavy snow drifts cause chaos for travellers.
If the conditions are just right, snow can cause chaos on Britain's roads.

The Met Office's long-range forecast is split into two parts, covering consecutive 10-day and a 15-day periods.

While the shorter five-day forecast can offer breakdowns by area and even indications of what time families in a given area should expect wind, rain, sunshine or snow, the long-range forecasts cannot offer the same level of detail.

Instead, they offer a general view for the whole of the UK.

The forecaster makes clear the reason for this on its own website, pointing out "small events currently over the Atlantic can have potentially significant impacts on our weather in the UK in several days' time".

“As we’ve got this colder air, it means there’s an ongoing chance of more of these weather hazards and icy conditions as well," says Dixon, reflecting on the long-range forecast earlier this week.

Probably pack a big coat (just in case).