MEDIUM TERM UPDATE - MORE HUMID, MORE RAINFALL SPREADING NATIONWIDE IN MID DECEMBER

** I am travelling this afternoon and in the absence of an evening update I will have the models and rainfall wrap coming up from 9pm EDT tonight**


There coverage of rainfall in recent days has thinned out as the air aloft becomes a little more stable. We have got a few troughs in the coming week that will still generate showers and thunderstorms, mainly over the east and southeast, as well as the tropical north.


The west, to remain dry and hot over the SWLD and extending north to the Pilbara. I will also mention that SA will be mostly dry for the coming 7 days but that may change depending on the evolution of the mid level trough across interior parts next week and how much moisture gets involved before it moves into the east.


Now from the 8/9th onwards, that mid level trough is expected to spawn low pressure system, tapping into that excessive moisture in the east and I would be very surprised if we are not dealing with a significant rainfall event for parts of QLD and NSW.


Additional flooding is expected to develop on the current guide next week for QLD and NSW with heavy rainfall potential. We have got a break in the heavy widespread rainfall for a little while, despite the presence of showers an thunderstorms this week. The rainfall becomes more widespread in the second week of December.


And what about the monsoonal weather? As mentioned in the morning update, we are tracking tropical lows in the medium term about mid month.


Lets take a look

FORECAST

Moisture Watch Next Week - December 9-16 2021

Deepening moisture over the north through this period in line with the emergence of a monsoonal flow over Australian Waters, (not clear whether this burst runs over land) will lead to enhanced PW values not only running over northern Australia but being drawn southeast and east through the nation primarily, some of this moisture may also be drawn southwest over WA as well. Regardless of the chopping and changing, following the high heat over the southern and eastern areas of the nation, moisture will lead to more cloud cover and rainfall developing through this period.

Rainfall Next Week - December 9-16 2021

Early through this period, we will may be continuing to deal with widespread rainfall in the east with heavy falls as the low in the east departs. Then it may be dry for a few days, fingers crossed. Rainfall during this period is currently carrying a low confidence badge due to the uncertainty around the tropical influences. While the northern monsoonal weather sorts itself out, the east likely to be under persistent easterly winds with showers developing. The heat over the south and southeast in a northerly flow may be drier, the moisture eventually spilling south from the north and east and will then bring the rainfall back in the form of showers and thunderstorms across most states with uneven rainfall distribution.

Rainfall Anomalies - December 2-16 2021

Rainfall signals remain above average for the east and north with widespread showers and thunderstorms persisting over QLD and NSW. The emergence of the monsoonal activity over the north also lifting the chances of above average rainfall. Over the west, with the shift in the pattern, the drier spell may persist for the far south and southwest, leading to below average rainfall during this time. Near seasonal values elsewhere, however these zones could swing either way, depending on what happens with the monsoonal activity over northern Australia.

Temperature Anomalies Next Week - December 9-16 2021

Temperatures following a rain event later next week over the east may turn hot and dry in advance of the monsoonal pattern establishing up north. This often will displace the heat and propel it southwards leading to a spell of above average temperatures over southern Australia before the rain and humidity takes over. So if you are looking for dry hot weather for a number of days, we may be in luck over western, southern and eastern inland parts of the nation. The east coast may remain below average with ongoing rainfall and onshore winds.

DATA - Refer to the video for more information


12Z GFS Surface Pressure Pattern and Rainfall Distribution - Next 16 Days

The pressure pattern from this morning. You can see the latest run underneath.

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

Note the difference in the tropical weather and the placement of low pressure in the east as well. Where the monsoon forms (could be over Australia, could be in the Pacific) will determine the rainfall and temperatures moving into mid month and into Christmas.

18z GFS Precipitable Water Anomalies - Next 16 Days

Deep moisture returns over northern Australia and the movement of the tropical weather will determine where the moisture ends up in the medium term into Christmas.

18z GFS Rainfall Accumulation - Next 16 days

Note the tropical feature off WA - this will create havoc with the rainfall outlooks nationwide. I cannot stress this enough. Low confidence until we see more consistency on the weather over northern Australia.

12z Euro Rainfall Accumulation - Next 15 days

12z CMC Rainfall Accumulation - Next 15 days

More details coming up from 9pm EDT with the latest information on the model wrap and rainfall. The next major update tomorrow from 7am EDT and another 6 week outlook coming up Friday.