Shortening days, good diurnal temperature range with cool/cold minima and a lack of wind are optimal imo.

Sydney neither has cool/cold minima nor calm conditions in autumn, which is why we really don't see colour here.

Horticultural sites often speak of "chilling time"- the amount of hours below 7C a plant needs to produce fruit etc. Perhaps autumn colour is dependent on a certain amount of "chill time"

For the best in autumn colour you need a wettish summer without too many hot dry windy days that can wreck foliage on soft-leaved deciduous trees, followed by a dry-ish Autumn that has lots of calm sunny days and cold clear nights.Ideally with temps falling repeatedly below 6 or 7 degrees. If you can luck it in for a couple of early frosts then that is when the colour will be truly spectacular.
We had a really chilly Autumn here in 06 i think it was and the colour was fantastic, the last couple of Autumns have been ordinary, too wet in early Autumn and cloudy nights that dont allow the temp to drop.

Interesting you mention a wet summer and my 7C mark as well. I think you're a cool climate horticulturalist/gardener so I'll hand the floor to you avalon:).

Models bring back warm (but not hot) weather at the end of next week, maybe summers' " Cheyne-Stokes stage.

just my observations from many years. lately i have been thinking that it really has a lot to do with sunlight in Autumn and shortening daylight hours. Its hard to say what actually has the biggest positive effect on Autumn colour.
You can see deciduous trees growing in places like Thredbo Village where they have summer temps that are as cold as Melbournes winter temps, yet the trees keep there leaves on and grow. It must have more to do with the shift in seasonal temps than just getting low overnight temps. If that makes sense?

Anyhow, i hope we get a good one this year.

Yes I know it has to be a combination of factors. My observations make me feel that drier late summer weather and early Autumn dryness help. Sometimes you see changes come noticeably earlier in drought conditions (or so my twisted memory thinks).

I think it was Blizz tracked down some really good info on this last year in the Autumn thread I started back then - worth a look.

A very autumnal feel here in Walcha this morning with a foggy 1.9 degrees (2.8 at Salisbury Plains). Plenty of deciduous trees have decided to prepare themselves for winter- some in full colour.

Wow Ron, I did not see that coming. Just the usual cold foggy drizzly here but no clear sky above like you.
Quite cold yesterday with a range of 6.9 to 12.8.
Geez I hope this Autumn is at least dry and sunny, really badly need that before winter hits.

Good effort there Ron

Your neck of the woods is definitely frostier than here in Bathurst.

PD - today won't be any better I suspect. We had a bit of a spit here was all - nothing exciting.

I'm sure there'll be an Indian summer to enjoy at some stage, even I would like a bit of sun now as the UV gets a little less intense. 106 mm here overnight- a bit more than a spit over this side.

I hope to take a trip to Walcha this winter, would like to experience a -10C morning and hopefully some freezing fog too.

Certainly feels like autumn on the NSW coast.. oh what i would give for a 25C+ day, there were plenty of those in recent years at this time of year, now we're sitting on 15C (as is most of syd)

Won't have to wait too long Boris. Tomorrow will easily exceed 25C, 30C may be given a nudge in parts of Sydney as the low moves off. OCF still calling for a full day of sunshine and 28 deg, whilst GFS has 850 temps up to 12-13 and westerlies for most of the day. Not complaining as we could use a little bit of a dry out.

Most of next week will also be at or above 25 deg. Autumn might be creeping in on the tablelands but Sydney and the coast must wait till April. Might be 15 deg now but this is in the middle of an ECL, much like Darwin drops to the low 20's in the middle of the monsoon. In short- it's a temporary anomaly.

I dont see how we'll exceed 25C let alone 30C with these southerlies sticking around til monday not to mention chance of showers on various days of the forecast.. we'll see what happens anyway, certainly hope your right William.

The very coastal fringe will be quite different (esp overnight) to places like Windsor etc as Autumn goes further.

Inland will have warm to even hot days still but nights out there will start to fall a bit.

Yep, Windsor although still technically on the coastal plain is not as affected by the prevailing SSTs. Also they are coming from a higher base, where 30C is the average summer maximum (but not this summer), so March usually feels significantly cooler for them.

Currently just below 20 deg with a fresh westerly wind, that is autumnal but won't last long. For seasonal change there has to be a clear and defined change in prevailing conditions i.e. not a flash in the pan. March can see plenty of 'flashes in the pan' but the real change is in April (I'd argue that for Bathurst too).

Sorry SB - the whole feel of somewhere like here changes late Feb early March. It's VERY different to the coast, where the time lag of the change is many times greater.

How it feels now is a world away from 3 or 4 weeks ago. We will still get days over 25 (only a few) but the nights have turned a noticeable corner, morning has a real coolness and sometimes a slight chill. Evenings cool off much more quickly now. We are going to have increasing nights of single digits (already had a few) and not getting above 10 to 12 much at all.

Talk to pretty much anyone out here and they will say that Autumn has begun even without knowing the numbers, the FEEL has changed noticeably.

April - yep changes even more once the Equinox is gone but March is a drop of approx 3 to 4 degrees in max and about 3 to 4 degrees min - that's a noticeable change.

Guess we'll have to agree to disagree on this one

The standard for autumn in Bathurst is obviously a lot cooler than Sydney, I'd argue 'true' autumn there starts with the first ground frost or at least a string of mornings below 5C. Single figure mornings are still quite common on the tablelands (though scattered) in Jan and Feb, Goulburn Airport got down to just below zero in that cold change in January. For Sydney, my standard is when you no longer sweat of a night time- to put a temp value on it maybe sustained minima below about 16C/60F.

I categorise March as somewhere between summer and autumn- 'summer lite' or 'pre-autumn', yes there is a change from high summer (Jan and Feb) but I wouldn't call it true autumn. Again, just my viewpoint .

Anyway debates like this are ultimately pi$$ing into the wind a little as Mother Nature will do what she wants as we all know.

I am still struggling with Sydney's forecast of 27 for today?. Yet Sunday they have only 23?. I would have said 25 for both days.
Yes a clear early autumn feel now, maybe pre-autumn before the proper autumn. A few leaves starting to turn colour a bit more over the past week, clearly the colours are beginning on some trees although still very much early stages and many trees that have not noticed anything yet as well.
Temps on most nights now 10 or lower as well while mostly above 10 before.

Winds will be westerly today and SE'ly on the weekend. GFS has 850 temps up to 13 this afternoon, with clear skies 27 should be easily reached and probably exceeded, I'm going for 29C-30C across the Basin this afternoon.

Agreed RE: Sydney's forecast max. Maybe 27-28 out this way but in the city i just dont see it happening. Happy to be proven wrong though after such miserable weather all summer.

Definate Autumn feel this morning. Heavy dew, 12c min, fog in the west with a clear sunny day and max's in the mid 20's. Couldnt be more Autumn if it tried!

Yes, classic autumn this morning but it's a teaser: as I've said above March offers a preview of autumn but most of the month is generally warm without the heat of Jan and Feb. Looking at Sydney more closely, average temps are pretty much the same in December and March, and decile 1 maximum temps do not fall below 20C until April:

http://www.bom.gov.au/climate/averages/tables/cw_066062_All.shtml

Autumn should bring the chance of cooler (sub 20C) days for Sydney, and sub 15C days for places like Bathurst and Canberra.