MEDIUM TERM MOISTURE WATCH

Morning update from the modelling still not offering much consistency in terms of the tack and placement of the moisture and subsequent rainfall opportunities. But the one thing modelling agrees on - there is moisture to work with during the coming 2 weeks. We don't usually see persistent moisture pooling during July so this will keep rainfall chances up for parts of the country.


Let's look at the mechanics for the coming 2 weeks. We can see a pattern that is evolving before our eyes, and I do think that will repeat itself 2 times during the coming 2 weeks.


Mechanics of moisture movement.

Upper high over the northern parts of Australia is driving hot and dry weather over the north for the next while. It is helping to produce upper easterly winds to the north of Australia driving moisture west through Indonesia and that moisture is then being absorbed into the jet stream, turning the moisture south and then southeast over the Indian Ocean and feeding into cold fronts. The northerly movement of the polar jet is helping to pull the moisture southeast over WA today and we can see the result of widespread rainfall and storms for WA as the airmass clashes. The gap between the upper high to the north and the polar jet to the south will assist in the moisture being rapidly drawn southeast through SA and then into the eastern states this week.

Satellite Imagery of the mechanics

The above diagram being played out below. This shows the mechanics and watch this over the coming days. It will be the reason we see widespread falls across many states this week. The meeting of the airmasses, copious moisture and the mechanics drawing the moisture across the nation.

18z GFS - Precipitable Water Values over the Indian Ocean for the coming 2 weeks. - Valid Monday 12th of July 2021.

The moisture profile is very high over the coming 10 days through the Indian Ocean and much of that is being utilised through the WA and adjacent inland areas as the jet stream transports that along the northern periphery of frontal weather (which is covered off in multiple posts this morning). The moisture is expected to recycle via Indonesia, spreading west through the archipelago and then turn to the south and southeast as it encounters the upper northwest winds. So this event that is occurring through WA this morning, will be repeated once again later in the weekend and another major rainfall event will develop from that. The current transportation is expected to take it through WA and offshore SA, but as you can see the model spread above is divergent and expressing a high degree of uncertainty.

18z GFS - Upper level wind profile and moisture transportation over the Indian Ocean for the coming 2 weeks. - Valid Monday 12th of July 2021.

Note the surging northwest winds over the west coast of Australia extending back over the northern Indian Ocean, this providing more rainfall opportunities this week and into early next week. Through the latter part of the outlook, the moisture then retreats further north with an upper high over northern Australia breaking down, a new upper high developing over the central Indian Ocean causing the moisture to be less likely to impact the nation for the later stages of the month, but frontal weather continues and that does contain a reasonable moisture supply.

12z Euro - Simulated Water Vapour Satellite over the Indian Ocean for the coming 10 days - Valid Monday 12th of July 2021.

Certainly a very productive period of moisture coming through the northern Indian Ocean and that moisture does spawn two rainfall events, the one today over WA spreading east and another event towards the end of the weekend into early next week. Then the moisture plume will break down as the weather conditions shift around Australia and the Indian Ocean meaning the moisture will retreat for a period back north of this region towards Malaysia and India.

12z Euro- Simulated IR Satellite over the Indian Ocean for the coming 10 days. - Valid Monday 12th of July 2021.

Rainfall chances look to remain high with fast moving fronts, two low pressure systems moving through the southern and western parts of the nation emanating out of the Indian Ocean. Moisture content remains high up until the end of the forecast period which is the 21st of July. So another active 10 days, with multiple frontal passages to come through and interaction with moisture.

Model moisture spread from the 12z mode sets this morning expresses the major divergence in model data this morning, meaning follow up rainfall could be quite challenging to forecast. I am favoring WA to get the bulk of the falls, but this could change through the week.


Model spread - Valid Monday 12th of July 2021.

Potential Rainfall - Medium term outlook connected to possible low pressure system spreading through the west and south, blended data and the average across the data sets this morning - Valid Monday 12th of July 2021.

I will once again update this detail this evening, get another 2 data sets under out belt and see where it stands.



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