MEDIUM TERM FORECAST

The modelling continues to be in relative good agreement this week with a moisture plume spreading across the nation from northwest to southeast. We have moisture increasing over the northern tropics thanks to a burst of easterly winds, so heat levels coming up over the NT and Cape York, the showery weather reserved for north QLD.


Another are of moisture is rotating west of the high pressure system today, through southern QLD and will move into northern NSW today. While there is no rainfall expected, the sky will turn partly cloudy in response to this moisture being drawn south.


That moisture brings the widespread rainfall for southeastern areas of NSW and eastern VIC mid week into Thursday.


More details on the shorter term forecasts can be found in your state based forecast package from this morning.


Moisture Watch Week 1

The modelling of the moisture is in good agreement this morning and the tight cluster of members should provide a higher confidence in the forecasts until the weekend. Moisture should start to filter over the north of the nation with easterly trade winds starting to develop and freshening later in the weekend. Another modest moisture source should rotate around a high and link up with a cold front passing through the southeast inland. The moisture streaming in from the northwest will continue to move across the nation, though it is decoupled from the cold front and likely to bring little to no rainfall over the outback but could drift into QLD this weekend and combine with a trough sitting in the east to increase the shower activity.

Moisture Watch Week 2

The modelling of the moisture in the second week is still uncertain and the areas of highest rainfall potential keeps changing run to run, however during the past 18hrs, the last 3 data sets have started to see a higher chance of rainfall appear over the eastern inland of NSW and into VIC with rainfall chances also increasing for SA with a plume of moisture coming out of the north and northwest as well as the northeast. This moisture then pools over the region, waiting for a low pressure system to pick up the moisture and turn it into areas of rainfall. The chance of this occurring is increasing. It may begin as early as this time next week. The moisture over the north continues to stream in via the easterly winds thanks to a high sitting in the Tasman Sea freshening the trade winds. This is bringing above average moisture levels to the north and east. Then another port of moisture may develop from the northwest once again, via the jet stream, that could bring a cloud band through outback WA into SA later on in the period to end the month.

THE DATA SETS UNDERPINNING THE FORECAST


18Z GFS Surface Pressure Pattern - Next 16 days

The model has increased the amount of low pressure systems linking up with the moisture through Australia over the coming 2 weeks. As you can see the weather in the medium term could become this active IF it all comes together. CMC and GFS are aligned in this thought where Euro is still the drier model but also has got rainfall about now, where yesterday was running a bit too dry. I will point out the major cloud band developing over the northwest of the nation in this particular run, now while it will likely disappear in the next run this afternoon, that is classic negative IOD activity right there.

18Z GFS Rainfall Next 16 days

Note the amount of low pressure lifting the moisture into areas of productive rainfall. Over the coming 2 weeks, many areas would receive 1-2 months rainfall IF THIS WAS TO VERIFY. But the potential is there for widespread rainfall at least. Who gets exactly what is uncertain for now. The wettest areas do appear to be NSW, VIC and parts of SA at this time. It does shift from run to run, however in recent model data the focus is now starting to shift to the southeast and eastern inland. The tropics look unsettled and humid throughout this period, showery periods for the east coast and the west dries out before more rainfall potential at the end of the month.

18Z GFS Precipitable Water Anomalies - Next 16 days

No real change in the forecast period with the weather becoming interesting from the weekend with a stalled boundary over QLD interacting with a decent moisture profile to produce the chance of inland showers and storms and showery weather along the coast. The moisture next week then begins to deepen dramatically over the central and eastern inland and this moisture profile is likely to be drawn south into a trough and front rolling through the southern states. Rainfall chances have increased overnight for mid next week. Another major surge of moisture also being picked up for later in the sequence over northwest and northern Australia and that should spread southeast as well for the end of the month.

12Z CMC Ensemble Precipitable Water Anomalies - Next 15 days

The CMC is in good agreement with GFS in terms of more widespread moisture being lifted in rain bearing systems as low air pressure runs across the nation. The humidity also running high over the tropics through this period. The resolution in the modelling becomes poorer the further you go out, but note the moisture streaming across the nation from northwest to southeast, again in line with the GFS idea of an inland rainfall event possible at the end of the month. Onshore winds brings more showery weather to the east coast of QLD which will pool over eastern inland areas of NSW and QLD.

12Z CMC Rainfall Next 15 days

Good agreement with GFS with the bias over the eastern inland which is expected if the easterly winds begin to dominate. Rainfall mainly early and late through the period for the western parts of the nation. Humidity increasing ahead of the build up starting date with showers developing. All of that moisture moves south and east throughout this period.

12Z EURO Ensemble Precipitable Water Anomalies - Next 15 days

Still running a little too dry in my opinion but there are useful bursts of rainfall connected to the moisture running through the nation this week. The Euro was slow to connect the dots compared to GFS on this weeks rainfall distribution. The weather in the medium term on this model is expressing uncertainty with rainfall spreads of 0-100mm for many locations through the eastern and southern inland on the meteograms, which again expresses the uncertainty out there. I am still aligning myself with the GFS.

12Z Euro Rainfall - Next 15 days

This is the driest model out of the three, it does not see the moisture coming across the north and northwest of the nation and keeps the west dry after this event over the coming 2 days. The bias of wet weather will be in the east, but the model is suggesting high pressure will hold firm over the east reducing rainfall. The wettest part of the nation will be over the FNQ coast and western TAS.

Looking at the deterministic modelling


12Z ACCESS Rainfall Next 10 days

The ACCESS model also shows moisture coming through from the west this week, can track that rainfall peaking over the southeast with moisture coming in from the northeast and north and being lifted into areas of rain. We also have moisture increasing over the north with trade winds returning. Moisture increases next week over the southern and eastern inland with an upper trough starting to introduce rainfall in the day 7-10 window.

12Z KMA Rainfall Next 12 days

This is in reasonable agreement with ACCESS and the other global models for this week. That means forecast confidence is high in the timing and scale of rainfall over the southern and eastern states. Next week you can see moisture also increasing over the inland with an upper trough floating through the southern inland of SA and into eastern Australia. But the forecast confidence is low. There is some chance of rainfall redeveloping next week for inland areas and most all models show this, it is just a matter of where.

Temperatures for the period will follow the same pattern with increasing humidity meaning temperatures near to above normal for most of the nation, away from the southwest, that is in the absence of dry cold southwesterly surges. The GFS does indicate a colder shift coming into southeast areas from the 22nd but it does not penetrate far inland.


18Z GFS Temperature anomalies Next 2 weeks

Note that colder trend over the southeast but nothing brutally cold at this stage for the nation in the coming 2 weeks. Warmer for much of the continent which suggests the early build up over northern Australia is increasing in chance.

Another update to come tomorrow on the medium term.








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