The Australian Weather Forum

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Latest 3 month rainfall outlook is out by the BOM for Winter updated Today May 22nd and good to see that BOM are now baseing their forecasts on dynamical models instead of statistical models like they always have in the past this is the first time they have made this change.

Key elements from this outlook by the BOM

A wetter than normal season is more likely for large parts of northern and eastern mainland Australia

Chances of above or below normal rainfall are roughly equal over southern WA, Tasmania and parts of the tropical north

Climate influences include a warmer than normal eastern Indian Ocean, a neutral tropical Pacific, and warm local sea surface temperatures

Outlook skill is moderate over southern WA and the northeast half of Australia.


Details
The chances of above-median winter rainfall are 60 to 70% over a broad area of Australia extending from the northwest across to the southeast (see map above). Such odds mean that for every ten years with similar climate patterns to those currently observed, about six or seven years would be expected to be wetter than average over these areas, while about three or four years would be drier. However, it should be noted that over the tropical north of Australia, it is seasonally dry at this time of year. The median rainfall at many tropical locations is between 0 and 1 mm for June to August, and even a small amount of rain would exceed the median.

Over the rest of the country, the chances of a drier or wetter winter are roughly equal.

Climate influences
The tropical Pacific has remained ENSO-neutral since mid-2012. Climate models surveyed by the Bureau of Meteorology suggest sea surface temperatures in the tropical Pacific Ocean are likely to sit on the cool side of neutral during winter 2013.

Four of five international models surveyed by the Bureau favour the development of a negative Indian Ocean Dipole (IOD) event sometime during winter-spring 2013. A negative IOD during winter-spring increases the chances of above normal rainfall over southern Australia. This is reflected in the rainfall outlook, with much of southern Australia expecting above normal rainfall.

Warmer than normal ocean surface temperatures currently surround much of the continent. Warmer ocean temperatures can provide more moisture to the atmosphere, which in favourable weather conditions (e.g., interactions with fronts or northwest cloudbands) may result in increased rainfall.

How accurate is the outlook?Outlook confidence is related to how consistently the oceans and broadscale climate affect Australian rainfall. During winter, model accuracy shows the outlook to be moderately consistent over the southern half of WA, most of the NT, Queensland and northern NSW. Elsewhere, the effect is only weakly to very weakly consistent (see further details below).

Climatologists will continue to monitor conditions and outlooks closely for any further developments over the coming months, with information on the likelihood of El Niño available fortnightly at the ENSO Wrap-Up. For a summary of Pacific and Indian Ocean outlooks, please see the Climate Model Summary.

I think we are tending wetter and cooler into the second half of this year with widespread moisture feeds coming from the Indian Ocean and near La Nina conditons in the Pacific come the end of year. We could go full blown La Nina but have to wait and see what the warmer water towards the Phillipines does and whether a Kelvin Wave or two gets it over to the South American area and suppresses the cooling.

Bering Sea looks cold so the cooling will continue and the depths from where the cooling is coming from is still looking good.

We will have to wait and see, however with the SAM going negative and the Indian Ocean providing above average rainfall, there will be some monster systems across the country over the coming couple of months while the Pacific sorts itself out for our potentially wet and humid summer.

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Thanks for posting that Johnno. It is certainly looking very interesting the coming 6 weeks. How much more rain can the north get out of this current setup is anyones guess.

For us in the southeast expect more of these humid conditons which may save us from a dry cold winter however elevate temps and reduce the ski seaon a touch.

The current GWO/MJO is looking ominously similar to June 2010. I think the odds are now very much in favor of a fully blown LaNina by Spring this year. Combine this with a Negative IOD and we could be looking at 2010/11 all over again...

http://www.esrl.noaa.gov/psd/map/images/gcm/gwo_40d.gif" onclick="window.open(this.href);return false;

Yes Strato it does look eerily familiar doesn't it? You would think all the signs are there for another drenching if it goes the same way as 2010. The current set-up is certainly one of little or no cold air incursion from the south, and all moisture incursion from the Indan Ocean at present, it makes you just feel as if something big is brewing.

Has anyone else noticed that the N/W cloudbands seem to have disappeared recently. At the same time there has developed a curious large cool patch of water in the mid-Indian Ocean, extending to the northwest corner of the country. Do others think this cool water is killing off the tropical infeed to Australia at the momnent? While we have had some reasonable rainfall recently, there certainly haven't been any of the really "big" events that some were predicting and which we could expect with a classic negative IOD setup. A large pool of cold water in the central Indian Ocean is not what I recognise as a classic negative IOD. Others thoughts are welcomed.