The warmth is building over Ireland and the British Isles as the so called ‘Spanish plume’ get’s going. As explained in recent days, a Spanish plume or heat surge from Spain is created by the squeezing and forcing of air between a low off Ireland and high over Germany or the near continent. That’s what we’re seeing now and what is presenting us with our warmest air of summer.

However, the fact we have a hot dome extending from Spain to the UK is not simply down to low and high pressure in our ‘local area’ but it’s all part of a shift in the upper atmosphere, generated some 10 days ago, some 10,0000 miles away. You may remember me mentioning Super Typhoon Neoguri which weakened but took a N then NE track over Japan.

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That push of hot, humid, tropical air into the Northwest Pacific created a hemispheric wide ripple effect which pumped a ridge up into the Western side of North America which in turn brought down some of the coldest mid-July air on record to the Plains and Midwest US. While the deep trough dug down over North America, the ridge then popped north again from Spain to the UK. This in fact was highlighted in a video from the BBC Weather Centre: http://www.bbc.co.uk/weather/feeds/27704153

Let’s take a look at the current global 500mb height anomalies. Look at the current ridge/trough positions. Rather interesting!

As the heat and humidity builds northward today, colder air above 10,000ft will be sweeping over top, thus thunderstorms WILL and are breaking out in the southern UK as well as Ireland. In fact it’s been a very stormy morning, check this map out…

Over 13,000 strikes between 7pm and 9am this morning.

Here’s the latest 500mb height chart off the ECMWF.

Note all the energy converging, producing a deep trough west which has helped usher in the hottest air of summer from Spain where it’s been in the low 40s to the UK where it will be in the low 30s today.

It’s not so much the big trough out over the Atlantic but the much smaller feature that’s attached to the trough that’s sparking the thunderstorm activity. That feature will expand and sit over the UK this weekend forcing waves of energy into the hot, humid air which is brought in in the first place.

Strong to severe cells will cause issues tomorrow (Saturday) for a large swath of France up into England as well as Belgium and the Netherlands. Expect blinding rains which is likely to cause flash flooding for some, large hail and even damaging winds. We cannot rule out a small tornado threat either.

The 500mb chart clearly shows the boundary, strongest upper energy sliding right over the UK where there’s a lot of hot, humid fuel. Remember the mid and upper levels cool substantially with the incoming front, sharply increasing the temperature gradient and speed at which the air lifts!

Here’s the ECMWF surface charts through the next 42 hours.

By Sunday, the model has the trough diving south and breaking away from the main upper flow (jet stream), becoming a cut off low over or near Italy, that will cause issues down there but while that system exits to our SE, another strong ridge can already be seen lifting out of the Azores, taking aim at the UK early and mid next week.

Even this weekend, with all the storminess, don’t expect it to properly cool, we go from low 30s to mid 20s in the Southeast and will likely bounce back to the low 30s again within 5 days as the new ridge appears.

Here’s the 500mb anomalies at 96 and 144 hours. With the core of the ridge centred over the Norwegian Sea, I expect the core of warmth to be over Scotland and Northern Ireland later next week.

See today’s video for discussion.

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Tags: spanish plume, UK heatwave