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OK so to help out and explain what I've been doing with ensembles I introduce to you the Adiabaitc lapse equation!Its quite simple.Take your temperature at 850hpa and multiply by 1.053 and you will get what the surface temp should be in ideal conditions! Again for these extreme hot plumes this is going to be a good approximation. Again you will need a low humidity and cloudless skies for this to be reached. The equation is in kelvins so for 25C at 850 you have to do (25+273.15)*1.053 - 273.15 which gets you 40C Applying this equation for a few T850s we get:T850 22C -> 37.6CT850 23C -> 38.7CT850 24C -> 39.7CT850 25C -> 40.8CT850 26C -> 41.9CT850 27C -> 42.9CT850 28C -> 43.9CT850 29C -> 45.0CT850 30C -> 46.0CT850 31C -> 47.1CT850 32C -> 48.1CT850 33C -> 49.2CT850 34C -> 50.3C You can perhaps see why I got so excited about that 18Z run last night showing 28C on the south coast. So for the magic 40 we do really need T850s above 25C (allowing for a bit of lee way with clouds and moisture) .
OK so to help out and explain what I've been doing with ensembles I introduce to you the Adiabaitc lapse equation!
Its quite simple.
Take your temperature at 850hpa and multiply by 1.053 and you will get what the surface temp should be in ideal conditions! Again for these extreme hot plumes this is going to be a good approximation. Again you will need a low humidity and cloudless skies for this to be reached.
The equation is in kelvins so for 25C at 850 you have to do (25+273.15)*1.053 - 273.15 which gets you 40C
Applying this equation for a few T850s we get:
T850 22C -> 37.6C
T850 23C -> 38.7C
T850 24C -> 39.7C
T850 25C -> 40.8C
T850 26C -> 41.9C
T850 27C -> 42.9C
T850 28C -> 43.9C
T850 29C -> 45.0C
T850 30C -> 46.0C
T850 31C -> 47.1C
T850 32C -> 48.1C
T850 33C -> 49.2C
T850 34C -> 50.3C
You can perhaps see why I got so excited about that 18Z run last night showing 28C on the south coast. So for the magic 40 we do really need T850s above 25C (allowing for a bit of lee way with clouds and moisture) .
Nice. So that record sounding back in 2019 would have given just over 40C had conditions been optimal. I'm not sure what the 850mb temperature actually was when the 38.7C record was set - by 00Z the following day the 20C isotherm was pretty well hugging the east coast.
This is a good site for discussion of the 2019 heatwaves - the graphic comparison of the soundings really shows up the differences. https://www.stratusdeck.co.uk/blog/the-anatomy-of-a-mega-heatwave
Nice. So that record sounding back in 2019 would have given just over 40C had conditions been optimal. I'm not sure what the 850mb temperature actually was when the 38.7C record was set - by 00Z the following day the 20C isotherm was pretty well hugging the east coast. This is a good site for discussion of the 2019 heatwaves - the graphic comparison of the soundings really shows up the differences. https://www.stratusdeck.co.uk/blog/the-anatomy-of-a-mega-heatwave
Great link, thanks!
Will add that for that plume, even if the conditions had been optimal I don't think it would have happened because I'm not convinced there is anywhere inland enough in the SW for the sea breeze to not have a major effect. So that plume in 2019 was much too far west aswell as moisture being brought in.
One other factor I didn't mention is that I've simplified the equation by making the assumption the pressure is 1020mb, in higher pressure you don't need quite as high T850s and in lower pressure you need higher ones.
GFS 12z drops the furnace heat.
GEM looks a very hot run though.
The equation is in kelvins so for 25C at 850 you have to do (25+273.15)*1.053 - 273.15 which gets you 40CApplying this equation for a few T850s we get:T850 22C -> 37.6CT850 23C -> 38.7CT850 24C -> 39.7CT850 25C -> 40.8CT850 26C -> 41.9CT850 27C -> 42.9CT850 28C -> 43.9CT850 29C -> 45.0CT850 30C -> 46.0CT850 31C -> 47.1CT850 32C -> 48.1CT850 33C -> 49.2CT850 34C -> 50.3C
Useful, thanks
So when do we officially consider this hot spell to begin?My benchmark has generally been somewhere breaching 28C. We’re nowhere near so far this week - nothing above 24C. Could happen on Friday, or at a push and with a following wind (and less cloud than forecast) Thursday. Quite an unusual heatwave where we don’t know if in only 4 or 5 days it will be 30C or mid 20s, but we kind of know it’s likely to be in the 30s in over a week’s time.
Probably as early as Saturday TBF
30c knocking on the door for many places by then.
It remains on, despite this morning’s GFS op. And this morning’s GFS op doesn’t stint on the European heat either, it just displaces it. Southern Iberia gets to 45+ this weekend and then sticks with it every day until 384 hours, peaking at 50C. Unprecedented.All other op runs showing heatwave conditions for the UK. Only question is whether we threaten records.
At the moment it is looking likley the uk will get 2 or 3 days at most of extreme heat,very similar to what happened mid June. It certainly does not look as if it is going to last,thank god! As with the models in winter overcooking the cold iam awaiting the inevitable downgrades wef this weekend. My bet is somewhere will hit 35c-36c on one day but to get 40c in this country we need a prolonged spell of heat beforehand.It might happen but very unlikley imo.
Well this morning's 06z GFS gives us one day of 41C. And I would say the op was a disappointment/downgrade. A downgrade that gives the UK 41C is quite something.
Ideal for me would be at least a week of 28-32C and then one extremely hot day, or 2 at a push.
Some interesting facts about the highest recorded temps in each of the European states:
Highest temperatures in Europe: A map and list of records • viborc.com
A good chunk of them have recorded 40c or more in the past, even in the 'near continent' regions, but Greece contunes to hold onto the the top spot with its 48c that was recorded in Athens
Another 39C in this evening's GFS, though GEM looks like it would peak lower. Meanwhile the 40s start in Southern Iberia. 41C tomorrow, then it's up from there: 44, 46, 45, 45, 45, 48, 48, 45, 42
A good chance of the all time Spanish record going I'd think. For reference it's 47.4c recorded just last August.
And the Portuguese record also of 47.4C set way back in 2003.
The timing and peaks of this look like being uncannily like August 2003, but 2 days in advance, so it's worth running a day by day comparison. Yesterday was Friday 1 August - cloudy, with a high of 25C in the far SE (Manston that year if I recall). Today is Saturday 2nd August when in 2003 it reached 27C. We hit 30C on the Sunday.
Arome is now in view and gives maxima of 26 or possibly 27C today, and 29-30C tomorrow.
Some interesting facts about the highest recorded temps in each of the European states:Highest temperatures in Europe: A map and list of records • viborc.comA good chunk of them have recorded 40c or more in the past, even in the 'near continent' regions, but Greece contunes to hold onto the the top spot with its 48c that was recorded in Athens
Since that article was written, Italy took over the top spot - see the updates near the top.
The European record is now 48.8C in Syracuse, Sicily, on August 11 2021.
Met Office longer range forecasts have downplayed the heat somewhat, saying just "possibly hot".Quite telling that.