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


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3 minutes ago, Winter1981 said:

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. 

If you read back through the pages this has already been answered think it was@johnholmes apologies if it was not you John 

C.S

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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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1 minute ago, cheshire snow said:

If you read back through the pages this has already been answered think it was@johnholmes apologies if it was not you John 

C.S

Yes, the answer could be found on the FAX charts.. there was a trough or something (i too didnt view it) stretching up from Biscay.

 

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1 hour ago, KeegansPerm said:

Gawd a 'quick' skim through suggests it is a very complex paper. Interesting that they suggest more than one parameter, (if I'm reading it correctly).

Edited by johnholmes
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12 minutes ago, mushymanrob said:

Yes, the answer could be found on the FAX charts.. there was a trough or something (i too didnt view it) stretching up from Biscay.

 

Yes it was a clearly marked trough on the 06Z Fax chart and fitted what happened over some parts. Odd that the lunch time BBC Met trained forecaster made no mention of this. Perhaps the senior man laid down the instruction. It does happen.

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2 hours ago, johnholmes said:

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.

 

Amongst all the heatwave cafuddle I really appreciate these updates John.

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The second half of August probably nothing like as amazing as the first half judging by the GEFS 6z mean?.don’t shoot the messenger, it’s the current trend but certainly the first half of August is going to break heat records if it hasn’t already and who is to say there won’t be further pleasant surprises further into this month?..already we have rescued this summer from oblivion following a pish poor July!😜

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Still some way to go with the heat!!! And some classic storm activities are a cert!!  Trust me when I say here in Uxbridge.. it’s possitivly stiffling.. already 28c .. yesterday was bordering unbearable!!!🔥🔥🔥🔥🔥

80119B4B-9EF5-4034-949F-67CBA0F29EA2.png

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Are we starting to see a trend to a more unsettled spell from Wednesday onwards? Most going more unsettled from the weekend barring GEM. Perhaps tying in to falling momentum towards mid month.

image.thumb.png.bc7364e702694b7d3a6bfe9a8303fb5d.png

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1 hour ago, johnholmes said:

Gawd a 'quick' skim through suggests it is a very complex paper. Interesting that they suggest more than one parameter, (if I'm reading it correctly).

Agreed it's very complex statistics. The main point I was trying to draw out of it is the broadscale synoptics (especially mid-upper troposphere) are the key measures via which NWP centres compare each other against.

Generally NWP is not optimised for any one thing (surface temperatures, snowfall accumulations, tropical cyclones, snow depths, wind speeds) and we must look at the individual fields with that in mind. It's all a compromise, with the main aims of development being to perform well against others NWP models in the bench mark statistical skill scores (which correlates with give broadscale forecasting). Although I suspect the GFS may sacrifice this slightly to better resolved some of the non-linear features such as cold pools with severe convection, which is used for initialisation and boundary conditions for higher resolution models run across the USA....these often mess up the broadscale!

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3 hours ago, johnholmes said:

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.

 

Your interpretation of these maps is really interesting. I am seeing positive anomalies over and to the north of the UK on all three charts, including the 8-14 day NOAA that you say shows a general westerly flow. Would you mind clarifying why you see those as showing a return of westerlies?

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7 minutes ago, wellington boot said:

Your interpretation of these maps is really interesting. I am seeing positive anomalies over and to the north of the UK on all three charts, including the 8-14 day NOAA that you say shows a general westerly flow. Would you mind clarifying why you see those as showing a return of westerlies?

All 3 show an overall pattern in the contours that has a mainly westerly flow in the broad scale?

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Last post from me for a wee while but with my optimistic hat on, to be honest that’s the only hat I own but what I’m trying to say is the second half of August ( fag end ) of summer won’t necessarily be pish poor!..in the meantime, enjoy these golden days of summer, it’s really very exceptional what’s happening right now (especially across the s / se) and we will look back on this with a warm glow when the autumn gales and rain arrive!😉

B4F8C952-5EF1-4015-9FBD-88ED882F4A91.thumb.png.fc7ae217fbae670264fdcc5c3d41e74c.png8B4153E8-F8D1-4FC1-A2C9-6D2F649CE4D0.thumb.png.4b1e80dd7d3c3dacf07ed5dd30a5740c.png

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@Tamara Thank you for noticing my message and responding so thoroughly. Your response clarifies some issues that have been persistently bothering me. My intuitive sense of the dynamics under discussion has been immeasurably enhanced, which I always feel is a good indicator of understanding. 

I do have further questions - several about the apparent consistency of the twin low frequency tropical convection signal over around a year up to June, even as we saw major changes to average synoptics and conditions here and across Europe. But I will aim to ask more when appropriate in response to your frequent, excellent updates. 

For now, can you say more about how you would expect that signal to evolve? Are long periods of stability typical? And is that why you use the term 'default', because at any given moment there is a relatively stable configuration driving default conditions. Or could we realistically see the current standing wave arrangement disrupted or shifted at any moment?

And a big thank you again.

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28 minutes ago, johnholmes said:

All 3 show an overall pattern in the contours that has a mainly westerly flow in the broad scale?

OK, but don't the contours always necessarily show a broadly westerly flow everywhere, albeit with southerly and northerly tilts in places? The dashed anomalies on the NOAA charts clearly show positive anomalies stationed over and just to the north of us.

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7 minutes ago, wellington boot said:

OK, but don't the contours always necessarily show a broadly westerly flow everywhere, albeit with southerly and northerly tilts in places? The dashed anomalies on the NOAA charts clearly show positive anomalies stationed over and just to the north of us.

Pretty much. Takes something truly exceptional like the BFTE cold spell in 2018 to bend the 500mb flow back east:

B80E9A1D-C758-4657-8549-C4A40FBEBC52.thumb.gif.015e67294e09a2e0f6f956da03e1f8c6.gif

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Latest Ukmo shows a flatter northern arm with the cut off upper low less intrusive in the south of the U.K. and would lead to a more settled outlook ...... more feasible than the 00z run based on general ens guidance .....

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1 minute ago, bluearmy said:

Latest Ukmo shows a flatter northern arm with the cut off upper low less intrusive in the south of the U.K. and would lead to a more settled outlook ...... more feasible than the 00z run based on general ens guidance .....

You can see another hot day on Thursday getting squeezed out - ECM wasn't far off this.

UW120-7.GIF?08-18

 

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I'm thinking it's nae really worth over-analysing each and every model-run, just now: apart from the general picture -- a lot of thunderstorms from late Monday onward, and hints of cool-down, anytime from Thursday, what's to be gained; other than a god-almighty headache?🤕

And who knows when and where the storms will strike...?:unsure2:

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Afternoon all 🙂

31c in East London today making the roast lunch - indoors but well ventilated - perfectly pleasant apart from the insects.

Looking at the Arpege charts for the next few days:

arpegeuk-41-27-0.png?08-17arpegeuk-41-51-0.png?08-18arpegeuk-41-75-0.png?08-18arpegeuk-41-99-0.png?08-18

Plenty of heat still to come for southern and south eastern areas through to midweek but the nature of the heat profile contains some subtle changes on a day-to-day basis.

The highest temperatures tomorrow and Monday look to be along the south coast (presumably with a NE wind those areas would see the longest track of hot air over land which is counter-intuitive to the traditional S'ly plume for which the coast often has slightly cooler temperatures owing to the brief passage of the very hot air over the cooler English Channel). There are some extraordinary values forecast for NE France and Belgium as well.

By Tuesday the hottest air is starting to draw away east and by Wednesday the hottest areas are right along the east and south east coast as the heat heads toward the Low Countries and Germany and France cools down a notch.

Another way to look at it is to use the Humidex measure of heat plus humidity:

arpegeuk-47-27-0.png?08-17 arpegeuk-47-51-0.png?08-18arpegeuk-47-75-0.png?08-18arpegeuk-47-99-0.png?08-18

Some really uncomfortable numbers coming up for southern and south eastern areas with the Humidex hitting 40 on Wednesday. That suggests both Tuesday and Wednesday look more likely to have thunderstorms than tomorrow or Monday but those storms could be real brutes.

  

 

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