Autumn Forecast Thread

[Glacier Point]

Next to January, autumn has represented the zenith of positive temperature anomalies for western Europe over the last 25 years. With a sustained run of below average temperature anomalies over the last few months, added to other -ve anomalies in the last 18 months, this September to November period will provide valuable insight into our climatic position - whether we stand a realistic chance of a more average winter pattern or whether normal service will continue.

In the more immediate term, the season does however offer some rock-solid suggestion of a more traditional pattern and I would like to use this thread for seasonal and inter-seasonal analysis

Starting with the context of the autumn outlook and the likely key factors:

1) Quasibiennial Oscillation (QBO)

The westerly QBO event of 2008 is mirroring nicely four other cycles. I've been following these for the last year now and they correctly spotted the emergence of the westerly phase in March. This event is likley to have peaked with a second peak in the Autumn before a decline to an easterly QBO switch in March-April 2009.

The QBO is an important factor to consider because of its influence on: (i) tropical convection - related to the height of clouds, state of upwelling in the atmopshere and stratospheric wind shear; (ii) temperature of the polar stratosphere and stratospheric wind anomalies related to (i)

Reanalysis of the similar years suggests tropical convection (-ve OLR) to be centred in the west Indian Ocean. It also suggests that 30mb stratospheric zonal wind anomalies will continue to be weak and negative over the polar region supporting further blocking structures.

This teleconnects to MJO type responses for phases 1 and 8:

Sep:

Oct:

Nov:

..... which generally favours an upper low over the UK with alternate phases of blocking to the north over Greenland and Scandinavia. Also noted is the current declining state of zonal winds (favouring upwelling in the atmsphere) which is likely to halt as the QBO peaks once more before declining again resulting in twin peaks in tropical convective activity (and all the implications thereafter).

2) Northern Hemisphere Sea Surface Temperature Anomaly (SSTA)

Taking a tour of the overall arrangement of SSTA -

a. substantial warm anomalies over the NW Pacific which extend to depth and which are likely to persist over the autumn.

b. cold anomalies to the Pacific NE south of Alaska.

c. cold anomalies W140 - these extend to some depth with -10C anomalies recorded.

d. weak cold anomalies characteristic of a residual La Nina.

e. variable anomalies over the Indian Ocean but generally above average to the equator and central Indian Ocean.

f. warm anomalies off Newfoundland and the NW northern Atlantic Ocean which extend to depth.

g. cold tropical Atlantic anomalies which are likely to be reinforced considerably by the hurricane season.

h. a trending cold but still warm equatorial Atlantic which is likely to chnage over time as subsurface cold water is upwelled due to seasonal changes.

i. warm water anomalies off the south American coast with some hint of colder anamalies appearing close to the continent.

Points a, b, c and d are strongly indicative of the -ve PDO phase that has existed since September last year (and arguably beyond to 2005.

http://www.jisao.washington.edu/pdo/PDO.latest

This is important to consider because the prevelance of cold water anomalies (which are likely to hemispherically stay the same or increase over time) will persist the -PDO and, more importantly, persist the low angular momentum base state (easterly wind anomalies are a direct result of cold water anomalies).

The last 18 months has seen a consecutive run of -ve GLAAM anomalies. This is not an accident or chance and the run includes the back end of an El Nino event which tends to favour westerly winds.

http://www.cdc.noaa.gov/Correlation/glaam.data.scaled

The overall base state of global winds is perhaps the most fundamental seasonal and inter-seasonal consideration. This helps to couple the ocean-atmospheric response and this offers a better insight than just the El Nino Southern Oscillation (ENSO) measure which I take this season to be neutral.

Reanalysis of the overall arrangement of SSTA in the preceeding 3 months gives the following pattern:

Similar years are as follows:

This suggests the following patterns for the three months and overall 500 hPa height anomalies:

Sep -

Oct -

Nov -

overall projection -

... which again is indicative of an unsettled pattern with alternate phases of blocking to our NE and N.

Delving deeper into these comparable years, we see that the base state is trended towards a low angular momentum - in other words, a La Nina type pattern. Indeed, the Septembers for the years with a similar arrangement of SSTA spent 78% of their time in the Global Synoptic Dynamic Model (GSDM) phases 1,2,3. These three phases teleconnect to the following upper circulations:

http://www.cdc.noaa.gov/map/clim/gsdm.composites.shtml

.... another signal for unsettled weather for the UK with alternate phases of blocking to our NE and N.

So we have several factors all pointing in one direction - continued blocking to our north - unsettled type pattern to persist - low angular momentum base state to persist and strengthen. In instances such as this, there is a high probability that the overall pattern will follow the trend infered by each of these factors.

In terms of the contextual autumn forecast I would recommend fist visiting the UK MET seasonal forecast:

http://www.metoffice.gov.uk/weather/seasonal/autumn2008/

I would position my views as being more in favour of above average rainfall given the upper level pressure pattern favoured and close to average temperatures for the first part of the season then becoming above average towards the second half. A key reasoning in this not being much colder than average is the element of Scandinavian blocking inferred.

Turning towards September....

Outgoing long-wave radiation anolamies indcate a falling GLAAM in line with the seasonal trend with positive OLR anomalies over the west Indian Ocean and tropical Asian area. -ve OLR anomalies exist within the east Indian Ocean however although in line with the seasonal trend, westerly bursts of winds have rapidly appeared and then been removed from the atmosphere as the overall base state asserts. Compare it to a camp fire in drizzly rain -the embers are glowing and petrol is added from time to time causing flare ups but the rain takes its toll as the flames are dowsed and the embers smoulder. For the September and season ahead, the drzzly rain is likely to get heavier making the overall camp that bit wetter.

This is likely to result in the GSDM orbiting through phases 1, 2, 3, 4 with possibly a longer spell in the first three phases compared to the last few months before a return to phase 0/8 at the end.

Reanalysis of these phases for medium aplitude 1-3 (as above) and low 4:

... which re-affirms an unsettled start and middle to the month with a transient mid-latitude ridge week 3 before unsettled weather to end.

Overall month close to average temperature and above average rainfall.

Edited August 31, 2008 by Glacier Point

[johnholmes]

thanks GP, yet another superb piece of work, pulling in all the factors which you have such a good understanding of.

I suspect many others like me find much of it not totally understandable but your logical arguments leave me able to 'see' what you are driving at and how you arrive at it.

Me, I'll stick to 2-3 weeks ahead through the autumn and winter once I restart in about 2 weeks.

[mountain shadow]

Excellent stuff GP, pity we don't get this much information from the Met on there longer term forecasts. I notice you disagree with there forecast in terms of rainfall...........good luck.

[Gavin P]

Excellent piece of work GP. :o A wetter and cooler autumn than we've been used to for many years, will come as something of a shock to the system to many, IMO!

[Terminal Moraine]

I cannot imagine how much time you must put into researching these forecasts, G.P, but from this end at least, it's time well spent. Like John, I don't fully understand the local meteorological implications of all the parameters you mention and usually have to read your detailed posts several times (sometimes I feel as I did as a 12 year old studying trigonometry) but the effort is well worth it.

Excellent stuff!

[BLAST FROM THE PAST]

GP

Excellent again and I must say I find pretty much on the right track inasmuch that my method doesn't disagree too much at all. Rather than do month to month like the summer I'm going to do a full autumn outlookmiddle of the month as am on hols from Friday. September still to be mainly settled month with blockingn to NE and a general E/SE flow.

BFTP

[Glacier Point]

Thanks all.

Upper level zonal winds showing a definate fading, possibly the start of some hint of westerlies..

http

://www.cpc.ncep.noaa.gov/products/stra...AS_NH_2008.gif

http://ds.data.jma.go.jp/tcc/tcc/products/.../heit_u_nh.html

... still negative anomalies present though..

http://www.cpc.ncep.noaa.gov/products/stra...JAS_NH_2008.gif

and more suggestion that the core height anomaly for the season is likely to be centred towards Svalbard - northern Scandinavia in line with composite reanalysis for the base state pattern..

[londonsnow]

fascinating stuff GP. thanks very much

[Anti-Mild]

Perhaps a HP centred over Scandinavia will help the ice formation over the coming weeks in that area and may even inhibit the SST anomalies, although I'll be the first to admit that I'm not that clued up with respect to oceanography !

[Brightspark]

The analysis is as follows.

March 2008 24 wet days out of 31

April 2008 16 wet days out of 30

May 2008 7 wet days out of 31

June 2008 15 wet days out of 30

July 2008 20 Wet days out of 31

August 2008 25 Wet days out of 31

September 2008 so far 9 wet days out of 10

as you can see as the months progressed it is increasingly becoming wetter

Note May 2008 was the better month with 7 wet days out of 31.

I have a pretty cool theory ( at the moment we are in the peak of the new United Kingdom Monsoon season due to the loss of trees throughout the rain forrests around the Globe and people driving around in high polluting cars)

The loss of trees mean domes of moisture are heading straight into the UK from the USA and South America.

My theory is that November will be a dry month and assuming the pollution from all these cars doesn't blank the atmosphere, it should be a sunny month with a lot of frosts. Later followed by Snow falls

I am uncertain about October Does anyone know? (My guess is dull)

[Tim]

I have a pretty cool theory ( at the moment we are in the peak of the new United Kingdom Monsoon season due to the loss of trees throughout the rain forrests around the Globe and people driving around in high polluting cars)

The loss of trees mean domes of moisture are heading straight into the UK from the USA and South America

That doesn't explain month to month fluctuations though. People will drive cars all year round and trees have been cut down in the Amazon for over 30 years now at least.

The figures you wrote to me just follows tradition really. Spring & early Summer tend to be the driest time of the year (I've heard the Atlantic is traditionally quietest in May). The wettest tends to be mid/late autumn sometimes mid winter.

Edited September 11, 2008 by Tim

[BLAST FROM THE PAST]

That doesn't explain month to month fluctuations though. People will drive cars all year round and trees have been cut down in the Amazon for over 30 years now at least.

The figures you wrote to me just follows tradition really. Spring & early Summer tend to be the driest time of the year (I've heard the Atlantic is traditionally quietest in May). The wettest tends to be mid/late autumn sometimes mid winter.

Indeed that doesn't look a cool theory to me.......completely non evidential and unsupported by empirical evidence.

BFTP

[Brightspark]

30 years of chopping down trees across the equatorial belt 10o North and South of the Equator is affecting the climate.

Why do you think the climate is progressivelly getting wetter and what explanation can you offer for the disappearance of frosts in the winter months?

The affects of these warming winters include the disappearance of certain native insects and plants and Plants coming out at the wrong time of year etc

Strange outbreaks of diseases in hospitals brought about by increasing humidity and warmer winters.

Thats a breeding ground for this.

It is a known fact that our past colder winters would never have allowed these types of diseases to have survived as long as they do now.

Look at the diseases they keep finding in the water supplies Ecolie and speriddium ( Forgive my spellling)

And can you explain why nearly every storm system in Central and North America always ends up on our shores.

I can:

If you destroy a Dam Wall the result is flooding

If you take away the trees from the equator domes of moisture head towards the coldest spots ( The North ) ie The UK.

This is like when you take a bath, the steam from the bath settles on the tiles and drips all over the place

The trees kept a certain control on these domes of moisture 10o North and South of the Equator like a double Dam Wall.

That's why they are called rain forests.

Now the UK is like a Rain Forest!

That's why every year people are being washed out of their houses on a regular basis.

Some people say "I have lived here for 50 years and this has never happened before"

Statistics or reports say "This has never happened in 200 years etc"

Though they did have a big storm on 3rd November 1703 where 8000 people got killed, I can't remember the summer very well as i wasn't born then. They only lived in simple houses.

30 years ago we did not have the amounts of cars on the roads like we do now and added to this you have more cars, travelling slow on Motorways with bigger engines than ever before.

This means much higher levels of pollution.

If a car travells from A to B along a given route in 5 minutes and is not impeded, it will give out less polution than a car on that same route that takes 30 minutes because of traffic jams.

Here we are talking about millions of cars day in and day out in that 30 minute example.

Where do you think all that pollution goes?

It aint out of space.

It is trapped in our environment.

What effect do you think that will have?

In effect it puts a blanket around the world that makes it warmer! You aint got so much heat radiating back into space.

What happens if you put a blanket on your bed?

It makes you feel warm.

It's not science but it sure is common sense.

Have any of you fine people got a more rational explanation without blinding me with rather large graphs and big word terms.

I would say that sums it up.

Night everyone.

this is Mike signing out

Take care and God Bless

[laserguy]

Ta for the effort gone into that,Mike! Interesting,and though it's probably best suited to the enviro threads,makes you wonder why govt and greens keep banging on about CO2's pernicious effects they overlook the fact that vehicle exhausts kick out more water vapour than CO2,and water vapour is a far more potent GHG! Here's the equation:

2C8H18 + 25O2 ~> 16CO2 + 18H2O

That water vapour did not exist as water before - it was made by the combination of 2 petrol molecules with 25 oxygen ones. Over time that's an awful,awful,awful lot of water vapour introduced into the atmosphere. Make of it what you will,but I have to wonder from a climate change point of view why the emphasis is on the lesser volume and lesser potency of CO2 whilst water vapour is completely overlooked. Hmm... but the plants must love all that CO2 and water vapour,just like me wandering into a pie shop with a big sign saying "everything free today".

[Gavin P]

Interesting theory, except, I'm not sure the climate IS getting progressively wetter. Sure we have more more flooding events, but that can be explained by increased building on flood plains. We may get heavier downpoars, but that could be explained by the warm seas around the UK, which we know are mainly driven by the warm AMO that we've been in since the 1990's.

Don't forget that from November 2004-April 2007 we had a very prolonged dry spell. It never reached drought proportions, but it was certainly an exceptionally dry spell. In the mid 90's we also had a drought, which was replenished by an extended wet period in the late 90s, reaching its peak in autumn 2000. Rainfall always evens out, IMO.

Edited September 20, 2008 by Gavin P

[BLAST FROM THE PAST]

Well the settled September theme bore out but later than I had suggested, bd for me as I planned my UK holiday round it.

Anyway onto October and changes are afoot. Pressure will build to our NW and a northerly theme will dominate the month wth a succession northerly inursions bringing a fairly chilly theme. I am picking up signal for a notable LP system to hit the UK and timing is still unsure but it will likey change the pttern and bring an anticipated miler feel for the latter 3rd of the month. So HP over Greenland and N Atlantic with Troughing over Scandi for first 10 days to 2 weeks [cold] and then a notable storm and then milder for last 3rd.

More updates as we go along but below average CET sub 10C

BFTP

[Glacier Point]

Lots to talk about as we enter October.

First up, September's observed pattern has verified extremely well with the overall autumn forecast height anomalies. This gives a lot of confidence that the base state has been captured really well by the analogues. This gives us confidece that the overall outlook will not deviate far from the autumn forecast.

September so far:-

Autumn forecast:-

If anything, September's pattern bears a close resemblance to Octobers' based on the SSTA composite analogue giving encouragement that we might be 'ahead of schedule' as we approach the boreal winter.

If there was one unexpected during September, it was the strong burst of westerly winds associated with a large amplitude MJO event in Phase 5 which delivered a classic mid latitude response.

http://www.bom.gov.au/bmrc/clfor/cfstaff/m...Last40days.html

This lead to the Global Wind Oscillation moving into phases 4-8, the most westerly projection for some time. What is of interest here is whether this cycle occurs once more or whether we slip back into a more Nina type pattern - which I favour. It is worth noting that ENSO monitors have dropped of late, and subsurface anomalies in the east Pacific continue to suggest a weak Nina for the late winter period:

http://www.bom.gov.au/climate/enso/indices.shtml

http://www.ecmwf.int/products/forecasts/d/...al_time/xzmaps/

Also worth noting from the current SSTA plot is the developing warm anomalies in the central Indian Ocean.

Whilst current outgoing long wave radiation anomalies signifiy low tropical convection in the region (and the global wind oscillation remaining negative for some time), this is likely to stimulate convective activity in the central Indian Ocean. This is likely to teleconnect to a strong mid Atlantic ridge weeks 2-4. This is illustrated by MJO composites for phases 2 and 3:

Looking at the zonal wind and height anomalies over the polar field provides insight into a sub-seasonal trend:

What these show is a tendency for downwelling to occur in the atmosphere - related to the QBO - once more, peaking into December and likely to promote further episodes of northern blocking.

Putting this all toghether, we have a number of different factors all seemingly pointing in one way. The global wind oscillation is likely to orbit through phases 1-4, then 5-8 as easterly wind anomalies are added then removed from the atmosphere:

The GWO composites for these phases set out the evolution of weather patterns - think of this as a model extending for the next 30 days at 3-5 day intervals:

In summary, a variable and often meridional pattern with an unsettled 1st half and then slightly more settled 2nd half of the month before months' end and another northerly. Overall, temperatures close to or slightly below average and rainfall close to average.

Overall forecast upper pattern:

[johnholmes]

can't disagree with that overall idea GP

how about in a shorter term, say 7-10 days ahead?

I'm thinking, in particular, about how deep any subsequent low will be and how far south from the remnants of Hurricane Kyle and the Tropical storm locked in beneath it as they move across the Atlantic?

Edited September 28, 2008 by johnholmes

[Glacier Point]

how about in a shorter term, say 7-10 days ahead?

I'm thinking, in particular, about how deep any subsequent low will be and how far south from the remnants of Hurricane Kyle and the Tropical storm locked in beneath it as they move across the Atlantic?

We should be in GSDM phase space 2 or 3 at that time - the ridge associated with phase 1 holding up the progress of Kyle. This should place an upper low in the eastern Atlantic which edges towards the UK which will likely assimilate the TD. During phases 3-4 this upper low deepens and is likely to be centred as a substantial trough over the UK.

[johnholmes]

tks GP

all very uncertain on the position the two combined systems will have in the vicinity of the UK; 120 hours and all 3 are in fair agreement but after that diverge quite widely

one to watch

[Optimus Prime]

Perhaps surprisingly, Metoffice have somewhat changed their Autumn forecast today, going for near normal or below average temperatures to continue;

http://www.metoffice.gov.uk/weather/seasonal/autumn2008/

[Michael Fishermans Friend]

Perhaps surprisingly, Metoffice have somewhat changed their Autumn forecast today, going for near normal or below average temperatures to continue;

http://www.metoffice.gov.uk/weather/seasonal/autumn2008/

Yeah noticed that - changed from the mild and dry conditions they mentioned a monthor so ago, cheeky! - If November continues in the same vain then perhaps they might back track on winter - maybe?

[0000]

Yeah noticed that - changed from the mild and dry conditions they mentioned a monthor so ago, cheeky! - If November continues in the same vain then perhaps they might back track on winter - maybe?

It seeems very possible Tim