30 Jun 2015

UK heatwave: 10 things you need to know

1 – What’s causing the heatwave?

The burst of summer heat is being caused by a plume of hot and humid air moving towards us from Spain and Portugal. Temperatures there have been as high as 40-45C in recent days.

2 – How hot will it get?

Temperatures are expected to be well above average across the whole of the UK in the coming days, as the heat and humidity builds.

Wednesday is expected to see the peak of the heat, with 34C likely in the London area. However, temperatures will widely reach 28-30C across much of central and eastern England.


The rest of England, along with Wales, Northern Ireland and Scotland, will see temperatures in the range of 22-28C, although some coasts may be a little cooler, with sea breezes and coastal mist.

3 – How long will it last?

The spell of hot weather will wax and wane over the coming days, with temperatures dipping a little on Thursday, before the heat surges back across England and Wales on Friday and Saturday.

The hot weather finally clears eastwards on Sunday, with temperatures returning close to average.

4 – How much sunshine will there be?

This is a tricky one, as it depends on where and when thunderstorms form – something which there is still some uncertainty sun_bluesky_g_wpabout.

What I would emphasise, is that this isn’t going to be a cloudless blue sky heatwave. Cloud amounts will vary day by day, with a mixture of clouds and sunshine. This will influence maximum temperatures.

5 – High UV

The sun is close to its highest point in the sky at this time of year, meaning that UV levels in the coming days will be high, bordering very high.

Another important point, is not to be fooled by a slightly cooling breeze. UV levels are not related to temperature and you will still burn, even if it feels cooler!

6 – Pollen levels

If you suffer from hay fever, then it’s a case of sneezes all round for the rest of the week, with high or very high levels of grass uk_pollen_g_wppollen expected.

Strong sunshine will cause pockets of rising air (thermals) that will lift pollen up in the sky in the daytime, before it falls back to the surface as temperature fall in the evening.

This means that the evenings and nights could be particularly testing for runny noses and itchy eyes.

7 – Air pollution

With this spell of heat, pollution levels are generally expected to be low to moderate, with just isolated areas of high pollution possible in East Anglia on Wednesday.

If the area of high pressure was sitting over us, rather than just to the east of the UK, air pollution would have been a lot worse, with no wind and stagnating dirty air. Thankfully, there’ll be enough of a breeze to stop this happening.

8 – Severe thunderstorm risk

As the heat and humidity builds, there is a chance of some isolated severe thunderstorms during the next few days.

uk_lightning_g_wpThe first batch of these look possible on Wednesday across north east Wales, northern England and southern Scotland – something for which the Met Office has issued a yellow “be aware” warning.

With such a huge amount of energy in the atmosphere, there could be torrential rain, pea-size hail, frequent lightning and gusty winds, giving a risk of flash flooding.

9 – Health risk

While some of us will be enjoying this burst of summer heat, it does pose health risks for the very young, elderly and those with chronic illnesses.

The Met Office issued a level 2 heat-health watch for much of England from midday Tuesday until 6am Thursday to highlight this fact.

10 – Will the heat break any records?

The highest July temperature on record for the UK is 36.5C, measured at Wisley in Surrey on 19 July 2006.

While there is a 30 per cent chance that we could see somewhere reach 35C tomorrow, it is still short of that record high.

Don’t forget, you can get the latest forecast on the Channel 4 Weather website. If you take any pictures of summery weather or thunderstorms, you can send them to me on Twitter – @liamdutton

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