MAJOR RAINFALL EVENT DEVELOPING FOR A LARGE AREAS OF AUSTRALIA.

A major northwest cloudband is expected to thicken and become active with areas of rainfall during early next week, as a strong cold front and trough moves through the southwest of the nation initially, before steadily progressing east throughout next week taking the rainfall chances throughout the nation.


The potential for widespread winter rainfall is running high next week covering multiple states at one given time.


The precipitable water values are running at about 25-50mm offshore the northwest coast of Australia, being pumped into the jet stream which is screaming through the mid sections of the nation, very traditional for this time of year. The one ingredient that we need to see widespread rainfall break out is in association with a trough or cold front. There is a large scale system developing next week which expected to do just that, send a large scale rain band into motion over WA, spreading southeast into SA and then the southeastern and eastern inland.


Precipitable water values - Next 2 weeks - GFS 18z run - Valid Thursday June 17th 2021.

Note the amount of moisture that is not only pulled in from the northwest, but as the system moves from WA through SA and then into the east, but as it heads towards the eastern states, moisture is drawn out of the northeast to northerly flow over the eastern states, which could reinvigorate the rain band over the eastern states as the change moves through, so rainfall numbers may be increasing over the eastern inland of QLD and NSW. There are further rainfall signals coming for southwest WA as well during the period leading towards the end of the month, which will again translate eastwards through the southern states, so an active phase is developing again.

The fast flow pattern and the northward movement of the westerly wind belt, the sub tropical ridging over the mid section of the country, will keep the winter weather systems moving over the southern parts of the nation. Can these tap into more moisture streaming out of the Indian Ocean?? That remains to be seen, but the potential is there, looking at the satellite imagery today, there is certainly a link that can be established between that moisture source and the westerly wind belt during the course of not only next week but also weeks to come.


Upper flow pattern at 18000ft showing the colder air through the southeast states initially steadily moving east, but keep watch for the heights (blue/red shading) over the northwest of the nation merging it a large system early next week with widespread rainfall moving throughout the nation with that area of instability.


GFS 18Z 500mb flow pattern - Valid Thursday 17th of June 2021

The fast flow pattern I have been speaking about to round out June looks set to verify with further rainfall expected beyond the major rainfall next week with another strong cold front hitting the southwest of the nation once again at months end.

So with all the cloud and rainfall potential, how much can we expect to see? Well quite frankly this far out, it is a low confidence forecast but I can advise on range (though I do provide detailed forecasts for industry and do provide those details upon request). The overall trend is positive for widespread light to moderate rainfall at the worst outcome with the potential for scattered heavy falls along the path of the cloud band and along the frontal axis as it crosses through southern parts of the nation.


The raw data feed from the Euro model is very generous with the rainfall spread and this is usually the most conservative model in the suite, but the most accurate.


Euro Rainfall Spread - Raw Data - Valid Thursday 17th of June 2021

Note the spread of rainfall eminating from that large area of convection offshore the northwest of the nation being drawn into the nation from the northwest to the southeast. Some excellent signs for agricultural areas of SA which have been dodging consistent rainfall all year.

So the rainfall spread for the coming 10 days is fairly unchanged, though I am lifting numbers over the southwest of the nation in line with a follow up front later in the period which could bring another round of heavy rainfall and strong winds. I am lifting rainfall over parts of the southeast as the low gets another in feed of moisture from the northeast to northerly flow that develops as the system approaches steadily from the west. Numbers have also come up over parts of QLD and NSW as a consequence of this as well.


Next Wednesday - Surface pattern showing a low moving through the southern parts of the nation with a significant amount of moisture being drawn into the northeast flow, still coming from the northwest with main dynamic support along the front and near the complex low driving rainfall, but with the convergence, moisture and lifting mechanism, I fully expect more rainfall to break out along the front as it moves through the inland during Wednesday or Thursday next week so watch this space.

Rainfall for the next 10 days - Valid Thursday 17th of June 2021.

Need more weather information? Email me at karllijnders@weathermatters.org for more details.

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