I have been banging on about the importance of the moisture sailing in from the northwest out of the Indian Ocean into the nation, via the jet stream, being the catalyst of returning Australia to more normal wintry conditions that we are accustomed to.
Widespread cloud and rainfall is beginning to break out in front of a wave of low pressure that is developing throughout the southwest of the nation, we have been talking about this for the last week and now we are in the period of seeing the prognostics play out in real time.
Broad northwest cloud band developing in response to moisture surging south into a cold and unstable airmass. The polar jet and the subtropical jet, meeting to produce a broad band of rain and thunder. Monday June 21st 2021.
I spoke about the importance of moisture being drawn in ahead of the system, in phase, where the moisture is captured by a lifting mechanism bringing rainfall. This is critical in the development of rainfall events in winter.
This was the graphic I drew up showing the moisture being drawn south in upper level northwest winds through to the inland of WA ahead of that front and cold airmass. Rain breaking out over the inland of WA as a consequence.
These weather systems are crucial to bringing winter rainfall to large parts of the nation, as generally the weather for this time of year is a lot drier for inland areas, and southern areas rely on frontal weather, while the outback, typically remains dry.
In these years, when the Indian Ocean is in a negative phase, the moisture profile over the Indian Ocean is higher than normal and this leads to more of that moisture being drawn south via the jet stream. This in turn means more frequent inland rainfall and higher chances for inland areas recording above average rainfall.
Negative Indian Ocean Dipole - General overview.
Lets take that theory back to the short and medium term forecasting and we can track that moisture from the northwest via the Precipitable Water charts, showing that a abundance of moisture exists over the region north and northwest of Australia.
We have weather systems that are being analysed to bring rainfall through inland Australia.
Precipitable Water Values - For the coming 2 weeks - Valid Monday June 21st 2021
The corresponding surface pattern with rainfall distribution also showing follow up rainfall for large parts of Australia during the coming fortnight with a few waves of low pressure on the board.
Surface Pressure Pattern and Rainfall Distribution 6hrly - Valid for the coming 2 weeks.
Each wave has some interaction with the moisture source sitting off the northwest of the nation and the potential for one of these to spark another major rainfall event in July.
So with that rainfall will be widespread and potentially heavy in pockets over the coming 10-14 days. The models certainly like the idea on the first 2 systems in the coming 10 days, where GFS has another system beyond this with even more rainfall but it is in the lower confidence medium term. BUT there is significant support for this to unfold given the climatic conditions and drivers in place.
KMA - Korean Met Agency - Rainfall for the coming 12 days - Valid Monday 21st of June 2021.
Rainfall forecast for the coming 10 days - Valid Monday June 21st 2021.
So keep watching with interest, it could become an issue of too much rainfall as head into July and then August, which may set the stage for flood issues down the line for inland areas of the east in particular and more rainfall for areas that may be getting crops out of the ground as well.