Model Output Discussion - Into Summer 2020.

[Ice Day]

Good to see no drama's on the overnight runs, still on for a very warm/hot week across the country.  The ECM Parallel on board as well 120, 144, 168.

  

  

Could we breach both 30C and 90F next week 

[Ice Day]

The 6z out to 144 and pretty much in line with the 0z, but bringing the warmth slightly further west (although fine details at this range are relatively pointless).  Suffice to say, another hot run incoming:

 

[Guest]

GFS 06Z looking really good out to next Thursday, however the cynic in me (And I'm pretty damn cynical) says I'm not sure I trust GFS with a second surge of warmth from Friday through the weekend. 

[Daniel]

Latest gfs 2m charts still hot! 

[Man With Beard]

GFS 06Z follows a mini-trend this morning by building a second Azores High towards the UK around Thursday:

This traps the heat around the UK for longer - although it is about to be displaced on the chart below for Sunday 28th, the run is hot from Tuesday 23rd up until this timeframe.

  

 

[I remember Atlantic 252]

looks okay

[summer blizzard]

Far from becoming clearer the Euro this morning was even more complex. Relative to the 12z run the core of the heat is reduced to Weds/Thurs however it drags on until Sunday rather than Saturday (beginning Tuesday). Unfortunately it also has that drop in pressure at day 6 followed by an area of low pressure slowly trying to make progress south. Much less thunder potential also and potentially cloudy for Scotland and Northern Ireland especially from Thursday onward.

The GFS model much like yesterday makes less of this drop in pressure mid-week and simply builds the Azores High north, it also never really clears the warm uppers until Monday and like last night has a slower (and likely more thundery and wet) breakdown. Interestingly though it completely tones down the uppers and indeed the 15C isotherm does not make it to the UK on the 6z so hot but not at all exceptional for June. 

The two things we can take from these runs for clarity are..

1) The peak impact is reduced and likely Wednesday/Thursday is when we will see our hottest temperature (probably north west of London). 

2) The duration of the 25C+ period at least now extends from Tues-Sunday if not Monday whatever happens. 

 

[Wimbledon88]

Certainly the 6z has watered down any prospects if a prolonged heat spell. As has been said, nothing unusual for SE this time of year. 3 hotish days and then a cool off. Remaining cool and rather unsettled midlands northwards throughout the period. 

[h2005__uk__]

Essex, Suffolk and Norfolk missed out on the peak of the heat during the first hot spell of 2019, but joined in 3 weeks later when a similar burst of heat arrived in the UK (see attached maps).

Is the heat next week likely to include the eastern counties as it usually does, or miss them like in June 2019?

[Frosty.]

Looking at the Gfs 6z operational, 30c is deffo under threat during the second half of next week and I imagine that because the Gfs is famous / infamous for underestimating maxima in these situations..90f is under threat (32c)..the truth is out there..!..jeez I sound like the x files..oh and I’m all out of reactions, as usual..sorry Zak!!!!

Edited June 19, 2020 by JON SNOW

[Zak M]

06z GFS is still looking hot for the south

   

@JON SNOW

Apology accepted 

Edited June 19, 2020 by Zak M

[ChannelThunder]

18 minutes ago, Zak M said:

06z GFS is still looking hot for the south

   

And that's an old-school plume sat in Spain, with the required Atlantic low sitting in the right place to help scoop it up to us! Fingers crossed!!!

[MATTWOLVES 3]

A fair few ens bringing in the +16 uppers perhaps a cut off point towards the Midlands Southwards! One thing for sure its going to be very warm in most places and after the last couple of days of persistent rain and cool temps, that will be most welcome here. So get your sangria and sun hats at the ready folks..

[NorthernRab]

1 hour ago, Wimbledon88 said:

Certainly the 6z has watered down any prospects if a prolonged heat spell. As has been said, nothing unusual for SE this time of year. 3 hotish days and then a cool off. Remaining cool and rather unsettled midlands northwards throughout the period. 

Has it? Strong high pressure anchored over Scandinavia and the continent with low pressure out in the Atlantic drawing in south to south-easterly winds? Sounds pretty conducive to prolonged heat if the conditions are right. 

[mb018538]

850s are above 10c for 7 days in a row. That’s a warm spell in anyone’s book.

[Frosty.]

31 minutes ago, NorthernRab said:

Has it? Strong high pressure anchored over Scandinavia and the continent with low pressure out in the Atlantic drawing in south to south-easterly winds? Sounds pretty conducive to prolonged heat if the conditions are right. 

Agreed, looking at the GEFS 6z mean there’s plenty of positives to accentuate, especially the second half of next week in terms of hot potential!..as there was on the 0z..and...as it’s the u k, breakdowns, cooler blips are to be expected as we are not in the Mediterranean but to be honest, I don’t see much to be negative about, at least  for those in the southern half / third of the u k during the upcoming period!

[Singularity]

We can't go drawing much in the way of conclusions yet - too much spread on what goes on with the heat low over France or thereabouts starting Wednesday.

The long run of negative frictional torques emanating from the tropics has finally ended, which reduces the probability of the jet stream orientating such as to quickly lift the heat low out northward. Remains to be seen how soon we see overall AAM climb sufficiently to steer the polar jet on a SW-NE orientation from the mid-Atlantic - this will have a big say in just how long the heat low could be trapped, if it doesn't made a quick exit on Thursday (that outcome is still possible, just has lowered likelihood thanks to the FT change).

 

Longer-term, CFSv2 remains keen on total AAM rising to become above-normal in the 1st half of July. Judging by the GFS runs of the past two days, that model is starting to explore that idea too now, though not consistently (e.g. 00z really went for it but 06z looks to have got cold feet a few days from run's end).

So, reasons to be hopeful that July won't take as long as June to provide some 'high summer' weather, if that's what you're looking for.

[Mark wheeler]

Good to see the Navgem is being consistent even if it is consistently wrong with it uppers .

 

Can I ask a question and yes I know it’s hypothetical as the uppers are wrong , but what’s the likely top temperature if these  charts really did come off ?  

Edited June 19, 2020 by Mark wheeler

[SMU]

3 minutes ago, Mark wheeler said:

Good to see the Navgem is being consistent even if it is consistently wrong with it uppers .

 

Can I ask a question and yes I know it’s hypothetical as the uppers are wrong , but what’s the likely top temperature if they charts came off ?  

36-37 - if sustained 38-39

[MattStoke]

25 minutes ago, Mark wheeler said:

Good to see the Navgem is being consistent even if it is consistently wrong with it uppers .

 

Can I ask a question and yes I know it’s hypothetical as the uppers are wrong , but what’s the likely top temperature if they charts came off ?  

[Mark wheeler]

21 minutes ago, Steve Murr said:

36-37 - if sustained 38-39

Thanks Steve , Much Appreciated 

[Man With Beard]

While we wait for the 12Zs, a look at the ECM clusters from this morning between D11 and D15 (30th June to 4th July). Note the change in anomaly colours represents the switch from June means to July means

    

Overall, clusters 1 and 3 maintain high anomalies close to the UK after perhaps a short NW phase on cluster 1. The two clusters combined contain 70% of the ensembles, so it's a 70/30 split in favour of more summery weather as July begins, with warm to hot temperatures. Cluster 2 is a cooler and more changeable, particularly in the north.

[Tamara]

On 14/06/2020 at 15:34, Tamara said:

Musing here to an extent, but for what it is worth, should the tropical signal align further c/o that anomalous warmth in the tropics and the polar cell remain stable - irrespective of what extended ensembles and associated cluster data suggests currently as a snapshot in time (yes, that phrase again) -  look for that trough to the NW to start align itself in such a way to allow some hot and potentially thundery conditions from the south later this month

 

36 minutes ago, Singularity said:

We can't go drawing much in the way of conclusions yet - too much spread on what goes on with the heat low over France or thereabouts starting Wednesday.

The long run of negative frictional torques emanating from the tropics has finally ended, which reduces the probability of the jet stream orientating such as to quickly lift the heat low out northward. Remains to be seen how soon we see overall AAM climb sufficiently to steer the polar jet on a SW-NE orientation from the mid-Atlantic - this will have a big say in just how long the heat low could be trapped, if it doesn't made a quick exit on Thursday (that outcome is still possible, just has lowered likelihood thanks to the FT change).

Longer-term, CFSv2 remains keen on total AAM rising to become above-normal in the 1st half of July. Judging by the GFS runs of the past two days, that model is starting to explore that idea too now, though not consistently (e.g. 00z really went for it but 06z looks to have got cold feet a few days from run's end).

So, reasons to be hopeful that July won't take as long as June to provide some 'high summer' weather, if that's what you're looking for.

The tweet from @Singularityvery good post explanation of it has been removed to preserve reading space

I also re-copied my own post of last weekend because it was made in anticipation of the same events (as so well interpreted of that tweet). Rising frictional torque in the tropics impacts rising mountain torque tendency in the extra tropics - as the addition of westerly winds in the tropics changes the inertia within the greater atmospheric circulation. The inflection point at which that forward momentum is added is identified as the frictional torque mechanism itself. There is a lag period of time it takes to impact wind-flows in the extra tropics c/o rising mountain torque tendency as the rossby waves created by the wind-flow additions propagate poleward. The overall increased momentum of the turning force exhibited on the Jetstream (the positive torque) is the vehicle to increase angular momentum tendency. The propagation of these rossby waves is the means to amplify the Azores sub tropical ridge in our part of the NH.

Such an increase in angular momentum tendency should register in the days to come on the Global Wind Oscillation plot. Posted below. Based on its customary two day consolidated lag, this has paused during this week in Phase 2 (the La Nina attractor phase) - and some days prior to the forward momentum that is to come in the forthcoming week period.

How much deficit of AAM that is recovered from the negative easterly inertia period that started impacting the extra tropics in early June (and broke down the NW European anticyclonic domination during May) will determine how long our downstream ridge and very warm/hot spell holds together next week. Much as @Singularitydescribes well

The ECM and its ensemble data looks to be suggesting that the mid Atlantic ridge might try re-asserting approaching the months end - indicating the spike in momentum reversing once more as part of a (possible) longer term negative trend to momentum in the atmosphere. It remains to be seen what diagnostic support there might be for the CFS forecast for AAM recovery sustained into the first half of July based on its known issues with amplitude propagation.

On the other hand, it is also true that other proxies such as the Southern Oscillation Index point to an overall very neutral pressure differential in the Pacific that is not following the script of a descent of the atmosphere into a traditional La Nina type summer.  A +ve SOI trend is traditionally a sign of La Nina establishing in the Pacific

 

So the extra tropical forcing continues to assist sub tropical Azores ridge development downstream and something of a cap on the amplification potential in the Pacific that would usually occur in the circumstances.. As stated previously, the less amplification in the Pacific, the less chance there is of a retracted Atlantic ridge gaining a sustained foothold. The lack of any summertime stratospheric forcing on the troposphere is also helping the cause for sub tropical ridging.

So suffice to say, there are a lot of pitfalls in general NWP at the moment for the extended period because relatively small adjustments one way or the other will have quite some impact on whether we stay at least part under downstream ridge influence through early July or whether the downstream trough becomes more and more dominant.

I have annotated the GWO plot based on the uncertain forecast options. These are just rough and ready scribbles simply to give a very simplified guide to the calculation in play within the atmosphere. The failure to consolidate Phase 4 is the decidedly faster route to end of the very warm spell whereas a greater orbit to Phase 4 would make quite some difference and provide a ridge solution maintained for at least some days longer into week 2 (end June/start of July)

[Azazel]

I’m not bothered about a breakdown as long as it’s thundery - however, in recent years the heat just sort of fizzles out with drizzle moving in.

[Zak M]

I will bank that from the 12z ICON, thanks!!

Edited June 19, 2020 by Zak M