Model Output Discussion - Mid Summer Onwards

[Geordiesnow]

32 minutes ago, damianslaw said:

Equivalent of March sometimes delivering coldest conditions, 2013 being a prime example.

Except without climate change, we shouldn't be seeing anywhere near these extraordinary 850 temperatures at this time of year, August is usually the warmest month in the northern hemisphere but we are seeing it more and more of warm air lingering longer at all latitudes and the polar vortex struggling to form during September.

Depressing looking back at charts from the 1960s and seeing the marked difference between then and now. There is no way this set up would deliver those type of 850 temperatures back then. It's only for the fact perhaps temperatures at the surface may not be as high as the charts suggest means this event is not as noteworthy as it should be.

Either way, whilst a southerly will occur, there is uncertainty how hot it will get, how much cloudcover there will be(seems certain Monday and Tuesday should be the sunniest days of the week) and of course the storm risk which looks like could be a factor from Wednesday onwards.

[alexisj9]

39 minutes ago, damianslaw said:

The upcoming spell won't feel anywhere near as hot as an equivalent spell of warmth in June to mid Aug or even in May. The sun is much weaker now, and the hours of heat much shorter in duration. 

It'll depend on humidity, how hot it feels, and I think might be some who don't expect the sun to be strong enough burn.

[Don]

6 minutes ago, Geordiesnow said:

Except without climate change, we shouldn't be seeing anywhere near these extraordinary 850 temperatures at this time of year, August is usually the warmest month in the northern hemisphere but we are seeing it more and more of warm air lingering longer at all latitudes and the polar vortex struggling to form during September.

Depressing looking back at charts from the 1960s and seeing the marked difference between then and now. There is no way this set up would deliver those type of 850 temperatures back then. It's only for the fact perhaps temperatures at the surface may not be as high as the charts suggest means this event is not as noteworthy as it should be.

Either way, whilst a southerly will occur, there is uncertainty how hot it will get, how much cloudcover there will be(seems certain Monday and Tuesday should be the sunniest days of the week) and of course the storm risk which looks like could be a factor from Wednesday onwards.

With all that heat lingering to the south of us during summer and extraordinary 850 temperatures, it shouldn't be of much of a surprise that it would pay a visit to our shores at some point, be it July or September.  As you say though, without climate change, this would have been very unlikely.  Remember back to New Year, when many warm records tumbled across the continent, so this is clearly not restricted to summer!

[Cheshire Freeze]

1 hour ago, Metwatch said:

@CreweCold There's your tropical nights outside of London. I think even I would have issues sleeping with this after a day of low 30s

I'll still be surprised if we see 20C+ minima at official stations outside of London...but we'll see.

You need to remember also that a lot of discomfort indoors over summer during heatwaves is due to the house structure heating up. 20C isn't a bad temperature to sleep in per se (ideal room temperature is 19-21C) but during summer the structure of the house will heat up quickly and will have little chance to cool down overnight (short nights). This effect will not be as pronounced so your house should stay relatively cool.

My example of this is last summer. My room was at 31C during the July heatwave but didn't rise above 26/27C during the August one. It's even later in the year now so I don't expect to be suffering in anything much above 24C or 25C as a maximum. 

Edited September 2, 2023 by CreweCold

[LetItSnow!]

1 hour ago, Geordiesnow said:

Except without climate change, we shouldn't be seeing anywhere near these extraordinary 850 temperatures at this time of year, August is usually the warmest month in the northern hemisphere but we are seeing it more and more of warm air lingering longer at all latitudes and the polar vortex struggling to form during September.

Depressing looking back at charts from the 1960s and seeing the marked difference between then and now. There is no way this set up would deliver those type of 850 temperatures back then. It's only for the fact perhaps temperatures at the surface may not be as high as the charts suggest means this event is not as noteworthy as it should be.

Either way, whilst a southerly will occur, there is uncertainty how hot it will get, how much cloudcover there will be(seems certain Monday and Tuesday should be the sunniest days of the week) and of course the storm risk which looks like could be a factor from Wednesday onwards.

I can only think of a couple of examples pre-21st century where the 20C line made it to the UK. I’m confident we’ve seen it more since 2015 than in the entire 1851-2014 period that the reanalysis covers. 

Ironically in the cold summer of 1879 it clipped the southeast on the 3rd of August that year. When I look at many heatwave charts from the past I’m always struck at how tame they were. Classic summers like 1976 and 1995 never saw depths of heat like we tap into now. 

[Scorcher]

7 hours ago, Metwatch said:

@CreweCold There's your tropical nights outside of London. I think even I would have issues sleeping with this after a day of low 30s

He won't have it that very warm nights are possible in September though...

I've said all along, if the air mass is warm enough, it doesn't matter much about the longer nights.

Superb GFS run again this morning. It extends the very warm spell well into next weekend.

 

[Jason M]

1 hour ago, Scorcher said:

He won't have it that very warm nights are possible in September though...

I've said all along, if the air mass is warm enough, it doesn't matter much about the longer nights.

Superb GFS run again this morning. It extends the very warm spell well into next weekend.

 

To illustrate your point we have seen very high night time temperatures in mid winter in recent years. Double figures or even teens are nothing noteworthy anymore.

[I remember Atlantic 252]

2 hours ago, Scorcher said:

He won't have it that very warm nights are possible in September though...

I've said all along, if the air mass is warm enough, it doesn't matter much about the longer nights.

Superb GFS run again this morning. It extends the very warm spell well into next weekend.

 

Aye, potentially very warm nights, 18 degrees the low for areas away from London, could be looking at warmest spell of 2023, disagree with anyone who says nights cooler under southerly just because its late in season

[Derecho]

Pretty remarkable output this morning with those saying this would be a few warm days and nothing else looking a bit silly now. Judging by the GFS 00z, we could have 5 consecutive days with a 24 hour mean CET above 20C (6th - 10th). That is quite exceptional. The mean after 10 days would be around 19.9C and despite some cooler incursions after that, we would still be on 18.4C by the 17th.

So very impressive for early September and before ANYWEATHER bleats on about 1906 yet again lets keep a sense of perspective here. We can still get record cold in a warming climate (March 2018) and back then you could still get record heat. Despite that, the CET for September 1906 was near average and lets not forget global temperatures during that time.

Spot the difference, some sobering output for climate change deniers.

I think even the nights will feel uncomfortable as next week progresses.

[WeatherEnthusiast]

12 minutes ago, Derecho said:

Pretty remarkable output this morning with those saying this would be a few warm days and nothing else looking a bit silly now. Judging by the GFS 00z, we could have 5 consecutive days with a 24 hour mean CET above 20C (6th - 10th). That is quite exceptional. The mean after 10 days would be around 19.9C and despite some cooler incursions after that, we would still be on 18.4C by the 17th.

So very impressive for early September and before ANYWEATHER bleats on about 1906 yet again lets keep a sense of perspective here. We can still get record cold in a warming climate (March 2018) and back then you could still get record heat. Despite that, the CET for September 1906 was near average and lets not forget global temperatures during that time.

Spot the difference, some sobering output for climate change deniers.

I think even the nights will feel uncomfortable as next week progresses.

Unbelieveable GFS 00Z run. I was wrong about next weekend being much cooler.GFS Humidindex (Feels like value of 39 degrees by Thursday, still 31 on Sunday 10th.  Lows of 29 in London one night next week

Edited September 2, 2023 by WeatherEnthusiast

[WeatherEnthusiast]

Could be more unsettled on the 12th September as a Trough lands over the UK according to ECMWF this is in agreement with the GFS model . Lots of rain over the UK by day 10 particularly over Wales (Snowdonia could see heavy rain by the end of the week) .  In the shorter term here is the pressure chart at 18.00 today 

Edited September 2, 2023 by WeatherEnthusiast

[Scorcher]

19 minutes ago, Derecho said:

Pretty remarkable output this morning with those saying this would be a few warm days and nothing else looking a bit silly now. Judging by the GFS 00z, we could have 5 consecutive days with a 24 hour mean CET above 20C (6th - 10th). That is quite exceptional. The mean after 10 days would be around 19.9C and despite some cooler incursions after that, we would still be on 18.4C by the 17th.

One poster actually said yesterday that this was going to be a 'short-lived' spell- despite all the evidence pointing to the contrary. No matter what you do there will some who continue to talk nonsense to suit their agenda.

The GFS does indeed look very warm for almost the entire run. Interesting that the Met Office and BBC haven't yet shown temps as high as the GFS is showing for next week though. This is rather surprising to me as I can't see too many issues with temps being held back next week now.

This upcoming setup looks considerably more impressive than the September 2021 spell when we reached 28.4C here:

Tuesday next week:

GFS:

 

ECM:

Edited September 2, 2023 by Scorcher

[Singularity]

58 minutes ago, Jason M said:

To illustrate your point we have seen very high night time temperatures in mid winter in recent years. Double figures or even teens are nothing noteworthy anymore.

Indeed. High dew point, high relative humidity air can prop up temps even when there’s little wind.

On the other hand, if the setup becomes as slack as most modelling now indicates for Thu-Fri, some degree of inversion is likely to form overnight in relatively low lying areas, a process GFS tends to underestimate. So it could well be that we see high elevation weather stations recording some of the highest minima.

It’s going to feel pretty strange after almost no such heat in all of Jul & Aug. When we saw similar heat in Sep 2021, it wasn’t as long since the last for many central & western parts due to a hot week in July.

[WeatherEnthusiast]

2 minutes ago, Scorcher said:

One poster actually said yesterday that this was going to be a 'short-lived' spell- despite all the evidence pointing to the contrary. No matter what you do there will some who continue to talk nonsense to suit their agenda.

The GFS does indeed look very warm for almost the entire run. Interesting that the Met Office and BBC haven't yet shown temps as high as the GFS is showing for next week though. This is rather surprising to me as I can't see too many issues with temps being held back next week now.

This upcoming setup looks considerably more impressive than the September 2021 spell when we reached 28.4C here:

Tuesday next week:

GFS:

 

ECM:

Isnt the key issue here that temps cant be that high because we have lost much of the strength of the sun now! Thats why BBC and Met are being much more conservative with their temperature predictions. 

[Derecho]

Just now, WeatherEnthusiast said:

Isnt the key issue here that temps cant be that high because we have lost much of the strength of the sun now! Thats why BBC and Met are being much more conservative with their temperature predictions. 

They tend to be conservative about temperatures a few days out. Expect the forecast temperatures to nudge upwards as they get closer to T24.

[Scorcher]

6 minutes ago, WeatherEnthusiast said:

Isnt the key issue here that temps cant be that high because we have lost much of the strength of the sun now! Thats why BBC and Met are being much more conservative with their temperature predictions. 

That doesn't account for this at all and not that simple- the sun is still easily strong enough to lift the temps well over 30c- as we've seen in past Septembers in less impressive setups than this one.

For example-September 13th 2016- 34.4C at Gravesend.

[LetItSnow!]

7 hours ago, LetItSnow! said:

I can only think of a couple of examples pre-21st century where the 20C line made it to the UK. I’m confident we’ve seen it more since 2015 than in the entire 1851-2014 period that the reanalysis covers. 

Ironically in the cold summer of 1879 it clipped the southeast on the 3rd of August that year. When I look at many heatwave charts from the past I’m always struck at how tame they were. Classic summers like 1976 and 1995 never saw depths of heat like we tap into now. 

Really am bemused at people disagreeing with this. Have the past eight summers not been enough to show this? I mean, screw the 20C line we’ve had like 22-25C. Before then your heatwaves usually had 12-18C and 20C was extremely rare.

[Scorcher]

3 minutes ago, LetItSnow! said:

Really am bemused at people disagreeing with this. Have the past eight summers not been enough to show this? I mean, screw the 20C line we’ve had like 22-25C. Before then your heatwaves usually had 12-18C and 20C was extremely rare.

You only have to look at who disagreed with your post and that tells the whole story...

It's undeniable that the 20C isotherm is reaching the UK a lot more often than it used to. We could easily pull up charts to prove this. Even some of the hottest summers of the past never get close to 20C hPa temps. 1976, 1995, 1983 are prime examples. 

[danm]

10 minutes ago, Scorcher said:

You only have to look at who disagreed with your post and that tells the whole story...

It's undeniable that the 20C isotherm is reaching the UK a lot more often than it used to. We could easily pull up charts to prove this. Even some of the hottest summers of the past never get close to 20C hPa temps. 1976, 1995, 1983 are prime examples. 

Absolutely undeniable that the 20c isotherm is reaching the UK far more often now than it used to. 

[alexisj9]

1 hour ago, I remember Atlantic 252 said:

Aye, potentially very warm nights, 18 degrees the low for areas away from London, could be looking at warmest spell of 2023, disagree with anyone who says nights cooler under southerly just because its late in season

Can't get colder than whatever the DP is, DP 18 temp 18 and will feel yuk with a 100% humidity. Looking forward to it, not.

[alexisj9]

1 hour ago, Derecho said:

Pretty remarkable output this morning with those saying this would be a few warm days and nothing else looking a bit silly now. Judging by the GFS 00z, we could have 5 consecutive days with a 24 hour mean CET above 20C (6th - 10th). That is quite exceptional. The mean after 10 days would be around 19.9C and despite some cooler incursions after that, we would still be on 18.4C by the 17th.

So very impressive for early September and before ANYWEATHER bleats on about 1906 yet again lets keep a sense of perspective here. We can still get record cold in a warming climate (March 2018) and back then you could still get record heat. Despite that, the CET for September 1906 was near average and lets not forget global temperatures during that time.

Spot the difference, some sobering output for climate change deniers.

I think even the nights will feel uncomfortable as next week progresses.

It was basically that one run of GFS that had Franklin go north. So the warm up happened but then broke down before the southerly draw starts. At least GFS now agree with the others re Franklin, the a relief.

[alexisj9]

1 hour ago, WeatherEnthusiast said:

Unbelieveable GFS 00Z run. I was wrong about next weekend being much cooler.GFS Humidindex (Feels like value of 39 degrees by Thursday, still 31 on Sunday 10th.  Lows of 29 in London one night next week

Hopefully that doesn't happen, would be hotter than the night before the 40⁰ temps happened.

[alexisj9]

58 minutes ago, Singularity said:

Indeed. High dew point, high relative humidity air can prop up temps even when there’s little wind.

On the other hand, if the setup becomes as slack as most modelling now indicates for Thu-Fri, some degree of inversion is likely to form overnight in relatively low lying areas, a process GFS tends to underestimate. So it could well be that we see high elevation weather stations recording some of the highest minima.

It’s going to feel pretty strange after almost no such heat in all of Jul & Aug. When we saw similar heat in Sep 2021, it wasn’t as long since the last for many central & western parts due to a hot week in July.

Yuk, thinking about it, if the DP is 18, temp low land 18, feeling yuk, up on a hill the temp could be 20 something in that scenario. Wouldn't feel nice, but would be rather interesting.

[sundog]

That's it, get in!!  Not that I am taking that chart too seriously given the time frame. (11th)  But come on autumn.

Edited September 2, 2023 by sundog

[MP-R]

1 hour ago, alexisj9 said:

Can't get colder than whatever the DP is, DP 18 temp 18 and will feel yuk with a 100% humidity. Looking forward to it, not.

Given the time of year, fog could be a possibility. That’s how the 2021 heatwave started here.