Welcome to the first of our new series. Every Tuesday and Friday I'll take you through the drivers of our weather, highlighting any changes over time and things to watch out for. It covers weather elements like temperature and rainfall, and how they are driven by moisture from the Pacific and Indian Oceans, as well as bursts of energy (SAM and MJO).
Welcome to the first of our new series.
Every Tuesday and Friday I'll take you through the drivers of our weather, highlighting any changes over time and things to watch out for. It covers weather elements like temperature and rainfall, and how they are driven by moisture from the Pacific and Indian Oceans, as well as bursts of energy (SAM and MJO).
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As this is the first one I'll go into greater detail, then the following editions will be quick and easy to digest.
Here we go!
The current weather maps shows a large low (that brought the recent QLD and NSW deluge) moving out to sea. Only one surge coming into the southeast from the associated trough. A large high in the middle, and new troughs and fronts approaching the southwest.
That pattern keeps the rain in the south and gives the north a break (or a return to regular winter sunshine). The next 8 days rain:
From Monday to Sunday only the far southwest could exceed the average rainfall for this week in July. We are entering a quieter period. This doesn't mean no rain for the rest, but below the average:
This quieter weather means clear nights, and if high pressure takes charge there can be frost for those susceptible to it in the blue areas:
We're still in a period of colder than average days in the north and east, while warmer air is likely to come in from the southwest. Again, above or below the average for this time of year - not a summer heatwave(!):
Looking at the two boxes of interest in the Pacific and Indian Oceans, the Pacific is now only very lightly shaded cool blue (and certainly not near a warm orange).
The Indian box's area of blue has deepened in colour over the past few weeks. That is the sign of a developing Negative Indian Ocean Dipole (the Indian equivalent of La Nina):
So, the Pacific Ocean pushes a little moisture towards Australia (less moisture than over summer and autumn, but not the opposite situation - it's not taking the moisture away), while the Indian Ocean is increasing the moisture available to send towards Australia.
This is helped by warm oranges around much of Australia to help drive that moisture in.
The Pacific Ocean shows we are out of La Nina (green area) but nowhere near El Nino (brown area). The Consensus of the models shows that we may enter another La Nina towards the end of the year (which would be our third in a row). No model likes El Nino:
The Indian Ocean models are all singing a very similar tune - Negative Indian Ocean Dipole (green area), coming out of it as we naturally do in summer:
This means lots of moisture will be pushed towards Australia for the rest of the year.
But... moisture is just one part of the rain equation. You can have bucket loads of it, but if there isn't any low pressure in your area, it won't produce any rain.
So, we look at SAM and MJO to see what the low pressure is likely to do.
After spending much of summer and autumn in positive, SAM finally went negative to bring a big dump for the start of the snow season. Then it went positive again and there's been a break in the snow while QLD and NSW were drenched:
If that signal goes back into positive green again, then further lows could impact NSW and QLD - but the neutral signal corresponds with the break we have for the next week.
The other driver is the MJO. It's a pulse of tropical energy, and whenever that comes near Australia it acts to bring the lows and moisture together, as we saw over the past week. This signal looks to be going back into neutral, then possibly into a drier phase. This could offset the push for low pressure if SAM goes back into positive.
That's a lot of info, and the next one will be just the highlights now that we are all on the same page. The next update is due on Tuesday morning. Make sure you are signed up (free or premium membership) to get them delivered to you. And as always, you can see each of these graphics and more under our Rain Outlook and Seasonal Outlook pages under Jane's Update.