It’s struck me during this extended warm spell that there’s a pattern that appears every year without fail on the charts, which even in warm summers like this never seems to transpire: the real extended heatwave. I am wondering why.

Many many times on charts this summer we’ve seen a pattern evolve where hot uppers - 15C and above - become established over the UK and stay for many days in a row, occasionally rising towards 20C. Daily maxes are in the mid 30s and Atlantic fronts are held at bay as high pressure sticks around over the near continent.

The last time this actually happened was in August 2003. Before that, as far as I can see, June-July 1976. Nothing in between was as hot for so sustained a period. That’s twice in 40 years. The heatwaves in 1995, 2006 (which got closest) and 2013 were much more muted affairs, albeit sustained. The 1990 and 2015 records were short lived plumes.

I have seen these sustained heatwaves on NWP charts several times every year in the last few, but they don’t transpire. Why?Models going mad, or just luck?

I would disagree on some counts.

From late July to about 23rd August 1995 there was an exceptional heatwave in the south. Long runs of high temps including plenty of 30c+ days led to the hottest mean monthly max in Southampton- beating any calendar month in 1976.

You don't mention July 1983- yet at the same station, which incidentally was by the water, the mean max of above 26C was accompanied by a mean min of over 16C.

I was surprised July 2006 was given such a high accolade at the time- there was a hot spell for 4 days, then a little heatwave for 6 from 16th-21st and a less exciting event in the following week. 

July 2013 delivered over a week of temperatures of 27+ except 20th. 

2003 was quite exceptional as you say, but this spell, although spread across 2 calendar months, is looking like tupping all but 76, July 83 and 95 for longevity. The intensity is not there though.

Unlike drought, there doesn't seem to be a defined heatwave. 

Probably more common actually as record highs in the UK are rather high compared to average maximums. 

It might also be worth pointing out that August 2003 was not exceptionally hot here as the highest temp was 31.8C in Leeds. That's about the same as 1995, 2001, 2011 etc. The extreme high temperatures were mostly in the SE. In fact,  on the same day Kent reached 38.5C, here in Leeds it was only 28C.

August 1990 remains the benchmark for heat here and for most of the north I suspect. 1995 also managed 4 consecutive days above 30c which no other year since has managed. 2003 managed 2 consecutive days above 30c. 

Thanks for clarifying that; I hadn't realised. I would be inclined to treat the definition with caution though only because this was reached in March 2012 and possibly December 2015- I just can't bring myself to use term heatwave then!

I believe it’s possible for this country to see mid 30s for 5 days or more. We nearly got there in 2903 and patterns giving this show up regularly on GFS runs for example. But we’ve not had this yet.

For UK with large oceans around we getting temperatures as far as we can get without heat import from high 20's to 31C or 32C at best providing no sea breeze killing it off like now.  What we getting is the same thing in Moscow few years ago with endless HP and due to huge landmass they getting 35-40C easily than here.    With HP over here we normally get up to 25-27C home grown warmth but due to extreme dryness and warming up ground and sea temps are aiding to reach higher temps easily.  We had prolonged HP days before but never strike on the longest summer days.

I alluded to this in the model thread yesterday or the day before. It seems like in the UK, to get seriously hot upper air (18-20C+) you need low pressure to the south/southwest to act as a “pump” to push the hot air northwards. That will almost always lead to some kind of breakdown, unless the high to the east can push back westwards and cause that really hot air to stagnate over the UK again.

You could say that. Winter heat waves do exist, and I'd imagine quite a big section of December 2015 would fit the definition for many areas.

Having not had a full night’s sleep since the end of June, it feels like a heatwave to me, with the exception of last Wednesday’s mid-20s maximum (though high humidity meant it hardly felt cooler anyway!).

Regardless of definition, it’s been a June and early July (and still counting) to inspire awe for its persistent Mediterranean-style weather.

 Yes that is the normal heatwave in this country with a few very hot days turning very humid, thundery breakdown followed by fronts pushing in from the west. This year is very unusual, for instance next week turning cooler from the east with the heat being pushed westward  A very unusual year. Was it forecast earlier in the year  to be this warm and dry over the bulk of the country. The dryness is nationwide in different levels of severity. Even my relations up near Lairg, their lawn is crisp and brown.

The ironic thing about this summer is that we still haven't had a proper heatwave !

Normal heatwaves occur as a result of a plume. 

This years heat has been largely self generated thanks to high pressure overhead and self perpetuating as the boundary layer dries and creates a warmer environment. 

i suppose that’s why it’s been so dry. But next weekend may see a traditional plume followed by storms 

Just to be clear though: the thread was about real heatwaves, not plumes followed by storms. 9 times out of 10 when we get warm weather it’s either a short-lived plume, or longer lasting but less hot settled spell. Real heatwaves combining longevity with heat do happen though, and June/July 1976, June 2006 and August 2003 are examples. And the NWP dies produce some of these at the moment although - as in my initial post - generally not in the op run.