NATIONAL WEATHER PICTURE - EVENING EDITION - WEDNESDAY 19TH MAY 2021

Headlines


  • Quiet weather pattern continues to evolve

  • Showers creeping onto the east coast

  • Showers developing for southeast Australia overnight.

  • Pattern flip next week.

Well for a weather watcher/forecaster, it is quite boring at the moment, with not a great deal of weather to occupy the mind at the moment.


If you were looking for rainfall - sadly not a lot over the coming week for the eastern, central and northern inland of the nation. The better chances will be back in SWLD of WA and through the southern and eastern coastal areas with weak fronts and onshore winds.


High pressure dominating the Australian charts at the moment and likely to be the case for a number of days to come for the short term.


National Satellite - Valid Wednesday May 19th 2021.

Bone crushing subsidence over most of Australia keeping many places fine and dry. Some high cloud over the southern states is fair weather. Convective cloud, low topped showers moving parallel to the coast in NSW and QLD, now starting to move closer inshore this afternoon and this evening.

The pattern is lending itself to keep the rainfall coastal and inland areas dry. High pressure moving east over the coming days will take the shower activity from the southeast coast to the east coast, with a damp weekend on the way with passing showers.


Otherwise we have to wait til later in the weekend for the pattern flip to develop, with a front lurching up from the southern ocean to reach the SWLD of WA with gusty winds and cooler change with showers. That will see the winds become northerly over the east with temperatures on the rise through the weekend and into early next week.


GFS Temperature anomalies for Monday 24th May, showing that push of warm dry air into the east while the west finally cools down after 10 days of well above average temperatures.

The main mechanism for the pattern flip will be a strong cold front that is set to move through WA as you can see above, this pushing the high into the Tasman Sea, and allowing the frontal weather to move east next week.


However, with the upper high so strong in the Tasman Sea, the front will likely peak to the west of SA and VIC, meaning that the bulk of the heaviest rainfall will drop in WA with lighter falls for the east. Something is better than nothing I guess.


GFS 00z Run at 500mb showing the front peaking over WA early next week.

By Tuesday the system is being weakened by the upper high over the Tasman, forcing the long wave trough to push southeast with first front also sliding southeast through the southern states.


GFS 00Z run at 500mb for Tuesday May 25th 2021.

And by Wednesday, all that is left is a weak cold front being analysed through the southeast inland. There will be some patchy falls along this boundary as well as a lot of cloud, but not the widespread rainfall that it could bring - however this is a week out and may still change, but on current guide it is looking lean for rainfall.


GFS 00z run at 500mb showing the front petering out over the southeast states, however a parcel of colder air may hang back over SA, which is also an element to watch.


As a consequence rainfall, is quite lean over the coming week still, but the better rainfall odds are still placed as advertised over the last week for southern Australia, beginning in the last week of May into early June, with a northward surge of westerly winds. That signal is still present on charts this evening.


Rainfall for the next 10 days - GFS. It has a bias on more coastal rainfall with a system developing over the east towards the end of the month. Euro is opposite and has more rainfall for coastal areas next week. So these charts will continue to iron themselves out over the coming few days. Valid May 19th 2021.


For eastern areas of the nation, the onshore flow should start to freshen mid to late this week with showers increasing Friday onwards with a damp weekend on the way from about Noosa through to Newcastle. The heavier of the falls are expected for NSW coastal areas north of Newcastle with fine and dry weather south to the VIC border along the coast.


Satellite imagery showing the onshore winds now dragging that low level moisture onto the coast with isolated showers forming under the cumulus. But as the winds turn more unstable easterly on the weekend, the showers will have a little more punch to them through this region. Valid Wednesday May 19th 2021.


The rainfall forecast for the coming 6 days - was issued yesterday but is still applicable for today given the current guidance from the 00Z model run.

Rainfall chances then shift to the south of the nation next week, starting off in WA, with the strong system rotating through on Sunday bringing gusty winds, showers and possible thunderstorms. The major impact will be in the temperatures falling away from the mid to high 20s down to the mid to high teens. With passing showers and thunderstorms, it will be quite a shock to the system.


Temperature anomalies running well above average out west through Friday and Saturday with that cold front lurking to the south, ready to pounce on Sunday. Valid Wednesday May 19th 2021.

And there is the marked change in conditions for the nation, with the west feeling that colder air and showery weather, contrasting with a very warm airmass racing east and south ahead of the front on Monday and Tuesday. Valid Wednesday May 19th 2021.

With the showery weather over a number of days, starting Saturday through Monday, rainfall could stack up for parts of the SWLD with over 50mm possible about the inland areas facing west along the Darling Scarp, down to the southern coastal areas west of Albany.


Rainfall for the next 10 days - Two frontal passages expected through this period, but upwards of 30-50mm could fall widespread this weekend into Monday,

This front will be the one that comes across the southern coastal areas next week, bringing up rainfall chances. Some of it could still accumulate nicely even though the system is in decay. It will depend on how much moisture can survive the journey across and be utilised by the cold front as it passes through. That we will know more about over the weekend.


Precipitable Water Values - Early next week ahead of the front look promising, but it will come down to the lifting mechanism that will be in place that will determine how much rainfall is occurring and how widespread it will be. Valid Wednesday May 19th 2021.

Much better signals for rainfall exist beyond the scope of 10 days out in the late month into June with more frontal weather as the SAM goes negative. That will see more chances of the westerly wind belt moving north.


Southern Annular Mode - Forecast for the end of month. Follow the bold red line. A few members are going well below the neutral values with a handful going the opposite way, but the bias is negative.

As a consequence the rainfall at this stage should become more widespread over the coming two to three weeks.


Rainfall for the next 16 days - Valid Wednesday May 19th 2021.

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