Model output discussion 9th April onwards

[mushymanrob]

Well i dont see anything bad on these charts... ok, that shortwave feature over the weekend *might* upset things a bit, but concentrating on one wetter run whist other runs are drier and sunnier is a bit daft imho.

these charts suggest the Azores high ridging Eastward across the UK, thus supporting most of the operation runs that currently show this. To my eye, these charts suggest a lot of fine summers weather, no heatwave (yet) but certainly drier than normal, only a light westerly mean upper flow, plenty of sunny/bright/fine summers weather....

[mb018538]

3 minutes ago, mushymanrob said:

Well i dont see anything bad on these charts... ok, that shortwave feature over the weekend *might* upset things a bit, but concentrating on one wetter run whist other runs are drier and sunnier is a bit daft imho.

these charts suggest the Azores high ridging Eastward across the UK, thus supporting most of the operation runs that currently show this. To my eye, these charts suggest a lot of fine summers weather, no heatwave (yet) but certainly drier than normal, only a light westerly mean upper flow, plenty of sunny/bright/fine summers weather....

Trouble is you'd look at that 6-10 day 500mb chart and expect a lot of decent weather....but in reality it could possibly be very wet over the next 6-10 days in a large number of locations:

[summer blizzard]

Looking at the 0z runs today and only a small amount of progress has been made with regards to the cut off low causing confusion.

So the movement today has essentially been from the GFS and Euro (not GEM - that keeps the status quo) to shift the upper low east of the Azores which is different to a few days ago. What happens afterwards is essentially one of three solutions which we currently have no consensus on..

1) As per GFS0z if the upper low gets picked up east of the Azores then it just strengthens the low while it's near western Europe. 

2) As per Euro if the upper low stays east of the Azores then it will try to build a ridge above it much closer to the UK. Not a suitable scenario in all likelihood but a low humidity and high sunshine solution that would please most.

3) Partial phase. This is essentially the plume scenario but the lack of it on the models suggest low likelyhood. Likely the models either think the jetb streak will be too flat and just pick it up or nowhere near.

Probability favours the GFS/Euro over GEM on the 0z out to day 10.

Edited June 22, 2021 by summer blizzard

[Frosty.]

The ECM 0z ensemble mean looks increasingly settled in the mid / longer term as the Azores high / ridge influence becomes stronger?.. !!!!... (broad brushstrokes) BUT it really could be a decent end to June / start to July..to me it’s a very acceptable mean for the height of summer?! ?  

 

 

Edited June 22, 2021 by Jon Snow

[Jeremy Shockey]

ECM 0z ensemble mean

Looking very promising. Decent mean for the end of June / start of July 

[Guest]

GFS 06Z looking wet, and cold over the weekend and June take another turn for the worst. Its rapidly turning into something as bad as the weekend just gone, possibly worse given they were sort of dry. Widely 30-60mm across much of E+W. Nearly all the below accumulated precip is Sat + Sun. Max temps again in south look like being pegged back once again into the low to mid teens. GFS now doesn't have 20C being reached here until the 2nd July - Utterly dreadful!

Edited June 22, 2021 by Alderc

[Josh Rubio]

@AldercThat’s quite a lot of rain forecast for Central areas. Going through the charts, it almost looks like a stationary front, with increasing intensity through Saturday and Sunday. 
 

Caused by that nearby green blob I assume? 

[minus10]

31 minutes ago, Alderc said:

GFS 06Z looking wet, and cold over the weekend and June take another turn for the worst. Its rapidly turning into something as bad as the weekend just gone, possibly worse given they were sort of dry. Widely 30-60mm across much of E+W. Nearly all the below accumulated precip is Sat + Sun. Max temps again in south look like being pegged back once again into the low to mid teens. GFS now doesn't have 20C being reached here until the 2nd July - Utterly dreadful!

Think we are going to have to wait until beginning of July for some improvement going by gfs6z. Even then not brilliant i suspect for those in the east or near east coast if this verifies...might not be so bad on the south coast though...

[ChannelThunder]

1 hour ago, Alderc said:

GFS 06Z looking wet, and cold over the weekend and June take another turn for the worst. Its rapidly turning into something as bad as the weekend just gone, possibly worse given they were sort of dry. Widely 30-60mm across much of E+W. Nearly all the below accumulated precip is Sat + Sun. Max temps again in south look like being pegged back once again into the low to mid teens. GFS now doesn't have 20C being reached here until the 2nd July - Utterly dreadful!

I can't remember who it was, but somebody in here urged caution about the good start to June and highlighted that the same thing happened in 2007 (I think?) before turning to dross. Whoever that was, they look to be on the right lines looking at the upcoming period coupled with the weekend just gone.

Edited June 22, 2021 by Lance M

[Frosty.]

Here’s a small sample  of what early July might bring from the GEFS 6z   as for the mean, it’s not bad, the Azores high / ridge waxes and wanes but there is no strong signal for any significant Atlantic influence away from the far nw / n?....as I’ve been saying, it could be a decent end to June / early July for the majority?....  

 

 

[mushymanrob]

4 hours ago, mb018538 said:

Trouble is you'd look at that 6-10 day 500mb chart and expect a lot of decent weather....but in reality it could possibly be very wet over the next 6-10 days in a large number of locations:

Well the anomalies would have to be wrong for us to see those rainfall totals.. which they could be, but thats 1 run, the anomalies are consistent. So i very much doubt we would have that amount of rain... in saying that, it may not be as settled as the anomalies suggest.. is rainfall that heavy really possible with a positive anomaly of between 60-90 DAM? i dont know..

But besides that, even IF that pesky shortwave feature delivers a wet weekend, it only delays the fine summery weather, the outlook IMHO is pretty good.

[Downburst]

42 minutes ago, mushymanrob said:

Well the anomalies would have to be wrong for us to see those rainfall totals.. which they could be, but thats 1 run, the anomalies are consistent. So i very much doubt we would have that amount of rain... in saying that, it may not be as settled as the anomalies suggest.. is rainfall that heavy really possible with a positive anomaly of between 60-90 DAM? i dont know..

But besides that, even IF that pesky shortwave feature delivers a wet weekend, it only delays the fine summery weather, the outlook IMHO is pretty good.

ECM for next week and rain anomaly

And the Temp anomaly

Since end of May I've been living a charmed existence over here, still 0.8mm for the month, lots of sun and tan and mean temp running 0.6c above monthly average. Certainly not complaining if we get a little rain over the next couple of days.

[Tamara]

4 hours ago, Uncle_Barty said:

Matt Hugo on Twitter trying to pour cold water on those hoping for much of an improvement going forward...

"Caution required over this signal for high pressure to build into the British Isles from the W through late June...We are still about to see a trend towards a -ve AAM regime. A more changeable/unsettled pattern still remains more likely towards months end/early July..."

Olá a todos

21 to 23C has been the benchmark each day here in Portugal since the second part of last week, and has allowed a lot of outdoor work to be completed without seeking sanctuary in the middle of the day from an inferno in the sky This,, following some heat and spectacular evening thunderstorm activity in the first part of last week. These much cooler levels are very conducive for getting things done throughout the day, but are distinctly below average for Portugal while at the same time they would constitute acceptable levels of warmth for many in the UK - very evidently compared to the parallel cool-off that has happened in the UK over the same period and induced some truly unseasonal coolness along with the rain

The heat is set to ratchet up here again during this week and indeed, following several practice tests over recent weeks, is probably the makings of summer proper to come most likely well into the autumn (as defined by seasonal months).

As far as the UK is concerned, its less straightforward as it often is the case, though that said, the risks of overplaying a changeable/unsettled pattern are at least as large as the converse in my opinion. Why is this the case? Long explanations but quite clear conclusions in essence.

It is correct to state, as for example @Singularityhas done from a read back of recent days posts, that another lull phase of the 'mini ENSO cycle' (aka high frequency tropical phasing) is in progress - but it is also true what he says that it is not as simple as an x+y= fixed formula either when, it comes to -ve AAM = unsettled and cool and +ve AAM =settled and or even thundery and hot warm (in context of summer at least)

The Global Synoptic Dynamical Mode (GSDM), in its most simplistic terms, gives an overview of global wind-flow budgets and an insight, through graph and plot depictions of cross sections of wind-flow, latitudinally and also of longitude - where -ve wind-flows (easterly) and +ve wind-flows (westerly) are occurring at a given time, and on a rolling forward basis.

The aggregate total of these wind-flows tells you whether there is surplus -ve or +ve inertia within the global atmospheric circulation - and as part of a break-down on this wind-flow budget, measures the turning force of torque mechanisms (where changes in flow occur and generate of flow) switches, and express them in terms of angular momentum tendency  (-ve or +ve) according to the overall wind-flow budget within the global circulation.

On this basis the pattern is more likely to retrogress during phases of dominant deceleration of wind-flow as easterly wind inertia is added from the tropics and beefs up sub tropical ridging in the Pacific and then the Atlantic -while at the same time these retrogressions create a downstream trough response. The converse holds true when westerly winds are added from the tropics into the atmospheric circulation and forward momentum adjusts the rossby pattern wavelength poleward and eastwards. This all sounds a bit like the x+y formula though doesn't it?

What is of far more importance is the ongoing tendency of momentum within the atmospheric circulation (not the total -ve or +ve aggregate of momentum. Also, at what latitude and wavelength, and indeed in what hemisphere (which can have stratospheric effects and define the respective annular modes at the poles) momentum is being added or taken away.

To put some context of there here and now,  some GSDM plots will follow in due course to explain the current wind-flow budgets and how they are impacting the numerical modelling. Also some suggestions as to how the diagnostic might evolve NWP in the foreseeable future.

As a prelude to this: the previous post earlier this month suggested that strength and amplitude of the MJO 'mini ENSO cycle would determine tendency of momentum and whether the anticyclonic pattern of the earlier part of the month would tend to hold a similar wavelength or, show an inclination to retrogress. There was also a suggestion that NWP might overdo suggestions of retrogression in the longer range based on the state of the summer polar field (much more stable as predicted since the strong feedbacks of the late winter and much of the Spring) and also based on the fact that trade winds have eased more generally as La Nina has taken more of a backseat and this has been something of a floor on angular momentum tendency (the amount of easterly inertia propagated from across the tropics)

To illustrate both these proxies:

The southern oscillation index (SOI) as a pressure differential sign-poster within the Equatorial Pacific sign posts a sustained neutral trend and points to a cap on the amount of easterly inertia potential generated within the tropics

Another way of representing this modest impact is within the Hovmollers plots which show only sporadic trade wind phases  (easterly inertia shaded blue) across the tropics with pockets of forward momentum (westerly wind convergence zones shaded red) c/o cyclonic impacts across the African continent, Indian Ocean, and the far eastern Equatorial Pacific. 

All said, frictional torque tendency has no doubt still turned negative as tropical convective activity has waned rather quicker than anticipated earlier in the month (Lets express this as a measure of the amount of easterly wind inertia that creates a negative torque response and creates sub tropical high pressure amplification at the inflection point of where easterlies replace westerly/forward momentum.

 

Note however from the plot that a large proportion of -ve tendency is evident within the southern hemisphere and that this means that impacts within the northern hemisphere are muted by proportion.

Notwithstanding that, the effect of modest upstream -ve torque tendency within the tropics, is to inflate and retrogress equatorial ridging into the sub tropics, occurring, as said. at the source of inflection point of -ve torque in the Equatorial Pacific where convective suppression is evident. Frictional torque tendency usually leads mountain torque tendency as these inertia switches propagate between the tropics and extra tropics. The lagged impact of added (but limited) deceleration inertia from tropics> extra tropics in accordance with the laws of conservation of angular momentum is to add (weak) forward momentum strength to the downstream jet from the Pacific (within the extra tropics) across North America into the North Atlantic,

So the spectre of a beefed up sub tropical ridge downstream in the Atlantic, and with a relatively diffuse jet stream riding across the northern flank of the ridging sounds about right with what is being advertised by NWP. Modelling has been consistent with this, but also is struggling with the proportions of this inertia which, as suggested, is not manifest of any full blown summertime La Nina wavelength response. As is/has been well commented on by others, this is producing erratic intra day solutions based on very flabby cut-off low pressure areas breaking off from the diffuse Atlantic jet coming off the US and dropping south around the perimeter of the sub tropical ridging.

The recent -ve inertia switches are represented in wind-flow phase plot depiction form by the Global Wind Oscillation - which is a barometer of how much impact (-ve or +v) the atmospheric circulation is acting co-operatively or 'destructively (a-typical) to the base state. Based on calculated tendency of AAM (which budgets together aggregate global torque contributions to wind-flow) we see, once again, only weak to moderate -ve tendency on the jet stream - producing proportionately weak Nina-esque impact on the pattern

 

As such, the GWO has laddered very slowly down into a quite incoherent and weak Phase 0 signal - which is hard to define in synoptic terms, but erratic and fitful discontinuous retrogression amidst the pockets of equally tatty pockets of cut-off low features is the sum of the parts.

Trying to assess independent parts of the atmospheric budgets through composite matches is fraught with error based on the present scattergun wind-flow inertia budgets that have to be seen as a complete GSDM diagnostic rather than back of a fag packet assumptions about neutral ENSO states and assumptions about MJO modelling. The latter has to be viewed based on periodicity timelines which operate up to 60 to 90 day timescales (with empirical feedback loops within them).

On this basis, and in the absence of taking into account any of the various interlinked factors, it is not possible to predict the GWO with any accuracy without looking to see how much potential bandwidth there is within the atmospheric circulation to release latent Nina-esque forcing (low angular momentum regime) Or indeed any other forcing at any other given time based on torque mechanism strength that can be created within weak GWO forcing as part of a strongly neutral atmospheric response and behaviour network

The resultant dogs breakfast pattern, as expressed in synoptic NWP terms, looks sustainable till the tropics give the pattern a kick as the next high frequency wave likely gears up heading through July.

However, sub tropical Azores ridging based on feedbacks loops assured within a weakly negative/neutral atmospheric and ocean base state, offers lead on the pattern in the period heading into the first part of July. Its hard to see the GWO having a floor limit much below a very weak Phase 0/1/2/3 treading water orbit - and based on the benign state of the polar field, this gives little appetite for poleward amplifying Atlantic/Greenland ridges trapping suppressed low pressure systems across mid latitude such as happened in strongly tanking -AO La Nina summers of 2007 and 2011 etc.

Therefore, all in all, that brings the summary back to the opening gambit. Better to not overstate the -ve inertia potential of this pattern during this 'lull momentum' phase which has evidential limitation as shown through proxies and GSDM diagnostics. I would be watching for resumed eastward progression of quite strong Azores ridging (possibly towards Scandinavia) during July with a continuing stable polar profile to support keeping the jet stream to the north for those in NW Europe (UK) closest to such traffic. This should put something of a lid on any inroads of frontal systems brushing across those further NW in UK and NW Europe. Those of us further south in Mediterranean southern Europe  maybe should keep an eye on true heatwave potential and make the most of getting outdoor work done in the garden and on the land before siesta time and air con take over proceedings

 

 

[Man With Beard]

GFS and UKMO have certainly taken the worst case scenario for this weekend. The dartboard low now gets stalled over the UK, and this also prevents high pressure establishing so that the whole of next week's chances of being settled are scuppered.

A little reminder when reading ensemble means in summer - even just a slight mean depression in heights in comparison to surroundings can hide trough features, when they are small.

Given we are so close to T0, hard to see how a wet weekend will be avoided. Unlucky considering all the high pressure around.

[Methuselah]

GFS 12Z at T+291 isn't bad:         

[Scorcher]

36 minutes ago, Man Without Beard said:

GFS and UKMO have certainly taken the worst case scenario for this weekend. The dartboard low now gets stalled over the UK, and this also prevents high pressure establishing so that the whole of next week's chances of being settled are scuppered.

A little reminder when reading ensemble means in summer - even just a slight mean depression in heights in comparison to surroundings can hide trough features, when they are small.

Given we are so close to T0, hard to see how a wet weekend will be avoided. Unlucky considering all the high pressure around.

The BBC still aren't going for much rain at all this weekend and nor are the Met Office at this stage.

If the weekend was going to be as catastrophic as many are predicting on here I'm sure they would have picked it up by now.

I would be shocked if they are trumped by an army of amateur model watchers in here- but stranger things have happened I guess!

[Djdazzle]

31 minutes ago, Scorcher said:

The BBC still aren't going for much rain at all this weekend and nor are the Met Office at this stage.

If the weekend was going to be as catastrophic as many are predicting on here I'm sure they would have picked it up by now.

I would be shocked if they are trumped by an army of amateur model watchers in here- but stranger things have happened I guess!

I wouldn't - it's happened loads of times.

The last 5 days have been the most sunless that I can remember in June. This June is rapidly descending into one of the worst second halves I can remember.

Another test of the models vs anomalies for the weekend. A trough parked over the UK was certainly not a favoured outcome. If that happens, we really are one of the unluckiest places.

Edited June 22, 2021 by Djdazzle

[Guest]

2 minutes ago, Djdazzle said:

I wouldn't - it's happened loads of times.

The last 5 days have been the most sunless that I can remember in June. This June is rapidly descending into one of the worst second halves I can remember.

Another test of the models vs anomalies for the weekend. A trough parked over the UK was certainly not a favoured outcome. If that happens, we really are one of the unluckiest places.

Take your pick, GFS dumps 40-80mm widely over E+W by early next week, GEM concentrating the rain over the south coast again with 40-80mm more.

Second half of June is rivalling everything we faced back in May.

And not to quote myself but I said 2-3days back inconsistent modelling is never good for the UK and never leads directly to a dry, settled pattern. Once again this is true, awful output. 

[NEVES SCREAMER]

I think the best thing to do is build a massive roof over UK. Put an artificial sun up the corner. A few heaters spaced around . Ambient temp about 23c. With the scope to pretend the odd heatwave by turning the heaters up to 29c. A sort of scaled down centre court at Wimbledon. 

[Man With Beard]

Well not sure what the ECM is drinking. At T96, rather than have one UK trough, it's split them into two, one either side of the UK  

[Man With Beard]

I don't trust this ECM but I hope it's right. Warm and sunny by Monday if it's true 

 

[Mike Poole]

3 minutes ago, Man Without Beard said:

I don't trust this ECM but I hope it's right. Warm and sunny by Monday if it's true 

 

No I don’t trust it either, it is those 2 cut off lows, the one over by the Azores seems consistently modelled but the one that might impact our shores is all over the place in the modelling. 

[Djdazzle]

As long as one of the big three show unsettled, that will be the outcome. It always seems to happen like that. The UKMO has showed some more settled solutions over recent days, but not supported by other models.

[mb018538]

31 minutes ago, Djdazzle said:

As long as one of the big three show unsettled, that will be the outcome. It always seems to happen like that. The UKMO has showed some more settled solutions over recent days, but not supported by other models.

Yeah it wasn’t really fully supported, which is was I why surprised Marco tweeted saying that high pressure was going to win out a couple of days ago. It was always touch and go, and if anything like the ukmo or gem run verifies tonight, some southern areas will see 4 inches of rain in a few days, and flooding will be the talking point rather than summer heat!

[Mike Poole]

No science to support this, but I often find new month new weather.  Maybe it is just perception, but ECM T216 starts July on a very positive note: