The heat and windy weather is spreading from SA into VIC, NSW and western QLD today bringing Summer back for many who have been experiencing the colder than normal weather for many months.

The hot airmass is connected to the severe heatwave conditions over the outback/desert regions of the nation, which in itself is not unusual for this time of year ahead of monsoonal weather developing.

A trough moving through SA brought high based dry storms yesterday, and it is now on into VIC and NSW today with scattered to numerous showers and thunderstorms developing, the storms becoming a lot more aggressive with modest moisture being fed into the trough as it rolls east.

Organised thunderstorms are forecast later this afternoon over eastern VIC and NSW where storms may produce damaging winds, heavy rainfall and a low end threat of large hail.

For the remainder of the nation, it is cooling down over SA with settled weather and mild to warm weather south of the heat dome over southern and western parts of the nation with ridging moving in from the Indian Ocean. Your forecast remains unchanged right through Christmas.

Up north, the tropical weather is expected shake and bake from next week into Christmas and New Year with one or two tropical lows floating about.


Rainfall Next 10 Days - December 18th 2021 - December 28th 2021

Rainfall is becoming more widespread across the model data sets this morning for eastern and northern Australia. Thunderstorms creating a bit of chaos when it comes to picking your exact rainfall but note that locally heavier rainfall is more likely to be seen across NSW, the ACT, through QLD and obviously over the northern tropics where the monsoon is expected to form offshore the coast. The models are struggling on when to introduce that unstable northwest flow over northern Australia which would then increase rainfall totals upon arrival. The wild cards for heavy widespread rainfall sweeping the nation will be connected to any tropical low pressure system that forms and crosses the coast and we have seen a range of ideas about that and will continue to see models chop and change. For the east coast, onshore winds, feeding a trough will increase rainfall from mid next week. The west and over much of SA and into western NSW through VIC, remaining mostly rain free for now beyond the weekend.

Rainfall Next 16 Days - December 18th 2021 - January 2nd 2022

Rainfall continues to build over northern and eastern Australia with a deep moisture supply. The weather will turn quite humid through inland areas of the east and north and along the passage of any low pressure system over northern inland areas of Australia, with rainfall totals increasing. Remaining dry and settled for southern areas of the nation near persistent ridging and subsidence. This takes us through to the beginning of 2022

Thunderstorm Forecast Saturday

Thunderstorms are forecast to be more widespread this afternoon and evening through VIC, NSW extending back into central Australia and over the NT and WA. The storm focus most robust over the Top End and over the southeast of NSW including the ACT and eastern VIC. Scattered storms could be gusty and heavy with small hail in the southeast. Storms could be gusty all the way through central Australia with little rainfall but tend heavier and gusty over the Top End where sufficient moisture returns and tends deeper along the north coast.


Thunderstorm Forecast Saturday

Thunderstorms are forecast to develop during Saturday afternoon in a hot and unstable airmass. Storms are initially elevated with damaging winds the most likely concern, with heavy rainfall leading to flash flooding and large hail risks over the southeast of NSW and eastern VIC where forcing is a little deeper. Thunderstorms will contract to the east during the evening.

Large Hail Risk Saturday

Large hail is a moderate chance over the eastern high country where the forcing is greater during the afternoon and evening and there is more wind convergence.

Flash Flood Risk Saturday

Flash flooding may occur over the southeast inland of NSW and into eastern VIC where thunderstorms train over wet catchments. A low risk as outlined extends back into the Riverina but it is low.

Damaging Winds Risk Saturday

Damaging winds is the biggest concern and while there are wind advisories for the strong gradient winds, thunderstorms pose the bigger challenge tomorrow with squalls up to 110km/h possible.

Thunderstorm Forecast Sunday

A cold front captures the slow moving trough and invigorates it over VIC and NSW during Sunday with storms tending severe with high winds and locally heavy rainfall. Small hail also possible in the stronger storms. Gusty winds and little rainfall expected over the outback, however as you move further north to the northern Top End and Kimberly, storms tend heavy with the chance of locally heavy rainfall.

Thunderstorm Forecast Monday

Thunderstorms contract into northern parts of the nation and become isolated in the east as the trough weakens and the dynamics supporting severe weather moves southeast and away. Heavy thunderstorms are possible over the northern third of the NT through to the Kimberly with a trough deepening over the region. Some of these storms could be gusty.

Tropical Depression Formation Risk - December 23-30 2021

Watching the region north and northwest of Australia where a tropical wave may begin to move into favourable conditions for further development into a low pressure system, enchanting rainfall but also allowing for a northwest flow to be drawn into the north of Australia enhancing rainfall as well.


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

A fast moving front today through the southern parts of the nation will invigorate a trough moving into VIC and NSW which will kick off thundery gusty weather, but bring about a cooler shift for the southern states after a hot Saturday. That cooler air won't arrive for inland areas of the southeast and east until Sunday afternoon behind the front proper. Thundery weather could be severe in the southeast and far northwest of the nation today. The trough then stalls out over NSW and QLD during Sunday with periods of rain and thunderstorms developing with those possibly severe in NSW, the ACT and QLD. A deepening heat low over the interior will keep the showers and storms going over inland areas of WA and NT with heavier rainfall for the coastal areas. The west and south through next week, into Christmas and New Year at this time looks seasonal, settled and sunny. For the east and north of the nation, the troughs will drive afternoon and evening showers and thunderstorms for much of the period with heavy falls for the NT and QLD, especially closer to the coasts in both regions. The low confidence forecast continues in relation to the monsoonal activity and how that spreads through the nation in the medium term.

12Z GFS - Precipitable Water Values - Next 16 Days

The moisture deepens over the course of the week ahead, we have a dry airmass that is dominating southern Australia and this will be in place for the majority of the outlook thanks to the high pressure nearby. The tropical weather is becoming more active with deeper moisture moving in from the north and west. A trough nearby leading to more rainfall developing. Over the eastern seaboard, onshore winds will pump moisture into inland QLD and NSW through to the ACT but struggle to pass further south until later in the period, when a more robust trough emerges through central and eastern Australia. The moisture from the developing monsoon in this edition of GFS places it over northern and eastern Australia keeping the west relatively dry.

12Z GFS - Rainfall Accumulation - Next 10 Days

Rainfall ramping up over the east and southeast throughout the week ahead with a series of troughs moving through the eastern inland triggering thundery weather, onshore winds returning will feed these troughs for NSW and QLD. The northern tropics ramping up in activity through this week and into Christmas with the monsoon on the prowl. The south relatively dry for much of the next 10 days.

12Z Euro - Rainfall Accumulation - Next 10 Days

Pushing the moisture a little further offshore WA and the NT hence why it is not looking as wet up north, but that could result in cyclone development. Scattered showers and thunderstorms over the east and southeast for much of the week ahead with uneven rainfall distribution. Dry weather remains in place for a good slab of the week ahead across southern Australia post the front and trough over the southeast.

12Z CMC - Rainfall Accumulation - Next 10 Days

Amplifies the monsoonal flow over the NT and Kimberly but not quite into Cape York. The southeast and east is thanks to the system passing through today and tomorrow and then again from mid to late next week with a developing trough, that will introduce better rainfall into QLD and northern NSW. The south of the nation and into the southwest should remain dry through Christmas.

12Z GFS - Rainfall Accumulation - Next 16 Days

The extended GFS amplifies a low over the Top End and pulls that into QLD and merges the moisture from the monsoon with the moisture pumped in via easterly winds which are likely to be ongoing for eastern Australia on top of a high. So the very wet signal continues. The west and south looks mostly dry for now, the rainfall over the east of VIC is conditional on the tropical feature moving into QLD. No tropical low of note on this run but as mentioned this will chop and change and expect further changes into the medium term.

12Z Euro - Rainfall Accumulation - Next 16 Days

The extended Euro single run with no adjustments shows that shift to the west with the moisture over northern Australia and an amplifying tropical feature. Moisture deepens over the remainder of northern and eastern Australia while much of southern and southwest of the nation looks dry for a while into January 1.

I will have another update at some stage this evening after a few Christmas events to attend. A reminder that I will be in transit on Monday to the NT so I will be possibly incommunicado for a period while getting there, with all the border requirements it may be a long journey - wish me luck!

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