In Depth Model Discussion, Analysis and Summaries

[ZONE 51]

If model runs are to be believed then that will soon change .

nimbilus-It is looking that way (: they can flip positive for a brief period, then back again.

What state is the QBO in at present? could someone explain how the QBO affects the AO? thanks.

Edited October 9, 2010 by nimbilus

[chionomaniac]

nimbilus-It is looking that way (: they can flip positive for a brief period, then back again.

What state is the QBO in at present? could someone explain how the QBO affects the AO? thanks.

Try reading the first post here (save me rewriting it out)

[johnholmes]

I can only repeat what ch has posted, the data he and GP placed in this thread last autumn is well worth reading for anyone new or indeed to remind some of us just what the links are and how to understand them.

Hopefully ch you will do a similar thing to last Autumn into winter with GP hopefully also posting his thoughts.

For those new to much of this, yes to oldies like me its got some difficult concepts to try and get your head round but please do take the time to read the posts from 2009, and again do ask questions, that is the only way any of us learn.

end of another jh sermon!

[knocker]

I can only repeat what ch has posted, the data he and GP placed in this thread last autumn is well worth reading for anyone new or indeed to remind some of us just what the links are and how to understand them.

Hopefully ch you will do a similar thing to last Autumn into winter with GP hopefully also posting his thoughts.

For those new to much of this, yes to oldies like me its got some difficult concepts to try and get your head round but please do take the time to read the posts from 2009, and again do ask questions, that is the only way any of us learn.

end of another jh sermon!

Will follow your advice John.

[snowking]

Not sure I understand, I thought AO/NAO were simply expressions of pressure differentials, and not drivers in themselves. In other words, AO/NAO do not 'play a role' in any seasonal outcome, they are merely expressions of the pressure state in the Atlantic/North Atlantic, and of course one would expect to see negative values in a colder winter because colder winters are often characterised by blocked patterns i.e. higher than average pressure to our west/north west. In other words negative AO/NAO is merely another facet one could reasonably expect to see in colder winters, and not in any way a contributing factor to the cause of colder winters ?

You're completely right but they are representing the differentials - the changes in these differentials (i realise thats a slightly flawed sentence but hopefully you understand what I mean) play big roles in driving the patterns we get in the UK. Whether they're physically a 'factor' or not, the changes in their state represent a correlative relationship to the conditions across NW Europe, and this relationship is highlighted perfectly by the example of the 2007 data.

Kind Regards

SK

[summer blizzard]

nimbilus-It is looking that way (: they can flip positive for a brief period, then back again.

What state is the QBO in at present? could someone explain how the QBO affects the AO? thanks.

The QBO is in a strengthening westerly phase (+QBO), this would normally lead to stratospheric cooling and a +AO, however at the moment La Nina seems to be having the bigger effect on the AO, hence the -AO forecasts.

[snowlover2009]

The QBO is in a strengthening westerly phase (+QBO), this would normally lead to stratospheric cooling and a +AO, however at the moment La Nina seems to be having the bigger effect on the AO, hence the -AO forecasts.

Im really positive we will see a very negative nao, but even if the QBO is strengthening, 1979 produced the goods!

[Guest FireStorm]

below is a pdf giving my ideas on how realistic is the prediction from GFS and now ECMWF for a coldish snap in 7-10 days; largely for newcomers and trying to help them get used to the terms which many of us use in both the tecknical and model threads over the coming months.

Part 6 from 8 October 2010-lrf.pdf

the 7:30 on comment at the end should read 70% to 30% of it happening, however brief in the time period dealt with.

Sorry to be slightly off topic.. This is part 6? Does anyone have parts 1-5 for me please?

[cooling climate]

The QBO is in a strengthening westerly phase (+QBO), this would normally lead to stratospheric cooling and a +AO, however at the moment La Nina seems to be having the bigger effect on the AO, hence the -AO forecasts.

With an increasing AAM and GWO moving into phase 4 plus MJO in phase 5 the outlook period is anything

but Nina.

If my way of thinking is correct an increased AAM would mean more flux and wave breaking into the lower

stratosphere. I say lower stratosphere as the upper stratosphere is capped if you like by the +QBO.

Another good indicator of where the upper atmosphere is heading is by looking at the zonal normalized

geopotential heights and if you compare these to the previous years when we had cold or mild spells and

northern blocking things are looking very favorable.

http://www.cpc.ncep.noaa.gov/products/stratosphere/strat-trop/

[weather eater]

With an increasing AAM and GWO moving into phase 4 plus MJO in phase 5 the outlook period is anything

but Nina.

If my way of thinking is correct an increased AAM would mean more flux and wave breaking into the lower

stratosphere. I say lower stratosphere as the upper stratosphere is capped if you like by the +QBO.

Another good indicator of where the upper atmosphere is heading is by looking at the zonal normalized

geopotential heights and if you compare these to the previous years when we had cold or mild spells and

northern blocking things are looking very favorable.

http://www.cpc.ncep.noaa.gov/products/stratosphere/strat-trop/

I like to know GPs thoughts here CC, because Chionomaniac in a reply to me on the general model thread suggested that GP is expecting a big drop in the AAM back to a More Nina base state.

[Glacier Point]

Tendency in angular momentum is up. However, strong Ninos and Ninas typically wax and wane. It's part of the process that strengthens the relative phases (SSTs are falling across ENSO regions now).

This doesn't diminish our base state and there is likely to be a very strong rebound in angular momentum as the westerly burst in winds is scrubbed. The convection in the Indian Ocean which is driving this increase in angular momentum (directly and indirectly) is going to drop sea surface temperatures there paving the way for strong tropical suppression in the next 4-6 weeks further driving home a strong Nina.

In the meantime, GWO phases 2-3-4 all teleconnect to anomalous ridges to our west and north west during October, November and December. Rinse and repeat.

[weather eater]

Tendency in angular momentum is up. However, strong Ninos and Ninas typically wax and wane. It's part of the process that strengthens the relative phases (SSTs are falling across ENSO regions now).

This doesn't diminish our base state and there is likely to be a very strong rebound in angular momentum as the westerly burst in winds is scrubbed. The convection in the Indian Ocean which is driving this increase in angular momentum (directly and indirectly) is going to drop sea surface temperatures there paving the way for strong tropical suppression in the next 4-6 weeks further driving home a strong Nina.

In the meantime, GWO phases 2-3-4 all teleconnect to anomalous ridges to our west and north west during October, November and December. Rinse and repeat.

Thanks GP I think I understand things better it backs up your post of 29th Sept "Extended long range model tools would appear to be going this way. A lesson perhaps to take forward into the winter though. 2-3 weeks after Nina surges we may see jet pulses which could well be interesting in terms of setting up periods of Atantic troughs and, as these decline, eddies in the jet and Scandinavian ridges".

[Glacier Point]

Thanks GP I think I understand things better it backs up your post of 29th Sept "Extended long range model tools would appear to be going this way. A lesson perhaps to take forward into the winter though. 2-3 weeks after Nina surges we may see jet pulses which could well be interesting in terms of setting up periods of Atantic troughs and, as these decline, eddies in the jet and Scandinavian ridges".

No problem - and the quote should read something along the lines of 'discontinuous retrogression towards southern Greenland given the degree of the mountain torque and spike in relative angular momentum that has just occured'.

[BLAST FROM THE PAST]

No problem - and the quote should read something along the lines of 'discontinuous retrogression towards southern Greenland given the degree of the mountain torque and spike in relative angular momentum that has just occured'.

Hi Stew

Once we get the first cold shot it will start the ball rolling turning this autumn around and a prolonged below aveage period will set in. Of interest IMO is the potential pattern of LPs darting NW to SE as the pattern repeats.....that'll spice the weather up. I think we could see a pattern like BC will experience under Strong Nina conditions....and this Nina is goona be significant.

BFTP

[weather eater]

No problem - and the quote should read something along the lines of 'discontinuous retrogression towards southern Greenland given the degree of the mountain torque and spike in relative angular momentum that has just occured'.

Discontinous retrogression

There is one situation which occurs in the long wave pattern that needs to be mentioned: discontinuous retrogression. When the wavelength from one long wave trough to the next one downstream becomes excessively large compared to the rest of the hemisphere, the downstream trough is often replaced by a new trough that forms farther west than the position of the original downstream trough. In a loop of this situation it appears as though the downstream trough suddenly shifts westward or 9 upstream in a discontinuous manner. In reality, a new trough forms and the original downstream trough weakens.

I wish that was my work.

Edited October 9, 2010 by weather eater

[johnholmes]

Discontinous retrogression

There is one situation which occurs in the long wave pattern that needs to be mentioned: discontinuous retrogression. When the wavelength from one long wave trough to the next one downstream becomes excessively large compared to the rest of the hemisphere, the downstream trough is often replaced by a new trough that forms farther west than the position of the original downstream trough. In a loop of this situation it appears as though the downstream trough suddenly shifts westward or 9 upstream in a discontinuous manner. In reality, a new trough forms and the original downstream trough weakens.

I wish that was my work.

your work or not its essentially correct

with 4 major troughs around the hemisphere this apparent change does occur as momentum creates what seems like a 'new' major trough only for it to be swallowed up by the original major trough.

watch the 500mb charts for the northern hemisphere to see this happen in real time.

Sorry to be slightly off topic.. This is part 6? Does anyone have parts 1-5 for me please?

partly my fault as I've not really numbered them this year, unlike the 3 previous years, but you will find them all in the technical thread area, you may have to search a bit as they go back over several weeks if not a couple of months or so.

hope that helps, if not pm me and I'll try to help.

jh

[Supercell 89]

Hi guys, i must say i love reading this discussion as i've learnt so much.

I've just been trying to read up about Discontinous retrogression and i think i understand what it is but can somebody clarify if i have this right?

Is this when a trough becomes very large and as a result a new one forms further west, which in turn weakens and eventually shifts the original trough westwards to merge with the new one?

If this is right how do you think this will play out in the up-coming winter?

[ZONE 51]

Thanks for the reply's, im understanding more how it all works, the more i do the more exciting it becomes! .

[johnholmes]

What sort of weather seems most likely as we head into November?

A quick idea this evening so sorry no charts.

The predicted spell of colder weather that the models showed for this weekend onwards seems very likely to happen, 90% I would say. Lasting into next week with fairly widespread frosts and some snow for the highest Scottish hills. Less likely elsewhere but the devil as always is in the detail so closer to the time will be clearer.

So into the further outlook for the end of October and early November. A very quick summary would be that the Atlantic is likely to be more blocked than mobile for most of that period.

The QBO and MJO both suggest that events away from the tropics are suggesting blocking as the most likely option. Some indication with data about ENSO that mainly supports this. As we get closer in the time scale then AO, NAO and PNA are not quite in sync especially in the later stages of their predicts. Maybe that is just one of the blips I suggest a couple of sentences on? Of course just where that blocking occurs is the vital part and for the UK where does the major trough lie. West of or over/east of the country? Best estimate I suggest at the moment is that it will move between about 12-15 west and 10 east through the period but with most of the time over/east of the UK. This would mean the UK being on the ‘cold’ side of the trough for much of the time. Temporary changes to a milder flow are going to occur in my view with secondary troughs swinging through the main trough-ridges and causing these to move as suggested above. All 3 500mb anomaly charts appear to be singing from the same hymn sheet. That is with very slow moving major trough-ridges, and the relevant one for this country predicted by all 3 to be east of the country with a marked upper ridge over the eastern Atlantic giving a 500mb flow north of west with relatively low contour heights (not necessarily the same as the 1000-500mb thickness), in the late October time scale. Changing the time scale again and having a peep at the 30mb temperature and it could not follow the ‘normal’ line more closely. This time last year it was similar but the other indicators showed surface high pressure to our east with the main trough to the west of the country. So the weather pattern is rather different this year to the same time last year.

So in summary-mainly blocked and with the major upper trough spending more time over/east of the UK than west of it. This would suggest temperatures below normal for the whole country. However there are indications that at least for some of the time that the surface high will have its centre of gravity south of 50N with depressions in that period running along their preferred track between Iceland and Scotland thus giving more unsettled spells of weather especially further north. Its too far ahead to be able to suggest if towards the period end one may allow a return to a northerly spell. . Frost and snow then with about the average values for most areas for late October into early November. Not much sign of any major gales but that can easily change as the models get greater detail and continuity later in the period.

Sorry it’s a bit of a rush this evening, no charts and a bit jumbled up so do ask questions and I’ll try my best to answer any.

Edited October 15, 2010 by johnholmes

[Glacier Point]

The recent increase in tropical convection over the Indian Ocean has increased total angular momentum to above average.

However, like an elastic band ready to snap back, the atmosphere is a strongly negative base state. The SOI for example has been tanking positive recently indicative of deep La Nina conditions.

First indications tonight that this process is underway.

Relative angular momentum leaving out the QBO signal is trending downward:

http://www.esrl.noaa.gov/psd/map/images/reanalysis/aam_total/glaam.sig1-21.90day.gif

and frictional torques are leading this removal of westerlies from the system:

http://www.esrl.noaa.gov/psd/map/images/reanalysis/aam_total/gltauf.90day.gif

Mountain torques should follow this lead driving down angular momentum. Tendency in angular momentum is sharply down:

http://www.esrl.noaa.gov/psd/map/images/reanalysis/aam_total/gltend.sig.90day.gif

Already the GWO has swung into phase 8:

http://www.esrl.noaa.gov/psd/map/images/gcm/gwo_40d.gif

Composites for phase 1:

evolving to >

which basically support a ridge in the Atlantic with a hint of height rises to the NE before a probable strengthening of the mid Atlantic ridge towards month's end.

[MR EXTREMES]

thanks gp very intresting stuff looks like a return to height rises at months end.

la nina is really stiring the teleconnections looking like you got your work cutout for the next month or so lol.

cheers.

[BLAST FROM THE PAST]

which basically support a ridge in the Atlantic with a hint of height rises to the NE before a probable strengthening of the mid Atlantic ridge towards month's end.

Hmmm, just like the ECM 12z shows. The model to watch

BFTP

[johnholmes]

my pc seems to have 'lost' some of my links!

Can anyone post links between MJO and 500mb flow patterns please, noaa based?

many tks anyone

jh

[Thundery wintry showers]

MJO composites:

http://raleighwx.easternuswx.com/MJO.html

and MJO forecasts:

http://www.cpc.noaa.gov/products/precip/CWlink/MJO/mjo.shtml#other

[johnholmes]

tks for 2nd one Ian

1st one I get web page could not be found?