Updated: May 24
Mixed signals persist for next week, once we get the rain and storms off the board over eastern Australia and we reset with high pressure moving into the east, opening the door for the next wave of frontal weather coming out of the Indian Ocean.
The question remains, can one of these fronts tap into the moisture source from the northwest, via the jet stream, with a large cloud band forming in response?
I certainly believe that is more likely to happen than not, it is just a matter of WHEN and how that front approaches and where the link between moisture and the front will be, determines the rainfall spread.
In the coming 2 weeks, there are good signals for precipitable water values increasing over the west and spreading south east. If you have been following along since launch day, this has been a fairly consistent theme over recent days for the medium term and continues today.
GFS 18z Precipitable Water Values - Next 2 weeks - Valid Wednesday 30th of June 2021.
Watch for the green shading ahead of the fronts rolling through the east. Also note the importance of the onshore wind flow in the east that is feeding an inland trough too. We will see the easterly component more often through our spring with inland troughs likely to feed off that moisture and then moisture streaming in from the northwest. In the short to medium term, rainfall chances for southern inland Australia will be confined to what is happening out west.
The signal for the global ensembles are relatively mixed still, though I think they are too dry given the current observations offshore the west and northwest coasts of Australia. So the guide from my point of view is that increasing rainfall chances next week over the west and northwest will graduate further south and east during the second week of July and a wet end to the month looks likely from this point in time. BUT it is medium term forecasting and if you are reading this, you understand the parameters.
Euro Ensemble - Rainfall for the coming 15 days - Valid Wednesday June 30th 2021.
Picks up the rainfall event over the east with good agreement, but the large area of light rainfall over the west and northwest signifies a low confidence forecast with some members out of the 51 member data set suggesting huge rainfall but there are more that are showing less.
GFS Ensemble - Rainfall for the coming 16 days - Valid Wednesday June 30th 2021.
More members have rainfall of significance coming through interior WA into SA mid month but keeps the rainfall strictly coastal over the coming 7 days as the SAM remains positive then neutral, but as you have seen earlier and above, there is a lot of moisture to work with over the second week in this medium term forecast.
CMC Ensemble - Rainfall for the coming 15 days - Valid Wednesday June 30th 2021.
Very much showing more rainfall potential that the other two with many members out of the 25 showing widespread rainfall in the second week of July coming through WA into SA and I am more inclined to side with this solution due to current observations.
So putting that all together here is my 16 day rainfall forecast. This product is always low confidence as it takes us into voodoo land, but it gives those that are desperate to see what I am working with behind the firewall, and what guides my forecast. I am suggesting those through interior WA and into SA be prepared for increasing rainfall chances from as early as later next week.
Rainfall for the next 16 days - Valid Wednesday 30th of June 2021.
This is based off ensemble data for the 2 week period and is a conglomeration of the data so it is smudged out with less detail but there are interesting signals for July.
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