I know you are just talking potential, but it's very difficult to get t-storms on the time (Friday afternoon) of that tephigram, as the strong upper level ridging will kill off ascent.

 

Yeh that was probably not the best example tepigram, especially as there isn't really any CAPE above the stable layer anyway! I think the general point kinda holds though that getting a stable layer in the lower atmosphere and significant shear could result in some severe thunderstorms.

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Yeh that was probably not the best example tepigram, especially as there isn't really any CAPE above the stable layer anyway! I think the general point kinda holds though that getting a stable layer in the lower atmosphere and significant shear could result in some severe thunderstorms.

True, but only if convection and ascent can be initiated.

 

 

True, but only if convection and ascent can be initiated.

 

Cold front approaching from the west should be a good lifting mechanism.

Not sure if it will be enough to overcome the stable layer though. Anyway I'd expect quite alot of metoffice warnings in the 'low probability, high impact' catogary!

 

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Can anyone verify if the 576dm thickness line has ever reached the UK before?

 

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Well, experts or not, boundary layer or not, the 12z GFS paints a still-remarkable picture in the south at 850hPa, but a much less remarkable one down at ground level.

Saturday still looks to be the peak of it, but it's a short window of opportunity. I also notice that the silly high dew points are now entirely absent - no more 27s and 28s, but that shouldn't be a surprise to anyone considering that a) temperatures are generally forecast to be lower than that and b) those would have been 3 or 4C higher than the record UK dewpoint.

Friday in the SW and Saturday more generally in the south are still shown as having high dewpoints, but that's a long way out and still very much subject to change.

The 12z MetO, meanwhile, shows the 20C 850 isotherm not even reaching the SE of the UK, instead only affecting the SW. Again, there is potential there for some really high temperatures IF (and it's a big if) a foehn-type effect were to set up in the lee of the hills, but that's not presently shown by the model.

The German ICON run is the most bullish regarding the extent of the plume, but it's not supported by the major runs out so far.

 

And this is why Darren, along with James, still provide the the most unbiased and worthy analysis on the weather forum world. 

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Looking at tonight’s charts I think the most notable thing about this week’s weather is going to be some extremely heavy rain on Monday night into Tuesday morning for central southern areas, potentially with some thunder. After that, for all the talk of record-breaking plumes it looks like mid to high 20s at most and 90% of the public wondering what the fuss was about.

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Looking at tonight’s charts I think the most notable thing about this week’s weather is going to be some extremely heavy rain on Monday night into Tuesday morning for central southern areas, potentially with some thunder. After that, for all the talk of record-breaking plumes it looks like mid to high 20s at most and 90% of the public wondering what the fuss was about.

 

BBC still saying a 31c somewhere , all a bit vague on the latest week ahead .Looks like the hottest place end of the week will be further west, maybe Cheltenham area?

2m temps continue to look unexceptional on the output I have seen this morning. One point I will add is that IME it is now virtually unheard of for the big agencies (I include the Met) to massively override the NWP forecasts. At times they still make minor adjustments, but increasingly their role is to: interpret the data, summarise it, package it and present it to the public. I know that has caused some issues with "old school" forecasters, but this isn't the place to discuss them. The key point is that unless the NWP starts shifting we are unlikely to see temp forecasts being manually increased. 

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BBC still saying a 31c somewhere , all a bit vague on the latest week ahead .Looks like the hottest place end of the week will be further west, maybe Cheltenham area?

That’s 5C higher than the GFS which only has maxima of 26C, in the west on Fri and east on Sat. I haven’t looked at the temperature output from other models in detail but it all looks very underwhelming now. Still the chance of some impressive storms tonight though. 

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That’s 5C higher than the GFS which only has maxima of 26C, in the west on Fri and east on Sat. I haven’t looked at the temperature output from other models in detail but it all looks very underwhelming now. Still the chance of some impressive storms tonight though. 

The GFS shows 28°C in parts of the south on Friday and Saturday (or 29 for the latter on some versions of the charts - perhaps a graphics/resolution issue?) 

https://www.wetterzentrale.de/maps/GFSOPUK00_114_48.png 

https://www.wetterzentrale.de/maps/GFSOPUK00_138_48.png 

http://modeles2.meteociel.fr/modeles_gfs/runs/2019062400/132-778PUK.GIF?24-0 

 

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The GFS shows 28°C in parts of the south on Friday and Saturday (or 29 for the latter on some versions of the charts - perhaps a graphics/resolution issue?) 

 

MetO and GFS concur on this, after which we will be reminded that we are an island off the eastern shore of an ocean, and more subject to Atlantic influences than continental ones. GEFS shows temps back down to average, not much rain in the south, rather more in the north, and GFS charts for a week ahead showing LP off the Atlantic having a major influence.

But in the meantime, I'm looking forward to tonight's thunder. Widespread heavy rain moving up on a line from Bournemouth to Coventry in the early hours before the disturbance breaks up, with some very intense cells on the eastern edge e.g. for Reading and Cambridge (with as always the word of caution that thunderstorms have a mind of their own)

https://www.metoffice.gov.uk/public/weather/forecast/map/gcp3nqsgd#?map=Rainfall&fcTime=1561388400&zoom=8&lon=-0.85&lat=52.56

 

(We seem to be due a thunderstorm and three fine days, not the traditional three fine days and a thunderstorm)

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Soundings confirm what's going on. Complete wind reversal by the time you get to the 750hpa level. Temp at the surface, in this case is 20C which decreases a little as you move up the boundary layer and then sharply increases again to a maximun of what looks about 23C at about the 900hpa level. We have a very stable inversion layer near the surface.

This kind of profile is actually not all that uncommon in the states. Its actually quite dangerous. A stable layer near the surface can give rise to huge thunderstorms because the CIN allows CAPE to build to much higher levels than usual (thunderstorms don't just rain out).

Strong shear also makes supercell type conditions favourable.

Again this kind of thing makes thunderstorms somewhat less likely due to the highly stable layer near the surface but if enough CAPE can be built up to overcome the stable layer you can potetnailly get some quite severe storms.

Actually in this case it wouldn't - you can have too much of a good thing. You need the right amount of directional shear for supercell thunderstorms, and in the case of complete revervsal with height this is too much.

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Looking at UKMO the main period for the highest 850s will be Thursday to Saturday

Thursday sees a very distinct split with those closer to the east coast struggling in the mid teens but further west into the mid 20s

A similar picture on Friday with central & westerns areas in the mid maybe upper 20s but closer to the east coast temps stay lower but up a tad on Thursday

By Saturday, it's all change as the western side sees a dip in temps whilst the east sees an increase with highs in the London area approaching 30c

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I think its isohypse for geopotential height. I often use 'isopleth' though as that works for anything!

 

I can't find 'isohypse' in the OED - maybe it hasn't reached the frequency criterion for inclusion, but 'isopleth' certainly is in there, confirming your usage with the definition:

"A line (either imaginary or on a map or diagram) connecting points for which  some chosen quantity has the same value ..." with the example: " Isobars are isopleths of pressure, isotherms are isopleths of temperature, and so on."

That one was a new word for me.

 

And on the models...

As mentioned by DEW, something that struck me when looking at the 00Z GEFS for London: http://old.wetterzentrale.de/pics/MT8_London_ens.png is how little rainfall is shown for the period covered.

 

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Also looks like a big cool down on the way for the end of the month.

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2m temps continue to look unexceptional on the output I have seen this morning. One point I will add is that IME it is now virtually unheard of for the big agencies (I include the Met) to massively override the NWP forecasts. At times they still make minor adjustments, but increasingly their role is to: interpret the data, summarise it, package it and present it to the public. I know that has caused some issues with "old school" forecasters, but this isn't the place to discuss them. The key point is that unless the NWP starts shifting we are unlikely to see temp forecasts being manually increased. 

That twitter graphic was both wrong and unprofessional. They probably had that view because the EC ensemble and some other models still had much less N.Sea influence, but it was still wrong.

Anyway, there is still a role for mets, but they have to be really good as the models keep getting better. That role is in 2 areas mostly:

• understand the drivers of weather where possible, which can help immensely in periods of model volatility or pre-empting big model shifts. People who cannot do it think it's impossible to do, but it is possible and very valuable indeed.


• better post-processing of model output: bias correction can be really sophisticated (not just adding 2-3C on sunny summer days or lowering raw output by 2-3C in cold winters nights), but you can even have pattern dependent bias correction etc. Even amateur mets identify systematic model errors (e.g, the winter northerlies of GFS which then become topplers or the tendency of the EC op runs to produce too many cold easterlies in winter at days 7-10 etc.).

Mets who don't do this find themselves increasingly just relaying model output and being subject to its errors and volatility, so they add little value. This is a process that Keith Browning (a great met teacher) had called meteorological cancer.

 

Wind direction for Friday (the highest 850s). Its still got a northerly component for most of the SE. Only place really managing to advect that warm continental air is the SW.

I suppose though a relatively small change in wind direction could have a big impact on temperatures.

EDIT: Some record high temperatures possible for the channel islands?

 

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The key point is that unless the NWP starts shifting we are unlikely to see temp forecasts being manually increased. 

Btw there is little chance of that happening, it's almost certain that the surface will decouple from the 850hPa and Wed & Thu will actually feel cool & fresh for most with an obvious west to east gradient. Friday still quite fresh for the eastern half, but increasing warm and humid for western areas (esp SW).

It is possible though to see some funky localised readings west of Dartmoor or the welsh mountains. Cornwall will also have very gusty winds.

 

Heathrow sometimes sees rapid heating and falling dewpoints during southerly flow in heatwaves, as the Surrey Hills are nicely placed to create a little wave to the South. But with an Easterly the problem is there’s no North-South topographical barrier to create turbulence until you get to at least the Cotswolds. I doubt the Chilterns would be quite high or continuous enough.

A few thoughts about leeward or unusual spots: Saunton Sands, Plymouth, Aberystwyth, Valley (remember Aug 2003?), possibly Southampton or Bournemouth if things are more Northeasterly.

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Arpege has 26C 850s at just 90 hours out, over Devon. Surely that would be a UK record, regardless of the surface temps (also about 25-26C according to Arpege!)

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