The Australian Weather Forum

Looks Positive to me Gordon.. Latest weekly reading for IOD is +0.58

http://www.bom.gov.au/climate/enso/indices.shtml" onclick="window.open(this.href);return false;

At the top click near the Variable button and click on the down arrow and will give a small list of Nino temps go to the bottom to IOD index time series and will give you the weekly temp

Yes I see what you mean Johnno. When I looked at the graph yesterday the overall trend line seemed downward from about May, but today it has shot back up.

I've had a quick look at the initial output for the next Bureau seasonal outlook for Oct-Nov-Dec due to be issued on the 19th of this month and it's showing an increased chance of drier and warmer than normal conditions over SE Australia (and wetter than normal conditions over western and northern Oz).

From the BOM updated Today...

Pacific approaches La Nina. Positive Indian Ocean Dipole develops.

http://www.bom.gov.au/climate/enso/" onclick="window.open(this.href);return false;

Johnno that seems a bit odd, when NOAA announced last week that we are now in La Nina, are the BOM disputing that claim by announcing we are "approaching" La Nina?
Cheers, Geoff.

Geoff » Wed Sep 14, 2011 7:59 pm wrote:

Geoff wrote:Johnno that seems a bit odd, when NOAA announced last week that we are now in La Nina, are the BOM disputing that claim by announcing we are "approaching" La Nina?
Cheers, Geoff.

BOM are stupid simple as that...

Sorry SupercellImpact , l have to strongly disagree with your comments regarding BOM
BOM employees are highly trained individually and experts in their field.
As a human race none of us can say we have mastered the intricacies of the weather or in fact any Science.
Expecting perfection from BOM or NOAA would be unrealistic

So what is the standard criteria for calling a La Nina.? Is it defined by the World meteorological organization or does each country have its own definition .

PS. I've started to save for water cartage this spring/summer..LOL..seriously

Geoff » Wed Sep 14, 2011 6:59 pm wrote:

Geoff wrote:Johnno that seems a bit odd, when NOAA announced last week that we are now in La Nina, are the BOM disputing that claim by announcing we are "approaching" La Nina?
Cheers, Geoff.

NOAA said that the La Nina had developed in the northern tropical Pacific Ocean. It didn't say that a La Nina had developed in the Southern Hemisphere. Just clarifying that.

This article defines a La Nina as
"A sustained SOI above +8 usually indicates the presence of a La Nina event. "

http://www.dtnprogressivefarmer.com/dtn ... 3809f80221" onclick="window.open(this.href);return false;

I believe the Americans measure it interms of the ssts anomalies along the Equator as there prime reason while the BOM take more into account the SOI and longterm trend of it being there 1st factor

Yeah sorry Crikey I didn't think of it that way.

No worries Supercellimpact. I admit l have in the past been somewhat critical at times. It wasn't until l tried to understand the weather myself ,that l came to realize the complexities involved in forecasting. LOL

Anyway ..found this excellent article on La Nina returning and its impacts on the US.
I thought a La Nina was just a rain event
but this article describes the havoc a la Nina can cause for hot, cold , wet and dry etc.in the US in particular . I don't know if a La Nina can cause droughts in Australia?
This article was an eye opener for me!. It is titled
The Return Of La Niña Is Bad News For Drought Stricken Southern USA
Just a few snippets below but go to the link for the remainder of article
La Niña, one of the primary contributing factors to extreme weather around the globe during the first half of 2011, has re-emerged in the tropical Pacific Ocean and is forecast to gradually strengthen and continue into winter.

Forecasters from the National Oceanic and Atmospheric Administration (NOAA) have upgraded their La Niña Watch to a La Niña Advisory.

The strong 2010-11 La Niña contributed to record winter snowfall, spring flooding and drought across the United States, as well as other extreme weather events throughout the world, such as heavy rain in Australia and an extremely dry equatorial eastern Africa.
...
Mike Halpert, deputy director of NOAA’s Climate Prediction Center said: “La Niña also often brings colder winters to the Pacific Northwest and the northern Plains, and warmer temperatures to the southern states. This means drought is likely to continue in the drought-stricken states of Texas, Oklahoma and New Mexico”.
http://www.irishweatheronline.com/news/ ... 37640.html" onclick="window.open(this.href);return false;

Johnno basically summarised it correctly. NOAA determines La Nina's and El Nino's based on the SST anomalies in the central/eastern Pacific (in the NINO regions) while the Bureau doesn't quite have such a concrete criteria/thresholds. At the end of the day, the difference is somewhat academic. Both organisations have assessed that there has been some cooling in the central/eastern Pacific consistent with the La Nina side of neutral. One of the other reasons why NOAA is leaning more firmly towards a La Nina is because their climate model, CFS has been more optimistic of a stronger La Nina event than others.

Also, the ENSO cycle is one of the biggest oscillations in the climate system and not only affects Australia but many other regions like the western and southern US, South America, parts of eastern Asia, etc in different ways such as tornado activity, enhanced or decreased rainfall and temperatures, etc.

The coming La Nina is not good news for eastern Africa. They need rain desperately.

The 4-week EC ensemble probability forecasts are currently showing very faint "wishy-washy" chances of wetter than normal conditions across southern parts of SE Australia sometime during the 26th Sep - 2nd Oct period. The uncertainty is pretty high though. This is associated with moderate probabilities of lowering pressures showing up across central, south and southeast Oz.

What's more interesting is its suggestion of stronger probabilities of colder temperatures spreading across an area of eastern Australia including southern QLD and NSW early/mid next month (although VIC isn't currently included in this area of stronger signal). It's also suggesting lowering pressures near or off the east coast around then. However even the EC ensemble can be somewhat hit and miss at this range so not something to hold breath over just yet.

Thanks for the insight into model predictions Ken
Noticed the length of the cloud fronts in the southern hemisphere have increased in length and thickness over the past week,( re: metoffice world sat pic B&W) . They are up to about the 25 deg latitude mark approx atm.
Possibly related to a double node (2)of neg SAM which is currently at neg 2.3 atm as Johhno suggested
Maybe when the fronts are longer or extend further north,they can capture more moisture from the equatorial zone to return poleward. Therefore more moisture available .
In relation to cold signature for SE Queensland and NSW and a low pressure signature. It sort of reminds me of the status quo.
Massive ( large) highs in the Tasman drawing in Polar air on their eastern flank and more ECL's. or tasman lows in between those massive highs .
In other words. Pattern not changing.?

All the main models are diverging widely for the coming weekend and onwards. GFS says inland heat low with moisture pumping in from the East, BOM has high pressure dominance, EC has a monster cutoff low in the Bight...

Just finally got some time to have a really good look around. Been insanely busy and still keep an eye on things on here and weatherwise.

I think we are going to cop it all over again. Seen a distinct shift this week in the models, and despite the +IOD its looking ominous for the next 6 months. I know its hard to imagine topping last year but i dont think its out of the realms if all lines up. Especially considering the upper troughs are stronger again this year due to the Earth cooling. We have seen some remarkable weather in the last 18 months, but none more remarkable than what we are seeing in the last 2 weeks.

Just think, Dps have been almost negative for the majority of the last few months through the interior, and the weather refuses to transition into normal spring patterns in mid Sept as it usually would. So, with the IOD against us, we have an anomalously warm patch in the southern Indian introducing mositure in to the Westerly wind belt, thus strengthening precip for the mainland when one would expect a dry period. The water vapour satellite holds the key, quite clear that moisture is finding a way to deliver extreme storms through a great portion WA, and also Sa and Vic.

And this is without even talking about the La nina yet, which is going to be strong again, as i forecasted many months ago, and may even go triple dip, which i will confirm in the next few months. Next month is critical to this outcome, by the end of October i will confirm my position, but at this stage well above avergae rainfall for Vic, and much more punishing storms because i dont think the mid layers will be saturation point like last summer. No coincidence tornadoes have been sighted regularly the last few weeks.

I don't have any technical insight to add, but I did read in the paper the other day (can't remember which one) that the BoM are expecting "above average" activity in regards to severe storms in Victoria this Spring/Summer.

Edit: Just came across this map, which doesn't really confirm anything, but I'm sure some people will find it interesting to look at...

Anthony Violi wrote:So, with the IOD against us, we have an anomalously warm patch in the southern Indian introducing mositure in to the Westerly wind belt, thus strengthening precip for the mainland when one would expect a dry period

Agree Anthony, I've been trying to get peoples attention to this for a while now, the wet season storms over Africa are flooding the westerly belt with moisture, which is carried directly across to us, just look at this WV loop, it's been like this for a few weeks now...
http://www.ssec.wisc.edu/data/geo/index ... thod=flash" onclick="window.open(this.href);return false;