MEDIUM TERM FORECAST - MODEL WRAP ON RAINFALL EVENT THIS WEEKEND.

The models starting to settle down on the idea of rainfall spread with the first system, not so sold on the idea of what happens beyond the weekend into next week, with a split camp in the global modelling in recent days, where some of the agencies plant a low pressure system over the eastern seaboard, other models say no, and plant a high through the nation bringing a week of benign seasonal and settled weather.


Lets have a look at the latest medium term wrap in the vlog this morning.


Rainfall for September 1-8 2021

Rainfall largely confined to the cold front passing through the southeast and south this week before the system lifts north and then spreads over parts of eastern inland Australia. The models are struggling on how the colder air that follows the system behaves, whether it rides up over the eastern inland or over the Tasman. If it goes over the Tasman Sea, then it will be a drier look, if it passes through the eastern inland, then it will be wet, so will be monitoring that element which is the wild card. Otherwise once the system passes through and you are in colder air, the weather will be largely benign.

Rainfall for September 9-16 2021

The presence of a large high over the southern parts of the nation with ridging extending into the Tasman Sea will see the bulk of the nation dry and settled, though are cooler in the eastern and southern inland. Over the east coast, easterly winds are forecast to be present and the rainfall smear does head inland a bit, but the bulk of the rainfall will be along the coast with moderate accumulation possible. Rainfall may return to the west just outside of this period.

Rainfall Anomalies - Next 2 weeks

Rainfall anomalies connected to the system passing east and north through the nation this weekend, where some areas of outback NT and NSW could record more than a months worth of rainfall. Otherwise a dry signal continues for southern parts of SA and into SWLD with the high pressure system is anchored over the region and the moisture with this lead system being drawn to the east of these states. Otherwise weak signals for rainfall to be above average over the north connected to rogue showers and seasonal weather expected elsewhere with largely dry weather for the deserts out west and outback QLD.

Temperatures for September 1-8 2021

The above average temperatures will begin to move north and east in the coming days so expect to see the blue shading moving north over the coming days and the hot weather contract back to the tropics. Farmers and graziers should be on alert for the potential of frost and a issues regarding vulnerable stock with the colder weather sweeping through the nation over the coming days.

Temperatures for September 9-16 2021

The cooler bias continues over the eastern inland through mid month with a slow moving high anchored over the Bight broadcasting long fetch southwest winds over the region with dry air combined with the colder southwest winds. The weather out west will improve with a warmer northwest to northerly flow developing on the west of the ridge. The heat values, though above average over the north, will be accompanied by less humidity through this period.

I talk about these data sets in the video, but if you wanted to play them again for your own interpretation.

18Z GFS Surface Pressure Pattern for the coming 16 days

18z GFS Rainfall for the coming 16 days

18z GFS Precipitable Water Anomalies next 16 days

The anomalies underpinning my forecasts


Rainfall Anomalies - next 2 weeks

Euro Ensemble

CMC Ensemble

GFS Ensemble

GFS Temperature Anomalies next 2 weeks.

The Indian Ocean is certainly not our friend at the moment, with a dead basin just offshore Australia. We are going to have to rely I think, and this is just a thought I am reviewing, that the tropics firing off earlier than normal and the Coral Sea and waters over the north being warmer than normal may project moisture down through the nation bringing up rainfall.


Is the IOD still negative, marginally, but as I have been talking about for the past 4 weeks, we needed to see it perform ahead of frontal weather and that has not occurred so now we need to adjust forecasts and I hope agencies start to do this.

The simulated IR Satellite Imagery for the coming 10 days showing a very dry airmass across the Basin bordering Australia, so no influence from this region at this time for the coming 10 days

This is looking at the next 10 days over Australia and you can see the dead dry air over the northwest of the nation, but note the moisture offshore QLD now, feeding troughs over the east and then frontal weather passing over the eastern parts of the nation.

Finally, the BoM have got a lot of green on the board as well for the outlook period, but remember that CLIMATE OUTLOOKS are less reliable than your shorter term forecasts. I see brown for parts of WA in the outlook periods, but all it takes is a storm outbreak and these areas could record above average rainfall. The takeaway is, the wetter weather will be the further east you are this spring and summer, and flooding is still a concern through NSW and VIC as mentioned, with still a risk over outback areas of SA and NSW through southwest QLD.


I said this last year and many times during my two decades of forecasting, the weather will do what it will do. It is important that you cross check the forecasts with the data sets, the short and medium term forecasts and that is why I update them so frequently because the weather is a moveable feast and arming you with the up to date information gives you a chance to make informed decisions. Look at the skill sets, the data sets and then take the average of all of these.


Spring Rainfall Outlook - BoM

Rainfall Outlook into January - BoM

The weather is not a perfect science and never will be, not one forecaster can tell you ahead of time how much rainfall you are going to get, we can offer ranges and guides but I hope this analysis is useful and makes sense and gives you what you need. It is going to be frustrating for the coming months with many areas being pummeled by rainfall and other areas that want it, remaining dry. So a heads up on that.

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