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


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3 minutes ago, Man With Beard said:

But as I mentioned earlier ... with cloud around, a really good temperature prediction may not be possible until each morning, lots of cloud will kill it, no cloud will see it soar - EDIT @Mapantz post above is a case in point of what too much cloud will do!

I for one, hope it is wrong, and it stays clear all day. Especially after today's model blunders!

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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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6 minutes ago, D.V.R said:

Why? Does extreme heat in Europe have an affect on weather models performance?

Heat lows potentially forming must be very hard to model or may not be picked up at all. Then you have the issue of how the Atlantic interacts with all of it. I’m not an expert though - maybe somebody else could comment?

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2 minutes ago, Djdazzle said:

Heat lows potentially forming must be very hard to model or may not be picked up at all. Then you have the issue of how the Atlantic interacts with all of it. I’m not an expert though - maybe somebody else could comment?

Ok, that makes sense.

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Evening all 🙂

We're in two forms of model discussion currently it seems - the "nowcasting" of the hot spell which has rather overshadowed the usual discussion of the medium and longer term prospects.

Starting with the former and looking at the WRF-NMM charts for a change:

nmmuk-0-27-0.png?07-17nmmuk-0-51-0.png?07-17nmmuk-0-72-0.png?07-17

The heat profile changing with each day - Saturday sees the hottest air confined to the south coast, Sunday sees a wider distribution of heat but not quite as strong as today and Monday suggests the heat easing away to the east with only the far SE still under hot conditions.

Let's move on and there seems a general concensus by midweek the hot conditions will ease back to something which although still warm will be much more tolerable (at least for me😞

Looking to the charts for next Thursday:

ECM1-144.GIF?07-0gfs-0-144.png?12gem-0-144.png?12UW144-21.GIF?07-19

That's ECM, GFS OP, GEM and UKMO at T+144 for comparison.

I'm struck by how far to the north the Azores HP is ridging in mid-Atlantic and while GEM looks the outlier, the others all keep the trough near or over southern Britain.

There's a huge amount of uncertainty (as you would expect) after these charts but there seems (as we see many summers) a struggle between the ridging Azores HP and a growing trend for LP to develop to the NW and seek to join with the trough across the British Isles.

There doesn't seem to be any sign currently of a renewed substantial push of heat after the current spell though that doesn't mean there won't be warm or possible very warm conditions as Exeter suggests - it's a classic NW/SE split but that's far from resolved and the other option of a negatively aligned trough through the British Isles cannot be discounted.

 

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21 minutes ago, Portsmouth Sun said:

Of course it is not right, all other models that are more highly regarded are no where near this solution.

I see these next few days as a learning process with the models. We've seen plenty on how the perform with a straightforward plume, but how do they perform with a complex heat low to the south? It will be very interesting to look back at the end of this week. ECM, UKMO, fairly consistent so far aside a couple of wobbles at the start of the week, will they beat all again?

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I’m thinking that Monday could possibly be the hottest day in this period. Flow from a continent that will have been roasted for several days. Does, as others have said, depend of cloud / convection.

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4 minutes ago, Man With Beard said:

but how do they perform with a complex heat low to the south?

Not very well I don't think?!

It's not out of the question to see something special in terms of max temps on many coastal areas tomorrow. 

No model managed to pick up on an 8 degree drop in temperature in parts of Dorset, or other large temp drops either side of that. 

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11 minutes ago, Djdazzle said:

I’m thinking that Monday could possibly be the hottest day in this period. Flow from a continent that will have been roasted for several days. Does, as others have said, depend of cloud / convection.

With a baked continent and a languid flow off the continent, albeit with a NE gentle flow, a cloudless sky in Hampshire, Sussex or Kent could really produce the goods. Homegrown thunderstorms may very well be an issue further inland, but the synoptics looks good for the SE coast.

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I actually had a look through the UKV 15Z run earlier and dismissed that Saturday chart as a load of cobblers - way off with regards to temperatures.

UKV 18Z run below is much more what we would expect.

Saturday 12:00: 13:00 14:00 and 15:00.

84A9B0CF-D65B-42E5-91A4-3A5E21554AF8.thumb.png.c8a03a120ef6306d405555f66ec47a3d.png99F75B55-5AF1-4399-9DB7-47DBEB7533F9.thumb.png.05f17615c85d96581d66bb6635d64af6.pngE5AD7AC3-B41E-43E5-8472-8FA9A8EF79A4.thumb.png.6b8279ac2fac837629a0b10a637c75e1.png9DA149AF-AB30-42AD-8E75-5742BFA837C4.thumb.png.a9bb59623c38b16e13a5670aec5cd3ba.png
 

2601E063-8827-4487-B6F6-5734A74019AE.thumb.png.b9a2f4fafc39a0ac508c028a8e5eeb8c.png

 

Edited by Mr Frost
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6 hours ago, MattStoke said:

36.3’C at Heathrow currently. Hats everywhere can rest easy 🙂 

DAAB97F4-EC56-4E87-8D58-82AE3167623A.jpeg

I thought this might be of interest in the, what seems like, perennial discussion about the Heathrow temperature readings

image.thumb.png.2845672d1c054d87f7786ccae0be8cbc.png

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10 minutes ago, johnholmes said:

I thought this might be of interest in the, what seems like, perennial discussion about the Heathrow temperature readings

image.thumb.png.2845672d1c054d87f7786ccae0be8cbc.png

In some ways it’s weird that St. James’s Park isn’t normally top as it’s closest to Central London.

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11 minutes ago, johnholmes said:

I thought this might be of interest in the, what seems like, perennial discussion about the Heathrow temperature readings

image.thumb.png.2845672d1c054d87f7786ccae0be8cbc.png

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

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2 minutes ago, MattStoke said:

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

I wonder what temperature it and Heathrow would have recorded this year if it wasn't for Covid and lack of flights. 

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8 minutes ago, MattStoke said:

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

Nah, but it could be the fact that it is very close, if not enveloped by the biggest UHI effect , yep, London.

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Not sure if the wriggling trough feature played a part in this but some pretty interesting temperature contrasts on my run down from SE London to Brighton.

Left at 2030 in 30c,headed out on the Kent stretch of the m25 24c.

M23 around Gatwick 21c

Then a sporadic climb to 26c again in Brighton at 2200.

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30 minutes ago, DAVID SNOW said:

Nah, but it could be the fact that it is very close, if not enveloped by the biggest UHI effect , yep, London.

But Heathrow is downstream from Kew and the hottest flows, so it’s not like Kew is getting a benefit from the Heathrow tarmac advecting NNW is the hottest flows...

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1 hour ago, Mr Frost said:

I actually had a look through the UKV 15Z run earlier and dismissed that Saturday chart as a load of cobblers - way off with regards to temperatures.

UKV 18Z run below is much more what we would expect.

Saturday 12:00: 13:00 14:00 and 15:00.

84A9B0CF-D65B-42E5-91A4-3A5E21554AF8.thumb.png.c8a03a120ef6306d405555f66ec47a3d.png99F75B55-5AF1-4399-9DB7-47DBEB7533F9.thumb.png.05f17615c85d96581d66bb6635d64af6.pngE5AD7AC3-B41E-43E5-8472-8FA9A8EF79A4.thumb.png.6b8279ac2fac837629a0b10a637c75e1.png9DA149AF-AB30-42AD-8E75-5742BFA837C4.thumb.png.a9bb59623c38b16e13a5670aec5cd3ba.png
 

2601E063-8827-4487-B6F6-5734A74019AE.thumb.png.b9a2f4fafc39a0ac508c028a8e5eeb8c.png

 

I saw this aswell very large diffrences at such short notice. I don't rate UKV that highly tho had 29c here today and I got 32c gfs and ecm performed better they both had 31c that's not the first time.

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1 hour ago, johnholmes said:

I thought this might be of interest in the, what seems like, perennial discussion about the Heathrow temperature readings

image.thumb.png.2845672d1c054d87f7786ccae0be8cbc.png

Tarmac at Heathrow causing higher max on sunny days would also likely cause lower min on clear nights - especially as Kew more surrounded by city (UHI more pronounced at night-time as I understand it). Hence similar mean temps but Heathrow breaks the max temp records?

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37 minutes ago, Higher Ground said:

Tarmac at Heathrow causing higher max on sunny days would also likely cause lower min on clear nights - especially as Kew more surrounded by city (UHI more pronounced at night-time as I understand it). Hence similar mean temps but Heathrow breaks the max temp records?

They are average max temps, and Kew usually has warmer days than Heathrow. Kew has a frost hollow effect, and has some of the lowest average minima in London. Heathrow minima are also cooler than most of London. 

If the Met Office hadn't shut down weather stations at Greenwich, Camden, LWC and Gravesend, Heathrow wouldn't be claiming all of the temperature records. The PWS in Whitton closely matches Heathrow temperatures.

Edited by B87
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30 minutes ago, B87 said:

They are average max temps, and Kew usually has warmer days than Heathrow. Kew has a frost hollow effect, and has some of the lowest average minima in London. Heathrow minima are also cooler than most of London. 

If the Met Office hadn't shut down weather stations at Greenwich, Camden, LWC and Gravesend, Heathrow wouldn't be claiming all of the temperature records. The PWS in Whitton closely matches Heathrow temperatures.

Ah yes - in my defence I thought looking at the title of the bar chart: "Average monthly temperature" and the closeness of the Kew and Heathrow temps was enough to extract the vital information.... Glad you corrected me, and useful info in your post, thanks 

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ECM this morning still has a lot of warm air over the UK by Friday morning. A full breakdown looking like Thursday at the very earliest, but possibly Friday for some parts - on this model.

A much larger area of the southern half in very hot air for Tuesday, with 30-35C possible across quite a wide section of central/eastern England, and mid to high 20s throughout the whole of England + Wales aside the western extremes.

Wednesday still very hot SE.

Other models a bit quicker on the breakdown this morning.

Edited by Man With Beard
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24 minutes ago, Man With Beard said:

ECM this morning still has a lot of warm air over the UK by Friday morning. A full breakdown looking like Thursday at the very earliest, but possibly Friday for some parts - on this model.

A much larger area of the southern half in very hot air for Tuesday, with 30-35C possible across quite a wide section of central/eastern England, and mid to high 20s throughout the whole of England + Wales aside the western extremes.

Wednesday still very hot SE.

Other models a bit quicker on the breakdown this morning.

Looks like a recipe for slow moving torrential thundery downpours from midweek especially I feel some may see a real deluge so it’s not quite most agreeable summer BBQ weather.

Edited by Daniel*
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Still lots of disagreement this morning on how the breakdown plays out.

GEM builds a full Azores high in by day 9/10, ECM probably worst and leaves us in a messy and fairly unsettled no mans land.

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7 hours ago, B87 said:

They are average max temps, and Kew usually has warmer days than Heathrow. Kew has a frost hollow effect, and has some of the lowest average minima in London. Heathrow minima are also cooler than most of London. 

If the Met Office hadn't shut down weather stations at Greenwich, Camden, LWC and Gravesend, Heathrow wouldn't be claiming all of the temperature records. The PWS in Whitton closely matches Heathrow temperatures.

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. 

Edited by Daniel*
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