In Depth Model Discussion, Analysis and Summaries

[feb1991blizzard]

Just wondered if someone could post a description of what Angular momentum is and how it affects our weather patterns.

[Jack Wales]

In the image below, which captures the growing influence of westerly wind bursts, look to the left hand side to see the latest westerly wind burst associated with the MJO.

This is about to weaken and easterly trades restrengthen a little.

This will take the GWO into phase 0 which signals the strengthening of the ridge in the mid-Atlantic allowing a weak tough to drop over the top into NW Europe.

However, don't panic. The weakening of the westerly wind bursts will reverse in June and a slight falling off in angular momentum is a pre-requisite to the trough in the Atlantic re-setting.

Hi GP, Is this due to the stubbourness of the current atmospheric base state? As I see it if the GWO swings into phase 0, the atmospheric lag will take us into mid June at the earliest until we observe a pattern change here in the UK. Also I'm concerned at the potential signals of height rises to our north and in the Arctic, what's your take on this and how could they impact upon our summer synoptics?

so your summer forecast still has a higgh chanceof verifying gp?

Confidence very much still high in the forecast Atlantic trough, ridge over western Europe scenarion.

Dear me Geoff! I don't see how much more specific GP could be!!!

Just wondered if someone could post a description of what Angular momentum is and how it affects our weather patterns.

Here are some useful links...

AAM1

AAM2

Hope this helps.

Edited May 19, 2011 by Jack Wales

[feb1991blizzard]

Here are somne useful links...

GWO

AAM

Hope this helps.

Thanks.

[geoffw]

Hi GP, Is this due to the stubbourness of the current atmospheric base state? As I see it if the GWO swings into phase 0, the atmospheric lag will take us into mid June at the earliest until we observe a pattern change here in the UK. Also I'm concerned at the potential signals of height rises to our north and in the Arctic, what's your take on this and how could they impact upon our summer synoptics?

Dear me Geoff! I don't see how much more specific GP could be!!!

Here are some useful links...

AAM1

AAM2

Hope this helps.

sorry guys i was knackered last night

[SteveB]

It sounds like to me that there might be a delay to the heat, maybe starting the first /second week of June?

[Costa Del Fal]

Hmmm, not too keen on seeing what was looking like a dry week ahead possibly turn into a fairly wet one especially midweek. A pretty slow moving low looks like becoming rather anchored across the country now around Wed-Fri. Plenty of rain is a possibility. Even into FI its not looking too great. Is the High pressure set up as previously forecasted still on but delayed or has a spanner been thrown into the works that could change the picture for some time?

I certainly hope its not the latter! Thoughts please?

[Jack Wales]

Recent observations have given me some potential concerns about us experiencing a hot & dry type summer (June especially). This being due to the current (La Nina) atmospheric base state, characterised by a mid Atlantic ridge and a NW to SE Jet stream over the UK. This is proving somewhat reluctant to displace despite the ever weakening La Nina in the Pacific.

Lets look at the SST profiles for 8th May and 22nd May below…

You will note that La Nina pattern has continued to weaken with positive anomalies observed migrating westwards into the key Nino 3.4 region. Although on the down side the Atlantic sst profile is far less favourable than it was at the beginning of the month. Look how the warm anomalies over Western Europe have retreated over recent weeks. This IMO could encourage the jet stream towards the UK.

Finally the Southern Oscillation Index has switched positive again, indicating an increased presence of Easterlies over the tropical Pacific which could inhibit any change to the atmospheric base state, in the short term at least. Here are the daily SOI archives back to 1999 (note how 2003 and 2006 summer period recorded strongly –ve values).

SOI

What concerns me is that I believe in the last couple of weeks of May, the summer pattern begins to emerge and summer really does start to ‘show its hand’. The weather models are clearly having difficulty with the current pattern hence why any settled synoptics keep getting pushed further back into FI.

I’d love to be corrected on my interpretations but as I set it, the overall global pattern is far less clear cut than it was maybe 2 -3 weeks ago and to me a La Nina type summer cannot be ruled out, especially for June. Having said that, I recognise that we are still in May and with the ever diminishing –ve ENSO sst pattern, there is a lot that can change over the next few months so maybe its not all doom and gloom!!

Edited May 24, 2011 by Jack Wales

[Alex]

Interesting stuff Jack Wales, I'm assuming the temperatures anomalies of the oceans vary very much and can as seen above change alot during a couple of weeks.

I'm hoping that GP can rectify the poorer news with some better news?

[feb1991blizzard]

Great post Jack. So it looks like its not as nailed on to get a hot summer as i thought and a cold showery atlantic LP dominated summer is still possible. Mind you i hope any remnants of the la nina are gone by the winter to increase our chances of a sustained negative AO and NAO.

Edited May 24, 2011 by feb1991blizzard

[Glacier Point]

I wouldn't too concerned, indeed, the pattern at present is a very good precursor and I would be more worried if we were getting blistering heat. Think of May as the same as November, Ice in November and ducks and all that !

The SOI has shifted positive in line with a weakening MJO wave and general scrubbing of westerlies from the atmospheric circulation as a result of the strong increase in westerlies on the back of the MJO which reached high amplitude in the last few weeks. We should see a general falling back in angular momentum over the next 2-3 weeks before the next westerly wind burst is due to start somewhere around the 10th June tied into the MJO booting up again.

The falling back in angular momentum should help shift the upstream ridge to the eastern US and displace the mean trough into the Atlantic allowing for the ridge to develop over Europe. The evolution to Scandinavian ridge needs the rise in pressure over Europe to happen first. Keep any eye also on pressure just west of Greenland as this should begin to fall over the coming week to 10 days which also teleconnects to pressure rise over Europe.

The presence of a ridge in the Atlantic is a good fit for phase 8 GWO / MJO type pattern but crucially this changes with the seasonal wavelength to more of a trough regime the longer time passes - a really nice example of how seasonal wavelengths can change a pattern.

The Atlantic SSTs still look to have a troughing profile particularly those within the sub-tropical area which is the key one.

Edited May 24, 2011 by Glacier Point

[geoffw]

so are you still expecting a hot june gp?

[bluearmy]

so are you still expecting a hot june gp?

he wrote that there was nothing to be concerned about re the summer forecast Geoff. june is proposed to be above average but dont think that this translates to 30 days of blistering heat.

there is currently little strong model agreement of any notable heat before the first weekend of june. that still leaves you nearly four full weeks of possibilities. patience needed mate. GP has given you the things to look for on the models.

[johnholmes]

so are you still expecting a hot june gp?

geoff-for heavens sake why will you not attempt to read carefully what has been posted and 'think' a little. Inexperience is no excuse for not trying to understand the basics that the more experienced folk are posting for you. Almost every time that you come on here you want more detail. Longer term forecasting 1 month and longer cannot ever give you much detail. GP has on more than one occasion, aside from his summer forecast, given firm indications of how he expects the weather to be, June, July and August. Now PLEASE try and be less demanding?

mods if you feel this is OTT then please delete.

[Jack Wales]

I wouldn't too concerned, indeed, the pattern at present is a very good precursor and I would be more worried if we were getting blistering heat. Think of May as the same as November, Ice in November and ducks and all that !The SOI has shifted positive in line with a weakening MJO wave and general scrubbing of westerlies from the atmospheric circulation as a result of the strong increase in westerlies on the back of the MJO which reached high amplitude in the last few weeks. We should see a general falling back in angular momentum over the next 2-3 weeks before the next westerly wind burst is due to start somewhere around the 10th June tied into the MJO booting up again.The falling back in angular momentum should help shift the upstream ridge to the eastern US and displace the mean trough into the Atlantic allowing for the ridge to develop over Europe. The evolution to Scandinavian ridge needs the rise in pressure over Europe to happen first. Keep any eye also on pressure just west of Greenland as this should begin to fall over the coming week to 10 days which also teleconnects to pressure rise over Europe.The presence of a ridge in the Atlantic is a good fit for phase 8 GWO / MJO type pattern but crucially this changes with the seasonal wavelength to more of a trough regime the longer time passes - a really nice example of how seasonal wavelengths can change a pattern.The Atlantic SSTs still look to have a troughing profile particularly those within the sub-tropical area which is the key one.

GP, interesting post again although I note the ensembles forecast the MJO to remain in phase 0 for the next 15 days, I expect that will change as you suggest when the next tropical wave kicks in. Also a very interesting point re the sst's, admittedly sst's aren't my strong point but I thought the diminishing warm anomlies would discourage the amplification of the jet and direct it nearer our shores, can you shed some light on how the sub tropical sst's are the basis for anchoring the jet as you expect? I applaud your confidence and look forward to see how the synoptics evolve over the coming weeks.

so are you still expecting a hot june gp?

Goeff, John has a point, however please don't be deterred from posting on the forum. Here are some friendly tips for you....

If I read a post I don't understand, I make a point of reseaching it on the internet until I find the answer. Ok this does take more time but I've found that it is an excellent way of gaining and embedding knowledge. The learning area on this forum is excellent and The Met offce and Climate Prediction Centre are always good first ports of call, here are their links...

Met office

CPC

Be careful though as I've lost myself for hours at times!! Joking aside though, you will find that you are not only able to better understand other members posts but will be better equipped to challenge them if necessary. If there is anything you are still unsure of, feel free to PM me and I'll see what I can do...

Edited May 24, 2011 by Jack Wales

[Costa Del Fal]

What are your views on the High retreating and more unsettled conditions returning around the 6th/7th June onwards GP at the moment? Is it likely to be a temporary blip or a pettern that is perhaps a bit harder to break out of than first thought. Its just some of the charts look like its back to square one after this coming week.

Cheers.

[Alex]

What are your views on the High retreating and more unsettled conditions returning around the 6th/7th June onwards GP at the moment? Is it likely to be a temporary blip or a pettern that is perhaps a bit harder to break out of than first thought. Its just some of the charts look like its back to square one after this coming week.

Cheers.

Reading GPs posts over the year and seeing the models, I think the models are being a bit too progressive I'n pulling the high back west. I think more of a flatter high to our southwest is correct but having enough influence over the country to keep us mostly dry with the exception of possibly importing some showers from time to time from Europe.

I then think once pressure can rise to our east, then the ridge will attempt the link up thus giving us our hot dry summer!

Edited May 29, 2011 by Alex

[Costa Del Fal]

Hmm, its very likely this Ridge will pull out west again bringing some sort of Northerly winds now. I need some reassurance from GP now :lol:. Ensembles look rather cool and slightly unsettled in places. Not keen on them at all today especially as they looked decent enough yesterday i thought. I dont think June is going to turn out quite as good as expected im afraid but lots can change and will certainly reserve any formal judgement of the month till between the 10th and 15th.

The CFS looks pretty cool and wet for June im afraid on the latest run. Flaming June- i dont think so sadly. July looks quite good on the CFS though.

Edited May 31, 2011 by Blizzards

[johnholmes]

Hmm, its very likely this Ridge will pull out west again bringing some sort of Northerly winds now. I need some reassurance from GP now :lol:. Ensembles look rather cool and slightly unsettled in places. Not keen on them at all today especially as they looked decent enough yesterday i thought. I dont think June is going to turn out quite as good as expected im afraid but lots can change and will certainly reserve any formal judgement of the month till between the 10th and 15th.

The CFS looks pretty cool and wet for June im afraid on the latest run. Flaming June- i dont think so sadly. July looks quite good on the CFS though.

CFS is almost as changeable from day to day as GFS is from run to run!

[Costa Del Fal]

CFS is almost as changeable from day to day as GFS is from run to run!

Very true indeed however i do look at it quite regularly to pick out trends and the latest trend isnt too good however July onwards is good.

[Glacier Point]

As of now, I suspect the ocean-atmospheric base state has entered El Nino conditions.

Considering tropical waves and tendency in earth angular momentum should be reaching its low point in the next few days, take a look a relative angular momentum anomly plot:

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

That's showing a +1 SD anomaly when we should be close to zero or below. Mountain and frictional torques may take us down a little in the next few days, probably bottoming out around 10th June. However, the significant message here is that the atmosphere is embracing a fundamental shift towards more El Nino-ish type characteristics. For western European Summers, read Atlantic trough, Scandinavian and continental Europe ridges.

A westerly wind burst has been initiated in the Indian Ocean (maybe a few days later than scheduled) and we are already seeing the modelling respond with some forwad inertia sending the cut off low off Newfoundland eastwards blowing the ridge in the North Atlantic and preventing the trough over western Europe from being a persistent feature.

From around 15th June onwards, mountain torque should spike very positive introducing a sharp burst of westerlies across the sub-tropics, beefing up the ridges to our south and enhancing the trough in the Atlantic.

The wildcard here is the persistence of easterly zonal winds in the North Atlantic c/o the strong final warming of the polar stratosphere but we're getting near to the Solstice when any such impacts should be outweighed by what comes from the south.

Basically, steady improvement from the south and east is the message in the next 7-10 day timeframe.

Finally, if we get the sort of pattern that both GFS and ECM extended means are suggesting, with teleconnective support, a lot of cold upper air will be dumped into the North Atlantic. With a block already in place over Scandinavia and the Continent warming aswell, that could set up a very sustainable and warm pattern for the summer season.

[snowlover2009]

As of now, I suspect the ocean-atmospheric base state has entered El Nino conditions.

Considering tropical waves and tendency in earth angular momentum should be reaching its low point in the next few days, take a look a relative angular momentum anomly plot:

http://www.esrl.noaa...m.sig.90day.gif

That's showing a +1 SD anomaly when we should be close to zero or below. Mountain and frictional torques may take us down a little in the next few days, probably bottoming out around 10th June. However, the significant message here is that the atmosphere is embracing a fundamental shift towards more El Nino-ish type characteristics. For western European Summers, read Atlantic trough, Scandinavian and continental Europe ridges.

A westerly wind burst has been initiated in the Indian Ocean (maybe a few days later than scheduled) and we are already seeing the modelling respond with some forwad inertia sending the cut off low off Newfoundland eastwards blowing the ridge in the North Atlantic and preventing the trough over western Europe from being a persistent feature.

From around 15th June onwards, mountain torque should spike very positive introducing a sharp burst of westerlies across the sub-tropics, beefing up the ridges to our south and enhancing the trough in the Atlantic.

The wildcard here is the persistence of easterly zonal winds in the North Atlantic c/o the strong final warming of the polar stratosphere but we're getting near to the Solstice when any such impacts should be outweighed by what comes from the south.

Basically, steady improvement from the south and east is the message in the next 7-10 day timeframe.

Finally, if we get the sort of pattern that both GFS and ECM extended means are suggesting, with teleconnective support, a lot of cold upper air will be dumped into the North Atlantic. With a block already in place over Scandinavia and the Continent warming aswell, that could set up a very sustainable and warm pattern for the summer season.

Oh man please be right!!! Sounds promising, so we are starting later than schedule I take it. Summer will quite possibly be under way good and proper for the second half of June. I like the sound of cold upper air digging into the atlantic, meaning one thing, the low pressure and cold uppers in the atlantic, pumping that warmth and hot air up to us and europe?

Edited June 4, 2011 by snowlover2009

[michail]

All sounds good to me! I can't see this trough( over the BI) lasting throughout the three months of summer. I've a felling that this summer will break the trend. ; - )

btw, Gaga rules!!!!

Edited June 4, 2011 by michail

[snowlover2009]

All sounds good to me! I can't see this trough( over the BI) lasting throughout the three months of summer. I've a felling that this summer will break the trend. ; - )

btw, Gaga rules!!!!

Yep she does indeed, she is the Queen!!!!! Exciting times!!!

[ZONE 51]

Oh man please be right!!! Sounds promising, so we are starting later than schedule I take it. Summer will quite possibly be under way good and proper for the second half of June. I like the sound of cold upper air digging into the atlantic, meaning one thing, the low pressure and cold uppers in the atlantic, pumping that warmth and hot air up to us and europe?

i think GPs updates are excellent, very well explained.

I think based on my own thoughts-we are looking at the possibility of a top summer in our top 10 for example! its hard for me to explain what i see as im not good at writing, it would be a jumble and i would get pulled for not making sense! i want to be able to explain the teleconnections-and other and be technical, maybe sometime il chat a bit more in depth. its not that i don't know, its that i can't say things the right way.

Edited June 5, 2011 by ElectricSnowStorm

[Thundery wintry showers]

I have a similar opinion to GP on how this month will pan out. We should remember that June is traditionally the month when the jet kicks into gear and the traditional July/August patterns set in, referred to by Philip Eden as the "June Return of the Westerlies" and I think there are plenty of signs suggesting that when this happens we will see a tendency for high pressure to build to the east with low pressure centred out west. I also get this impression when looking at the MJO composites for June and July.

Personally I'm thinking that the Atlantic trough will end up playing a significant role in our weather with the European highs being too far east to give us a prolonged anticyclonic spell, but if it results in a hot thundery pattern of the type we had in 1994 a lot of people will still end up satisfied. As always, though, only time will tell, but it's good to see that the N-W summer forecast hasn't been de-railed as yet, only delayed a bit.