[Model Output Discussion - Deeper into Autumn]

A beautiful illustration of a sequence of large effects occurring from something that can seem so insignificant.

First we have that splitting area of PV in the mid Atlantic allowing a low to move slightly further North than it's previous track.

You can see the split here in the mid troposphere (500mb height anomalies)  and in the upper tropospheric winds you can see that they are connected, possibly to do with the jet just off the west of Africa.

Then the effect of the split moving it further up and the Scandinavian ridge rides up it and moves closer to the polar vortex so the thermal gradient should be higher and therefore that split low has in a small way helped coupling between the troposphere and the stratosphere unless the Stratospheric vortex is too strong.

Slowed down so that you can see the dip in the height lines where the low is and it moves towards the African coast and the low splits with the southern most portion moving towards the African coastal low.

You can see the irrotational wind direction move southerly at the time of the splitting and the divergence increasing with the split.

Then in turn with the low's merging onto the African coast there's an increasing upper tropospheric jet and that has effects upon North African weather but does not seem to be associated with the MJO so I won't go over it.

There really is a lot that goes on with the weather and I just picked this little thing that showed up this run but as you can see little things can have big effects and that's often how forecasted cold go missing.

Bit off topic but these are some of the most satisfying GIF's for a weather enthusiast to see in my opinion.

 

 

[Model Output Discussion - Deeper into Autumn]

Good news, the GFS has sorted out it's problem.

Bad news, that means the zonal wind has very little support to become weaker.

Good news, the zonal wind has less support for an increase in zonal wind strength at the end of the run and about 25% of ensembles suggesting a weakening just beyond the 20th.

So still a lot of scatter as expected but as we get closer to time hopefully we'll see the increasing number of weaker zonal wind numbers becoming a trend.

Yesterday

Today

The mid-term GFS and GOES are agreeing on strong EHF stretching from Greenland to Scandinavia and a strong EHF anomaly over Stratospheric Siberia with hints of it stretching further down on the GOES so despite the GFS not being overly keen on a weak vortex I am very happy with today's run.

Beyond that the GOES stretches the Siberian EHF anomaly down to the surface. The GFS doing something similar.

I think for now, a normal Arctic vortex evolution would be best because  it would allow that strong thermal gradient to build but we'll have to see what happens. 

According to the GFS, the best cold pool in the upper troposphere and lower stratosphere will be around Scandinavia. So I think the best thing for vertical propagation based off the latest run would be for a return of the Scandinavian blocking around the 16th onwards and that may be where the support for the weakening of the zonal winds are but we'll have to see what happens.

There's no real chance of getting anywhere near the upper stratosphere yet but I would expect that and we're still very early on.

 

[Model Output Discussion - Deeper into Autumn]

I think that memory is a very bad way of looking back at history because you can often skip out parts that don't suit you and all of us are guilty of out biases and its nothing shocking nor bad. Biases make discussions and almost all of the time this forum is very good at keeping them respectful. There are simply too many drivers for us to notice patterns within drivers because there are so many crossovers. The atmosphere is 3D not 2D and air has its way of moving in the most annoying ways when you don't want it it to its sods law. I see a lot of non weather enthusiasts thinking the weather is easy to predict because they don't know about the MJO,ENSO, QBO, PJO, NAO, NAM. The differences between the GFS, ECM, GEM, UKMO,CFS, CMC. They don't know Rossby Waves from microwaves. Very little people here give themselves credit, you are all extremely clever and brave. It takes a lot to make Olivia think hard but the weather did. Vorticity, temperature, convection, shearing. Zonal winds, wind vectors, wind currents. You all understand a lot more than you are willing to admit and I think it's time you gave yourself a pat on the back.

Looking into the near future and the forecasted Euro-Scandinavian high looks to be getting closer and closer and of course I'll be wanting to understand how far it can vertically propagate and that largely depends on the strength of the zonal winds.

[Model Output Discussion - Deeper into Autumn]

The GFS for the upper part of  the troposphere at 240 hours shows just how much the GFS is overdoing the Rossby Wave evolution due to a strong thermal gradient. It seems to be a persistent problem with little support from even the GFS members itself. GOES 5 showing a much more significant cold pool over the Arctic.

Whilst looking further up into the atmosphere you can see the GEFS members do support the GFS properly this time but the elliptical vortex looks to be overly stretched away from the normal position centralised over the Arctic.

This can once again be observed in the 3D Vortex.

GOES with a clearly stable structure at 240 hours

GFS with a less stable surface and tropospheric structure and a weaker, slightly more elliptical vortex.

it is clear that the GFS is alone in the zonal wind forecasts even the (if slightly old) ECM has most members supporting what the GOES and other models show. Although the ECM does have a decent number of members giving the GFS some support even if the support is weaker.

The GFS is pretty much alone here but it's been alone for a while so I'm interested as to whether it's a normal problem with the GFS or the GFS has picked up a trend early as it can do.

The regime does seem to be moving towards a stronger blocking and may be circling to a -AO regime but this is my first time reading them.

[SE, London & EA - Weather Discussion]

A load of water on the surface of the roads here.

[Model Output Discussion - Deeper into Autumn]

The Stratobserve updates for today have come out so here's all the details, have tried to be as objective as possible:

3D vortex forecast

You can see the weak tropospheric to surface vortex with the forecast for some slight changes in positioning and weakening of the upper tropospheric/lower stratospheric vortex by day 7 seemingly from a wave propagating from somewhere around Scandinavia/Greenland depending on the tilting which is a god sign of some early troposphere-stratospheric coupling as has been shown a lot recently by the GFS. This could mean that the vertical thermal gradient is quite strong especially centred around the area just above Europe which is hinted at by the deeper orange shading closer to the surface there.

When we look at the 500k and 600k quantity's (forecasts are beyond the white lines), especially the temperature, it's clear that the thermal gradient does have some mixing between the warm and cooler values and so that should translate to some ascent of Rossby waves which we may see on the EHF's later but how much considering the thermal gradient is still not especially strong yet, would be difficult to determine. The vortex at those levels doesn't look particularly concerning in reflecting waves back down yet but it depends on the exact threshold of Rossby waving in terms of western velocity . Looking at the potential vorticity and there's a clear increasing gradient between those two layers that should help the future temperature gradient and the energy input for vertical wave propagation.

Eddy heat flux anomaly 

First off we have some EHF anomalies scaled over North America that might be able to reach the lower stratosphere but according to the GFS there is very little coupling with it not sending a wave that far up, the thermal gradient is decently strong but I don't think the GFS is keen on it's vertical energy for whatever reason, perhaps it doesn't have a strong western velocity threshold.

Then the GFS seems to over excite the Greenland and Scandinavian anomalies as well as a very strong Siberian Stratospheric wave which seems to extend it's flux down to the surface perhaps due to it's strong thermal strength and this pushes those two anomalies close together and the thermal gradient both vertically and horizontally extends up a wave of stronger than average zonal EHF and is perhaps the first sign of proper coupling.

The initial wave from North America forecasted here does look pretty strong but I think the fact that it's being blocked from properly propagating (try saying that tongue twister 50 times) further towards the Arctic vortex means that the thermal gradient is low when extending vertically so it just doesn't have enough energy.

The zonal wind forecasted by the GFS shows that it is very much an outlier right now with heating up the stratospheric polar vortex through weakening it's winds, so for now so I would take it's EHF forecasts with a pinch of salt but it is still arguably one of the best mid term models around and we cannot just ignore it like we do a lot of the time with the CFS. GOES5 is a lot less excited with the Siberian extreme as the GFS and so doesn't have the Scandinavian anomalies coupling that well and that shows here but it doesn't go out as far and towards the end of it's run starts to increase the Siberian anomaly so I think when it gets closer to time we may see that and we'll get a better idea of whether or not that and the Scandinavian EHF's will combine.

The Wave-1 amplitudes look to increase in the near future and then the GFS continues to increase it whilst the rest bring the amplitude back down although as they do that they begin to increase the Wave-2 amplitudes. It's interesting how much the GFS seems to be out of line even with it's own ensembles.

The forecasted EHF anomalies (beyond the white line) do show the anomalies extending much further up (well into the stratosphere) than previously associated with coupling according to the GFS.

What does GOES5 have to say about this?

It blocks the vertical propagation with cold anomalies that don't seem to show up on the GFS which may be the cause of a lot of the GFS's problems. The GFS does have some ECM support in terms of having a much less stabilised polar vortex so if the ECM was used here I think it would tend to back up the GFS here.

Here's the first problem, how does the Scandinavian ridge evolve?

Pretty well shown that it's going to form and advect closer to the Polar vortex.

The second problem though, how does Siberia evolve?

Is a lot more complicated because the anomaly is forecasted to be reflected down and models seem to struggle with the evolution of negative vertical movement with heat flux anomalies.

So it's GFS and ECM against the rest - may the best models win.

[SE, London & EA - Weather Discussion]

I must be one of the few people here who thrives in this weather, it reminds me of playing football in the garden for hours on end when I was 7 despite despite fact I was soaked through I never wore a coat and I still don't wear coats unless I have to therefore if it gets really bad a coat should suffice for me, I try to do the same with cold and heat.

[Model Output Discussion - Deeper into Autumn]

Whilst I'm waiting for the stratobserve to update, the GFS is modelling a significant wave to push up from the content over Scandinavia with probably enough thermal gradient with the upper troposphere/lower stratosphere considering it's positioning to begin the process of vertical wave propagation so I think we may see some troposphere-stratospheric coupling when those charts update. How far it may propagate will depend on the strength of the vortex.

Looking at yesterday's zonal wind as a guide and the zonal wind does seem to be relatively strong but slowly weakening at that time.

[Model Output Discussion - Deeper into Autumn]

13 hours ago, Eagle Eye said:

 

 

I talk a lot about radiative dynamics and thermal gradient here but what do I mean?

1)Heat fluctuations cause a large difference in heating. This produces Rossby Waves.

What are Rossby Waves?

2)Rossby Waves are undulating movements that stretch across the planet as demonstrated in this image.

3)This can cause significantly mild air in its process because it cycles up warm tropical air.

4)It can also cause barrelling low's depending on the background signals as well the torque signals.

5)This causes significant vertical difference in heat (vertical thermal gradient).

6)What happens to the atmosphere when this difference happens?

As seen in the initial production of Rossby Waves, a large thermal gradient pushes air to extend horizontally upwards. So when it occurs vertically, the same thing is going to happen, only vertically.

7)How far does this go up?

Thst depends on the strength of the zonal wind in the Stratosphere.

If the zonal winds are strong, the waves are reflected back down.

If the zonal winds are weak then the Rossby Waves can enter the Stratosphere.

The further the undulations in the troposphere stretch the higher their Western velocity threshold is. What that means is, the lower the number of Rossby waves, the stronger of a vortex they can penetrate.

8)What else can affect the propogation of these Waves when moving vertically?

If they are tilted westward when moving up through the atmosphere they will move poleward.

If they are tilted eastward when moving up through the atmosphere they will move towards the tropics.

9)

How does this affect the stratosphere?

It depends where these waves propagate from and how high.

The best scenario in terms of future cold is for a Scandinavian high to split the Stratosphere and allows the distribution of heat to move poleward and for cold to move towards the tropics. Another helpful area for vortex splitting events can be the Greenland high. You can also find helpful highs over Siberia as shown in the GIF below of the 2 These rely on local dynamics.

As a case study, 2018 springs to mind and why not?

Look at that high pushing up through Scandinavian and significantly weakening the Stratosphere by splitting it and causing that SSW.

A classic setup and a secondary wave pushing up mid way through to ensure a long Polar-Night Jet Oscillation recovery time.

 

 

[2022 tornado events, reports and chat]

 

Two dangerous tornado's in the last few minutes including multiple PDS warnings (could only find pictures of 1 for now). This one looks especially significant, possibly above EF3 but too early to tell of course.

2 tornado emergencies.

[Model Output Discussion - Deeper into Autumn]

The ECM Geopotential extended forecasts aren't all bad, there is some blocking that seems to exit towards the Arctic later on, hoping that's an upper tropospheric signal here and it's a vertically propagating wave signature but that's mostly hoping and this is way too far out to trust apart from the basic signal. Former SSW's have had early signals of exiting waves moving up from Tibet where Rossby waves can be generated by the large thermal gradient caused by the mountainous terrain however normally the signal is inverted with low Geopotential heights to the west and a high to the east. I explored this a little bit last year, it isn't the cause of all SSW's but it's a way of getting Rossby wave's forced (according to a few documents I've read that were pretty recent, no conclusive evidence).

Eddy heat flux forecasting shows that there is quite strong flux values in the high stratosphere according to the GFS, this may help Rossby waves forcing due to radiative transfer if/when they do enter the stratosphere. Later on in the run and we see some tropospheric coupling with high EHF deviations over the Scandinavian region forcing their way up into the stratosphere, they have a relatively weak signal but it's. good sign to see the GFS forecasting some genuine coupling in the near(ish) future. The radiative transfer in the troposphere is likely pretty normal for a driven MJO and La Nina signal but I think the strength of the thermal gradient is decently strong because of the forcing for the Rossby waves to vertically propagate. I wonder if frictional torque can transfer heat upwards because we live in a 3D world, there would be some deviations vertically propagating but that's just my midnight thoughts after very little sleep so I really wouldn't trust myself on this.

Vs GOES5

That has a weaker signal but this is early on and you can see some signs of coupling in far Eastern Siberia.

Previous run goes out a bit further and you can see those tropospheric anomalies trying to make their way up, this is where the Stratospheric vortex become important as it may just end up reflecting the waves back down, in which case, blocking signals in the Troposphere may weaken significantly with a weakening and depressing of the Rossby wave energy and so we will once again have to rely on probably the MJO re-entering phase 6 and driving up another blocking pattern but for whatever reason, it seems to be trying to do that quite a lot this Autumn.

Forecasted Eddy heat flux ensembles

A weakening of Eddy fluxes in the near future looks likely but slowly re-entering a strong radiative anomaly and so an increasing thermal gradient with the GFS being over the top so we may see heightened coupling in the far range of the GFS and so I wouldn't trust it as much (so the above is rendered half nonsense) but we've still got to give it's own chance because if it is correct then well done to the GFS. 

Wave amplitudes

Err, not much to say except what looks to be a strongly amplitude 1-wave signal towards the end of the run, not sure what this means as this really isn't my field.

Temperature

3D Vortex forecast

In the mid-term it does look like the GFS is showing a high amplitude coupling between the troposphere and the lower-stratosphere in Scandinavia however it does seem over the top at the moment compared to other models but I want that coupling so I'm going to say that the GFSis right here.

Eddy heat fluxes

You can see that heat flux coupling I was talking about with the propagation into the lower stratosphere right at the end of the forecast (first bit is the previous EHF values) with the stronger values just about reaching the upper troposphere and slowly migrating towards the lower stratosphere then the forecast ends.

Of course, almost all of this is in distant ,CFS like verification, land but it's good to see at least some signs that the vortex is being manipulated with this early on. Do wonder whether, if we don't see a SSW which is still the more likely outcome (I'd say at best a 35% chance of one this Winter but I'll stick with my earlier 25% for now), this could affect any surface cold and make it harder to reach cold at the surface or whether, a stronger blocking signal could work in our favour allowing cold to undercut it.

Normally wouldn't advertise a site but where I got these from

https://www.stratobserve.com

 

[2022 tornado events, reports and chat]

 

 

[2022 tornado events, reports and chat]

Semi-discrete Supercell, probably going to form the first tornado of the risk.

 

[2022 tornado events, reports and chat]

Surprised there's not more talk of this here,moderate risk, 15% hatched.

@The Tall Weatherman

The SPC's wording is scary.

"Forecast soundings show very favorable low-level and deep-layer shear profiles for updraft rotation and tornadoes (including strong tornadoes)."

[2022 tornado events, reports and chat]

Day 1 and is now an enhanced risk with a 10% hatched Risk.

I've picked out a sounding to have a look at.

I've circled a few bits to have a look at if you're confused on how to interpret soundings.

Circled in white

The EL (Equilibrium Level).

The level at which an air parcel is no longer buoyant. A parcel may still rise above this but only if there's strong kinetic energy in vertical movement.

Circled in green

The LFC (Level of Free Convection).

The level at which a parcel of air will begin convecting wiyhout any other forcing.

Circled in pink

LCL (lifted condensation level).

The level at which an air parcel lifted dry adiabatically will become saturated.

Circled in yellow (may be difficult to see)

CCL (convective condensation level).

Level at which the cloud base would form, you can find it where the deepoint and temperature profiles cross.

Circled in white

CT (convective temperature)

The surface temperature that has to be reached for pure convective clouds to form (very rare and needs a very volatile lower atmosphere). It's found by following the dry adiabatic at the CCL level down to the surface (as circled). If the CT is reached at the surface then clouds will form at the CCL.

Surprising to be going into this thread in November, late into 'fall season' @Kirkcaldy Weather. I think tonight could spring a surprise just need to make sure it doesn't over convective and form into linear segments early on.

[Model Output Discussion - Deeper into Autumn]

In the mid range and we do see some movement towards a more average but still blocked regime according to the latest ECM, interested to see what happens when the 500hPa's come out as the surface and the troposphere can still vary quite a lot and I can also determine (hopefully), the refractive qualities of the waves between the surface and tropospheric waves under the forecasted blocking regime.

[Storms and Convective discussion - 1st August 2022 onwards]

11 minutes ago, Azazel said:

Shame I didn’t have my proper camera but yeah. Impressive for November 

 

Absolutely amazing, do you know how long that low level cloud was like that because if looks a bit mesocylonic and if it was persistent, then the S word may just be true for it but hard to tell just from pictures.

[Storms and Convective discussion - 1st August 2022 onwards]

Lovely CB in the distance at sunset, loving all these sunset Storms I'm having recently.

[Model Output Discussion - Deeper into Autumn]

There does seem to be signs by the GFS that there will be increased troposphere-stratospheric coupling towards the end of the month as you can see by the strong heat flux anomalies reaching up to the lower stratosphere at 100 hPa. This suggests a high transferring of heat with height from low to high latitudes. The Stratosphere finds it difficult to transfer heat without tropospheric influence therefore you would think some troposphere-stratospheric coupling is taking place.

[Model Output Discussion - Deeper into Autumn]

9 minutes ago, northwestsnow said:

Really disappointed with how November is shaping up right now 

00z runs are settling on a strong Euro High/ Icelandic low combo..

Hopefully EC 46 will provide a bit of cheer later..

Thats not too bad there is some amplification and that's roughly what's been expected by the ECM weekly geopotential height anomalies and then after that there is movement towards being a Scandinavian high so some positives to take out of a bit of a negative run. Although the anomalies for a Scandinavian ridging are a while out its good to see the possibility showing up.

 

[SE, London & EA - Weather Discussion]

I do my own severe weather forecasts for Europe on twitter and yesterday I upgraded our area to my own level 2 (what I call significant impact risk) for last night and over the next couple days and I'm glad I did because it seems that along with the severe wind gusts, we got a lot of rain, enough for some road flooding making it dangerous to drive on the roads.

[Model Output Discussion - Deeper into Autumn]

Olivia decided that next up I'll be learning more about troposphere-stratospheric coupling, a good lead on from my last read so I found a document and this time it happened to be 8 pages so I'll happily accept that rather than an 80 page dissertation on the MJO .

As I mentioned before, planetary waves propagate into the stratosphere and change the speed of the westerly jet and transfer heat and momentum. The strength of the vortex determines the refractive properties of the waves. 

It should be noted that Arctic Oscillation takes about 3 weeks to reach the surface from 10hPa value due to how waves interact with the atmospheric flow.

Vertical propagating waves are reflected when they reach levels of western velocity above their threshold. The actual threshold decreasing with an increasing zonal wavenumber (i.e @Mike Poole's speciality and definitely not mine). The reflective propagation of waves is related to the tilting of the Rossby waves. A vertically westward tilting of waves is related to poleward propagation whereas it's the opposite for an easterly tilting with height.

The results of the experiment ran showed that a weak vortex with zonal wave number one, there is a strong coupling between the troposphere and the stratosphere and as discussed before depending on the exact wave movements and their resultant refractions. However, during times of a strong vortex, waves get disrupted in the mid troposphere due to a downward movement of their energy. So in other words, it's very unlikely for the Stratosphere to be significantly affected during times of a strong vortex and so a slow process of slowing down the vortex is probably the only way a SSW could occur in a year like that.

Luckily we're entering this year with not too strong of a vortex, however, the forecast is for a slow rise in vortex speed but beyond that it looks to stay relatively stable with a few runs going for strong Troposphere-Stratospheric coupling and a significant weakening likely associated with the interaction of a possible blocking regime. I think the vortex increasing on some runs is due to the possibility of a +NAO also showing up.

The forecast for mid November for the stratosphere won't show much but it does seem to show that the jet isn't entirely strong all the way around and there's a 3 wave feature in the Stratosphere if I had to describe it, that anomalously cold area in the NW Pacific is interesting as well. I'll be interested to see whether this comes to fruition and how it interacts with the vortex in the future. 

According to the GFS we do have a ridge forming over Scandinavia and there is at least a hint of some Pacific troughing although it is mostly ridging so if there is a strong dynamical coupling due to the vortex not being overly strong, we could see the first real signs of some coupling but beyond some minor movement I still think it's too early and the vortex slightly too strong to do anything other than weaken it for now but that does mean a weaker vortex going into Winter, I imagine it'll take a while to properly recover and by then another significant wave propagation could have occurred and caused the vortex to slow down further.

[SE, London & EA - Weather Discussion]

Can see the shelf of the squall line right now and it's amazing, really wish it was day because it looks very ominous but I don't have my phone with me right now just my laptop.

[SE, London & EA - Weather Discussion]

Wind really whipping up here, somehow, they're is still staying to the west of me for now, I think a PV lobe is probably situated in that area for now but it should slowly move eastwards towards me later on and so more Storms should pop up closer to me. An interesting setup this one, looks to very much determined by vorticity.

[2022 tornado events, reports and chat]

Interesting day 3 enhanced risk over parts of Texes and surrounding states.

What looks to be a QLCS with the possibility of multiple different line segments and embedded Supercells. As well as that, there may be some pre-frontal cells associated with the warm air advection and you would expect a pre-frontal lobe of vorticity. Although, the extent of CIN ahead of the QLCS is varied and so would be difficult to tell the chances of those potential cells forming.

Updrafts suggest these should be decently strong, perhaps some moderate hail associated.

CAPE should be good enough and there does seem to be a fairly hooked shape near the top of some of those hodographs mixed with the CAPE, embedded Supercells are therefore possible given that setup Although most of the line seems to be less hooked with the moderate shearing so it's unlikely to go away from being a QLCS. Hard to tell for now how broken up it'll be with some slight variation between model runs.

There is significant WAA (Warm Air Advection) and also cold air moving down supporting a highly active and energetic environment that Storms like.

Significant rain is possible based off the PWAT and so it looks to be a high precipitation setup this making it difficult to see tornado's.

Dewpoint checks out as being a classic setup with a sort of half dry line.

There's alright shearing but most of it is behind the system in Oklahoma.

The soundings look really supportive of an integrated Supercell and squall line mesh, looks supportive for moderate to high CAPE and the hodograph looks hooked but this was taken from the sounding of a forecasted embedded Supercell and the other hodographs are more suggestive of a QLCS with some more pronounced curvature for some embedded Supercells.