NATIONAL WEATHER PICTURE - AM EDITION - TUESDAY 25TH MAY 2021

Headlines


  • Welcome rainfall arrives in South Australia.

  • Rain developing for VIC, TAS and southern NSW Tuesday.

  • Drying out over the west.

  • Warmer and dry for the north and east.

Finally, some welcome rainfall has been falling over large parts of southern South Australia overnight with a front that is travelling east on Tuesday. Moisture in the jet stream has been reinjected into the front and this has caused a large rain band to form along the axis of the front as it moves east today.


That rain is moving into VIC and TAS this morning and into southern NSW during Tuesday afternoon and evening. Moderate falls are expected about the Great Dividing Range with this feature, with lighter falls elsewhere.


Clearing skies over WA today, with the airstream easing and tending more stable with a ridge moving into the region.


Ahead of the cold front over NSW and QLD, warm autumnal weather is continuing with clearer skies and a westerly wind regime developing.


National Satellite - Valid Tuesday 25th May 2021.

Cold front advancing east with a large baroclinic cloud band extending from the northwest through the southeast. Rain is falling under the southern branch of that cloud band through South Australia and into Victoria and Tasmania. Moderate rainfall has been observed.

Low pressure has formed in the cold airmass in recent days, and against all modelling has maintained a reasonable centre of circulation on Tuesday. Scattered showers and thunderstorms are presently rotating around this low pressure. Some areas of southeast SA and southwest Victoria could see some thunderstorm activity this afternoon with small hail.

The rainfall will extend eastwards into Victoria and NSW this afternoon with some moderate falls expected on the northern slopes of the Great Dividing Range in Victoria and the western slopes of the Snowies and Great Dividing Range in NSW Tuesday night into Wednesday. Some areas could see 30-40mm out of this system.


Rainfall forecast from Monday for this event - it is verifying quite nicely for most of the viewing area. Valid Monday May 24th 2021.

Rainfall was widespread over parts of South Australia up until 9am this morning. 35mm at Mount Hope was the top fall. 26mm at Streaky Bay also very welcome.


Observed Rainfall for the 24hrs to 9am on the 25th of May 2021.

The rainfall is expected to ease during Wednesday over NSW before clearing the inland areas during the day. Showers will remain fairly coastal through SA and VIC/TAS with onshore westerly winds. That will keep thick cloud cover in place and consequently back to cool gloomy conditions.


During mid to late week, conditions nationally become relatively benign once again with high pressure dominating the synoptic scale. That will send the inland back to cold nights with some risk of light frosts, especially at elevation, but rainfall will be very restricted to coastal areas of southern Australia where the cloudier skies will be.


Upper flow pattern later this week showing that high pressure taking control of the nation. In the Tasman Sea - there will be a significant shot of cold air with very strong southerly winds sending heavy seas into the NSW coast. That will bring drier air into the north of the nation with a reduction in temperatures. GFS 12z run Valid Tuesday May 25th 2021.

The weather then turns wet over WA with significant moisture pooling offshore later this week, being picked up by the next cold front, delivering widespread rain and thunderstorms once again to the west coast and SWLD. Some moderate to heavy falls are likely once again under this sequence.


Upper flow pattern for Saturday showing the long wave troughs on both sides of the nation, with ridging for the majority of the continent, leading to more settled weather for 95% of us. GFS 12z run at 500mb valid Tuesday 25th May 2021.


The weather will turn sharply colder with a low pressure system likely to form somewhere over the SWLD during the latter part of the weekend, into early next week. On the northern flank of this system, there will be a large cloud band form, but due to the ridging in the east, which is still likely to hold firm, not much rainfall is once again anticipated from this mass of cloud over interior regions.


There is the potential for a severe weather event to unfold from this low pressure system, but once again, as per yesterday, we will not know until we get closer to the event, which may be from Thursday or Friday this week.


Low pressure at the middle levels of the atmosphere along the south coast of WA bringing windy wet weather to the region. This system is expected to be up against it as it moves further east with ridging still in place across the southeast, blocked by the large scale winter weather over NZ. Valid Tuesday 25th May 2021.

Surface pressure pattern shows the system developing into a low pressure system, drawing in a rain band initially over WA and then that low driving the severe weather potential over the southern coastal regions. Meanwhile, a large slow moving high over SA and VIC will remain in place for a number of days, due to a significant wave of low pressure in the Tasman Sea, blocking the flow again.

So with that said, rainfall for the next 2 weeks remains quite decent for WA with moderate to heavy falls and numerous waves moving through the region. These systems will seep further east with dribs and drabs likely to bring patchy falls through this period. With the ridge holding firm over much of the nation, dry weather is likely over QLD and much of the NT and northern SA and NSW.


This is likely to be the driest spell for the east coast of Australia in the past 12 months. There will be showers running parallel to the coast over the weekend, but largely this region looks dry for the coming 10-14 days which for this area, is welcome.


Rainfall for the next 2 weeks - Valid Tuesday 25th May 2021.

So for areas further east over SA, VIC and southern NSW, remaining lean on the rainfall front beyond the system that comes through over the coming 24hrs. But that could change with a nudge to the east of high pressure over the weekend and into next week. So will watch trends. It is not a dry 2 weeks for the south of the nation, but the wettest areas will be over SWLD of WA and through western TAS.


Rainfall for the next 10 days - Valid Tuesday May 25th 2021.

Over northern Australia (who it is easy to forget about at this time of year), things are expected to dry out with a nice southeasterly surge anticipated over the weekend and early next week. Along that dry line, some showers could develop for eastern areas of the Top End with light falls of 10mm or so. Dry elsewhere with increasing fire dangers.


Over FNQ, showers, heavy at times between Cooktown and Cairns, with up to 50mm possible for the region, otherwise it is a bone dry outlook for inland areas of both these regions.


Relative humidity values - 2 week outlook - Valid May 25th 2021. Note that the overnights are usually more humid at this level which is very normal. But the day times are drier and get drier as we get into June which is climatologically accepted for this time of year.

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