Model Output Discussion - 1st June 2015 12z--------->

[Summer Sun]

GEM living upto its name this evening for early July turning hot or very hot in places

 

[Vorticity0123]

A period of cool, unsettled weather has been present during the last few days. However, change appears to be on the way, especially for (south)eastern areas of the UK. It is clear that temperatures will begin to rise from tomorrow on, but might there even be a period of very warm temperatures (say, 25+*C) on our doorstep, or not? In this post I will discuss the current setup of the weather, and look into detail about how the situation could develop over the next few days or so.

 

Current situation

 

For the current situation, take a look at the synoptic analysis as presented by the KNMI (Dutch weather institute) below:

 

KNMI surface level pressure and frontal analysis as of 12 UTC 23-06. Courtesy: KNMI.

Note that the arrows have been drawn in by myself as an illustration. As of the moment of writing, we are located in relatively cold air (to be illustrated below) to the south of a frontal system resembling the polar front (frontal zone to the south of the UK over the Alps). Two distinct areas of low pressure can be discerned, one being a complex area located over Scandinavia. As a result of this system, cool maritime polar air (blue arrow) flows out from the north over Western Europe with a couple of troughs moving along. This system has been the culprit of the cool and unsettled weather over the past few days, but will not be an important player in our weather anymore.

 

Another mature low pressure area is located to the west of Ireland. A frontal system is associated with the low, and this will be of importance for our weather in the coming days or so. The relatively inactive warm front currently located over Ireland is the harbinger of more warm subtropical air masses, which will take hold of the UK soon.

 

In between these two systems, a weak area of high pressure is located over the UK, which is bringing less unsettled conditions than seen before. This high is surpressing the activity of the warm front itself. Even though it is weak yet, it will become quite important as well in the period to come.

 

To illustrate the change in air masses associated to the warm front, take a look at the Eumetsat airmass satellite image below:

 

EUMETSAT airmass satellite image and 500 hPa heights (green contours) as of 18 UTC 23-06. Courtesy: Eumetsat.

 

Note the polar air extending all the way from northern Scandinavia into the Netherlands, and warm air (green) advancing from Spain northward towards the UK.

 

The 500 hPa heights also nicely explain the current synoptic setting at the surface, with a deep 500 hPa-trough located over the Netherlands and ridging occurring to the west of Ireland from the south. Also, the aforementioned frontal systems (also visible at the KNMI image) can be clearly seen by the cloud bands present.

 

Short-term prospects

 

For the short term-prospects, I will use GFS charts as an illustration. Two days from now, the ridge of high pressure present has become more prevalent across the UK, as can be seen below:

 

GFS MSLP and 500 hPa heights, 12Z run T+48.

 

Next to this ridge, it can also be seen that the low pressure area to the west of Iceland (and associated 500 hPa trough) has deepened somewhat and made a closer approach to the UK itself. With a low pressure system so nearby, conditions will never be fully settled, especially in Ireland. The remains of the low pressure area which has been dominating the weather over the UK and western Europe are still visible over northern Scandinavia.

 

It is also nice to take a look at the 850 hPa temperatures associated with this setting:

 

GFS 850 hPa temperatures, 12Z run T+48.

 

A first 'plume' of relatively warm air is advancing from the south into the low pressure area over the ocean. This is NOT the 'plume' that may bring very warm conditions to the UK. Also, relatively cool 850 hPa temperatures are present over Central Europe, associated with the low over Scandinavia.

 

Three days later (so 5 days from now) the situation appears to be becoming more and more zonal:

 

GFS MSLP and 500 hPa heights, 12Z run T+120.

 

When one focusses at the 500 hPa heights (colours), one can see that the isolines are more or less running west to east, indicative for zonality. However, taking a closer look reveals there is still a weak ridge present over Western Europe, with associated weak high pressure activity centered over Normandy at the surface. All other models and ensembles basically agree with this setting, which shows itself as a very small range of possibilities in temperature in the plume for London (see later in this post).

 

Spanish plume?

 

As has been alluded to by some of the posts above, there is a possibility of a Spanish Plume developing by mid next week (i.e. a flow of very warm air flowing from Spain towards Western Europe, often followed by thunderstorms; https://en.wikipedia.org/wiki/Spanish_plume). To reveal the synoptic pattern associated with it, the GFS ensemble forecast for 10 days out is included below:

 

GFS Ensemble MSLP and 500 hPa heights, 12Z run T+240.

On average, there appears to be agreement on a deep 500 hPa trough located somewhere to the west or over the UK, and a 500 hPa strong ridge is positioned somewhere over Central Europe. Such synoptic patterns are very favourable for advancing warm air towards Western Europe. However, as is usually the case with forecasts for 10 days out, the exact placement of the ridge and trough, and associated surface features will determine the ultimate fate of where the warm air will move to. Little can be said yet about where the warm air will land, but it seems to be probable at least that a burst of very warm air will advance to the north from Spain somewhere next week. The ECMWF ensembles (not shown here) also agree with this forecast.

 

To show what kind of possibilities still lie within the given average synoptic setting, take a look at the ECMWF and GFS operational forecasts for 8 days out:

 

http://www.wetterzentrale.de/pics/Rtavn1922.gif (GFS)

 

http://www.wetterzentrale.de/pics/Recm1921.gif (ECMWF)

 

Both models show a setting not particularly favourable for very warm air advancing towards the UK (all too far east if one takes a look at the 850 hPa temperatures, though it has to be said that if one looks one or two days earlier, both models show some warm air also touching the UK). Yet the most striking is that the GFS is much further east with the trough than the ECMWF is. Hence, the warm air is already much further east than on the ECMWF on this particular date.

This is just to show how that, despite the upper air pattern beiing pretty certain, small changes can still have major implications on the weather to be experienced at the surface. A final illustration for this uncertainty is the ECMWF plume of London from today 00Z run:

 

ECMWF 00Z ensemble temperature forecasts for London, consisting of 50 individual calculations. Courtesy: MeteoGroup.

 

Up to the 29th of July, little spread is present in the ensembles. However, after that the spread increases dramatically, with broadly speaking a range of temperatures between 17 and 30*C being possible for next Tuesday.

 

Conclusion

It is clear that the weather is going to stabilize and warm up somewhat for the UK over the next few days. Afterwards, it seems certain that a circulation favourable for warm air advection from the south will set up, with a ridge over central Europe and a trough somewhere over or west of the UK. However, the exact positioning of the aforementioned systems (which is of course everything but a done deal for more than 5 days out) could be the difference between a series of very warm days and very cool weather for southeastern parts of the UK in the near future. The northwestern part of the UK appears to remain mostly unsettled though. Possibly more opportunities for some very warm days lie ahead behind the start of next month, as has been alluded to by Tamara. An interesting period in weather forecasting lies ahead, that is for sure.

 

EDIT: In a few weeks time I will try to post some updates in the teleconnective thread as well.

 

Sources:

http://www.weer.nl/

http://www.wetterzentrale.de/

http://knmi.nl/

http://eumetrain.org/eport/euro_18.php?width=1366&height=768&date=2015062218&region=euro
 

Edited June 24, 2015 by Vorticity0123

[Guest]

Pure cherry picking showing those GEM charts, GFS in reality is a complete car crash. An every deepening low that's being progged to the north west of

Scotland drives what was the potential of warmer conditions deep into Central Europe before even getting close to the UK. Additionally further down toning of this weekend with temos barely making the 20c Mark.

[Methuselah]

Pure cherry picking showing those GEM charts, GFS in reality is a complete car crash. An every deepening low that's being progged to the north west of

Scotland drives what was the potential of warmer conditions deep into Central Europe before even getting close to the UK. Additionally further down toning of this weekend with temos barely making the 20c Mark.

But the models don't control the weather, Alderc; they merely give us an indication of things to come, that is better than simple guesswork...But, whatever the models 'say' - temps will easily exceed 20C somewhere, this coming weekend...And, as for what'll occur 15-days from now?? Then your guess is a s good (or as bad) as mine.

[Frosty.]

Since there was nothing worth posting on the Gfs 12z I see nothing wrong with posting these Gem 12z charts this evening. Let's hope we see heatwave conditions next week. The GEM has shown remarkable continuity from the 00z so let's hope it's on the right track.

Edited June 23, 2015 by Frosty.

[AWD]

As much as many of us don't want the 12z GFS conditions to verify, its still worth a mention as it will affect those on holiday/with outdoor plans etc.

[Methuselah]

As much as many of us don't want the 12z GFS conditions to verify, its still worth a mention as it will affect those on holiday/with outdoor plans etc.

Isn't the GFS supposed to be 'rubbish'?

[Guest]

But the models don't control the weather, Alderc; they merely give us an indication of things to come, that is better than simple guesswork...But, whatever the models 'say' - temps will easily exceed 20C somewhere, this coming weekend...And, as for what'll occur 15-days from now?? Then your guess is a s good (or as bad) as mine.

Off cours they don't, but people post charts as though they do. Experience tells us even a few days ago any significant warm up and potential plume always had a very good chance of being progressively remodelled away from the UK.

As for this weekend some places may exceed 20c, but under plenty of cloud and drizzle id say it would be more of an exception.

[Captain Shortwave]

We are seeing a second ex-tropical depression heading towards us (around the day 5/6 range it starts moving towards the UK), that could possibly add a little more uncertainty to the models as it will interact with our by now present Atlantic trough.

The ECM looks quite a bit better at day 6

 

UKMO

Looks like a rather broad warm sector which could deliver high temperatures in any sunny spells in the east.

 

GFS

Much much quicker with that low being several hundred miles further east (Just south west of Ireland compared to being in the mid-Atlantic on the Euros).

 

GEM

 

Quite a lot of uncertainty, is the GFS being way too progressive and we might still see a hotter pattern set up next week?

[Methuselah]

Off cours they don't, but people post charts as though they do. Experience tells us even a few days ago any significant warm up and potential plume always had a very good chance of being progressively remodelled away from the UK.

As for this weekend some places may exceed 20c, but under plenty of cloud and drizzle id say it would be more of an exception.

That, IMO, is a risky bet; 4-hours' sunshine, and anywhere south of The Wash could see 24-25? We'll see my friend...

[knocker]

The GEFS anomaly Wednesday has the trough just to the west of the UK but close enough to control the flow over the UK with the ridge away to the east. Temps around average. Moving on a week the trough has gone and with ridges western Atlantic and Europe a general swathe of HP across the Atlantic is the order of the day with probably a slack westerly flow and temps still around average but pleasanty dry conditions.

http://www.tropicaltidbits.com/

[mushymanrob]

Vorticity.... Excellant post, thank you very much.

[bluearmy]

ECM spreads show what is probably the worse case scenario with a system crossing the UK later next week

Uncertainty reigns!

Incidentally, what is definitely going to happen over the next 7/10 days is the removal of the se European low anomoly. things are definitely changing but what does it mean for the

UK?

Edited June 23, 2015 by bluearmy

[summer blizzard]

Neither the GFS nor Euro really threaten 30C. Hopes are dependent on the minor models i'd say..

 

[bluearmy]

Looking at extended ECM ens and Naefs means at T360 - hard pushed to see too many diffs

Not surprisingly, Anomolys not too far apart either

[knocker]

There is very much agreement between the GEFS and ECM anomalies for Wednesday so bearing in mind the surface detail has still to be resolved this would not show any great inclinations towards a plume over the UK as the trough is the controlling factor. In the ext period the ECM also follows the GEFs with the Azores HP coming into play with the HP eastern Europe giving the proverbial slack westerly flow over the UK.

http://www.tropicaltidbits.com/

[summer blizzard]

18z once again does not back any profound hot spell. 

 

[MR EXTREMES]

We are seeing a second ex-tropical depression heading towards us (around the day 5/6 range it starts moving towards the UK), that could possibly add a little more uncertainty to the models as it will interact with our by now present Atlantic trough.

The ECM looks quite a bit better at day 6

 

UKMO

Looks like a rather broad warm sector which could deliver high temperatures in any sunny spells in the east.

 

GFS

Much much quicker with that low being several hundred miles further east (Just south west of Ireland compared to being in the mid-Atlantic on the Euros).

 

GEM

 

Quite a lot of uncertainty, is the GFS being way too progressive and we might still see a hotter pattern set up next week?

But notice how the ex tropical storms don't make inroads into the uk....

In other words expect alot of heat from the sw and south and I believe this will be the general theme through the rest of summer.

Classic nino effects and some hot weather on and off to perhaps a thudery summer to.

[MR EXTREMES]

18z once again does not back any profound hot spell.

But the low pressure don't make it into the uk so it's pumping up warm air from the southwest tm air.

And even showing signs of drawing the azores heights up over the uk and renforcing the euro heights.

most of the uk looks average to above in the south and south east .

Edited June 24, 2015 by emotional rollercoaster

[mushymanrob]

well... (cherry picked chart but one that illustrates a good few days).



an outlier?....

the 00z might be a little progressive in suggesting this pretty hot evolution. but the noaa anoms over the last several days were having non of the quick flattening out and a return to westerlies after a breif hot day next tuesday.

the noaa have consistently suggested this pattern for next week



which to me suggests a euro-ridge, mid atlantic trough. a pattern that these charts expect to not be a breif affair but last several days. true the latest 8-14 suggest a weakening of the euro-ridge, but not really supporting the recent op runs which suggest a controling trough to our north by later next week.

so whilst i think the 00z is over emphisisning the possible pressure build to our east, i think previous runs from both the gfs and ecm have under estimated it, as per what the noaa anomaly charts have consistently suggested.

interesting times and one that may prove pivotal to the rest of summer.

[Man With Beard]

ECM T192 comes with a health warning! Record breaking heat across most of the UK!!

http://www.meteociel.fr/modeles/ecmwf.php?ech=72&mode=0&map=0&type=0&archive=0 - select T192

Do not adjust your sets, this is what it really shows!

(Just one run, of course...)

[Skullzrulerz]

ECM T192 comes with a health warning! Record breaking heat across most of the UK!!

http://www.meteociel.fr/modeles/ecmwf.php?ech=72&mode=0&map=0&type=0&archive=0 - select T192

Do not adjust your sets, this is what it really shows!

(Just one run, of course...)

This "record breaking" would be short lived in fact it doesn't even last for two days. Only one run on one model of course

[AWD]

This "record breaking" would be short lived in fact it doesn't even last for two days. Only one run on one model of course

Doubt whether it will last for 5mins, let alone days!

[cheese]

This "record breaking" would be short lived in fact it doesn't even last for two days. Only one run on one model of course

Well, let's put it this way - 20C temps at 850hpa, as far as I'm aware, have never reached past the SE corner of the UK, so to get them up to Scotland would produce some silly high temperatures - however fleeting. Plus the rest of the run shows it remaining warm in the S and E of the UK.

 

It seems unrealistic though.

Edited June 24, 2015 by cheese

[SMU]

Indeed the ECM is plume-tastic this morning with the +23c isotherm scraping the south at 192

Also the same timeline shows the +25 line in central France

To put this into context I would say any 850s north of +20c are as rare as the winter -15c ones & usually arent sustained -

If someone could post the ECM 192 for france its a sight to behold-

With lapse rates as high as 15c then high 30s could be the order of the day-

We would need a sustained run of this flow to see anything higher - again historically as the real time approaches the heat is nudged a little further east, & plumes - notoriously hard to pin down have even missed the UK totally in the past after seemingly being on a direct path at 144 ( again just like winter )

We also need to watch the low over biscay, with that flow & potential instability the sky could soon go bang with storms.....

Ciao