September CET

[stormchaser1]

Morning everyone

12.6c for me please

stormchaser1

[Mr Sleet]

One warm spell for Sept , 25-30 C for three days only.

Slightly below average for me, 13.5C.

[Glacier Point]

September - a tricky call with noted significant recent trending for much above average returns but more recent August form offering a more average outlook.

Statistically, a month for neutral Arctic Oscillation (AO) conditions to likely prevail with 59% of all Septembers since 1950 falling within the neutral bandings (+0.5 > -0.5), and a slight preference for -ve conditions if not with 19% of these recorded.

Recently, the AO has shown a neutral to -ve tendency with notable height anomalies since the end of August:

http://www.cpc.ncep.noaa.gov/products/prec...hgt.ao.cdas.gif

I suspect that with the cooling of the Pole we shall see this reverse, but for the first week to ten days I suspect this pattern to continue. The composite anomalies for the September AO look like this:

http://www.cpc.ncep.noaa.gov/research_pape...ASO.z500.ao.gif

The North Atlantic Oscillation (NAO) is strongly lead by the AO during this month:

http://www.cdc.noaa.gov/Correlation/Table/corr.table.sep

whilst the oceanic sea surface temperature anomaly (SSTA) signal for the NAO remains negative with strong anomalies in the northern sector and less warm anomalies over the sub-tropical region.

This leaves the door open for a SSTA-driven month which is now being influenced on a broader hemispheric scale by a weak El Nino:

Note also the arrangement of the North Pacific anomalies likely to induce an amplified flow pattern which will vary the Pacific North America (PNA) +ve and -ve as the waves are propogated eastwards resulting in ridge - trough sceanarios on the Eastern Seaboard of the USA.

Conditions in the Atlantic remain much the same as they did in the early Summer with a notable warm SSTA to the west and cooler SSTA to the east and south favouring a western ridge-eastern trough scenario in the jet with low pressure to our SW.

There are not many Septembers to allow a robust composite anomaly analysis, but for what it's worth, a weak El Nino (and for that matter neutral conditions) favour a strongly meridional pattern with the jetstream and Azores high pushed SW into Atlantic, but with a ridge solution over Scandinavia. This leaves the UK in a warm SW'ly airstream.

This solution fits quite well the likely SSTA drivers so I'll give the greatest probability to a neutral or even weakly -ve AO and NAO to prevail within the context of ridge-trough in the jestream over the Atlantic leading to an increasing ridge developing mid to late September over Scandinavia and shallow trough to our SW which will no doubt draw some warmth from ex-tropical depressions. This will be tempered somewhat by the continued low latitude ITCZ and -ve phases of the AO.

The sea temperatures to our SW remain much above normal, so given this and the prospect of some late September warmth, I'll go for a CET return of 1.2 above.

14.9 C for me thanks. GP

Edited August 30, 2006 by Glacier Point

[reef]

15.3°C for me, expecting average to warm maxima and high minima.

[SMU]

September - a tricky call with noted significant recent trending for much above average returns but more recent August form offering a more average outlook.

Statistically, a month for neutral Arctic Oscillation (AO) conditions to likely prevail with 59% of all Septembers since 1950 falling within the neutral bandings (+0.5 > -0.5), and a slight preference for -ve conditions if not with 19% of these recorded.

Recently, the AO has shown a neutral to -ve tendency with notable height anomalies since the end of August:

http://www.cpc.ncep.noaa.gov/products/prec...hgt.ao.cdas.gif

I suspect that with the cooling of the Pole we shall see this reverse, but for the first week to ten days I suspect this pattern to continue. The composite anomalies for the September AO look like this:

http://www.cpc.ncep.noaa.gov/research_pape...ASO.z500.ao.gif

The North Atlantic Oscillation (NAO) is strongly lead by the AO during this month:

http://www.cdc.noaa.gov/Correlation/Table/corr.table.sep

whilst the oceanic sea surface temperature anomaly (SSTA) signal for the NAO remains negative with strong anomalies in the northern sector and less warm anomalies over the sub-tropical region.

This leaves the door open for a SSTA-driven month which is now being influenced on a broader hemispheric scale by a weak El Nino:

Note also the arrangement of the North Pacific anomalies likely to induce an amplified flow pattern which will vary the Pacific North America (PNA) +ve and -ve as the waves are propogated eastwards resulting in ridge - trough sceanarios on the Eastern Seaboard of the USA.

Conditions in the Atlantic remain much the same as they did in the early Summer with a notable warm SSTA to the west and cooler SSTA to the east and south favouring a western ridge-eastern trough scenario in the jet with low pressure to our SW.

There are not many Septembers to allow a robust composite anomaly analysis, but for what it's worth, a weak El Nino (and for that matter neutral conditions) favour a strongly meridional pattern with the jetstream and Azores high pushed SW into Atlantic, but with a ridge solution over Scandinavia. This leaves the UK in a warm SW'ly airstream.

This solution fits quite well the likely SSTA drivers so I'll give the greatest probability to a neutral or even weakly -ve AO and NAO to prevail within the context of ridge-trough in the jestream over the Atlantic leading to an increasing ridge developing mid to late September over Scandinavia and shallow trough to our SW which will no doubt draw some warmth from ex-tropical depressions. This will be tempered somewhat by the continued low latitude ITCZ and -ve phases of the AO.

The sea temperatures to our SW remain much above normal, so given this and the prospect of some late September warmth, I'll go for a CET return of 1.2 above.

14.9 C for me thanks. GP

Nice post GP-

I like the linear correlation of the AO to NAO of 0.7 for Sept-

have you got the link for the Winter years- Cheers........

edit- just edited the link...

Steve

Edited August 30, 2006 by Steve Murr

[cheeky_monkey]

simply because no one else has pick it..im going 4 lonely old 13.4c

[PhilipEden]

An early steer on Not The Long Range Forecast suggests 14.5°C

Philip

[summer blizzard]

Tinybill: 11C

Stormchaser1: 12.6C

SteveB: 13C

Snowmaiden: 13.1C

Cheeky_monkey: 13.4C

Optimus Prime: 13.5C

Steve Murr: 13.5C

Mr Sleet: 13.5C

Hiya: 13.6C

Snowyowl9: 13.7C

Beng: 13.8C

AtlanticFlamethrower: 13.9C

The Abominable Snowman: 13.9C

Bottesford: 14C

Snowman2006: 14C

Ian Brown: 14C

Stargazer: 14.1C

kold weather: 14.2C

Shuggee 14.3C

Windswept: 14.4C

Anti-Mild: 14.4C

Nick F: 14.4C

Tugmistress: 14.4C

Wilson: 14.5C

PhilipEden: 14.5C

Stratos Ferric: 14.6C

Northern Light: 14.6C

Bham Chris: 14.7C

Stricklands: 14.7C

ScandiHigh: 14.7C

Senior ridge: 14.7C

Great Plum: 14.8C

AtmosFear: 14.9C

Terminal Moraine: 14.9C

Glacier Point: 14.9C

Roger J Smith: 15C

Blast From The Past: 15.1C

Summer Blizzard: 15.2C

Reef: 15.3C

Scorcher: 15.4C

The PIT: 15.5C

Rollo: 15.6C

Kippure: 16C

I have added in the CET predictions...

Glacier Point, i agree broadly with your analysis however my reading of the sea surface temperature anomoly charts seems to indicate winds from a dominant easterly quater as opposed to westerly.

Also, the seas to our south west are below average, not above, the feedback mechanisms of the recent cooler weather have wiped out the warm anomoly in the vicinity of Spain.

[Glacier Point]

Glacier Point, i agree broadly with your analysis however my reading of the sea surface temperature anomoly charts seems to indicate winds from a dominant easterly quater as opposed to westerly.

Also, the seas to our south west are below average, not above, the feedback mechanisms of the recent cooler weather have wiped out the warm anomoly in the vicinity of Spain.

The upper level anomalies might suggest an ESE type flow, but I think with a shallow trough out to the SW and jet flow strong to the south in particular, the lower levels would largely be SSW'ly overall. The current SSTA show a couple of hundred miles draw of air 0.5 - 1 C above to the SW whilst a mean trough there could only result in abvove average conditions I think.

[Cymru]

Hope I'm not butting in here as a new poster but I'll go for 14.6

[J10]

I'll go for 14.2c

[Anti-Mild]

Hope I'm not butting in here as a new poster but I'll go for 14.6

Welcome to the forum Cymru. Because you're new I'll let you off but traditionally our Welsh members get the last of the options in the CET threads !

[shuggee]

Hope I'm not butting in here as a new poster but I'll go for 14.6

Hi and welcome to posting on the forum Cymru

Enjoy!

[Cymru]

Thank you for the welcome Anti-Mild and shuggee Much appreciated.

I've been reading this forum for months now, since last Winter in fact. I must confess, I prefer Summer to Winter myself but judging by how busy it gets on here in the Winter there are lots of folk who prefer the colder months. I'm a bit of a novice myself when it comes to the weather but have picked up a lot of knowledge from this site.

Thanks again guys!

[Mr Maunder]

I'll have a guess at 14.3c

MM

[Michael Fishermans Friend]

Well I'm a big believer in sequences when it comes to CET's month by month so as we have just had one near normal September is bound to be above average! So I'll pip for 15.2C

Tim

[Thundery wintry showers]

15.5C.

[Guest Viking141]

Im going to have a punt at 13.6C.

Incidentally, talking of temps last night it was only 7C in Lerwick which is already cooler than most of September last year apart from the 17th which was 6.5C.

[Scribbler]

The last time September

..was warmer than August

1956 Aug 13.5 Sep 14.3

Uh Hm! According to the Manley CET figures, (borrowed from Philip Eden's www.climate.uk) September 1985 was just warmer than the August of that year - 14.74 to 14.62.

It would be nice to see this year follow suit but despite it being a "rotten" August it would still need a record-breaking September to do so.

Therefore, calculating that we won't be having a record-breaker, and having sucked on my old piece of seaweed, I proffer 14.9 as my figure for the September CET

[MP-R]

I would say about 14.5C. It's already been a warm start to the month here and with another warm week to come it should keep the CET up. The end of the month looks cooler though.

[Summer of 95]

15.2C for me

[STEVE M]

I'll go for 14.8

[snowsure]

Not sure if I am displaying correct etiquette here but I have a question.

What would be deemed as a "suitable" CET for September? What range of temperatures is classed as normal?

If this could be decided now it could stop the later discussions of "this month was/wasn't a freak."

Just a different angle I suppose.

Can I offer 13.9oC to the list of guesses scientifically calculated CETs?

[Stratos Ferric]

Not sure if I am displaying correct etiquette here but I have a question.

What would be deemed as a "suitable" CET for September? What range of temperatures is classed as normal?

If this could be decided now it could stop the later discussions of "this month was/wasn't a freak."

Just a different angle I suppose.

Can I offer 13.9oC to the list of guesses scientifically calculated CETs?

Interesting question. Why would you want to close off that discussion now? In any case, I think the answer has to be "it depends". Various posters have already cited typical CET, and generally speaking (though this is actually mathematically imprecise) about +/- 0.5C would be considered "about normal". Outside this it's either cold or warm, but such is the nature of averaged outcomes, and the infinite ways they can be arrived at over a month, that until you have seen both "what" and "why" it's impossible to decide in advance what might constitute a freak.

If we were writing an insurance policy and seeking to minimise risks I could see the point of the question. But we're not, so why close out what is in any case the unlikely event of potential for interesting discussion in this specific regard?

[snowsure]

Interesting question. Why would you want to close off that discussion now? In any case, I think the answer has to be "it depends". Various posters have already cited typical CET, and generally speaking (though this is actually mathematically imprecise) about +/- 0.5C would be considered "about normal". Outside this it's either cold or warm, but such is the nature of averaged outcomes, and the infinite ways they can be arrived at over a month, that until you have seen both "what" and "why" it's impossible to decide in advance what might constitute a freak.

If we were writing an insurance policy and seeking to minimise risks I could see the point of the question. But we're not, so why close out what is in any case the unlikely event of potential for interesting discussion in this specific regard?

A constraint now would stop hindsight rationalising.

I do not think I am alone when I say that rebutals that use "if only..." arguments seem a little impotent.

I note your own stab at the CET, so anything +/- 0.5oC of that would generally surprise you. Noting the way that the climate is warming, anything that is less than the 1961-90 mean would surprise many people.

The only risk-minimising I am doing is possibly preventing the circular arguments that appeared on the August CET thread. That stopped being "interesting" for me and I think, again, many others.