40 °C in July? Long-term trends need a pinch of salt

40 °C in July?
Long-term trends need a pinch of salt

Temperature map of England showing widespread extreme heat, with temperatures reaching 39°C near London, 37°C near Norwich, and over 30°C across much of the country, alongside a large warning symbol indicating dangerous conditions.

Another heatwave is possible, bringing more warnings. Hitting 40 degrees?

There's a lot of talk of temperatures hitting 40 °C in July, with specific graphs being shared online purporting to show the forecast, but is it true?

The short answer is no. Beyond three to five days it gets incredibly difficult to pinpoint specific weather conditions. So, posts suggesting highs of 40 or 41 °C around July 10th should be taken with a pinch of salt.

What is actually happening? These posts are using one extreme output of one weather model. Beyond the five day mark a forecast is no longer possible, only a trend of where conditions are roughly expected to reach.

The particular 40 °C claim on July 10th is an extreme scenario which is unlikely. If several model runs point in this direction, it becomes more reliable. This is not the case - the average trend currently shows temperature peaks around 10 degrees below this extreme outlook.

Therefore, at this point we know that we are likely to see another hot spell, likely becoming the third heatwave of the season, but we do not yet know how hot it will be.

Forecast vs trend

Forecasts focus on specific conditions in the short-term, usually accurate up to five days. Trends use data and probabilities to determine a more general outlook for a longer timeframe without details.

Trends are updated regularly with new data, and can change many times before we get to the dates mentioned.

Rather than stressing about the impact of a new record temperature, remember that the details will only become clear as we get closer to the date. Keep an eye on the 14 day weather card and the TemperatureRadar.

Ryan Hathaway