Model Output Discussion - Autumn arrives

[SunnyPlease]

1 minute ago, hotsummer said:

This isn’t too uncommon in hot airmasses. Usually the lower the DP the higher the temp can rise. And I guess this is technically a dry airmass rather than a ‘tropical’ one. 

Like Dubai, it can have either - high or low DPs. 28c not unusual but on occasion you’ll see single digits. Common in Lueait. But go inland UAE and it’ll almost always been low. Freezing not uncommon. Lack of warm seas. 

Seville earlier today was 42c with a DP of 4c. And here I suspect the hot air is aided by lack of moisture specially on Monday? 

Excuse my ignorance on the subject, but does that mean it will be quite a dry heat more akin to abroad rather than the sticky humid heat we often get?

[Cambrian]

I like these chart types in this situation, showing outputs of the 12z ECM operational run. Really useful. 

The short wave radiation chart for the 24 hours of Monday indicates a great deal of sunshine on offer for all, even the north of Scotland is doing fairly well.

Monday at 4pm - the flexible scale for 2m temperatures really picks out where the most extreme heat is modelled and has the added advantage that the axis indicates the top overall temperature modelled at that time, at 35.6 degrees. 

The temperature anomaly shows the relative heat compared with what we’re used to, 10-15 degrees above average for many parts. Spots in Cheshire, Shropshire and Norfolk are more than 15 degrees above average.

Same charts for Tuesday - more cloud about further west and north, a bit of a change getting underway. Highest temperature of 39.2 degrees on the flex chart serves to moderate some of the hues, even though it’s widely hotter, there is a much wider range. Extreme heat again across a large swathe of England, clipping parts of Wales and Scotland. A good chunk of England and parts of northeast Wales with temperatures 15-20 degrees above normal. 

  

[bluearmy]

1 minute ago, SunnyPlease said:

Excuse my ignorance on the subject, but does that mean it will be quite a dry heat more akin to abroad rather than the sticky humid heat we often get?

It seems that way - yes 

[Snowy L]

6 minutes ago, Steel City Skies said:

Anyone thought MOGREPS graphs underestimates 2m temps? At least going by the last couple of days which have showed 2m temps of 19C for Sheffield when in reality we hit 21C today.

 

Yes it has the 20C uppers in London by Sunday night, I would think 35C bare minimum from that on Monday, not maximum.

[bluearmy]

1 minute ago, Cambrian said:

I like these chart types in this situation, showing outputs of the 12z ECM operational run. Really useful. 

The short wave radiation chart for the 24 hours of Monday indicates a great deal of sunshine on offer for all, even the north of Scotland is doing fairly well.

Monday at 4pm - the flexible scale for 2m temperatures really picks out where the most extreme heat is modelled and has the added advantage that the axis indicates the top overall temperature modelled at that time, at 35.6 degrees. 

The temperature anomaly shows the relative heat compared with what we’re used to, 10-15 degrees above average for many parts. Spots in Cheshire, Shropshire and Norfolk are more than 15 degrees above average.

Same charts for Tuesday - more cloud about further west and north, a bit of a change getting underway. Highest temperature of 39.2 degrees on the flex chart serves to moderate some of the hues, even though it’s widely hotter, there is a much wider range. Extreme heat again across a large swathe of England, clipping parts of Wales and Scotland. A good chunk of England and parts of northeast Wales with temperatures 15-20 degrees above normal. 

  

The max temps on the axis are likely related to the continent on the chart 

[Paul]

7 minutes ago, Ben Sainsbury said:

This is the most mental set of MOGREPS 12z I've ever seen, for London too averaging 22C at 850hPa when you might expect somewhere across CS England coast to be even higher.

Indeed, Hampshire averaging 23c at one point..

[nick sussex]

The low humidity also means you’re less likely to get heat stroke . 

 

[hotsummer]

7 minutes ago, SunnyPlease said:

Excuse my ignorance on the subject, but does that mean it will be quite a dry heat more akin to abroad rather than the sticky humid heat we often get?

At DPs in single digits or subzero then it’ll feel dry yes. The only oppression will be the heat itself which tbh I feel is often the case here. People mistake heat and hot houses (which can have an affect akin to high DPs) for high humidity where it makes an actual significant difference. It’s not often DPs get too high here. That said, to see high temps and low DPs (as low as suggested) will be quite something given what we’re surrounded by! 

I’m not sure how this will play with storm potential? I could only see dry storms? But it seems all finely balanced. 

We shall see…

Edited July 14, 2022 by hotsummer

[mb018538]

Lots of talk about dewpoints- just a measure of the water content of the air. Image above shows California today with sub -10c….just means the air is incredibly dry. No real surprise for the upcoming heatwave given the source of the air!

[Methuselah]

12 minutes ago, Andy Bown said:

Not necessarily. There was a Saturday several years ago where 32c at 14.00 became 20c by 17.00 and in between was a band of cloud.

This looks similar with something like 35c down to 23c in a few hours.

And then there was a night back in 1975 when we watched a band of very active storms move SW-NE, for hours on end; and the following day was almost as warm as the one before it. You never can tell with temperature drops?

[Summer Sun]

12z ECM maxes out at 35c on Monday and 37c on Tuesday

Edited July 14, 2022 by Summer Sun

[SunnyPlease]

2 minutes ago, Summer Sun said:

12z ECM maxes out at 35c on Monday and 37c on Tuesday

ECM has been 3c off or so, so it's right in line for 39-40c. I still think Tuesday will see the absolute maximum.

[Man With Beard]

34 minutes ago, Paul said:

Impressive clustering on the 850's on the MOGREPS tonight - solid agreement up to tuesday. 

Not too disimilar in terms of 2m temperatures either - and Cambridgeshire peaking just shy of 40c..

 

What's also of interest is that this chart was 3C too low for Cambridge today.

Everything *at this moment* is pointing towards 40C on Tuesday.

The only way out is a faster breakdown, still just about possible but more likely to go the other way IMO, and that would probably only serve to make Monday hotter anyway.

[Mark wheeler]

Navgem Special train in coming . Choo Choo . Only 45c at 1pm

 

Edited July 14, 2022 by Mark wheeler

[Porto]

5 minutes ago, Mark wheeler said:

Navgem Special train in coming . Choo Choo . Only 45c at 1pm

I think it may be overdoing it slightly, like just a smidge. Tiny bit. 

[SunnyPlease]

5 minutes ago, Porto said:

I think it may be overdoing it slightly, like just a smidge. Tiny bit. 

Imagine if it isn't though....

[Man With Beard]

18 minutes ago, Mark wheeler said:

Navgem Special train in coming . Choo Choo . Only 45c at 1pm

 

And here's the upper air chart, take that GFS! (And everywhere else in the northern hemisphere bar the low countries and Morocco...)

 

Although GEFS P12 pushed it close, there was a 44C on here when zoomed in...

 

Edited July 14, 2022 by Man With Beard

[Bradley in Kent]

To add to the topic of dew points and interpreting figures in charts, DP is what the temperature needs to get down to for water vapour to condense onto surfaces. Put the DP figure against the air temp you have your relative humidity. 100% and you have fog. However, I'd love to know the calculation: DP of 20c against temp 30c = 66% assuming baseline 0c. However what is DP -10c against temp -2c? What's the baseline?

Relative humidity aside, DPs in the single digits make extreme heat very manageable. There's drama in the news (MO warnings, Cobra), but if DPs are what charts are showing I think sensible precautions would do us just fine even in upper 30s. 

My take:

Below 0c: dry as, you don't even build up sweat it evaporates so quickly. Any temp is fine as long as one hydrates.

1c - 7c: very standard most of the year in the UK. Body stays cool enough in heat apart from exercise. 

8c - 14c: air starts to feel moist, but any heat is still okay although exercise is rather hot and sweaty.

15c - 19c: getting clammy and exercise is a slog. Any heat starts to show its hand and people who aren't good with heat struggle. 

20c - 24c: just walking around is sweaty, things start to get difficult for everyone.

25c or above, your body can't cool off because sweat doesn't evaporate much. A sit down day. 

I've been in 48c with DPs around 5c, and 28c with DPs at 25c, easy to say which one was worse!

Edited July 14, 2022 by Bradley in Kent

[FetchCB]

37 minutes ago, nick sussex said:

The low humidity also means you’re less likely to get heat stroke . 

 

However low humidity can increase fluid loss in the body's attempt to cool itself in extreme heat leading to dehydration and then heatstroke. 

These conditions are pretty unique to the UK and as a consequence the public awareness of what is required to combat it woefully lacking

[Mizzle]

1 hour ago, SunnyPlease said:

I remember I got egg on my face with my mates in 2019 when I said London had the best chance of breaking the record and Cambridge/further north wouldn't get hot enough due to simple longer distance=lower heat distribution. Safe to say I was wrong lol.

I do believe though that there is a limit in terms of capability to set heat records the further north you go. Further south always has a much higher chance. It's possible Cambridge (incidentally where I live) could be the hotspot again, but I very much doubt it will be further north like Lincolnshire etc like the charts are showing).

Would the further North have lower chances of setting records because they haven't had as much heat in the preceding days? 

[Earthshine]

29 minutes ago, Mark wheeler said:

Navgem Special train in coming . Choo Choo . Only 45c at 1pm

 

Mighty Navgem, never fails to deliver

[Dbarb]

We need to be focusing on night temperatures not the daytime temperatures which grab the headlines. Yes it will probably hit 40 degrees but with low humidity honestly I don't think people will notice it as much when compared to past heatwaves. What I'm worried about is Monday night into Tuesday especially in the London area. The humidity will rise overnight and temperatures might not get much lower than 30 due to the heat Island affect. Thousands of people have the potential of death this night similar to France in 2003. The daytime temp is not what's going to kill.

[SunnyPlease]

9 minutes ago, Mizzle said:

Would the further North have lower chances of setting records because they haven't had as much heat in the preceding days? 

It's not impossible for a place further north to record the hottest temperature of a given day if that location has less cloud etc than further south. And yes, there is more chance of breaking/setting records the hotter a location was on former days. Basic physics - warmer to start with = higher likelihood of climbing higher. 

But because this upcoming spell is so fierce, there is a very strong likelihood of northern areas setting their all time temperature records.

In terms of setting a new UK temperature record, the further towards London/south the better. Again, basic physics. The further hot air has to travel north, the less potent it is. There are exceptions to this and there have been examples of far north locations setting high records, but it is very very rare. 

I'm sure someone will correct me, but I personally think it would be pretty much impossible for a location up north, say Manchester or higher, to break a UK maximum record.

Edited July 14, 2022 by SunnyPlease

[Earthshine]

25 minutes ago, Bradley in Kent said:

To add to the topic of dew points and interpreting figures in charts, DP is what the temperature needs to get down to for water vapour to condense onto surfaces. Put the DP figure against the air temp you have your relative humidity. 100% and you have fog. However, I'd love to know the calculation: DP of 20c against temp 30c = 66% assuming baseline 0c. However what is DP -10c against temp -2c? What's the baseline?

Relative humidity aside, DPs in the single digits make extreme heat very manageable. There's drama in the news (MO warnings, Cobra), but if DPs are what charts are showing I think sensible precautions would do us just fine even in upper 30s. 

My take:

Below 0c: dry as, you don't even build up sweat it evaporates so quickly. Any temp is fine as long as one hydrates.

1c - 7c: very standard most of the year in the UK. Body stays cool enough in heat apart from exercise. 

8c - 14c: air starts to feel moist, but any heat is still okay although exercise is rather hot and sweaty.

15c - 19c: getting clammy and exercise is a slog. Any heat starts to show its hand and people who aren't good with heat struggle. 

20c - 24c: just walking around is sweaty, things start to get difficult for everyone.

25c or above, your body can't cool off because sweat doesn't evaporate much. A sit down day. 

I've been in 48c with DPs around 5c, and 28c with DPs at 25c, easy to say which one was worse!

The equation describing dew point is rather non trivial and there's a few state variables which determine it. With dry bulb temperature, air temperature and relative humidity we can use the Magnus approximation, where relative humidity is just the ratio of the true vapour pressure of water and the saturation vapour pressure expressed as a percentage (although sometimes between 0 and 1).  The saturation vapour pressure is only a function of air temperature using the Arden Buck equations.

Interestingly, despite the models showing very low humidities the air would in fact contain similar amounts of water vapour as much colder air with higher relative humidity.  Around 4 times more water vapour can exist in air at 35°C than air at 10°C, with air at -30°C containing practically none.

Here's something I found online with more detail: https://ambientweather.com/faqs/question/view/id/1869/

Edited July 14, 2022 by Earthshine

[SunnyPlease]

15 minutes ago, Dbarb said:

We need to be focusing on night temperatures not the daytime temperatures which grab the headlines. Yes it will probably hit 40 degrees but with low humidity honestly I don't think people will notice it as much when compared to past heatwaves. What I'm worried about is Monday night into Tuesday especially in the London area. The humidity will rise overnight and temperatures might not get much lower than 30 due to the heat Island affect. Thousands of people have the potential of death this night similar to France in 2003. The daytime temp is not what's going to kill.

True.

Given the record minimum is 23.9C to my knowledge, it's not just going to be broken, it's going to be completely smashed.