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Model output discussion - August hot spell - how hot, how long?


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The ECM 0z operational screams thunderstorms ⛈ potential with very warm / hot and humid air pushing north across the whole of the u k through next week.:shok:🔥☀️🌩️

46699B49-A796-4438-A670-6410B32856E8.thumb.png.c2e952738a27175eae28f1109dcbfb48.png99CFE92A-A084-47AF-976A-6CDEB51D4B16.thumb.png.12e9199ef31aa95a9daddf3ffa590227.png591C8F1A-634A-43B8-ABD9-C81874EF064C.thumb.png.168ff26884d65d7012082747aed93dd5.pngECE9ABFC-9414-404C-A2E3-4D9DE817B025.thumb.png.65165ef50a2e3f76050f84cb7b50685d.png3A7A3ECF-0B38-4467-9C7C-2E1D987F107F.thumb.png.3b31699669f83b74aec2c567915ff0f2.png

Edited by JON SNOW
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Astonishing rebound in momentum transport that is behind the current spectacular synoptics and associated high impact weather. Both the heat, and also the powder keg potential for thunderstorms.

*** USING THE ECM TO FORECAST TEMPERATURES IN A HEATWAVE - A REVIEW *** I often make predictions based on models several days ahead, and then I find it useful to revisit these predictions after t

The reality is that NWP is wholly congregated on, but susceptible to be blindsided and over preoccupied by, the re-ignition of the low frequency tropical convective standing wave across Africa and the

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10 hours ago, MattStoke said:

Must be all the tarmac and aircraft at Kew Gardens that is responsible 😉 

Or Heathrow just happens to benefit from a small foehn effect, from the hills to its south and southeast, when winds come from the south or southeast...?🤔

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36 minutes ago, Daniel* said:

No I don’t think this is true at all certainly not in summer, the days Heathrow is warmest in country even not hot days in summer it’s a frequent occurrence often by more than 1C. I’m sure 1991-2020 averages will be revealing which will be available from 2021. Heathrow seems to be getting hotter at a faster rate compared to elsewhere my anecdotal experience. 

Average highs are warmer at Kew throughout the year. Lows there are some of the coolest in London though.

That must mean that Kew is warmer than Heathrow on cool or average days. Closing all of the weather stations that routinely recorded warmer highs than Heathrow probably has something to do with it, as well.

Edited by B87
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GFS still developing much more of a secondary heat low than the other models starting tomorrow. Yes, within 24 hours range now! Interesting to see such a persistent difference in how it resolves the same setup.

In the far-south west of Southampton this makes the difference between a very hot NE to E flow and a fresher NW to N flow that keeps maximums 3-4 Celsius lower. A huge discrepancy for one days range, for one not even related to much difference in cloud cover.

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20 minutes ago, MattStoke said:

The way some go on, weather stations should only be placed in the middle of nowhere where no-one lives. They seem to think the station is in the middle of the main runway and being blasted by jet exhausts. I’m surprised they haven’t claimed that the fire at Heathrow yesterday was the station being set alight by the Met Office and blaming the high temperature reading on that. It’s tiresome reading the same comments every time we get a hot day. As if the Met Office aren’t careful and don’t take certain factors into consideration when locating a weather station.

Well there's a couple of extreme views which are common: (1) Runways etc cause all the excess heat, end of story; (2) We can essentially ignore such factors as tarmac. Expressing one of these views will tend to bring out people with the opposite view.

But hyper-localised heating effects are real, and often bigger than city UHI effects. For example in the Feb mini-heatwave last year, the thermometer in my back yard recorded 26C in the shade near to sunlit fence and decking, even though the temp at local wx stations only got up to the high teens. So there seems to be at least a case to answer here.

As Daniel (I think it was?) suggested, I'd like to see a further breakdown of observed temps between Kew and Heathrow, and for more recent years. Adjusting for how sunny it is around typical time of max temperature, wind speed/direction etc.

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Going by the GEFS 00Z ens, it'll be next Saturday before the real cold (7C at 850hPa!😘) finally reaches Southern England. In the meantime, a thundery midweek looks odds-on...For everywhere but the Triangle & Cone, of course::oldlaugh:

t850Buckinghamshire.png    prmslBuckinghamshire.png

t2mBuckinghamshire.png    prcpBuckinghamshire.png

PS: Does anyone have any info regarding the severe/widespread storms that occurred in either late August or early September 1968? If I remember correctly, a soccer game (in Macclesfield) was abandoned, after several players were struck by lightning?🤔

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6 minutes ago, Higher Ground said:

Well there's a couple of extreme views which are common: (1) Runways etc cause all the excess heat, end of story; (2) We can essentially ignore such factors as tarmac. Expressing one of these views will tend to bring out people with the opposite view.

But hyper-localised heating effects are real, and often bigger than city UHI effects. For example in the Feb mini-heatwave last year, the thermometer in my back yard recorded 26C in the shade near to sunlit fence and decking, even though the temp at local wx stations only got up to the high teens. So there seems to be at least a case to answer here.

As Daniel (I think it was?) suggested, I'd like to see a further breakdown of observed temps between Kew and Heathrow, and for more recent years. Adjusting for how sunny it is around typical time of max temperature, wind speed/direction etc.

The reason I posted the chart last evening was to show how little difference there is between Kew and Heathrow. The argument crops up every year, every time Heathrow is shown as the hottest. Where does anyone want it sited? Maybe instead of the repeated comments in Net Wx you all write to the Met Office with your views. Oddly enough there was, I believe, none of this discussion about the London Weather Centre or the one in Manchester, both sited on flat roofs, close to air conditioning units, lots of tarmac type covering close by.

Edited by johnholmes
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To try and move the discussion to the weather outlook, the 500 mb anomaly charts are not on the same page, well not all 3 of them anyway. Noaa interestingly shows +ve ehights, 150 DM, so a reasonable value centred to the WNW of the UK. Overall there is still some degree of concencus for the UK trough, shall I call it this (?), down to Iberia.

Anyway have a look at the 3 charts and decide yourselves how the 6-10 day surface weather may pan out.

charts following

http://mp1.met.psu.edu/~fxg1/ECMWF_0z/hgtcomp.html

The 8-14 Noaa, as is often the case, smooths most of this out to show a general westerly flow from what it shows as the main trough way out west.

 

Edited by johnholmes
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How the Atlantic upper ‘cold pool’ gets ejected into the general european upper ridge is the current conundrum for days 4 to 6. not sure that ukmo has day 6 right but it is a 20% option from yesterday’s clusters. The current line of thought is that the northern arm is fairly flat to our north and doesn’t trough into nw Europe.  The meandering of the ejected cut off upper trough is I think, where our musings should lie 

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1 hour ago, MattStoke said:

It’s tiresome reading the same comments every time we get a hot day. As if the Met Office aren’t careful and don’t take certain factors into consideration when locating a weather station.

Bravo sir - it's a bit like missing balloon data at Christmas!

Anyway, this mornings runs are a bit of a kitchen sink job for the UK and Ireland.  Plenty of heat on offer in the short-term with chances of thunderstorms early to mid week, then it starts to look unsettled towards the end. That said, given the relative differences between ECM/GFS/UKMO at 144, anything beyond day 4 should be taken with a large pinch of sodium chloride!

image.thumb.png.0195f3b5be56b1fa152d59fb69b1fea4.pngimage.thumb.png.724945bdbabb7fc5ba84328a8c76fb9c.pngimage.thumb.png.8a8337a351ac42d8b1fc3baec58d430d.png   

 

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It's amazing how much we expect often expect of NWP whatever the weather element of interest. Remember that these models are generally scored via official metrics with their performance we geopotential height, temperature and winds speeds at mid/upper levels, not by how well they forecast a maximum temperature over London....examples can be seen in the paper attached.

Think of all the elements that models that cover a global domain have to forecast, from tropical cyclone tracks and intensities, precipitation accumulations from deep tropical convection to snowfall which is orographically enhanced by flow over high mountains. Temperatures from the hottest desert regions over sand surfaces by day, to the arctic with snow cover / permafrost in the dead of the winter night, to wind speeds and gusts over seas and mountains. These models also have to provide initial and ongoing boundary conditions for the limited area higher resolution models that nest inside them.

As these are unified forecast systems (one model forecasting all variables) each forecast element is a trade off against something else. For example if you were to try and fix the low temperature bias during warm days in the mid-latitudes....increasing temperatures could ruin CAPE and convective precipitation forecasts...with this then potentially ruining synoptic patterns.

GFS is often derided for its wildly varying synoptics which are often out of line with others across the UK. However from using it and the higher resolutions models that feed off it across the USA at short lead times I am confident that is performs better than others with several features of severe convection such as generating strong cold pools (and the hazards associated with these). I believe that this may be one of the models failings in synoptic forecasting as severe convection in the wrong location leads to large head aches for NWP (as we will no doubt see this week in the UK).

Even the UKV is a trade-off between all these different weather elements temps, cloud cover, wind, gusts, precipitation accumulations and many others...fixing one can worsen others. It's all a big trade off. We're lucky they are often as good as they are!

 

 

 

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Euro looks very messy in the way it breaks down, not really binning the proper heat (though probable storms) until Friday.

spacer.png

UKMO has the trough axis east of the UK as early as Tuesday meaning that by day 6 (same as the Euro chart) we are already in cool north westerlies.

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GFS is more or less on board with a more progressive version of the UKMO in that the trough axis is to the east and on wednesday night the trough starts to phase with the main jet.

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Putting aside GFS and GEM which are always raise the skepticism level the bulk of the argument between the UKMO and Euro (even within day 6 now) is about how far east the trough axis forms on Tuesday and the degree to which that trough then phases (the more it phases the deeper it gets and the further east is goes). 

It looks like whatever solution presents, it will be over by Thurs or Fri though in terms of 30C+.

 

 

Edited by summer blizzard
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2 hours ago, MattStoke said:

The way some go on, weather stations should only be placed in the middle of nowhere where no-one lives. They seem to think the station is in the middle of the main runway and being blasted by jet exhausts. I’m surprised they haven’t claimed that the fire at Heathrow yesterday was the station being set alight by the Met Office and blaming the high temperature reading on that. It’s tiresome reading the same comments every time we get a hot day. As if the Met Office aren’t careful and don’t take certain factors into consideration when locating a weather station.

Well a cynic (not me!) would say it would be on purpose to support the climate change 'agenda' 😄

Nonsense of course.

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h850t850eu.png h850t850eu.png
ukmaxtemp.pngukmaxtemp.png

Subtle but significant adjustments from GFS, moving it toward what recent ECM runs have been showing with impressive consistency. Less of a secondary heat low development.

h850t850eu.pngukmaxtemp.png

Tuesday increasingly showing potential to bring a secondary peak to the heatwave for some. Weak upper-level support serves to keep thunderstorms well-scattered.

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1 hour ago, General Cluster said:

Just like when I use to regularly see temps of 34-35C, when in the NW Highlands... which was quite obviously down to back-radiation for my white-painted house...But, if I know that and you know that, don't you think the Meteorological Office also knows that...?🤔

So, no, I really don't think there's a 'case to answer'...?

You're actually making the same point as me with your first para. I don't think the Met Office would dispute research showing that both city-wide UHI and local heating effects can be very significant (e.g. up to 5C in extreme cases for UHI at night-time). We may be considering different questions here - perhaps I've misunderstood the history of the debate on these forums as I'm a rare visitor.

My question would be, how much warmer are the recent record max temps at Heathrow than they would be if the site was in a location away from the airport with average levels of vegetation/trees around etc. There is a case to answer in this context, and it is nothing to do with whether Heathrow site meets official guidelines. I don't believe I've accused the Met Office of anything.

I won't post any more on this, as I know how annoying it can be when the model discussion is derailed. Please don't think I'm trying to stir things up; the opposite is the case. I think dispassionate analyis of UHI and hyper-local warming effects is really useful, and I'm very receptive to anyone who engages in this, whatever their findings.

Edited by Higher Ground
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h850t850eu.png hgt300.pngukprec.png

Tue night through Wednesday looks in with a good shout of starting off a more pronounced breakdown of the hot weather, as the jet stream finally manages to make its way in from the west. ECM 00z looked a little slower to get to this point, mind.

We often see heat lows escalate into quite vigorous LP systems once they interact with a trough to their west. I have a feeling this run will give that a go for Thursday.

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Certainly a cool down later in the week according to the Gfs 6z op, probably not what most want to hear but whatever, it’s what’s being shown!..doesn’t mean to say it’s right of course but it’s still pertinent?:shok:😜

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Just now, MattStoke said:

Do you mean if you add on the usual 2-3’C adjustment?

Yes sorry - certainly a potential if cloud clears, arpege is showing 34 with cloud cover this afternoon, so far today where I am the arpege temps have been very close  to actual temps maybe half a degrees out 

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Although the forecast was generally accurate yesterday i.e. hot, can someone please provide a meteorological explanation for why the detail was wrong i.e. the forecast for Worcestershire was hot and sunny. In reality in became cloudy by midday with a threatening sky and even big drops of rain. I have seen very little explanation of this, certainly not from the TV and radio broadcasters. As I say, an meteorological explanation would be great. 

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