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

The Met Office has suggested swathes of the UK could be set for a cold snap next week, with many areas also told to prepare for the possibility of waking up to a dusting of snow.

But while the official long-range forecast has warned of “wintry showers” – including snow – predicting Britain’s weather is rarely a straightforward affair.

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

How accurately can the Met Office forecast snow?

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.”

Is it possible to forecast an ‘exact date’ of snow?

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.”

How should I prepare for the Great British weather?

Probably pack a big coat (just in case).

What about ‘Arctic blasts’, ‘snow bombs’ and ‘Beasts from the East’?

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.”

What is the long-range forecast and how reliable is it?

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 current long-range forecast.

“But at this stage it’s too difficult to put that in any detail in terms of how that could look going into next week.”