May to start on a cool note

As April draws to a close, I think that most of us will agree that this month, along with spring as a whole, has served us well this year.

There’s been a good deal of fine, settled weather, pleasant spring warmth and not too much in the way of rain – something that’s very welcome following the heavy rain and flooding we had during winter.

With the days getting longer and the sun climbing higher in the sky, thoughts are no doubt turning to what kind of summer we’ll have this year. 

While predicting the weather for summer is not possible given the current reliability of seasonal forecasting, May is a month that can deliver our first taste of summer-like weather.

What does a typical May bring?

Typically, climatologically, the jet stream tends move further northwards and weaken during the month of May.

Because the jet stream follows the zone of greatest temperature difference between cold and warm air, as the northern hemisphere begins to warm up due to longer days, this zone shifts northwards.

In addition, the temperature difference in this zone tends to lessen, resulting in the jet stream generally travelling more slowly than in autumn, winter and early spring – giving less active areas of low pressure.

The average maximum temperature in May still exhibits the north to south contrast you’d expect. Much of England and Wales would normally see 15-18C, with Scotland and Northern Ireland 13-16C.

As for May rainfall, eastern areas tend to be driest, with 40-60mm. Western areas are normally wetter, with 60-100mm more typical.

Despite these average figures, May can still deliver a range of weather. I remember seeing snow fall at sea level in Cardiff on 6 May 1997 as I stared out of the window, bored, in a biology lesson at school. (Hopefully my GCSE biology teacher isn’t reading this…)

Yet at the other end of the spectrum, May can deliver summer heat. The highest ever May maximum temperature recorded in the UK is 32.8C, albeit occurring later in the month on the 29th.

May this year

This year, there are strong signs that May is going to start on a cool note, with a northerly wind bringing a burst of chilly air from the Arctic.

During the first few days of the month, daytime temperatures are likely to be below average. England and Wales will sit at around 10-14C, with Scotland and Northern Ireland around 6-12C.

There’ll also still be a chance of some frosty nights, especially in the countryside – although it does get harder for temperatures to fall too much at night as the days lengthen and the nights shorten.

The first week or so of May looks mixed, with brighter days interspersed by some occasional rain – as would be expected at this time of year.

At the moment, there are no strong signals as to what the weather is going to do mid to late May, but the detail will hopefully become clearer in the next week.

In the meantime, you can get the latest forecast on the Channel 4 Weather website. I’ll also be posting regular updates on Twitter – @liamdutton

Graphics: Met Office