MEDIUM TERM FORECAST - QLD RAIN AND MORE FROM THE WEST NEXT WEEK?

It does look like the cooler than normal weather is likely to stick around over the coming 5 to 6 days over the southern areas of the nation, with a series of troughs passing through, the southerly winds also keeping the cloud cover thick over the eastern side of the nation and a detached area of cold air through the middle layers contributing to the colder snap.


But many are looking for more rainfall, especially through QLD and SA/VIC which have generally missed out with the past system now sitting offshore.


Rainfall Outlook - Next 2 Weeks.

Rainfall easing over the east with two events in the short term to watch, one being over eastern QLD with showers and storms and the next major front coming through WA mid to late next week with showers/rain spreading through WA into SA and into the southeast. But there is some conjecture on that which you can see below, on how much influence that system currently has on rainfall further east. Then in the medium term, further frontal weather may see rainfall run across southern parts of the nation but the moisture over the inland will give rise to rainfall breaking out on the northern flank of the wave action over southern Australia. The tropics are expected to turn much more humid especially over QLD where rainfall may be heavy at times early next week and again during the first week of September. This moisture will run across the nation and influence rainfall opportunities into September. The Indian Ocean - it is far too quiet for a negative phase and I am getting close to adjusting rainfall forecasts in line with less of an impact on rainfall moving through spring. The system next week will tell the story. Just to give you some context to my forecasts moving forward.

Temperature Outlook - Next 2 Weeks

The warmer trend of weather is expected to increase next week, we know the coming 4-5 days will generally be below average, but next week, the temperatures could be as high as 12-15C above normal through southern parts of the nation ahead of that front moving through WA and SA. This could be replicated over parts of QLD and NSW in around 9-10 days time. If the high becomes slow moving which there is some signals it may, then a longer duration of above average temperatures are possible. Over the north it has been hot the past few weeks and that should continue for the next 10-15 days. The cooler bias over the southwest is due to a long wave trough parked offshore the west coast bringing onshore winds and showers from time to time. It will not be freezing but the cooler than average weather will continue for longer periods while the east is warmer than normal.

PRESSURE PATTERN


18Z GFS - Surface Pressure Pattern for the coming 2 weeks.

The surface pressure pattern is complex, we are losing the zonal flow, the west to east movement of systems, and now starting to see the spring time complexity being added to the charts in the short and medium term, making forecasting quite tricky, but that is spring. For now there is a good chance of showers and storms breaking out over eastern QLD especially through Central and Northern QLD with a trough combining with moisture (another sign of the seasonal shift). That moisture may run down the coast to about the Wide Bay. The other focus of the weather will be the high pressure system that eventually parks itself over the east (helping to feed the QLD trough). This high will send the nation into a very warm spell. There could be some centres breaking into the mid 30s through SA and low 30s further south, possibly to about Yunta in SA and Broken Hill in NSW. The next front you can see gets pulled south over the Bight in this run with areas of rain passing through WA sliding south and west of SA, but not too sure about that. In the medium term, the general trend is suggesting moisture to build over inland areas and rainfall possibly starting to develop along the northern flank of the waves passing over southern Australia. The tropics will be quite moist with a return to build up conditions into the second week of September. Otherwise I am not satisficed with the IOD influence at this time, next week's system is important to reveal what sort of impact it will have during the next 2-4 weeks.

18Z GFS - Upper Air Pattern for the coming 2 weeks.

Upper air pattern shows the troughs moving through the nation with the zonal flow from winter now retreating further south during the outlook, we are moving into a traditional spring set up where the short to medium term forecasting becomes tricky. We can see the ridging over the south of the nation (that is thanks in part to the SAM turning positive too) seeing easterly winds dominate at the surface. We just need upper troughs passing through the eastern inland of QLD and NSW to allow rainfall to break out to make the most of the moisture. At the very end of the run you can see a trough that develops over inland QLD and rainfall then breaks out, now that will not be there in the next run, but it is a good example of having all the ingredients in place to produce rainfall. We need a lifting mechanism, not just the moisture.

Areas of contention in the forecast are relating to the system coming out of the west next week. The GFS shows a highly anomalous low pressure system sweeping northwest through NZ and up through the Tasman, blocking the passage of high pressure over southeast Australia, which MAY (very low chance) cause the system peaking over WA and SA this time next week being forced south and leading to little impact of rainfall spreading east, and bringing a prolonged period of above average temperatures to the southeast and eastern parts of the nation. I am not of the belief of this occurring but will watch. That is why you are seeing less rainfall all of a sudden on the GFS.


Pressure pattern early next week for the nation, the low in the east and the one developing from the west will be the areas to watch as this will have large impacts on rainfall chances next week.

RAINFALL DATA

18Z GFS - Rainfall for the coming 2 weeks.

The moisture is limited in the coming 5 days over inland areas, with rainfall reserved for QLD and WA which we covered in the state based forecasts. The rainfall chances then become mixed mid to late next week. That is in part to the highly anomalous low pressure system moving northwest through the Tasman Sea, blocking the high moving east. After that resolves, we see moisture increase further over inland QLD which then is propelled west through to the southern NT, most of northern SA and northern and western NSW under a long fetch easterly flow. The rainfall you see break out over Central Australia is at the end of the first week of September. So there is something lurking out there. Just have to keep watch.

12Z Euro Control Member - Rainfall for the coming 2 weeks.

Showing a much drier trend today, yesterday was much wetter. Has the rainfall event over eastern QLD which is next week with the upper trough and onshore winds. Has rain for the southeast early on in the period, but this is now suggesting persistent high pressure over the nation with well above average temperatures throughout the period. This is a low chance of occurring, but what does have my interest peaked is the NO SHOW Indian Ocean influence throughout this period. That is now starting to undermine my confidence in the data we have been reviewing together for the past 2 months. We will see how it performs during the coming 2-4 weeks.

12Z Euro Ensemble - Rainfall for the coming 2 weeks.

This is showing more rainfall across the members throughout the nation but still a fairly dry look compared to other runs we have seen. Most members have rainfall for eastern QLD which is welcome but does not quite verify the system moving out of the west next week into the following weekend. I am not so sure on that given the dynamics in play.

12Z CMC Ensemble - Rainfall for the coming 2 weeks.

This is much more realistic compared to the other models this morning, given the current state of play, and the moisture that is building up over the nation, rainfall should easily return to the south and east during this time. Now the ensemble here has rainfall for QLD next week where the single run below which you can see, which is available to the public, is suggesting no rainfall. So I am leaning to rainfall breaking out over QLD being the main focus of rainfall during the coming week before the cold front stands up over WA and SA from later next week.

12Z KMA - Rainfall for the coming 12 days

Looking at the shorter term modelling, the single data sets, you can see the bias of dry air running through the nation. The battle will be can the moisture spread west through QLD and NSW and be drawn into the front passing in from WA through SA into the east, and fill the gap over western and northern NSW? The modelling suggests there are good signs for rainfall over eastern QLD seeping further inland and then rainfall developing over much of SA. The heavy rainfall over the southeast of VIC and NSW is with the weather ongoing today through Friday, but probably a little too heavy.

12Z CMC- Rainfall for the coming 10 days

I outlined in the ensemble data set (which is made of 30 members) that the single run below shows not much rainfall and has nothing over QLD. I disagree with that. But this is an example of where the moisture is non existent and the high pressure dominates. It is possible we see more dry air and stable weather, but it is the lower likely outcome amongst solutions on the table.

12Z ACCESS - Rainfall for the coming 10 days

The Access model does connect the dots a little bit, has the event over QLD next week and the front running over southern Australia with an uptick in rainfall chances later next week. The heavy rainfall over the southeast of VIC and NSW is with the system that is underway at the moment. The rainfall over SA later next week is more widespread as this model sees more moisture being drawn in from northeast and eastern Australia in the longer fetch easterly winds that develop as the high sits out in the Tasman Sea.

12Z Euro- Rainfall for the coming 46 days

The model that everyone loves to look at and wants to see, the low skill forecasting package from the Euro, shows a wet bias over the southeast of the nation with 150-250mm in the coming 6 weeks, again not impossible given the moisture profile, the dynamics in play, but this is banking on the IOD being a larger influence. I am not moving away from this idea just yet, but if the system next week which stands up over southern Australia fails to have any moisture drawn in from the northwest, then we need to review longer term forecasts and adjust accordingly. The IOD is expected to peak during October into November.

TEMPERATURE DATA

This is largely unchanged. The forecast cooler than normal weather that we are experiencing over large parts of the nation is expected to continue for the coming 4-5 days. The weather is likely to warm up next week with a northwest flow slowly starting to return once we lose the troughs and colder air that is sitting over the region. Temperatures over the nation next week could be into the 30s over large parts of the inland before the milder change. The north, warm and soupy weather to continue.

Rainfall is clearly the highest desired information at the moment along with temperatures and more details on this medium term outlook will be updated daily for the time being. Also look for the PM and AM forecast packages. Click on your region, ie. Southeast Weather for VIC and NSW and save that on your devices/PC so that you can come and go easy and bypass the information. For Climate Information you can see all the information in the Climate section.

118 views0 comments