In Depth Model Discussion, Analysis and Summaries

[Thundery wintry showers]

Very interesting thoughts, thanks for that. Thus if the teleconnections turn out to be near the mark, I get the impression of a cold and possibly snowy start to the season in November/December due to frequent northerly winds. After that perhaps becoming near average to fairly mild into January/February with a February 1999 style La Nina pattern (but which still doesn't rule out some further northerly outbreaks), unless we get a stratospheric warming event which could tip things back towards a colder snowier outcome. If that sort of thing comes off I think many cold/snow lovers will be reasonably satisfied even though such an outcome won't be comparable to last winter's offering.

[summer blizzard]

Hello again GP. I do not understand your comment about the stratospheric westerly wind values being +10 to +20 values.

Can you explain this? What does it mean?

How will this have an impact on the polar vortex?

Thanks again.

The equatorial stratospheric westerlies are a symptom of a +QBO, what he is saying there is that we will have a mature +QBO this winter with values between +10 and +20.

[BLAST FROM THE PAST]

Hey Stew, nice to see continued boldness and a very good call too I'd say. Are you issuing an autumn forecast or are you going to concentrate on building another comprehensive winter forecast? One thing I'll add re the HP sinking mid winter, I much prefer the thoughts of 08/09 as I think the jetstream will remain on its southerly placement and this will entice a prolonged colder theme [preventing to much sinking] IF it develops this way early winter.

I believe the longer term shift of the jetstream helped winter 08/09 be cold inspite of some unfavourable factors.

You mention the SSTA profile in the Atlantic, an expansion on describing those developments could be useful. Are you talking warm over cold over warm developing?

regards

BFTP

Edited September 8, 2010 by BLAST FROM THE PAST

[Guest harshwinter09]

The equatorial stratospheric westerlies are a symptom of a +QBO, what he is saying there is that we will have a mature +QBO this winter with values between +10 and +20.

No SB,

That is not the answer I am looking for, but thanks anyway.

I think its pretty obvious that a +QBO = polar westerlies.

But I want GP's answer to this as he's the most knowledgeable on here when it comes to these things.

Sorry.

[The PIT]

Thanks GP nice too see something technical posted again in this thread. I wonder how long it will take for the models too reflect this. ECM trending that way GFS not so.

[chionomaniac]

Thanks for your recent thoughts, Stewart.

Last winter we were fortunate that the stratospheric conditions were favourable right from the start of winter, with the polar vortex decreased in strength due to the enhanced BDC and -QBO having a knock on effect. When this was aligned with the 'La Nino' and the excellent NH snowcover a great winter ensued in terms of snowfall.

However, this winter I believe that we are going to start off on the wrong foot with the stratosphere. Presently, the polar stratosphere is cooling rapidly as it does every autumn. More of concern, though, is the temperature of the tropical stratosphere which is showing signs of warming and is warmer than it has been at any time last year in the run up to winter.

If this continues, then the differential between the polar and tropical stratosphere would be increased leading to a stronger vortex.

Whether or not this could disrupt the setup that you suggest that the strong La Nina will bring will be interesting to see.

[ASW]

Thanks for your recent thoughts, Stewart.

Last winter we were fortunate that the stratospheric conditions were favourable right from the start of winter, with the polar vortex decreased in strength due to the enhanced BDC and -QBO having a knock on effect. When this was aligned with the 'La Nino' and the excellent NH snowcover a great winter ensued in terms of snowfall.

However, this winter I believe that we are going to start off on the wrong foot with the stratosphere. Presently, the polar stratosphere is cooling rapidly as it does every autumn. More of concern, though, is the temperature of the tropical stratosphere which is showing signs of warming and is warmer than it has been at any time last year in the run up to winter.

If this continues, then the differential between the polar and tropical stratosphere would be increased leading to a stronger vortex.

Whether or not this could disrupt the setup that you suggest that the strong La Nina will bring will be interesting to see.

Though would it not depend on where the vortex set up shop for the winter? If as suggested a mid atlantic high becomes prominent, in that situation do you not get the vortex over Scandi? If the vortex was stronger that could result in lower pressure over Scandi, creating a bigger presure gradient between the high and low pressure, forcing stronger northerly winds over us and a colder air mass...

[Glacier Point]

Thanks for your recent thoughts, Stewart.

Last winter we were fortunate that the stratospheric conditions were favourable right from the start of winter, with the polar vortex decreased in strength due to the enhanced BDC and -QBO having a knock on effect. When this was aligned with the 'La Nino' and the excellent NH snowcover a great winter ensued in terms of snowfall.

However, this winter I believe that we are going to start off on the wrong foot with the stratosphere. Presently, the polar stratosphere is cooling rapidly as it does every autumn. More of concern, though, is the temperature of the tropical stratosphere which is showing signs of warming and is warmer than it has been at any time last year in the run up to winter.

If this continues, then the differential between the polar and tropical stratosphere would be increased leading to a stronger vortex.

Whether or not this could disrupt the setup that you suggest that the strong La Nina will bring will be interesting to see.

Yep - watching that one closely.

Curiously, there is a paradox that as a prelude to cold winter stratospheres, we tend to see a lot of blocking early doors - almost as the upper level weakness (upwelling) leads to an increase in tropopausal height and weakened polar westerlies. Hence my thinking that the blocking ridge will migrate poleward during November and December before it falls back given an increase in the polar westerlies during January.

[Glacier Point]

Hello again GP. I do not understand your comment about the stratospheric westerly wind values being +10 to +20 values.

Can you explain this? What does it mean?

How will this have an impact on the polar vortex?

Thanks again.

The QBO has monthly mean speed values measured in metres per second at 30mb over the equator.

Listed here are the values since 1948:

http://www.esrl.noaa.gov/psd/data/correlation/qbo.data

The relationship between QBO state and polar stratosphere during the winter is modulated by the solar cycle. Low solar activity and east QBOs are good for blocking (as per last year). Conversely, west QBOs during low solar favour no blocking. The reverse is true during high solar conditions. The mechanism is hugely complex and not one we fully understand however the Brewer Dobson Circulation (BDC)(general meridional hemipsheric circulatiuon in the stratosphere) is thought to be a key process. East QBOs under low solar conditions tend to intensify the BDC transporting more ozone to the pole. Ozone formation and presence leads to warming of the upper atmosphere through exothermic reaction. The opposite is true for the westerly QBO under low solar conditions.

A key measure of the BDC is the temperature differential between the stratospheric equator and pole during the autumn. Anomalous warm air over the equator signals desceding air which warms. Upwelling air cools. Hence, a warmer than normal stratosphere over the equator and cooling polar stratosphere signals a weakened BDC.

Hope that helps.

[chionomaniac]

Though would it not depend on where the vortex set up shop for the winter? If as suggested a mid atlantic high becomes prominent, in that situation do you not get the vortex over Scandi? If the vortex was stronger that could result in lower pressure over Scandi, creating a bigger presure gradient between the high and low pressure, forcing stronger northerly winds over us and a colder air mass...

Hi ASW, and welcome to posting on NW.

Firstly, there is a chicken and egg situation. Does the strength and position of the stratospheric vortex influence the tropospheric vortex strength and position or is it vice versa? I believe both are influencing each over. However, the stronger the stratospheric vortex is, the more likely it is going to override the tropospheric influences. So, if we have a strong central stratospheric polar vortex, any position of the tropospheric polar vortex is likely to be modified somewhat and any potential ridging in the Atlantic will be battling against a strong jet stream wanting to cut through it. Last year we saw a very disrupted tropospheric vortex that extended into the stratosphere - probably because the underlying strength of the stratospheric vortex wasn't cutting the mustard!

c

[Yorkshiresnows]

Thanks YS.

Yes, very much the ecxpectation that the low angular momentum base state, aided and abetted by the developing profile of SSTAs in the North Atlantic will lead to strong forcing for a mid Atlantic blocking ridge becoming shifted further northwards during November and December. It's also worth noting that analogues for tropical convection centred west of Indonesia (MJO phase 4-5) also support this solution.

The west QBO / solar combination will I think bring about a slow sink of the ridge to a mid latitude feature in January and February although the later we go the more vulnerable we become to a Major Mid Winter Warming of the stratosphere, much like 2008/9. Its worth pointing out the equatorial westerly winds in the stratosphere have increased and we may now be looking at values of +10 to +20 m/s this winter. This is already having an impact on stratospheric ozone concentrations and the Brewer Dobson Circulation which would appear to be weak, even at this early stage.

Hi G.P,

Many thanks for the answer and indeed the discussion from all that followed.

So, in a basic summary:

Cool to cold Autumn very probable .... continuing into December (possibly early January), with an increasing risk of January (as a whole) becoming milder with February following suit .......... unless a 2008/2009 stratospheric warming event (which becomes a real possibility) occurs ....

At least ... thats the prognosis for now ... with greater uncertainty as we go further out ?

Sounds good to me ...... a possible fine and seasonal start with all on the table for the latter period (though weighted to milder as we go on) ........

Lets role the dice !!!

Look forward to more of your (and others) posts as we head into the winter season.

Y.S

[BLAST FROM THE PAST]

There is of course a wild card to play in all this. 2 years ago there was some significant arctic volcanic activity and different to tropical volcanoes, the response to colder temps is a little delayed. More SO2 in the stratosphere leads to cooling lower down.

I'll lay my cards on the table, the perturbation cycle that started Feb 07 as a direct result of the solar and lunar cycle has triggered the southward shift of the jetstream...which I believe is longterm [indeed the Pakistan floods as an example were down to the 'very unusual' southerly track of the jetstream].....Unusual? I think not. This is IMO the driver. Also interesting of note that this collapse of the El Nino into the strength of the current Nina is the sharpest ever recorded.....food for thought?

BFTP

[summer blizzard]

The QBO has monthly mean speed values measured in metres per second at 30mb over the equator.

Listed here are the values since 1948:

http://www.esrl.noaa.gov/psd/data/correlation/qbo.data

The relationship between QBO state and polar stratosphere during the winter is modulated by the solar cycle. Low solar activity and east QBOs are good for blocking (as per last year). Conversely, west QBOs during low solar favour no blocking. The reverse is true during high solar conditions. The mechanism is hugely complex and not one we fully understand however the Brewer Dobson Circulation (BDC)(general meridional hemipsheric circulatiuon in the stratosphere) is thought to be a key process. East QBOs under low solar conditions tend to intensify the BDC transporting more ozone to the pole. Ozone formation and presence leads to warming of the upper atmosphere through exothermic reaction. The opposite is true for the westerly QBO under low solar conditions.

A key measure of the BDC is the temperature differential between the stratospheric equator and pole during the autumn. Anomalous warm air over the equator signals desceding air which warms. Upwelling air cools. Hence, a warmer than normal stratosphere over the equator and cooling polar stratosphere signals a weakened BDC.

Hope that helps.

Glacier Point, what do you make to my analysis which suggests that a mature +QBO (the period between the first and second peak where there is a slight weakening then strengthening) actually correlates with a cooler than average winter?

[Cheshire Freeze]

There is of course a wild card to play in all this. 2 years ago there was some significant arctic volcanic activity and different to tropical volcanoes, the response to colder temps is a little delayed. More SO2 in the stratosphere leads to cooling lower down.

I'll lay my cards on the table, the perturbation cycle that started Feb 07 as a direct result of the solar and lunar cycle has triggered the southward shift of the jetstream...which I believe is longterm [indeed the Pakistan floods as an example were down to the 'very unusual' southerly track of the jetstream].....Unusual? I think not. This is IMO the driver. Also interesting of note that this collapse of the El Nino into the strength of the current Nina is the sharpest ever recorded.....food for thought?

BFTP

I agree. I think we are in 'unknown' territory at the moment and I believe that what 'should' happen given the various teleconnections as suggested by GP and Chinomaniac et al, may not materialise at all. As you say there does seem to have been a general southwards shift of the jet stream and this is playing havoc with the theories on what 'should' happen and is producing some classic synoptics.

At this point I would bank a cold November and December and keep touching wood that January and February can produce some cold and interesting weather also.

[snowlover2009]

I agree. I think we are in 'unknown' territory at the moment and I believe that what 'should' happen given the various teleconnections as suggested by GP and Chinomaniac et al, may not materialise at all. As you say there does seem to have been a general southwards shift of the jet stream and this is playing havoc with the theories on what 'should' happen and is producing some classic synoptics.

At this point I would bank a cold November and December and keep touching wood that January and February can produce some cold and interesting weather also.

i think people should be wary on what they predict in a way, as i agree with what you are saying. i think we could be in new territory with all bizarre patterns of late,just because similar teleconnections have happened doesn't mean we will follow similar trends. i mean we could be in a new territory of weather with all these different variations of things QBO etc. as you say all these bizarre things happening will play a lot of havoc of what should happen in certain set ups. like people have compared this years patterns with other years, but there has been so many factors that are going to influence our weather in the coming months. also when i say new territory of weather i mean as in different kind of weather , with well known set ups not matching to one from the past, heres an example, lets say we had the exact same factors and influences as a winter like 1946/47, people would presume that would mean a very severe winter, when infact so much has changed since then it could be a totally different scenario. so while people compare this and that to other seasons, just be aware that we could be in a new era or territory of weather, completely different to other decades.

Edited September 8, 2010 by snowlover2009

[BLAST FROM THE PAST]

I don't totally agree that we are in 'new' territory, but that we are in diffrent territory to what many are used to. The patterns have been very uncommon since late 80s but I wouldn't say bizarre as they have been called in LRFs over the last 2 years or so. I think the response anticipated by GP looks very plausible which is in response to the significant La Nina that has formed. I think the La nina has formed in such quick time from the rapid collapse of the El Nino in response to the fact that we have entered the La Nina dominated phase of the perturbation cycle since Feb 07 [the change in summers and winters since then is IMO no coincidence].. Which I will say correlates well with the shift of the jetstream and the prevalence of a negative NAO.

BFTP

Edited September 9, 2010 by BLAST FROM THE PAST

[johnholmes]

for anyone interested my latest ideas looking towards mid October, pdf link below

lrf issued fri 10 sept 10.pdf

[MR EXTREMES]

for anyone interested my latest ideas looking towards mid October, pdf link below

lrf issued fri 10 sept 10.pdf

thanks john very intresting shame about the frost snow bit at the end lol,

mind you make a change to see some alantic activity of some sort this looks very possible.

cheers for taking the time.

[BLAST FROM THE PAST]

Another take on the potential for the HP in Greenland not to sink like my thoughts....BUT this is very early thoughts.

http://icecap.us/images/uploads/WINTER_201011.pdf

Winter to get progressively colder....and that is in my view too.

BFTP

[Kentish Kiwi]

Another take on the potential for the HP in Greenland not to sink like my thoughts....BUT this is very early thoughts.

http://icecap.us/ima...NTER_201011.pdf

Winter to get progressively colder....and that is in my view too.

BFTP

That article/forecast makes for very interesting viewing, especially considering the accuracy from last year (assuming that is actually what he/they predicted this time last year).

May I ask who wrote the above forecast?

[weather eater]

That article/forecast makes for very interesting viewing, especially considering the accuracy from last year (assuming that is actually what he/they predicted this time last year).

May I ask who wrote the above forecast?

Joseph D’Aleo, At least that's what it says at the top of the PDF.

[Kentish Kiwi]

Joseph D’Aleo, At least that's what it says at the top of the PDF.

Sorry, phrased that question badly. Obviously I can read the name, but I don't actually know who he is, as in what credibility he has or if anyone knows him...

[ribster]

Sorry, phrased that question badly. Obviously I can read the name, but I don't actually know who he is, as in what credibility he has or if anyone knows him...

Well a quick albeit search found this: http://www.sourcewatch.org/index.php?title=Joseph_D'Aleo

I guess some will dismiss him, because he is a climate change sceptic, seems credible enough to me though, and he seemed to be pretty close to the mark last year. Would love him to be right again this year, time will tell...

[BLAST FROM THE PAST]

Sorry, phrased that question badly. Obviously I can read the name, but I don't actually know who he is, as in what credibility he has or if anyone knows him...

His winter thoughts are based on solar activity and oceanic oscillations. It is a creditable forecast inasmuch the temp and atmospheric anomalies shown are what to expect during la nina and westerly QBO phases. The current solar activity / cycle IMO suggests an autumn and winter as per my signature and as I use [in my amateur way] a similar process I'm not surprised to see this. Interesting to see that it supports GPs view in early winter....I still think progressivly colder at this stage which hasn't changed since I sounded my thoughts in May, and indeed since the quite exceptional collapse of El Nino into a strong La nina as anticipated it has only been galvanised further. Caution though as it still is only 'early thoughts'.

BFTP

[Glacier Point]

Our impressive trade wind surge in late August / early September has begun to flux negative (easterly) mean zonal wind anomalies polewards repeating a similar drop in late June which dropped the global wind oscillation into a La Nina pattern. This time round, tropical forcing following on looks to be quite weak so a persistence of a low angular momentum base state throughout the autumn looks assured.

Relative angular momentum is impressively low driving the global wind oscillation towards phase 1:

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

Composites for phases 1-2-3 are somewhat variable (there is for example some difference between MJO and GWO plots) although my interpretation would generally be for an anomalous ridge into Alaska and tendency for blocking in the mid to high latitudes over the Atlantic.

Noticeable once again (I count this about 4-5 times now) whenever the models see a pulse of westerly winds over the sub-tropical ridges they programme a poleward shift in the jet in the extended range before realising that the Atlantic circulation is much more different with changes in the t72 -t96 period, usually manifested in the trough over the UK or Scandinavia being much more stubborn.