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In recent years we have had a series of short lived but potent plumes of hot air drawn northwards over us from France and Spain.

Why are these plumes so warm?... on July 4th 2015 we had one, a short lived 24 hour affair, we had one last year on July 25th that saw us break the all time heat record, and we had one on Friday that was a record breaker too, along with several others in recent times.

It cannot be as simplistic as "35c over France moving North = 35c in the UK"  can it? .... we have had, in the past, much lengthier spells of Southerlies that whilst hot, fail to be so potent.

Is there another factor at work here? something that increases the heat over the UK? As these plumes are transitory, is it the incoming cold front driven by Atlantic lows squeezing the warm air against the High to our East? These plumes do have a brisk Southeasterly breeze, maybe theres some dynamic thats causing the increased warmth...

Is it a super adiabatic? not that i understand that fully.. but our record heat brought about via plumes cannot be as simplistic as just direct heat transference can it.?

Below is the Sket-t chart for Nottingham for midday Friday.. is there anything on that that would support my thoughts?

 

superadiabat 2.jpg

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I’m no expert, but it has to be the intense warming of the Spanish plateau helping to generate the very high uppers (850hpa) and then simply being carried over relatively flat terrain and being uninterrupted. Similar to the Rocky Mountains heating the atmosphere and then creating heatwaves very far north at times past Alberta. Little foehn effects and local topography can also create heat traps, such as the fens, Northern Kent and West London seemingly, as well as the Eastern Trent valley. 

Edited by East_England_Stormchaser91
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Imo GW does go a some way to explaining it. Land temperatures building upwards more than the sea will on average, but even the seas are warming at a decent clip as well.

So the synoptics that used to deliver 33-34c now seem to deliver 35-37c type temperatures. 

There may also be argument that warming temperatures is forcing the subtropical belt northwards which is making south Europe drier and hotter in summer and makes it far easier to tap into that heat synoptically, so what would have previously been heat that wouldn't make it past France before skewing off eastwards is now close enough to on occasion punch into the southern half of the country.

Edited by kold weather
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Nah...im not buying it. i see SM has mentioned several times about the heating of the dry ground over France and Spain being responsible for our high temps.. who says the grounds dry there? they had tstorms like we did in June..?

The point is... heat rises, so IF our hot plumes are caused (at least in part) by advection of hot air, what is keeping it at surface levels?  why isnt it rising? THAT is the "thing" im after understanding, because if we knew what kept the heat in the surface layers, temp prediction would be better understood?

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  • 2 months later...

I think one of the things if not the main thing that stops intense surface heat rising is a strong temperature inversion, effectively laying extremely hot air over very hot air and stabilizing the very hot Continental Tropical airmass, at least until the next deep active cold front arrives.  This temperature inversion is created by a mass of very hot and dry upper level Tropical Superior air subsiding through a very deep layer of the troposphere and warming at the dry air adiabatic lapse rate.  This subsidence is strongest went its forced by both upper level convergence under the upper level ridge and upper level convergence under a right exit region of a jet streak.

Edited by Lettucing Gutted
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Heat records are being broken all over the globe though. It's not just a UK-France-Spain heat train phenomenon. Just the ultra rapid warming of the global climate in the last 20 years, which has really accelerated at pace! Everything is just a few degrees warmer than it would have been 30 years ago. The base state is warmer. There will be more scientific reasons for it i'm sure, but in a warming climate with more extremes, it's not that surprising what we are seeing.

From the wettest February on record, to the record breaking dry and sunny May, to the record breaking heatwave in August. All in 2020. These events just keep on happening so regularly. 

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