Indian Ocean Dipole starting to strengthen a tad towards a negative phase.
Southern Annular Mode (SAM) in positive territory this week
ENSO outlook starting to shift towards a cool neutral for years end.
Most climate agencies are beginning to release their upcoming outlook for the remainder of June and for the rest of winter in the coming week so will have a larger write up on that when it is released.
For now we are sitting in a real wintry mix with the very negative SAM from late last week impacting the nation at the moment with very cold air over much of contiguous Australia.
Rainfall has been plentiful during the last week in response to the SAM being active and copious moisture being drawn in from the Indian Ocean.
Some climate agencies claim that we are already in a negative IOD phase, and given the last few weeks of persistent moisture intrusions from the northwest, it is not unreasonable to call it that way. I am still on the side of it being cool neutral, I need a few more weeks before we call it a negative event. But those that need or have needed rainfall, it has been a productive week for many locations.
The ENSO outlook is also of interest with some climate agencies suggesting a weak La Nina may redevelop over the Pacific Ocean with that potentially bringing another wet end to 2021 and start of 2022. Back to back La NInas are not uncommon after a long absence. Watch this space I guess.
Rainfall Outlook for the coming 4 weeks - Valid Wednesday June 9th - Period 10th of June to 7th of July 2021. % chance of exceeding the median rainfall for this period against climatological averages.
The trend for more moisture to work it's way from the Indian Ocean through the central interior into the southeast is becoming more likely, especially when the SAM is negative and allowed to pull the moisture in via strong cold fronts surging north, as we have seen in recent weeks. The north of the nation has a lower chance of exceeding rainfall, but it is dry season so it is no issue. QLD is tricky in that some moisture may be drawn across the nation toward the end of this viewing period, with better odds of rainfall returning to central and eastern inland areas over latter winter into spring.
Temperature Outlook for the coming 4 weeks - Valid Wednesday June 9th - Period 10th of June to 7th of July 2021. % chance of exceeding the median daytime temperatures for this period against climatological averages.
It has been a cold year so far over southeast and southern Australia with below average temperatures spells being the norm for a lot of this year. I do think that will persist as we track into the remainder of June and into July with further cold fronts coming up from the south and from the west. A blocking pattern for the next 7-10 days will keep the temperatures below average, upper heights colder than normal and high pressure weaker than usual, so the procession of seasonal to below seasonal temperatures looks set to continue. Marginally warmer days over the north, that will be in line if there are any moisture build up via a weakening of the easterly or southeasterly flow pattern over the north.
Lets take a look at the RAW data from the modelling.
Euro for the next 4 weeks shows that wet bias with the resolving low pressure system over southeast Australia early in the period bringing those above average values, that will clear through the weekend. Interesting signals persist for the northwest and west of the nation with above average rainfall possible, but this is the peak of the wet season for WA so looking good for rainfall to be at least average for many areas. A dry look continues for the QLD region which for the most part is not unusual given the current climate drivers and the phase at this time. Dry over much of TAS is very conditional and reactive to the short term weather situation and I do believe that above average rainfall will return to the west and north of TAS in line with westerly winds returning.
Euro ensemble forecast - Next 4 weeks, rainfall anomalies. Valid Tuesday June 8th 2021
GFS also showing that wet bias over the southeast of the nation, and also cranking up falls for inland QLD with an upper trough, but since this update the trough looks weaker and more shallow, so I think this outlook is not as reliable as the Euro, which has performed quite well over recent months in picking large scale rainfall events and anomalies ahead of time.
GFS ensemble forecast - Next 4 weeks, rainfall anomalies. Valid Tuesday June 8th 2021
Temperatures are largely unchanged from the previous update, sticking with the Euro again with a much colder look for the nation, that has verified well against present and past observations with record cold nights, near record June days over recent times with that cold snap. GFS running a little too warm for my liking but it doesn't have the resolution as per the Euro. But always good to compare and contrast.
Euro ensemble forecast - Next 4 weeks, temperature anomalies. Valid Tuesday June 8th 2021
GFS ensemble forecast - Next 4 weeks, temperature anomalies. Valid Tuesday June 8th 2021
The climate drivers.
The Indian Ocean is of interest to me this update. We are seeing a strengthening of the negative phase in the Indian Ocean over the coming months, leading to the climate models pinging above average rainfall.
That is all good and well, but as I say often, we need a lifting mechanism to utilise the moisture, rather than having inactive large scale cloud bands drifting over much of the continent with no bang for buck from those features. So the forecast for now should be treated with that in the back of your mind.
However in recent times, and I contrast the above by saying, the seasonal frontal weather and troughs that have come through thus far into the season, usually give a good indication as to how the season will continue and it is progressively becoming wetter over southern and eastern Australia. We have seen a return to more regular rainfall over SA and inland NSW with the southern wet season ramping up, not relying on the troughs and tropics anymore. That is something also to consider.
Below is the latest outlook from the BoM relating to the Indian Ocean Dipole. They have it already into negative territory and deepening it further through July and now protracting through our spring time, in line with other global model agencies.
BoM POAMA model outlook for IOD region - showing that negative track through winter into spring before neutralising through late spring. That will bring up the rainfall chances.
The global model outputs suggest that in line with the BoM model remaining at negative values through the spring, CanSIPS and Euro, even UKmet coming towards a negative phase and the overall mean is trending further and further into negative territory. But forecast skill during this time is LOW.
Global Model Summary for the IOD region - September 2021.
The overall trend of a negative phase into October remains similar with a weakening of the IOD likely by the time we hit November into December which is generally in line with the start and onset of the northern wet season, quite normal. Forecast confidence is LOW.
Global Model Summary for the IOD region - September 2021.
So how does this play out on the climate models in terms of precipitation moving forward?
Well the ever reliable Euro model, which has the higher skill scores does bode well for those wanting rainfall during the winter and spring, though in all things, it is mixed blessings to have rainfall through spring time.
Seasonal Outlook - JAS - Rainfall anomalies for the Australia/Asia region.
Wet bias over much of the country, with the chance of more rainfall picking up from mid June onwards through August and then September as the IOD at this stage is forecast to peak. That would bring a cooler and wetter few months to most of the inland up to the western face of the Great Dividing Range in NSW.
Seasonal Outlook - ASO - Rainfall anomalies for the Australia/Asia region.
The wet signal ramps up for the August to October period, in line with the global modelling peaking the IOD through this period. The SAM is also important during this time as it could play a part in drawing in the warmer more humid air as the north of the nation warms, and then that air clashing with the bitterly cold southern ocean airmass. That may produce more dynamic inland weather events, with more moisture, more chance of rainfall. Perhaps....
Seasonal Outlook - SON - Rainfall anomalies for the Australia/Asia region.
Still a wet signal for much of the nation and note the values over northern Australia are elevated perhaps signaling an early start to the wet season once again with the IOD in negative phase and the Pacific trending towards La Nina values, that is something to watch as we go through the coming months. We saw the impacts of how much rainfall fell during Summer just with the La Nina.
Seasonal Outlook - OND - Rainfall anomalies for the Australia/Asia region.
Rainfall signals are weakening a tad but still above average through many areas, with the summer rainfall season kicking off over the north, the build up could be productive. La Nina may be called and peaking during this time, so if that is the case, this product would be housing a lot more green on it and with the IOD weakening, this may too contribute to better rainfall odds for the remainder of 2021 into 2022.
So there are some interesting signals in the Indian Ocean, positive for those who want rainfall for the last half of the year. I personally think it is better going into the hot season with more moisture in the ground so one can hope it can be productive on that account.
The ENSO outlook remains equally as interesting with the Euro model trending cooler and cooler each update. This model did pick the La Nina event quite early last year. It is similar to last year in that it is heading in that direction again. JMA (the Japanese weather agency) also signals a La Nina as does the highly reputable IRC outlooks. So I am still going with the neutral forecast for now, but it may shift in coming weeks.
Euro ENSO outlook for the remainder of 2021. Note most all members pop into negative territory with only a few above the positive line, which is a different look to a month ago.
So the short term take away is more of the same for Australia in the next 4 weeks, I think what you have experienced over the past few weeks, likely to be the case for the best part of the next 4 weeks but there are rumblings for a negative IOD and talk of La Nina developing end of this year.
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