Thunderstorms To Spread Across Ireland & UK But Warmth/Humidity Lingers, More August Thoughts!

Written by on July 21, 2013 in United Kingdom & Ireland with 2 Comments

While the heat comes roaring back in the South of Britain tomorrow, I am watching closely to coming 5 days with that low pushing in from the west. Rather than that system sweeping through, it will swing lines of heavy rain and storms from SW to NE across the UK and Ireland but be aware that we will remain warm, humid and that should fuel the stormy spells that we see this upcoming week. By no means is it a washout. We will see sunshine, warmth and humidity but look out when the next system swings through. We could get quite the light show. I’m hopeful that if you like a good ole summer thunderstorm, many of you will get that this week.

Looking later and further down the road. I see plenty of wet weather but also warmth too. We’re not entering a cool pattern but more less hot but remaining warm and humid. The BLOCKING HIGH that’s held with the core circling over the past 3 weeks moves enough to allow fronts in but stays close enough to our ESE that plenty more warmth and humid air advances from the S.

August is a month that I am trying to pin down more. The reason is there’s a tendency by longer range models to hold stronger heights over Western Europe but those warmer than normal SST’s concern me. There is likely to be further ‘hot spells’ lasting 3-5 days rather than 2-3 weeks but there could be spells in between with heavy flooding rains. Heights will remain fairly strong, remember stronger than normal heights close enough to the UK means warmth and humidity is nearby or indeed over us.

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There’s a LOT of heat across a large swath of Europe and even with low pressure around, the amount of heat means it simply gets entrained into these lows. Humidity increases I think during August from 2 sources, 1 from the South where the air and waters are naturally warmer in mid to late summer but remember the amount of warm water relative to normal surrounding us. That adds to the humidity in our lower atmosphere. This also fuels heavy rainfall. August is likely to be warmer but also wetter than normal. Don’t think I’m going for cooler than normal.

So, speaking of water temps. Here’s what we started off with at the end of June, remember what I said. This profile, given dry ground over the UK supports stronger than normal heights in July.


This is what we’ve got now thanks to those stronger heights and sustained warm temps. Persistent low pressure further north is thanks to low pressure being stuck up there and also note the cold waters off Iberia, again due to low pressure in the means, stuck there.


With a pattern which supports lower heights in August with a lot of heat and humidity remaining in the pattern, these warm waters should fuel spells of heavy rain and potential flash flooding events through August and even into September.

The late summer pattern continues to look like a mixed bag. Storminess, spells of heavy, torrential flooding rains, more heat and settled weather but in shorter bursts.

The GFS shows the waves of precip being thrown our way this week with CAPE values climbing substantially with plenty of low level heat and humidity while upper levels turn much cooler. With the high pushing to our ESE, the CAP is broken and so we all get some rain in coming days. The lapse rate will significantly increase over the next few days as the upper levels over Ireland and the UK cool while there’s plenty of low level heat and humidity. As each front swings an arm of precip through, embedded thunderstorms will form and some of these could be wild packing flooding rains, strong to even damaging wind, large hail, spectacular lightning displays and even a few funnels or tornadoes as winds begin to vary with height towards mid week.

Shower and thunderstorm chances increase over the South tomorrow where temperatures will soar in the Southeast to 34C as there is a squeeze play between the approaching low to the SW and high which will be positioned over the southern North Sea. This forces hotter, more humid air north from France but look out. That low to our SW will cool the 500mb level and so beefy thunderstorms can be expected, albeit in scattered or isolated fashion… Another warm, settled day further north away from low’s influence and where the CAP remains.

Here’s the CAPE values or measure of convective energy according to the GFS for tomorrow afternoon.

Courtesy/Owned by AccuWeather Pro

Courtesy/Owned by AccuWeather Pro

Here’s the surface/precip chart.

Courtesy/Owned by AccuWeather Pro

Courtesy/Owned by AccuWeather Pro

By Tuesday, heights lower further north up across Scotland and Northern Ireland and so the CAPE values climb as the front approaches. Expect heavy downpours and thunderstorms across much of Scotland Tuesday afternoon and it will remain warm at 20-24C with a real humid feel. This setup may in fact be the best in years, providing us with some great lightning displays as we haven’t seen this type of warm to hot pattern sustained since July 2006 and often these more substantial heat spells end with great thunderstorms. The soaking that comes from these embedded, towering cells will be welcome by many I’m sure. These cells should also cut the humidity a touch too.

Courtesy/Owned by AccuWeather Pro

Courtesy/Owned by AccuWeather Pro

Here’s the surface chart for Tuesday afternoon.

Courtesy/Owned by AccuWeather Pro

Courtesy/Owned by AccuWeather Pro

Later Tuesday!

Courtesy/Owned by AccuWeather Pro

Courtesy/Owned by AccuWeather Pro

Here’s the ECMWF which likewise shows a very active, stormy Tuesday afternoon and evening from Southeast England all the way up to the Northwest Highlands. This is likely to drop a lot of rain in a short space of time for many and produce strong embedded thunderstorms.

Courtesy/Owned by AccuWeather Pro

Courtesy/Owned by AccuWeather Pro

Here’s the ECMWF at 500mb showing a lot of energy and strong winds riding over top of the warm, humid lower atmosphere. This supports strong upward motion and increased convection, so thunderstorms are highly likely.

This shows strong upper winds racing overhead out of the SSE.

60 hrs

Courtesy/Owned by AccuWeather Pro

Courtesy/Owned by AccuWeather Pro

66 hrs

Courtesy/Owned by AccuWeather Pro

Courtesy/Owned by AccuWeather Pro

Once Tuesday evening rain and storms clear out into the North Sea yet more rain and storminess is crossing Ireland and Northern Ireland en-route to the UK, likely bringing more unsettled, wet and potentially stormy weather Thursday.

Here’s the ECMWF upper chart/850 temps.









By next Sunday, the model shows a trough anchored back over the UK, however it’s not going to be cold but nearer average for late July. The overall air mass right across Europe is warm to hot and an upper low merely keeps the heat at bay and supports additional unsettled weather.

Check out the Mediterranean basin! It turns intensely HOT and potentially dangerous for those vacationing from Iberia all the way to Israel. Warmth also extends north into Germany and Scandinavia while the really hot stuff lifts into Poland and western Russia.

To close, I thought I would show you something a little different. Below is the 850mb height anomalies off the Korean model for August. This is difficult to see I know but it’s interesting to see that it has ABOVE NORMAL HEIGHTS over Britain in early August with a fight between high and low pressure mid-month, then significantly above normal in late August. Significantly above which suggest more heat. Hope you can read this ok.


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2 Reader Comments

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  1. Mark Vogan says:

    I tried to do that but failed. I agree with you and apologise.

  2. Robert says:

    Would be helpful if you could circle or an arrow pointing to the uk in these pictures, so we know where to look. These pictures are detailed and small and very difficult to see.

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