Is it tougher to forecast UK summer weather?

Wednesday, June 17, 2015, 08:30 GMT - The last couple of weeks we have seen some unpredictable weather, making it tougher for forecasters to predict too far in advance.

Bona fide weather forecasters have managed to track the trend of the month quite well so far. Despite some media sexing up stories, weather forecasters are comfortable not being prescriptive when the data is inconclusive.

They indicate trends and give the most likely outcome based on the model data they have at that particular time.

But in the summer, predicting the outcome is trickier as weather systems and fronts are much smaller compared to winter.

“With the atmosphere, the smaller something is, the more difficult it is to predict,” says Dr Thomas Frame, meteorology lecturer from the University of Reading.

“We can be more certain of predictions when we’re dealing with larger, defined areas of high and low pressure,” he said.

In winter however, everything is amplified – low pressures tend to be deeper and high pressures are higher.

“So for example, a cold front or a low-pressure system in the winter is larger, more defined and easier to predict,” says Dr Frame. 

Larger cold fronts mean more rain, so meteorologists can forecast rain in the winter with a degree of certainty. 

“In the summer, the low pressure systems are much smaller and fronts aren’t as long, and because they’re less coherent and less defined, it’s tougher to pinpoint where rain will fall,” says Dr Frame. 

“We also get what’s called convective rainfall – the heavy and sometimes thundery downpours we experience in the summer – and that is difficult to forecast too.”

Convective rainfall can be very localised – i.e. it may rain heavily in one area but be completely dry 5 miles away.

“So, we can forecast why this rain will occur but not certain exactly where,” adds Dr Frame.

We all know the British weather is notoriously difficult to predict but forecasting continues to improve.

“Weather forecast accuracy has improved steadily over the decades, for example a 4 day forecast today is as accurate on average as a one day forecast was in 1980,” says Dr Frame.

“Forecasts are pretty accurate a few days ahead but they always have some uncertainty. How large this uncertainty is varies from day to day depending on the atmospheric conditions.”

It’s for that reason the best way to keep up-to-date with the weather is to regularly check the forecast for any changes…obviously here at The Weather Network UK!

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