In Depth Model Discussion, Analysis and Summaries

[summer blizzard]

There isn't really a forecast as such, but data can be find at a number of sites.

http://www.geo.fu-be.../qbo/index.html

http://www.cdc.noaa....lation/qbo.data

http://iridl.ldeo.co...lation/QBO.html

Of note is that even though we are heralding a negative QBO regime for this winter, it will be the westerlies that will be being flushed through at the lower stratospheric and upper tropospheric level in the tropics as can be demonstrated below:

How this influences latitudes further north is what I am left wondering. Will increased tropical westerlies invigorate the MJO and is this the reason why there has been an increase in GLAAM?

It is interesting that the run up to winter 2010 saw a similar pattern on your chart and yet saw a record negative -AO winter however that winter was an El Nino winter.

[Glacier Point]

Apologies for not being able to respond to some of those questions, home committments not allowing for time to respond properly.

Both total and relative angular momentum have taken a real hit in the last few days, courtesy of a strong removal of westerlies through a strong negative mountain torque over Asia with relative angular momentum showing a 1 SD drop towards near neutral values from the high point earlier this month. Tendency in relative angular momentum is off the scale indicating a significant shift in the long term atmospheric response to oceanic forcing and the overall 'positioning' of the base state has in my view tilted firmly towards La Nina.

Perhaps of greatest interest in terms of where we might be 'going', global forecast models are suggesting the current MJO wave to collapse in the 10-15 day period. The GFS ensemble (bias corrected version) suggests that by the end of the month the wave will have lost 2 SD units, which is perhaps a little progressive compared to other models but much the same theme presented by the UKMO and ECM modelling.

Why is this significant ? Well, a sharp collapse in the MJO (effectively hitting a wall of easterlies), adds further negative tendency to the global angular momentum budget. Add that to a likely negative mountain torque in 10 and then 20 days time (the usual periodicity for mountain torques tied into Rossby Wavelength), by the end of October / beginning of November, and we have ingredients for a second sharp downward correction in angular momentum taking us into firm La Nina territory.

If this comes to pass, then we may well have coupling between the atmosphere and ocean. Those building cold subsurface anomalies in the equatorial Pacific will be given every opportunity to be upwelled to the surface further reinforcing our ocean forcing on the atmosphere. Those increasingly bullish strong Nina forecasts issued by the CFS may well be closer to the mark than other ENSO forecasts.

Weatherwise, falling angular momentum in November tends to be associated with a low pressure signal towards our west / SW and rising air (ridge) over Scandinavia, so a generally unsettled pattern to start with, depending on how far west the ridge develops over Scandinavia. I suspect the tendency towards a mean ridge being centred close to the east of the UK for the end of October going into November, potentially with a ridge developing in the North Atlantic over a cut off low towards the Azores. Unsettled in the next 10 days or so, then becoming drier and more settled the further east and north.

[sebastiaan1973]

The latest forecast of the ENSO.

The average as low as -3 in februar and march! E.g. the outlook from IRI is based at a weak La Nina

http://iri.columbia.edu/climate/forecast/net_asmt/2011/sep2011/text/Europe.html

Edited October 19, 2011 by sebastiaan1973

[Radiating Dendrite]

The latest forecast of the ENSO.

The average as low as -3 in februar and march!

Great, and this means what in terms of weather?????

[sebastiaan1973]

Well I'm not an expert but I think that La Nina leads to a colder stratophere around the Northpole. Making the polar vortex stronger, high pressure can't reach enough to the north.

[lorenzo]

All this information is available on the site show here http://raleighwx.americanwx.com/MJO.html

On occasion last year this site vanished off line.

I have placed the charts in the cycles shown on the web page and tried to place the maps on the same location on each page so it's easy to compare as you click through.

Hopefully some use out of these if needed.. also saves having multiple windows open !

MJO Composites.pdf

[Glacier Point]

http://www.esrl.noaa...g1-21.90day.gif

Relative angular momentum has stabilised off (for now) at -1.75 SD, which is strong Nina territory, mainly through anomalous mean negative zonal mean anomalies 30N and 30S.

With the models appearing to be factoring in a large negative tendency in the tropical atmosphere in the next 10 days, this could well drop further and we are likely to see the Global Wind Oscillation orbiting in phase 1-2 for some considerable time.

This is a signal for a deep upper low centred west of close to the western fringes of the UK. With the GWO in this state, there is a strong likelihood of a downstream ridge developing, this time centred more towards France with alternating patterns where the upper low gets close enough to graze NW parts. So basically a signal for more wind and rain at times, especially to western and northern parts with the south experiencing the driest conditions.

Everywhere looks very mild to me within this pattern, and this looks good for a sustained period, not least becuase the plausible next move for the atmosphere is further downwards in terms of angular momentum. As the next dip in angular momentum forecast comes to a pause, we could well see a very mild phase as pressure builds over southern parts in the next 10-15 day period.

Meantime, as has been observed elsewhere in this Forum, the stratosphere is behaving as we would expect given a weak QBO signal and upper level westerlies are really starting to ensconse themselves over the Arctic providing optimal conditions for lowering of the tropopause and surface pressure falling driving the AO and NAO positive.

Edited October 24, 2011 by Glacier Point

[Liam J]

Very informative post GP, I don't really understand of all the technical and scientific explanations which are sometimes used in here.

So the current model outputs are exactly what you would expect them to be showing using the information and analysis you have provided - Generally mild and unsettled conditons with the worst of conditions the further north and west you happen to be?

Where can I view the NAO forecasts and is the long term predictions for the NAO to remain positive? I know that a +NAO is not good news for those looking for a cold spell of weather.

Edited October 24, 2011 by Liam J

[summer blizzard]

GP, very interesting analysis.

What is it that we need to see to shift that trough east so that we can get some polar maritime flows?

[Glacier Point]

http://www.esrl.noaa.gov/psd/forecasts/teleconn/

http://www.cpc.ncep.noaa.gov/products/precip/CWlink/daily_ao_index/ao.shtml

The shift in the mean trough eastwards is very unlikely I think given the upstream wavelengths. These need to set with a strong Aleutian Ridge - which is not forecast.

[Cloud 10]

The 12z NAEFS and the cpc 500mb chart seem to be singing from the same hymn sheet.

http://91.121.84.31/...-0-0-240.png?12

Climate Prediction Center - 8-14 Day 500mb Outlook

Better to have this sort of output now though,rather than in December!

Just on a side note,la nina is really getting into its stride now.

Edited October 24, 2011 by Cloud 10

[beng]

Just a comment on those SST anomaly charts. That warm anomaly to our SW is not good for cold (it will favour a West European ridge in the jet - which is what we're seeing right now). We're also seeing a warm up off the US Eastern seaboard - another bad sign for cold weather fans - although there's something of a cold shot on the way in that region.

Anyway still a good 20-30 days to go before I'd get too worried.

[lorenzo]

GP - superb work on the presentation with video and google doc included. Helped me fill in the gaps a lot on the charts posted.

A similarity for me is when you listen to the radio and don't know what the presenter sounds like, seeing a presentation was good. If that makes sense.

For this Winter it looks like the main evidence you present is that very strong signal for the Pacific Ridge, was there a similar ridge projected last year on re analysis as a prior to the off the scale Greenland Highs ? Its almost confirming that last years charts were indeed once in 100 yr anomalies leading to a once in a century cold snap.

Thanks also for the further information on interpreting the GLAAM - I could never get my head round the torque events and how they are factored in, the fact it is borderline El Nino is too confusing for me.

Now if only this was what a weather forecast on the TV looked like then am sure more folk would be interested..

[Gavin P]

Just took a look at Stuarts presentation. Awesome piece of work. Well done.

[Cheshire Freeze]

Just took a look at Stuarts presentation. Awesome piece of work. Well done.

Isn't it just. Seems like a very intelligent man, wish my knowledge and understanding was as vast!

[sebastiaan1973]

Thanks Stuart for your presentation, very interesting, I've put it too at a Dutch website for weather freaks. Just a little suggestion, if it is possible please some better sound and movie quality.

[len]

Could someone post a link to "The Presentation" referred to please?

[gottolovethisweather]

Could someone post a link to "The Presentation" referred to please?

http://www.netweather.tv/index.cgi?action=winter-thoughts-2011;sess=

Hope that helps?

BTW, it's not a forecast so don't go taking it as such, as Stewart has suggested, the actual forecast is out in November, only on netweather.

Cheers

gottolovethisweather

Edited October 26, 2011 by gottolovethisweather

[Glacier Point]

Here are the 12z GFS and 00z ECM 500 mb mean height anomalies:

Both show good consistency on a very deep upper low centred west of the UK by day 7. This has solid teleconnective support through the MJO and GWO swinging through phase 2.

What's of interest here is the likelihood of some very mild air being pulled northward and more particularly the potential for some rather warm nights, if not windy and showery.The diurnal range is going to be minimal here.

For interest, here's the 500mb composite anomaly for Novembers which featured a strong MJO wave through phase 8-1-2 in late October / November.

What is under active consideration is whether MJO waves like these can have an inter-seasonal impact stretching well into the winter. This would seem logical given the background La Nina signal that is being somewhat overridden right now and this pattern with the deep upper low to our west / north-west looks to have a long way to go. If this is the case, then the second half of the winter could be, interesting.

[BLAST FROM THE PAST]

Hi Stew

Hmmmmm, one of those anomaly years is 1985.......does that grab your fancy. What does seem apparent is that a sustained 'easterly' outbreak occurred in many of the Febs that followed this set up.

BFTP

Edited October 27, 2011 by BLAST FROM THE PAST

[Glacier Point]

1984/5 is the only one of two of those analogues with a La Nina background signal as all the rest were El Ninos. The upper atmospheric pattern was also similar for the preceding summer and I think a mid winter warming took place late December into January.

[BLAST FROM THE PAST]

On that analogue basis then Stew, the coldest winter month would be January for the winter. And on that basis, I would agree....and some.

BFTP

[Backtrack]

Here are the 12z GFS and 00z ECM 500 mb mean height anomalies:

Both show good consistency on a very deep upper low centred west of the UK by day 7. This has solid teleconnective support through the MJO and GWO swinging through phase 2.

What's of interest here is the likelihood of some very mild air being pulled northward and more particularly the potential for some rather warm nights, if not windy and showery.The diurnal range is going to be minimal here.

For interest, here's the 500mb composite anomaly for Novembers which featured a strong MJO wave through phase 8-1-2 in late October / November.

What is under active consideration is whether MJO waves like these can have an inter-seasonal impact stretching well into the winter. This would seem logical given the background La Nina signal that is being somewhat overridden right now and this pattern with the deep upper low to our west / north-west looks to have a long way to go. If this is the case, then the second half of the winter could be, interesting.

I loved that last part of your post.

'then the second half of the winter could be, interesting.'

Sorry, I'm too much of a novice to add anything of interest to this thread, I just stick to the normal model output discussion but I thought I would point something out.. That last phrase you posted just put a smile on my face. All that's missing from the end of that is a . Thank you

Thanks Stuart for your presentation, very interesting, I've put it too at a Dutch website for weather freaks. Just a little suggestion, if it is possible please some better sound and movie quality.

Did you ask Paul's permission for that?

That video could be copyrighted.

Edited October 27, 2011 by Backtrack

[Glacier Point]

Probably about time we started to talk one of the warmest autumn's on record.

The 30 day H5 anomaly chart shows nicely the pattern that we have experienced, in particular anomalously low heights over Greenland and Iceland and ridge centred over the southern UK and France. Note also the flat upstream pattern, Aleutian ridge sausage shape and low heights over Alaska.

The last week has seen a strong MJO wave passing through phases 8-1-2, which has arguably excited the existing backround signal, and in particular lowered heights to our west.

The key question for the next 30 days, what's going to shift a pattern that is now well ensconsed ?

There is no high (above 60-70N) latitude blocking signal except the poleward extension of the ridge over western Russia, and with upper level zonal winds on the increase, this looks likely to persist well into December.

The MJO is forecast to become weak (apart from over-progressive GFS which at the end of its run hints at a phase 8 orbit but probably not going to happen).

Angular momentum is low and set to remain so. Whilst this would normally be associated with a mid Atlantic ridge (like last November), our La Nina is evolving at a different pace and a different time compared to previous Ninas and the upper atmosphere is arguably having a big influence.

So basically an atmosphere stuck in a phase 2 (synonomous with convective centre in the Indian Ocean) type state which signals troughing in the Atlantic and ridge stuck to our east but unable to evolve into anything significantly 'game changing' for the time being. Net result, above average temperatures building on an above average September and well above average October.

[Thundery wintry showers]

Good detailed analysis there Stewart, probably not what a lot of people wanted to hear, but backed up by a large amount of evidence- certainly the phase 2 November composites for the MJO highlight that pattern well. I note that the general prognosis is for a shift into phase 3 according to the NOAA forecasts (though as you say the eventual shift into phase 8 is most likely a case of the GFS being over-progressive). The phase 3 composites have low pressure in the Atlantic but higher pressure over Britain suggesting quieter conditions, which is supported by many of the outputs after T+120.