Model output discussion - summer rolls on

[Captain Shortwave]

Can we please stay on the topic of model output please, many posts have been hidden. There isn't any need to discuss specific contributors to this thread or the manner that they post.

Thankyou

[Djdazzle]

Proof that the models are struggling with signals.

At 192 GFS has a high over Scandi.

At the same time ECM has a low there!

Edited July 30, 2018 by Djdazzle

[Djdazzle]

And somehow ECM 216 conjures up a northerly.

Does anyone else think the models are removing the Scandi heights too quickly? A few days ago there were comments that the HP would take a lot of shifting, yet the models seems to just brush it away.

[Mike Poole]

Well with the ECM failing to stick to the script, here's my take on the Global Wind Oscillation (GWO), so central to the posts of @Tamara. Risk of looking like an idiot here if I get this wrong!

The Earth and its atmosphere spin in space.  
Angular momentum (mass of system times angular velocity (speed)) of the combined Earth and atmosphere must be conserved, stay the same - always - law of Physics.
Atmospheric Angular Momentum (AAM) is the atmospheric component of this, the winds.
So if the atmosphere winds speed up the Earth slows down.
And if the atmosphere winds slow down the Earth speeds up.
There are a number of mechanisms by which this transfer of momentum from the atmosphere to the Earth and vice versa occurs.
One such is 'mountain torque' if the wind is blowing faster than the Earth is rotating and it hits a mountain range, it will push the earth on faster, thereby losing AAM.
If the wind is blowing slower than the Earth, a mountain range will push the wind on, slowing the Earth and increasing AAM. (Other mechanisms exist!)
Enter the jet stream blowing west to east.  Where it blows is important.  The mountain ranges in the N hemisphere are in specific places.
But whether the AAM is low or high affects the wiggliness of the jet stream too, and thereby our weather. Particularly in the UK, where the jet stream is so important.
How the AAM affects the jet stream is different at different times of the year.
El Niño promotes high AAM, La Niña the opposite, but this can be overwritten.
And this is where my knowledge breaks down.  The real skill is to translate this to a forecast.

The key point re the model output, is that this framework allows you to get an idea of what is and isn't possible, so get an idea of which model runs look plausible and which do not.  Fascinating subject and one about which I have so many knowledge gaps it's untrue.

Hope this is helpful.

 

Edited July 30, 2018 by Mike Poole

[mushymanrob]

oh dear..... todays 6-10 day anomaly charts supports the ecm 's western ridge pattern.  so not bad weather but the chances of a cool blast becomes much more likely then a plume (for that timeframe , after the weekends mini hot spell) .

if that ridging becomes established just there, its hello august 2006, whos only good point is that it was on the dry side of average.  locally at least that august was dull and overcast.  summer is over?

 

[mushymanrob]

5 minutes ago, Mike Poole said:

@Tamara
So if the atmosphere winds speed up the Earth slows down.
And if the atmosphere winds slow down the Earth speeds up.

 

 

eh?... i dont think thats true at all.. the speed of the earth is constant.

(sorry i couldnt remove the link to tamara)

[Mike Poole]

1 minute ago, mushymanrob said:

eh?... i dont think thats true at all.. the speed of the earth is constant.

(sorry i couldnt remove the link to tamara)

No, the angular momentum (mass times velocity) of the earth and atmosphere is constant.  The changes in speed of the earth are minuscule, because of its much much much heavier mass, but that's the whole point of this thing.

[Methuselah]

7 minutes ago, mushymanrob said:

eh?... i dont think thats true at all.. the speed of the earth is constant.

(sorry i couldnt remove the link to tamara)

 

Edited July 30, 2018 by Ed Stone

[Singularity]

ECM’s got the reduced westerlies but the amplified trough-ridge sets up way west of where it ought to... even knowing the limitations of modelling this is extreme enough to leave me wondering if it could really be that far wide of the mark.

Or perhaps I’m missing something, as my interpretation of the signals - guided by Tamara as best as I can interpret her analysis - leads me to see the range of feasible ridge positions for this coming Sunday to be from level with the UK to level with Sweden/central Scandinavia. Hence my recent concerns over what might come our way at relatively short notice should the models abruptly converge on the more eastern placement as the true limited degree of AAM fall (as El Niño puts it foot down) is realised.

I suppose the thing to do is not read much into the model runs at this time, much as Tamara advised earlier. Not even the ensembles and guidance (such as NOAA anomaly plots) derived from that.

[mushymanrob]

15 minutes ago, Mike Poole said:

No, the angular momentum (mass times velocity) of the earth and atmosphere is constant.  The changes in speed of the earth are minuscule, because of its much much much heavier mass, but that's the whole point of this thing.

fair play, my misunderstanding stands corrected

[mushymanrob]

9 minutes ago, Singularity said:

 

I suppose the thing to do is not read much into the model runs at this time, much as Tamara advised earlier. Not even the ensembles and guidance (such as NOAA anomaly plots) derived from that.

 

maybe, but their confidence ranking for the chart i posted is "FORECAST CONFIDENCE FOR THE 6-10 DAY PERIOD: WELL ABOVE AVERAGE, 5 OUT OF 5, DUE TO GOOD AGREEMENT AMONG THE MODELS AND TOOLS.

[Met4Cast]

I’m not sure where the surprise that charts have backed away from heat has come from? It never really had a whole lot of support on any of the ensemble suites and they never showed heat being sustained for more than a few days.

It’s not going to be washout by any means, but certainly no “heatwave” either.

[Singularity]

22 minutes ago, mushymanrob said:

maybe, but their confidence ranking for the chart i posted is "FORECAST CONFIDENCE FOR THE 6-10 DAY PERIOD: WELL ABOVE AVERAGE, 5 OUT OF 5, DUE TO GOOD AGREEMENT AMONG THE MODELS AND TOOLS.

Yes but, with all due respect to them,  I don't give a flying fish about that as their tools are model based, and some of those models are well out of kilter with what other approaches suggest should happen based on past precedent and the notion that those strangle far west solutions are related to the models not seeing the wood for the trees, as a large but ill-fitting oak looms large in the form of the completion of the latest tropical cycle (declining MJO).

I must say, it's surprising that they find such confidence anyway, when GFS and ECM have completely opposing SLP patterns for Scandinavia. I can see that they're playing it safe by going with a middle ground - their anomaly pattern corresponds to actual ridge placement that's neither as far west as ECM or as far east as GFS - but that's not to say that the middle ground is immensely likely to come about. Perhaps they have a margin of error wide enough that either the ECM or GFS outcomes would still count as a good result?

Also for what it's worth, NOAA don't currently make use of the GSDM that I and Tamara base a lot of our thinking on, due to a lack of recent research on their part.


I won't deny that no approach is infallible, though; something like the ECM 12z is by no means being ruled out on my part.

Edited July 30, 2018 by Singularity
Caveat = Life

[Scorcher]

15 minutes ago, Daniel Smith said:

I’m not sure where the surprise that charts have backed away from heat has come from? It never really had a whole lot of support on any of the ensemble suites and they never showed heat being sustained for more than a few days.

It’s not going to be washout by any means, but certainly no “heatwave” either.

You'd think listening to you and Mushy tonight that there was nothing noteworthy at all coming in the next few days in terms of heat. Just to be clear to anyone who is not well versed in reading charts, there is some heat coming, especially further south.

It won't be record-breaking but some of the temperatures in the south on Friday/Saturday would be the warmest of the whole year in a lot of summers!

BBC going for 32C in London on Friday, and the GFS is showing 33C- we could still end up with some places reaching the mid thirties. Now that's hot by anyone's standards. We didn't get near that in the whole of the summer of 2007. Hot in the south until Monday at least.

Funny how this amazing summer has skewed people's perceptions. 

Edited July 30, 2018 by Scorcher

[Summerstorm]

It might seem like a load of twoddle but once you read up about some of the factors that go into it it isn't that hard to understand.

To add on to what @Mike Poole said for anyone wondering what the GWO (Global Wind Oscillation) is this depicts the net  wind flows based on the AAM which shows whether the inertia in the atmosphere is more westerly or easterly based which may be mentioned from time to time.  Essentially there are 8 stages of the GWO with 1 through 4 indicating Low AAM and 5 through 8 indicating high AAM.

At the moment we want low AAM as the La Nina state is still hanging on and this promotes the strengthening of Sub Tropical HP belts such as the AH which is why the early summer was so dominated by constant HP due to the lack of energy in the Jet Stream which i think i'm right in saying. Conversely high AAM would promote the opposite promoting blocking in higher latitudes hence the increase in blocking over Scandinavia in the last few weeks fortunately we've mainly managed to stay on the warm side of the jet mostly due to high amplitude from the MJO but this week it has dropped (MJO) and this shows the effect this can have on our weather and is why posters like @Singularity have been commenting on saying they are worried about if the AAM doesn't drop then HP may be situated further east over Scandinavia or we may have higher latitude based blocking leading to a more Northerly component to winds as shown by the ECM this evening and this is what @Tamara is saying in her post i think hopefully this seems a little more simplified. 

Regarding Torques actually it's the Frictional Torque (FT) that affects the speed of the atmosphere and the speed of the earths rotation. Positive FT means a speed up in the earths rotation as the winds are westerly this = Lower AAM. Conversely negative FT is a net easterly wind and this helps to increase AAM. 

Mountain Torque or MT is slightly different and depends on the pressure systems on the sides of large mountain ranges such as the Himalayas and the Rockies. For example HP to the West and LP to the East means that the range is forcing easterly momentum speeding up the earths rotation the opposite means Westward torque and a slow down in the earth rotation.

The two Torques are part of calculating the AAM the clue to forecasting using these factors is to know what effect each of these has on different areas of the atmosphere for example knowing the affect of each stage of the MJO leads to and how this affects pressure patterns around the Northern Hemisphere as well as the affect the AAM has on this as well as tropical forcing in the oceans and this all needs to come together to make a forecast which i admire Tamara for all the more as this an extremely complex field of weather in which I've barely scraped the barrel. 

It might seem like a load of twoddle but once you read up about some of the factors that go into it it isn't that hard to understand. But a quick read of the thread for learning the teleconnections by BB1963 is useful to understanding this. Hopefully i didn't get anything too wrong here and that people appreciate this and it helps them to in some way gain an idea of what some of this means. 

Cheers James. 

P.S Teleconnections experts please feel free to correct me if i'm wrong with something 

 

Edited July 30, 2018 by Summerstorm

[Mike Poole]

GFS parallel/FV3 12z has the plume well on for the weekend, here T156:

And this one has the reload as well, T228:

Anyone wondering why I post this model, the verification stats for the FV3 are now available and it's currently No 2 (for Z500 anomaly, N hemisphere, T120).

 

[Methuselah]

18 minutes ago, Daniel Smith said:

I’m not sure where the surprise that charts have backed away from heat has come from? It never really had a whole lot of support on any of the ensemble suites and they never showed heat being sustained for more than a few days.

It’s not going to be washout by any means, but certainly no “heatwave” either.

I know what you mean (I think?)...while humanity makes plans, the gods sit back and laugh?

Our knowledge is finite...But our ignorance is infinite!

[Mike Poole]

9 minutes ago, Summerstorm said:

It might seem like a load of twoddle but once you read up about some of the factors that go into it it isn't that hard to understand.

To add on to what @Mike Poole said for anyone wondering what the GWO (Global Wind Oscillation) is this depicts the net  wind flows based on the AAM which shows whether the inertia in the atmosphere is more westerly or easterly based which may be mentioned from time to time.  Essentially there are 8 stages of the GWO with 1 through 4 indicating Low AAM and 5 through 8 indicating high AAM.

At the moment we want low AAM as the La Nina state is still hanging on and this promotes the strengthening of Sub Tropical HP belts such as the AH which is why the early summer was so dominated by constant HP due to the lack of energy in the Jet Stream which i think i'm right in saying. Conversely high AAM would promote the opposite promoting blocking in higher latitudes hence the increase in blocking over Scandinavia in the last few weeks fortunately we've mainly managed to stay on the warm side of the jet mostly due to high amplitude from the MJO but this week it has dropped (MJO) and this shows the effect this can have on our weather and is why posters like @Singularity have been commenting on saying they are worried about if the AAM doesn't drop then HP may be situated further east over Scandinavia or we may have higher latitude based blocking leading to a more Northerly component to winds as shown by the ECM this evening and this is what @Tamara is saying in her post i think hopefully this seems a little more simplified. 

Regarding Torques actually it's the Frictional Torque (FT) that affects the speed of the atmosphere and the speed of the earths rotation. Positive FT means a speed up in the earths rotation as the winds are westerly this = Lower AAM. Conversely negative FT is a net easterly wind and this helps to increase AAM. 

Mountain Torque or MT is slightly different and depends on the pressure systems on the sides of large mountain ranges such as the Himalayas and the Rockies. For example HP to the West and LP to the East means that the range is forcing easterly momentum speeding up the earths rotation the opposite means Westward torque and a slow down in the earth rotation.

The two Torques are part of calculating the AAM the clue to forecasting using these factors is to know what effect each of these has on different areas of the atmosphere for example knowing the affect of each stage of the MJO leads to and how this affects pressure patterns around the Northern Hemisphere as well as the affect the AAM has on this as well as tropical forcing in the oceans and this all needs to come together to make a forecast which i admire Tamara for all the more as this an extremely complex field of weather in which I've barely scraped the barrel. 

It might seem like a load of twoddle but once you read up about some of the factors that go into it it isn't that hard to understand. But a quick read of the thread for learning the teleconnections by BB1963 is useful to understanding this. Hopefully i didn't get anything too wrong here and that people appreciate this and it helps them to in some way gain an idea of what some of this means. 

Cheers James. 

P.S Teleconnections experts please feel free to correct me if i'm wrong with something 

 

One further point, what James describes as easterly or westerly, from the viewpoint of somewhere on earth, I think it's easier to imagine this if you envisage both the earth and atmosphere as spinning west to east one faster than the other. 

I'm not entirely convinced by your third paragraph though, I was of the impression that the fine weather over the last months has been as a result of higher AAM over the base state of the ENSO state, but others will be better placed to comment.

 

[mb018538]

Well those NOAA charts didn’t show a westerly centred high a couple of days ago - so if you ask me they weren’t completely accurate again. They had above average heights (which was quite obvious anyway) but the high was more UK centred. Net result is going to be temps probably 5-10c below where they may have been otherwise.

[Djdazzle]

3 minutes ago, mb018538 said:

Well those NOAA charts didn’t show a westerly centred high a couple of days ago - so if you ask me they weren’t completely accurate again. They had above average heights (which was quite obvious anyway) but the high was more UK centred. Net result is going to be temps probably 5-10c below where they may have been otherwise.

They seem to have flipped somewhat, which suggests they are still prone to it, although maybe less than the NWP output.

[Bartlett High]

Did I see 48c for southern Spain at the end of this week!! a European record apparently.

[NUT]

1 minute ago, bartlett high said:

Did I see 48c for southern Spain at the end of this week!! a European record apparently.

50 potentally on saturday......................

[damianslaw]

I said yesterday one of three scenarios most likely to play out, and the one shown by the models is the high pressure scenario, but not as I was thinking, a UK centred high, but one more west centred, hence a cooler northerly episode now showing its hand. 

There has been a sudden development in the models today, and that is the scandi trough feature, this wasn't picked up by the models over the weekend, and I tend to take note when such a synoptical development occurs in the 96 hr timeframe, more so than if shown in the 120-144 hr timeframe, sudden developments tend to happen quite suddenly, and in winter are the precursor to retrogression. Alas its not winter, but we may exchange a hot weekend in the south for a cloudy cool fest next week.

That heat low shown yesterday has been erased from all models.

 

[summer blizzard]

14 minutes ago, NTC said:

BBC weather for week ahead can't decide on next week Matt Taylor says the high might go east and bring hot weather over more of UK and storms but more likely the High will sit to the west and bring winds from North/North West and lower temps.

 

 

This suggests the Euro ensembles are backing the operational in the west solution. 

[SLEETY]

Ukmo has backed away from the extreme heat it was showing on the earlier 00z run,and met not so keen on very hot conditions now.Maybe the gfs and ECM have been nearer the mark this time,with cooler weather than was previous thought to develop.Whatever happens this has been the most exciting year for model watching that I can care to remember.