NATIONAL WEATHER PICTURE - AM EDITION - WEDNESDAY 26TH MAY 2021

Headlines


  • Showers easing for NSW Wednesday morning.

  • Showers for southeast Australia to continue on Wednesday.

  • Dry and warm in the north and west.

A cold front has weakened substantially overnight as a low pressure system attached to the system, washed out and moved south of Tasmania. The main dynamics driving the robust rain band yesterday through the southeast now collapsing and dying off conditions unfavrouable to support widespread rainfall along this system. You could almost now call the front a weak trough over central and northern NSW.


Showers will continue today for southeast SA, southern VIC and especially western TAS where some heavy falls are possible.


Out west it is warm and dry, though cloudy skies are expected from time to time, with a pressure trough offshore. That cloud will linger into Thursday, but little to no rain expected for the state.


Very warm through northern NSW and QLD ahead of the trough, which will move over the area on Thursday. Also quite hot and dry through the NT, with the above average temperatures continuing.


National Satellite Picture - Wednesday 26th May 2021.

The cloud band over inland NSW is thin and producing very light showers, most of these will clear this morning. The cold air through Bass Strait can be seen via the cold tops on the satellite, with some thunderstorms and hail over coastal areas of West Gippsland. High and mid level cloud stream into WA is mostly fair weather, a couple of showers possible under that, but the air is dry so no measurable rainfall likely. And high cloud off the southwest coast is also fair weather but will likely bring some obscurity to the lunar festivities tonight out west.

Temperatures behind the front this morning over the east are much cooler, with showers still ongoing over the southern coastline. Cold with frost about the inland of WA this morning with clear skies and light winds under a high. It is mild ahead of the trough through inland NSW and southern QLD, with well above average minima. Elsewhere, I would call it fairly seasonal, though still a bit soupy over the Top End this morning.


National Temperatures - as at 6am Wednesday 26th May 2021.

Rainfall for the next 10 days is again restricted to the southern coastal areas of Australia with onshore winds over the coming days, then onto the extreme eastern seaboard with a southerly wind change over Friday and Saturday. Then heavy rainfall developing over WA with the next storm system. That will be the wettest part of the country during the next 10 days with heavy falls and potential for a severe weather event to unfold through the SWLD.


GFS Rainfall Data - Valid Wednesday May 26th 2021.

Note the moisture pooling off WA during this period and being dragged onshore later in the run. This COULD be fed through the jet stream and may bring some rainfall into inland parts of the NT and QLD, possibly SA, but the confidence in this sequence is low.

Rainfall forecast for the coming 10 days - Valid Wednesday May 26th 2021.

I have gone with the higher confidence solution of keeping the inland of QLD and NSW dry for now with some models showing rainfall later in the run. I have been saying most of this week, with the low coming out of WA, we will likely get a better handle on that by Thursday or Friday this week. It is now looking more likely that system will drift towards SA next week bringing light falls to the west and south coasts.

The synoptic scale is starting to settle down, thanks to a ridge moving in. You may notice on the satellite this morning, the impacts that ridge out west and the one to the east of the nation had on the cold front and low moving over the southeast, forcing the system to not only weaken, but be shunted south. That will continue today, with rainfall becoming rather scarce across the nation away from coastal areas.


Broadscale Synoptic for the coming 7 days - highlighting the low pressure over WA - GFS 00z Run - Valid Wednesday May 26th 2021.



GFS flow pattern at 500mb - Valid Wednesday 26th May 2021

High pressure quickly ridging into the Bight and clearing skies. A weak front over the southeast later today will bring another burst of showers. The trough over inland NSW and QLD will become inactive and lift out of the states during this afternoon and evening.


That will likely continue for Thursday and Friday with high pressure the main feature.


GFS flow pattern at 500mb - Valid Wednesday 26th May 2021

High pressure strengthens over the Bight, heights well above normal over northern Australia meaning above average temperatures to continue for the remainder of this week in the tropics. A cold southerly flow will keep showers mainly parallel to the NSW coast over the course of Friday and into the weekend. Winds increasing over southwest WA with the next front approaching. Settling skies over the southeast.


In the Tasman we will see a strong southerly surge behind a whopper cold front over NZ, this will send up very large and powerful surf along the NSW coasts with a high chance of damaging surf about Friday through the weekend. Coinciding with high astronomical tides, erosion is possible along the east coast. A few showers for coastal areas is all that will develop from this system and falls will be light.


GFS flow pattern at 500mb - Valid Wednesday 26th May 2021

The ridge holding firm over much of southern Australia. The wave in the Tasman fully verifies and sends a surge of colder air into the eastern states, but showers are few and far between for the coast. Large and powerful waves likely. Heights coming down over the tropics so a few degrees cooler come the weekend. Rain and storms for WA with a cold front and upper trough starting to move over the region.


Out west, the next major storms system looms with a strong cold front, linking with tropical moisture to bring areas of rain and thunderstorms to good portion of the west coast and adjacent inland. Some moderate to heavy falls can be expected with this system.


As the front slows down during Saturday over the Wheatbelt, it is likely to be invigorated by a shot of cold air riding up from the south, thus helping to deepen the front into a low pressure complex over the SWLD.


GFS flow pattern at 500mb - Valid Wednesday 26th May 2021

A low pressure system forms in the upper levels and deepens at the surface off the south coast of WA bringing widespread rain and thunderstorms to the region, with moderate to heavy falls. Heights are falling over the mainland but with high pressure at the surface and a relatively dry airmass, no rainfall expected. Temperatures will be coming down for a lot of mainland Australia, over the north. Showers should continue for mainly the central and hunter coasts of NSW in southerly winds over the weekend with heavy seas. Dry elsewhere.


That low becomes slow moving during Sunday and Monday, with heavy rainfall, damaging winds and large seas over the coastal areas of SWLD. The location, timing, intensity and scale of the system will be determined in coming days, then more accurate rainfall and severe weather products can be issued, but for now the region of risk is rather broad along the west and south coasts.


All the while this weekend, in the east and southeast it will be mostly fine, partly cloudy and cool. Frosty nights to return to inland areas of NSW, VIC and southern QLD in light winds and clear skies. No rainfall is anticipated in these regions.


GFS flow pattern at 500mb - Valid Wednesday 26th May 2021

Deep upper low, which will be vertically stacked at this stage, over the south coast of WA with widespread rain and thunderstorms continuing and showers and hail for the inland of WA. Heights have come down over much of the mainland with a good surge of colder drier air coming through northern Australia. The ridge holding over southeast Australia this keeping a lot of the mainland rain free and sunny.


Next week that low over SW WA will begin to move east towards SA by Tuesday and should start to spread cloud and patchy rainfall into the west of the state. Light falls are anticipated for now, but it is a week out and this sequence will likely change given we are dealing with a cut off low pressure system.


Some models suggest to shift the low into the inland of SA, some modelling suggests to shift it east towards NSW and VIC and some shift it south and away from land. One way or the other, there will be some cloud and showers spreading along the southern coast of Australia under any of these scenarios, but it is how heavy and persistent the rainfall is that is uncertain at this time.


GFS flow pattern at 500mb - Valid Wednesday 26th May 2021

The ridge weakens over the southeast now allowing the low pressure system to lift out to the east or northeast, rather than the signals yesterday with a stronger high in the east forcing this low south. The euro model is very similar in this idea, but for now it is still a LOW confidence forecast. Light rain would move into southern areas of SA during Tuesday under this scenario, with showery windy weather continuing for southern WA with moderate falls. The zonal flow over the remainder of the nation is rather stable with no embedded low pressure at this stage so dry weather continues for the east and north.

Temperatures for the period will remain cool over the east and southeast with a high anchored west of the states here. This will likely persist over the weekend into next week as the southerly flow takes a while to ease. In the west, warm and humid northwest flow over the Pilbara will extend into the southern inland and western SA during the weekend and next week as a slow moving low moves south of the region.


GFS Temperature Anomalies - Valid Wednesday 26th May 2021

That southerly influence over the weekend will keep things pretty cool, despite it being cloudy and mostly dry. In the west, that warm and somewhat humid air will slowly filter eastwards towards SA come Sunday with more clouds than sun, but thanks to high pressure relatively dry weather for now.


Colder weather on the western flank of the low over the SWLD will keep temperatures slightly below average for most. Hot over the north, that will settle over the weekend before becoming very much above average next week.


GFS Temperature Anomalies - Valid Wednesday 26th May 2021

Then ahead of the low pressure wave moving into central parts of the nation, the warm air will be transported eastwards so some sunny warm days to kick off June over the east is likely.


So nothing brutally cold in the outlook period coupled with rain and strong winds, so graziers can take a breather. Farmers should be aware of the frost returning to southeast and eastern inland areas this weekend.


Severe weather possibility remains moderate to high for southern and western areas of WA this weekend, with that region of impact becoming refined as we go through the coming 48hrs.


Hot weather continues for the north, though a drier southeasterly surge will make it's way north over the weekend, before the temperatures heat up again into next week.




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