MEDIUM TERM FORECAST - THE HUMIDITY AND RAINFALL SET TO INCREASE FOR THE NATION ONCE AGAIN

We are seeing a reduction in rainfall coverage across the nation as a whole, but in the areas that need a break in the rainfall, the sad part is, the weather is set to remain wet and stormy. But how are we looking into the medium term?


Well more rainfall and humidity is set to build from about the 6th onwards, with two troughs setting up over the eastern and western interiors. The trough in the east poses a significant risk of more flooding with daily storms returning and the potential for more widespread rainfall developing.


The weather over the west stormy, but not as widespread as the eastern trough, however a noticeable shift in the rainfall and thunderstorm activity is expected to develop from about the same time (if not the end of this coming week) as the pattern resets and allows for the shift to rain returning to the west.


Overall the broad unstable and humid warm easterly winds will dominate the synoptic scale which is a rainy look for the nation at this time of year.


Finally, there is the risk of troughing developing along the east coast with showers and thunderstorms becoming widespread on and east of the dividing range during the medium term which could lead to flood renewals in NSW.


Lets take a look

Moisture Watch Next Week - December 6-13 2021

Moisture is set to descend once again from the tropics and after a relatively drier week through much of the western and southern parts of the nation, the moisture is set to return from the north and east with the prevailing easterly winds dominating the synoptic scale. Basically this will lead to rainfall chances increasing over northern and eastern Australia and then being drawn south as the high pressure over southern waters this week, dives further south during this period allowing for that moisture to also creep south. So warmer, more humid and unsettled as we go through this period.

Rainfall Next Week - December 6-13 2021

Rainfall bias under the synoptic scale is looking more likely once again over the northern and eastern parts of the nation, but the coverage will move south and west throughout Australia. The heaviest of the rainfall as has been the case for a long while, will be over the northern NT, much of QLD and NSW into the ACT. The coastal areas along the east coast need to pay attention to the rainfall increasing as onshore winds combine with troughing to produce heavy rainfall leading to flooding renewals, the area of heavy rainfall potential is wide and is between Mackay and Sydney at the moment, but this area will narrow. The weather out west also becoming unsettled with the west coast trough deepening and that will spread into SA as well throughout this time. So most territories through the country are likely to see more rainfall than not as opposed to this week.

Rainfall Anomalies - November 29-December 13 2021

Above average rainfall anticipated for the eastern parts of the nation with seasonal values elsewhere. The rainfall anomalies are moving away from the drier signal we had last week for the west and this is thanks to the higher chances of thundery weather returning. The weather over the north turning more active as we move into the middle of December which is normal but watching the development of the monsoon trough to the north of the nation and the rainfall numbers not quite widespread enough for above average rainfall confidence for SA but watching closely in the coming days, will leave it seasonal for this region against the data sets.

Temperature Anomalies Next Week - December 6-13 2021

Warm to hot and humid weather developing for large parts of the nation in the absence of any southerly wind fields approaching the nation. So whilst the searing dry heat may be way out west, that heat will transition to more humid weather with thundery weather develop and the weather over the bulk of the nation will remain humid and warm so if you are seeing white on the charts, the airmass will be heavy with moisture and so it won't be pleasant conditions. Values over the north should start to come down, but the heat has been stubborn this period and my forecasts have not verified for the tropics thus far, so hoping that shifts soon.

DATA - Refer to video for more details.


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

More details on the video but there are 2 flood potential events for QLD and NSW through this period with storms returning to all corners of the nation throughout this period with low pressure taking over.

18z GFS Precipitable Water Anomalies - Next 16 Days

The anomalies show the heavy moisture load over the east and the drier bias for the west, but note how the moisture over rides the drier airmass over the nation so the coverage of cloud and rainfall will increase throughout this time.

18z GFS Precipitable Water Values - Next 16 Days

Deep moisture still in place right throughout the period with the drier air bias further west over SA and WA.

18z GFS Rainfall Accumulation - Next 16 days

The numbers out east starting to get excessive again under the long duration easterly wind regime and deep moisture profile. This is leading to widespread rainfall coming back and falling over flood zones.

12z Euro Rainfall Accumulation - Next 15 days

Rainfall over the east coast tending heavier on the larger data sets which is of concern for additional flooding. Note the heavier rainfall slowly creeping south towards the tropical north.

12z CMC Rainfall Accumulation - Next 15 days

Note the moisture coming through the interior on the ensemble data set here where the Euro does not recognise it, but I am leaning with a wetter nation moving into mid month. The east coast carries significant concern for more flooding.

More in your state based forecasts this afternoon and I will be taking a look at the flood potential for QLD and NSW in the coming weeks in greater detail this evening in the evening rainfall and model wrap after 9pm EDT.