It is tricky trying to pick the weather to impact SA and VIC from Sunday onwards with the battle being fought between the ridge to the north, (which is migrating to a winter time location) and the westerly wind belt that is ridging north becoming the dominant weather feature on the charts next week.

A way of watching this battle is in the upper flow pattern at about 18000ft which shows the wavy flow pattern eventually winning the battle.

GFS 12z - Flow pattern at 18000ft for the next 2 weeks.

Note the high pressure ridge (red) being placed further north during the coming week and then the fast flow pattern taking over. Good news, there is no blocking pattern in the foreseeable future with high pressure dominance so the rainfall trends will continue to be above average for southern parts of the nation, especially if the moisture comes in from the Indian Ocean.

GFS 12z - Surface Pressure Pattern and Rainfall distribution

Note the amount of fronts passing through the southern parts of the nation with the fast flow pattern. GFS shows three attempts at moisture being drawn into frontal weather passing over southern Australia over the coming 10 days. I do think that the lead system next Tuesday will have a reasonable band of rainfall on it, triggered by the large thermal gradient and steep lapse rates in the atmosphere.

Euro 12z run - Rainfall for the next 10 days - Valid Wednesday 7th of July 2021

Running a little too dry in my opinion for the coming period but will continue to monitor trends, the other models are wetter and the ensembles are wetter as well so I suspect that numbers will be larger than what is being shown here.

Euro 12z run - Rainfall for the next 10 days - Valid Wednesday 7th of July 2021

And because the global models forget there is southeast SA, here is the broader view of the east for our friends down there. We can see better rainfall for the coastal areas exposed to the westerly wind influence, but again, running a little drier than the other models.

GFS 12z run - Rainfall for the next 10 days - Valid Wednesday 7th of July 2021

I think this probably closer to the truth with more moisture being drawn along the northern flank of the long wave as it passes from WA into SA then to the east over the course of next week. Patchy rainfall likely to develop under thick high and middle level cloud, denoting where the temperature gradient will be at its most intense. The rainfall will favour southern and mountain areas of SA and the southeast.

GFS 12z run - Rainfall for the next 10 days - Valid Wednesday 7th of July 2021

A look at the southeast and broader eastern view.

Rainfall for the next 10 days - Valid Wednesday 7th of July 2021.

No real change to the forecast package this morning though I have increased falls around the Adelaide region and parts of the YP and Gulf coasts, and the chance of receiving 2-5mm increases a tad for areas of outback NSW and into SA.

Rainfall for the next 10 days - Valid Wednesday 7th of July 2021.

Totals are creeping up a bit this morning, but will have a more detailed update this afternoon once we get another two data sets under our belts, the Sunday system is hard to forecast for SA with the ridge to the north the driving force as to the rainfall can be a little more extensive as that front slides away to the southeast. Next week looks wet and windy for coastal areas, with better odds on the front Tuesday bringing the most widespread falls.

Rainfall for the next 10 days - Valid Wednesday 7th of July 2021.

Rainfall totals look good for the southeast of SA and into southwestern VIC. These totals are likely to increase in coming days as more clarity on frontal weather moving through the southeast is revealed. Rainfall chances may also increase for parts of dry SA and VIC with a cloud band developing along a front early next week from WA. So fingers crossed those signals improve. No impact for VIC and SA with the rainfall event passing over inland NSW and QLD in the coming days. Note - I have increased totals in the last hour for parts of eastern Melbourne - with the latest data suggesting better falls for the East Central areas.

Rainfall for the next 10 days - Valid Wednesday 7th of July 2021.

And a closer look at that increased signal for rainfall east of Melbourne this morning, with the latest 18z data sets coming in.

The pattern and discussion.

The weather will remain mostly dry for the coming days under a firm ridge which you can see above, normal when we have long wave trough parked over WA. The residual impact of the positive SAM can be attributed to the rainfall breaking out once again through inland QLD and NSW later this week.

Once that low moves away during Saturday, the high will move away to the east and place SA and VIC into a northwest flow with warmer days and mostly fine weather. A weakening front will pass over the coastal areas of SA and VIC during Sunday bringing cloud and a few showers, could be a tad heavier if the ridge to the north does not beat down the front. Keep an eye on trends as it has been fluctuating.

The front slides away during Monday morning in anticipation of a stronger system rotating out of the west and this has the potential to bring more widespread rainfall from Tuesday for a good chunk of SA. The rain could be moderate at times and this may include all Ag areas, before moving onto VIC and southern NSW.

Follow up cold fronts in a broad unstable westerly flow will each bring a burst of moderate showers and there is the chance of more solid band of rainfall later next week as the winds veer more southwesterly as the long wave passes to the east. That would set up a couple of classic winter days, with widespread showers, hail and thunder with strong winds.

Beyond the 10 days, another large scale system looks to tap into moisture bringing another burst of rain and storms into WA which may onward spread through southern Australia but we have to get the next 5-7 days off the board to get better clarity on that.

For the forecast period of July 14-21 - will be keeping an eye on this part of the world while the frontal weather is continuing to lash our part of the world. This could provide follow up falls.

34 views0 comments