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


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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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I wouldn't be confident at all saying next weekend will be fresh and unsettled.  The hot air never really looks like shifting and Thursday could be the 8th day in a row of 30c plus. A few more tweeks in the models and Friday could see another 30c.  

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Unpleasantly hot in lowland East London - 31c but with higher humidity than the past couple of days barely mitigated by an E'ly off the Thames Estuary.

Not nice.

Looking ahead to the next couple of days, where will the heat be concentrated?

arpegeuk-41-27-0.png?09-17arpegeuk-41-51-0.png?09-18arpegeuk-41-87-0.png?09-06

That's the Arpege 12Z for Monday and Tuesday afternoons and the 00Z for Wednesday. Tomorrow looks as though it will be hottest to the west of Londn while Tuesday keeps the core to the heat more to the south. Wednesday looks horrendous with some very high temperatures to the east of London and along the east coast and if memory serves this is what we saw in 2003. The Sunday was the last day of the heat but it was strongest where it had lasted longest (the reverse happens with cold spells oddly enough).

Looking at the Arpege Humidex charts:

arpegeuk-47-27-0.png?09-17 arpegeuk-47-51-0.png?09-18arpegeuk-47-87-0.png?09-06

That suggests central southern England for the storms on Tuesday and more widely across the SE on Wednesday which is going to be a really unpleasant day in the SE of England.

 

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9 minutes ago, Captain Shortwave said:

Ignoring the next three days of potential heat/scattered thunderstorms. Thursday has the potential to be rather nasty.

UKMO used here

image.thumb.gif.6de5719e3d556c7e4fbcb10f19039a30.gifimage.thumb.gif.18df3fafbea1b2efedc915a543fea467.gif   
 

Low pressure forms over Iberia on Tuesday and then drifts over the Bay of Biscay towards the U.K. with the impact here looking to be during Thursday. A lot of heat and a lot of moisture. A good chance of something significant for those who want some proper humdingers.

Beyond this, well that low seems to want to spin back out into the Atlantic and possibly allow the heat to push north again. You would normally bet against this, but this is a far from normal situation.

best setup thunder/lightning wise for me recently was 13-17 June, not the hottest but big storms

gfs-2020061412-0-6.pnggfs-2020061512-0-6.pnggfs-2020061712-0-6.png

 

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Will there be a separate thread for thunderstorms next week guys?

I'm quite excited we could see some humdingers with the heat and slackening pressure..

Edit,I see there is one ongoing.

UKMO looks brill this evening.

A decent August,at last..

 

Edited by northwestsnow
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3 minutes ago, northwestsnow said:

Will there be a separate thread for thunderstorms next week guys?

I'm quite excited we could see some humdingers with the heat and slackening pressure..

 

I think we're seeing increasing humidity as well - my guess wild be central southern England on Tuesday and widely across the SE on Wednesday.

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1 minute ago, stodge said:

I think we're seeing increasing humidity as well - my guess wild be central southern England on Tuesday and widely across the SE on Wednesday.

A fascinating aspect of meteorology ..

And one I am trying to learn about, Tues wed Thurs could hopefully produce some crackers..

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3 minutes ago, Man With Beard said:

More attempts at the high minima record coming up according to ARPEGE

arpegeuk-32-66-0.png?09-18

Don’t want it any warmer at night than it has been, Friday night here was 22.3, last night 19.8, tonight I doubt it will go below 21, 25 is getting ridiculous in this county I wouldn’t mind it if we had air con in homes 👍

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55 minutes ago, Snowy L said:

Yet again it's UKMO against everyone else, would really like some support from the ECM later. 

It’s not that different with the upper pattern although slp shows a variance ......still tough for the nwp to get this upper low movement correct 

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Ec cuts some of the jet off from the upper low at day 4 which may make the feature less active and more meandering as the run progresses 

EDIT - that went well as a prediction !
 

incidentally, for all the chatter about difficulties with this upper low, todays ec 12z op is very consistent with yesterday’s 

Edited by bluearmy
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ECM favouring the dominance of low pressure after we see a breakdown of the intense heat on Thursday. Though the other side looks warm and humid with primarily warm or very warm air circulating. So mid/high twenties still possible (Especially towards the south east). That is of course if that low gains some momentum to move eastwards.....

Predicting beyond a day or so isn’t going to get any easier.

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Evening All.!!!! The hot spell is nothing out of the ordinary. Back in the 1930s temps peaked above 40C!  Anyway back to the hear and now...the low developing over the UK by midweek is a rain maker.  It won't be heat we are talking about , but the news headlines will be about torrential rain and flash  flooding. The computer model output but the extended weather pattern from next weekend onwards remains in the High Shannon Entropy region!!!!

ecmt850.096.png

h850t850eu-5.png

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3 minutes ago, ANYWEATHER said:

Evening All.!!!! The hot spell is nothing out of the ordinary. Back in the 1930s temps peaked above 40C!  Anyway back to the hear and now...the low developing over the UK by midweek is a rain maker.  It won't be heat we are talking about , but the news headlines will be about torrential rain and flash  flooding. The computer model output but the extended weather pattern from next weekend onwards remains in the High Shannon Entropy region!!!!

ecmt850.096.png

h850t850eu-5.png

Temperatures above 40°C have never been recorded in the UK.

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2 minutes ago, MattStoke said:

Temperatures of 40’C have never been recorded in the U.K., and temperature records were being kept in the 1930’s 😏

He really comes out with some rubbish sometimes!

And there is no indication that the low pressure will be wet for all.

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6 minutes ago, Djdazzle said:

He really comes out with some rubbish sometimes!

And there is no indication that the low pressure will be wet for all.

cant comment on the top one,

second one, correct who knows what will happen 

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4 minutes ago, MattStoke said:

Temperatures of 40’C have never been recorded in the U.K., and temperature records were being kept in the 1930’s 😏

Correct.

Accurate temperatures being recorded in the UK are relatively new.

To say 'this' temperature  is the highest ever is wrong.

Unfortunately we are missing many centuries of unrecorded temperatures and therefore 'missing' past extremes.

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24 minutes ago, DAVID SNOW said:

Correct.

Accurate temperatures being recorded in the UK are relatively new.

To say 'this' temperature  is the highest ever is wrong.

Unfortunately we are missing many centuries of unrecorded temperatures and therefore 'missing' past extremes.

That’s why I’m always careful to say ‘Highest recorded’ temperature.

Still true that 40’C has never been officially recorded in the U.K. and so the above claim that temperatures peaked above 40’C, is unsubstantiated.

Edited by MattStoke
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11 minutes ago, mushymanrob said:

Support here for the low to our south and a continuation of the warmth if not heat

 

610day.03.gif

Not convinced rob as the mean upper trough has edged over nw Europe rather than west of Iberia ....could be very messy as the difference between very acceptable summer conditions and the opposite may not be far apart .....

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17 minutes ago, mushymanrob said:

Support here for the low to our south and a continuation of the warmth if not heat

 

610day.03.gif

A bit too close a call for me! I have a funny feeling this chart allows for a UK trough within its margin for error.

On the ECM tonight, raw maxes of 33, 34 and 34 in the next three days. If the usual 2-4 degree adjustment is needed, then we could be looking at between 35 and 38 for maximum values.

My "adjusted raw" theory hasn't been quite as accurate today and yesterday, with an adjustment of only 1C and 1.5C degrees on these two days - the raw was 33C each day, but maxes have been 34 and 34.5. My conclusion, based upon comparing the relationship between official stations and the average from personal/private stations that publish in places like Wunderground, is that there probably have been maxes of 35/36C in the places the ECM predicted 33C (mainly inland Sussex), but they were so far from official stations that they haven't been recorded. This is because of the unusual wind profile in the heatwave at present. However, from Monday to Wednesday, maximum values return to areas close to Heathrow or Cambridge, where the true maximum is likely to be reported. If my theory holds true, then we may well see 35, 36 or 37 popping up in the maximums this week. It's all a learning "work in progress" 🙂

Edited by Man With Beard
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