A supplement to the outlook issued earlier this week, the latest data sets are now out.
Active frontal weather to continue for the coming 2-3 weeks with a westerly belt moving northwards. Might see a relaxation in the cold fronts in the 3-4 week range.
Indian Ocean to keep warming through the next few months, peaking during October, meaning the wet signal continues from the northwest through to the southeast and east as we go through the next 4 weeks.
Talk of a La Nina developing will not have bearing on the climate during the coming 4 week window but down the track it will play a part in rainfall distribution if it develops in our spring and summer. More on that here.
Rainfall Outlook - Next 4 weeks - Valid Friday July 9th 2021.
The wet signal continues for southwest Australia and extends through to the southeast of the nation over the coming 2 weeks inline with the wetter as we go theory for July. In line with that, we are seeing rainfall graduating further north through the month, along the jet stream with rainfall breaking through parts of outback Australia. Any rainfall through this area will send the rainfall for the month above average so it is no serious feat. The wet signal drags into August, and this is where the moisture may be a little deeper and the flow a lot more wavy bringing in moisture more regularly from the northwest through to the southeast, increasing rainfall chances.
Temperature Outlook - Next 4 weeks - Valid Friday July 9th 2021
Heat levels look to rise over northern Australia from this weekend with a persistent upper high developing, that heat then being trapped over northern Australia for the next fortnight, north of a jet stream. Temperatures cold this week over southern Australia, but I think the heat battle will win out and filter down after next week with more early spring time conditions developing with a wavy flow, large temperature fluctuations and the potential for this to spark widespread rainfall events as the battle unfolds.
THE CLIMATE DRIVERS
Southern Annular Mode - SAM - Neutral
The SAM is remaining highly volatile and the guidance is very poor at the moment. It is likely to trend negative this week with the frontal waves passing over southern Australia, but then from the 3-4th week range, it is uncertain where it will go. An even camp in the models with some going positive and some going negative. So for now it is neutral with a low confidence.
SAM Forecast Tuesday.
SAM Forecast Friday - note the difference in the outlook - so the low confidence strap is applied to this volatile driver.
Indian Ocean Dipole - IOD - Negative
The Indian Ocean is expected to remain negative and deepen this stance somewhat, the BoM model has now shifted the latest guide, but I am still going with a persistence forecast based off the data sets underpinning global forecasting. No change in the guidance in the latest data with the event set to peak in September/October with the chance of it lingering through December but the latest guide has shifted from that, but the confidence 6 months out gets lower. But for now a wet signal remains and that will increase later this month with the first cloud bands (which I have covered here )
ENSO - Neutral
But as covered above the neutral signal is becoming more La Nina like as we go through September and October which may overlap with the negative IOD which would spell flood potential for large parts of Australia so that is the major development in the data sets overnight. For now the signal is cool neutral and the BoM have not officially declared a La Nina watch like JMA and CPC but their model is indicating a La Nina in Spring/Summer.
BoM Forecast for the Pacific/ENSO region.
Next 6 weeks.
Rainfall looks to build further as we go through July but more so through August with a wavy flow developing and pulling in moisture from the northwest and dragging that through the western interior and through to the southeast over the coming 2 weeks, there should be one or two of these events develop.
Also the battle zone which I have spoken about multiple times this week where the heat and cold air is separated by a jet stream laden with moisture at times, could see widespread cloud develop with patchy rainfall over the inland periodically over the coming 2-3 weeks. This may bring above average rainfall over the inland.
There is a drier signal for parts of the east coast for this period, but like the past two weeks, it takes one area of low pressure to be in phase with moisture to bring rainfall to areas that are traditionally drier than normal.
Humidity will likely rise in the coming weeks over the NT in line with above average temperatures and this will spread into the northwest of WA. This above average temperature zone could breed lower air pressure and thus lift any moisture that rolls through the region from the northwest.
Finally the clash of the airmasses that will eventually play out as we track into August, if moisture gets involved with this zone and areas of low pressure roll through the battle ground, this can be the foundations for further significant rain events.
So overall there are many ways to achieve rainfall in the current climate.
12z Euro M - Rainfall for the coming 6 weeks. - Valid Friday 9th of July 2021
Rainfall as you can see from the ensemble data sets is running high and I must say, it is not that common to see the entire nation being painted in during dry season, especially the climatological peak of the dry season, so we have got an interesting 6 weeks on the way for many parts of the nation. This runs into August 21st.
12Z GFS M - Rainfall for the coming 5 weeks - Valid Friday 9th of July 2021
Very similar in the spread to Euro, which runs a week longer, but similar idea on the board with the wet signal going up a notch until August 11th.
12z CMC M - Rainfall Anomalies next 5 weeks - Valid Friday 9th of July 2021
The drier signal over the east is conditional on the westerly wind belt winning out, based off the SAM it is a low confidence forecast. But the increasing levels of above average rainfall is spreading throughout the nation and now coming over northern Australia.
12z Euro M - Rainfall Anomalies next 6 weeks - Valid Friday 9th of July 2021
Similar to CMC the rainfall higher anomalies are spreading throughout the nation and graduating further north each update. The rainfall accuracy over QLD is low and that can be denoted by this current event that has appeared in a signal of below average rainfall, so just because you see brown over QLD, that is still a low to moderate confidence forecast. The trend is the drier signal losing the battle as we go through the year.
12z GFS M - Rainfall Anomalies next 5 weeks - Valid Thursday 8th of July 2021
The driest out of all the modelling and again, throwing this out the door. It did not pick up the rainfall event coming through NSW/QLD in it's latest run, which was last night, before the event kicked off. So this is the least likely.
12z CFS - Seasonal Outlook - August to October - Valid Friday 9th of July 2021
The seasonal outlook is still looking very damp for large parts of Australia, and I think in coming updates a lot of green and blue will develop over northern Australia, especially once we get July off the board. You can see my seasonal outlook here
Temperatures are warming, we have seen a shift towards a warmer signal and now with the short to longer term modelling expressing this idea, I am now adjusting my forecasts. Sometimes you need to wait to see real time data to verify what the models have been expressing and this is something that I will start to introduce for the coming 4 weeks. I still think GFS is running way too warm.
12z Euro M - Temperature Anomalies next 6 weeks - Valid Friday 9th of July 2021
This week to 10 days will be cold over southern Australia with a burst of wintry weather rolling through as the SAM trends slightly negative, but again low confidence in that forecast. But there will be cold winter westerly winds. After that the flow becomes wavy and the heat may win out over WA, drifting down through southern and eastern states ahead of frontal weather, adding more dynamics into the atmosphere for robust weather events later this month and into August. That I do think is rather plausible.
12z CMC M - Temperature Anomalies next fortnight - Valid Friday 9th of July 2021
This expresses that cooler week coming but see the battle ground setting up where the temperature anomalies are close together, this is what you want if you are after widespread rainfall and dynamic weather events.
Next update on the Climate will be Tuesday next week. I will have a few more little quick updates on the drivers in the mean time.