Met Office dismisses claims a ‘500-mile snow bomb’ will hit UK

The Met Office has dismissed claims that a "528-mile snow bomb" is set to hit the UK on Thursday, adding that it's made no mention of it in its forecast for the week.

Media reports this week reported an "ice blast" heading towards Britain, set to leave the north of Scotland to the Midlands, threatening to leave much of this region blanketed in snow.

News outlets referred to weather maps by WXCharts showing snow cover over large parts of the country later this week, but the Met Office has said it isn't quite that simple.

Referring to a "week-ahead" forecast, published on Monday, a Met Office spokesperson told Yahoo News: "As you see, no mention of a ‘528-mile snow bomb’."

The forecast, presented by Aidan McGivern, speaks of a "drier week of weather to come", and the only mention it makes of any kind of snow is some falling over the Pennines and the Scottish mountains on Friday.

Long range forecasts on the Met Office's website for 10-19 March make no mention of snow at all, let alone a snow bomb. The organisation dismissed similar claims in February of an even larger "630-mile ice bomb".

On its website, the Met Office accepts that as talking about the weather is a "national obsession", it is understandably going to be a popular topic for the media to pick up on.

However, it says the UK's weather is very often not nearly as "exciting or extreme" as "misleading or exaggerated" headlines often make out.

"Indeed, even when the weather is dramatic, we sometimes still see skewed or misleading headlines," the forecasting body adds.

What is a snow bomb?

The unofficial term "snow bomb" is used interchangeably with "weather bomb", which is defined by the Met Office as a "low pressure system whose central pressure falls 24 millibars in 24 hours in a process known as explosive cyclogenesis".

A millibar is the amount of force required to move an object weighing a gram, one centimetre within one second.

Explaining this phenomenon, the Met Office says: "Rapid acceleration of air caused by the jet stream high up in the atmosphere can remove air from the column, reducing its weight so causing pressure to fall at sea level.

"This in turn sucks in air which converges from surrounding regions resulting in faster and faster rotation of the circulation, in the same way that ice skaters spin faster by drawing their arms in. The resulting winds peak over a period of a few hours and can be strong enough to bring down trees and cause structural damage."

Why is it so hard to forecast snow far in advance?

As it is so cold higher up in the atmosphere, most precipitation starts off as snow or "supercooled raindrops" but will usually melt as it moves through warmer air, the Met Office says.

Whether or not it remains as snow as it hits the ground will depend largely on the air temperature further down.

There are a few factors to consider when forecasting snow. For example, if the air hanging over the UK has come from a colder region, often further north, then there's a higher probability of precipitation developing into snow.

During the winter, intense precipitation can keep temperatures lower closer to the ground, increasing the chance of heavy rainfall turning into snow.

Weather fronts between warm and cold air also play a role, the Met Office says, adding: "These fronts can introduce the moisture and conditions for snow to fall. There’s often a fine line between who sees snow and who sees rain, which is one of the reasons forecasting snow can be difficult.

"With a range of factors to consider, forecasting snow accurately in the UK can be one of the trickier forecasts to do accurately.

"Forecasting snow in the UK isn’t like some other places along the UK's latitude, where snow can be quite reliably forecast days or weeks in advance."

The Met Office says that often, headlines making claims of snow weeks or months in advance are "based on very little meteorological knowledge, adding that "one-off, individual weather charts for weeks away cannot represent a definitive forecast with anywhere near the certainty that some media outlets apply to them".

Read more

• UK weather: Maps show which parts of Britain could see snow this week (The Independent)

• Stunning scene as aurora borealis spotted in Herefordshire (Hereford Times)

• Global warming may be behind an increase in the frequency and intensity of cold spells (The Conversation)