MEDIUM TERM - UPDATED INFORMATION ON THE SAM AND MJO TOO.

We are seeing an end to this period of high rainfall, severe weather, severe storms and high humidity with NSW and QLD looking at more settled weather pattern establishing. The big driver? The SAM tending neutral and into possibly a negative phase. Once again this will bring a chance for the westerly wind belt to migrate a little further north, bumping up the high pressure ridge, leading to a drier picture for much of the nation.


Up north, there are some signals that the MJO may rotate around northern Australia through the latter part of the month. Whether that rotates through Australia or north of the nation remains to question.


But overall, it is looking much more settled which is a relief, the flooding however over vast areas of the east will continue to be with us for sometime so we do need to see a drier picture for at least 4 weeks in the east. I do not think we will see that, but we could piece together a settled fortnight which a few days ago was not looking as possible. So that is good news.


FORECAST

Moisture Watch Next Week - Friday 11th-18th March 2022

Moisture will return from later this week into the weekend with a port coming in via a resurge in easterly winds over QLD and NSW and another coming in from northwest and western Australia with the jet stream pulling in moisture from the Indian Ocean. The values are nowhere near the levels we have seen in recent weeks but it is sufficient in normal seasons for rainfall to return. The moisture levels over the tropics are near seasonal at this time but if the MJO rolls through to the Indian Ocean, then we could see higher moisture levels as we track into later next week, propping up the chance of more widespread rainfall developing for the last 10-12 days of the month across the nation.

Rainfall Next Week - Friday 11th-18th March 2022

We know that the east is very wet in the coming few days and that has been covered off many many times. So lets look further ahead. The nation from Wednesday through Friday looks pretty quiet, with rainfall retreating to the northern tropics and along the east coast, but more frequent in QLD and northeast NSW. The rest of the nation settled. Then we see a new trough developing later Friday into the weekend over western QLD and NSW and this could see showers and thunderstorms increasing in coverage this weekend, some of the storms could turn severe but isolated heavy falls only at this stage. Some of the modelling is supporting more widespread falls this weekend and again next week as another trough from SA which brings light rainfall to Ag SA, but then runs into the moisture over the east and pulls in more moisture over the inland of QLD, NSW and into VIC with the chance of rainfall increasing from this time next week into the middle part of next week. Will have to watch that. Tropical weather at seasonal rainfall expectations at this time but that could change with the MJO coming through northwest areas of WA.

Rainfall Anomalies - Friday 11th-18th March 2022

Drier than normal weather continues for the west of the nation and extends into Central Australia as well and near normal weather for the north of the nation. Lighter rainfall expectations in comparison to where we are today are likely for the east coast but additional rainfall is likely at this time for QLD, NSW/ACT and VIC through the weekend more prominently next week.

Temperature Anomalies Next Week - Friday 11-18th March 2022

Temperatures are likely to be above average through this period for all areas apart from the east coast which is still expected to see widespread showers and onshore low cloud so that theme continues, but overall, temperatures of up to 5C above the norm is likely as the neutral SAM phase allows the northwest to westerly winds to try and return to areas over the south of the nation.

DATA


18Z GFS Surface Pressure Pattern and Rainfall Distribution - Next 16 Days

The GFS shows the clearance of the weather this week, but come Friday we have a deepening trough over western QLD and into NSW then dipping into VIC and the remainder of NSW this weekend. Some of the rainfall could be heavier through inland NSW and into southwest QLD. The coverage of the rainfall is likely less widespread than previous weeks but some areas could walk away with another month's worth of rainfall with thunderstorms. The remainder of the south should be fine into the weekend ahead of that moisture streaming in ahead of a trough leading to widespread showers developing across the weekend and more likely next week with a stronger system emerging out of SA. There may be a few showers and thunderstorms through Ag SA next week as that trough moves through but light falls for now. The weather over the west of the nation is likely to be mostly dry. A west coast trough could kick off some showers and storms well north of Ag WA but not too far away. The weather over the tropics leaning seasonal, drier in pockets against expectations but nothing too unusual for this time of year. Will have to watch the MJO very closely to see whether that gains strength and pace as it moves through the Indian Ocean. Something to watch up there. FNQ and through the east coast of QLD, the onshore winds will provide daily showers and cooler weather with the trade winds persisting.

18z GFS Precipitable Water Anomalies - Next 16 Days

You can see that surge of moisture coming in from the north and east with the winds veering into the northeast over the weekend. This is thanks to high pressure moving south of the nation and into the Tasman. This will help to spread moisture west across QLD, NSW and VIC. A trough coming out of WA into SA will link up with this moisture (while bringing some elevated PW levels in the upper atmosphere) and see the rainfall and cloud become more extensive into next week so more inland rainfall is likely, light for SA but moderate for NSW/ACT and VIC. Coastal moisture will remain very high in the east in the lower levels via onshore winds. Drier airmass over the western interior nearer the persistent ridge will continue and the tropics look seasonal.

18z GFS Rainfall Accumulation - Next 16 days

Rainfall does spread throughout the east and north of the nation in greater coverage with a large spread of rainfall expected as we move through this time next week with a more substantial trough coming in from SA and running into the moisture over the east. Otherwise fairly quiet elsewhere with no organised rainfall event.

FURTHER READING

I have spoken about the drivers over the past few weeks as these are great indicators of what is happening in the broader global climate driver scene. We have spoken about La Nina at nauseum for months and months and months. Now we are seeing the back of that phase but the impacts still continue for the eastern areas of the nation at the moment.


However we are seeing significant shifting in some of the climate drivers suggesting the La Nina is beginning to ease over the Pacific and that is being reflected primarily in the Southern Annular Mode data sets.


Traditionally, when you have the La Nina, you have more positive SAM events which we have seen. When the La Nina breaks, you get more variability in the SAM and shorter duration positive SAM events. We are starting to see that now.


Southern Annular Mode - Next 2 Weeks with the past 4 months of history.

Note that the La Nina developed in October 2021 and from there we saw a persistent positive SAM phase that eased back to neutral conditions and then would quickly return to positive phase. This was broken back in February with the first dip into negative territory which heralded the start of the ENSO starting to shift back to neutral conditions. There are signals of another neutral to negative phase developing next week which could be the longest period away from a positive phase since last September. This would be a stronger signal yet that the La Nina phase is coming to an end and will likely resolve as forecast in Mid April. Now this driver is very hard to predict ahead of time but as mentioned above, it does provide plenty of clues as to where things are heading in the Pacific and how the season is evolving.

MJO - Next 2 Weeks

There is some moderate signals for increased tropical activity approaching northern Australia through the medium term, through this period outlined, but whether it runs over the nation or to the north remains the question for a while. One element with the MJO is the ability for moisture to be drawn south and east through the nation from WA into SA through to the eastern inland with the jet stream more wavy under the neutral and negative SAM phase. This could see rainfall increase over western and central parts of the nation and then into southern parts of the nation as well, as the westerly wind belt starts to rise north and meet the moisture coming into the nation via a MJO phase passing north of the nation. We are moving into the cooler season so this is where the pattern shifts and the distribution of rainfall also begins to shift.

So looking better, quieter for the east but there are many that need rainfall, especially for WA and pockets of SA and Central QLD.