Southern Europe and northern Africa’s heatwave in recent weeks has led to some discussion around how temperatures are displayed on weather forecast maps, with some suggesting ‘alarmist’ colours are used. However, the reality of the Met Office colour scale is a little more mundane than some online chatter would have you believe.

An impactful heatwave

Make no mistake about it, southern Europe and northern Africa have been experiencing impactful temperatures in recent weeks, well beyond their averages for the time of year.

Met Office Meteorologist Paul Hutcheon, who is on duty looking at global weather for the Met Office, said: “Although the extreme heat is now more confined to central and eastern Mediterranean and southeastern Europe, there has certainly been an impactful and long-lasting heatwave in southern Europe in recent weeks, with temperatures often exceeding 40C.

“This has not been ‘normal’ temperatures for the region. In recent weeks, temperatures have regularly been well in excess of average for the area, reaching into the mid-40s Celsius in some places.

“Temperatures are now relenting slightly, with a weak cold front pushing across the region in the latter part of this week.”

How are temperatures displayed in forecasts?

For Met Office weather forecasts, the scale for displaying temperatures is static. This means that the same scale is used no matter the time of year or the region on screen. It provides a consistent view of temperatures throughout the year and makes it easier to make comparisons in conditions across the Earth or between seasons.

Met Office Presenter and Meteorologist Alex Deakin explained: “The temperature scale covers from -55C to +55C and is consistent throughout the year. This ensures that a 22C day will appear as the same colour no matter when or where it occurs.

“For the UK, our usual climate is generally between 5C and 25C so these are the shades of colours that viewers are most likely to see. We use the lightest shade of yellow for the lower temperatures in that scale and get progressively darker with warmer conditions, transitioning from shades of yellow to shades of orange and red.

“When extreme temperatures occur, like we’ve seen in southern Europe, we get towards the darker end of the colour scale, which people don’t tend to see in their forecast very often. So rather than being alarmist, it’s simply a continuation of the colour scale into temperatures that aren’t often displayed, which is reflective of the region seeing temperatures that are rarely experienced.”

Contrary to some misleading online commentary, temperatures quoted in Met Office forecasts are air temperatures. This means it’s a reading of the temperatures at a height of 1.25m above the ground inside a Stevenson Screen.

The same static Met Office colour scale is sometimes used to show changes in air masses, that is when the characteristics of the air are going to change on a large scale bringing a different feel to the UK weather. These air mass temperatures are taken a little way above the surface at around 1.5km and so often appear cooler than the temperature forecasts.

Sliding colour scales are also used for other weather types in Met Office forecasts, including for rain, cloud and, at times, wind.

Accessibility in forecast colours

Everyone needs to be able to understand weather information clearly. That’s why accessibility is in mind with how temperature colours are displayed. Those who are colour blind can find it tricky to differentiate between different colours, though different shades of the same colour can be easier to understand.

Alex continued: “Rather than lots of different colours showing temperatures, it’s much more accessible to those who are colour blind to use fewer colours overall and instead work within shades of light and dark. That’s why we use lighter shades of yellow for slight warmth like 8-12C, but darker shades of red the higher up the temperature you go.

“We do exactly the same for cold temperature extremes, with lighter shades of blue for more ‘normal’ cold temperatures, with it gradually getting darker the colder it goes.”

Find out more about how we measure the weather.

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