NATIONAL WEATHER PICTURE - MORNING EDITION WEDNESDAY 12TH MAY 2021

Headlines


  • Severe thunderstorm outbreak continues over eastern QLD and NSW.

  • Heavy rainfall easing slowly through eastern VIC and southeast NSW.

  • Showery change still expected over southeast Australia later this week.

  • Weak change for WA, but remaining warm.

Nationally it is a quiet start to the morning away from the eastern third of the country, with a large high pressure system currently set up over WA and that is now ridging through to central parts of the nation, with a dry air mass and subsidence controlling a large part of the nations weather.


A weak cold front has crossed through southern WA today, and that has split the ridge in half - with a new centre of high to rapidly build in later today returning the west to dry skies with light winds.


That front will move east over the course of Thursday knocking out the trough and upper low from the east, and clearing skies there, but bringing the rain back to southern SA, VIC and TAS from Thursday with a colder showery airmass.



Over the south of the country, it is mild with an easterly flow. Temperatures are above average to start the day, the last morning like that for quite a while with a pattern flip on the cards. That front you can see above is set to bring a major drop in temperature with some of the coldest weather we have seen so far this year, expected this weekend.


A secondary shot of colder air coming up behind a front late Friday into Saturday will have a greater impact on VIC and TAS with widespread showers, with local hail and thundersqualls. Snow developing down to 900m in Victoria and 600m in Tasmania. Light showers may even make it to the Southwest Slopes and ACT during Saturday morning with a cold shot of dry air to follow.


That sets the stage for major frosts on Sunday morning right through early next week over large parts of eastern Australia, with the coldest mornings of the year to come. Hopefully that sorts out a few of the mice out in regional areas.


The showers will keep going to late Sunday over southern VIC and western TAS so a gloomy cold weekend is on the cards with very slow improving next week.


Temperatures will remain below average over the east with nights very much below average and daytimes struggling to reach average despite the sunshine, from that cold base start.


Euro Upper Air chart at 18000ft showing the flow pattern over the coming 10 days. Valid May 12th 2021.

Rainfall for the coming 10 days looks very coastal over Australia, as mentioned in recent updates. That trend does not look like changing anytime soon, which again is in line with the climate updates and medium term forecasting offered earlier this month. Now we are moving into that benign period.


Euro Rainfall 12z run Valid May 12th 2021 - Rainfall for the next 10 days.

GFS which goes out a tad longer to the 16 day range, is still supporting that wet signal returning come the 22nd of May onwards over western parts of the nation and then spreading east towards the end of the month. Now the below forecast rainfall accumulation will chop and change, but I do fully expect rainfall to ramp out to round out May and kick off June with above average rainfall expected for southern and western parts of WA and perhaps better rainfall scooting across to the southeastern states with frontal weather.


Rainfall over inland QLD for later in the run is not likely at this stage, however if moisture from the jet stream can come across and link into an upper feature, then sure, the below would eventuate, but I dare say it will be gone by the afternoon run.


GFS 18z rainfall accumulation for the coming 16 days - Valid May 12th 2021.


Rainfall forecast for the coming 10 days - Weather Matters Valid May 12th 2021.



Active weather continues to develop near an upper trough that is parked over eastern inland QLD and NSW, triggering multiple rounds of showers and thunderstorms, some have been severe overnight and this morning.


The thunderstorm coverage is expected to remain heightened over the coming 12-18hrs as the system slowly begins to lift to the east and north as the upper low over NSW begins to move east.


A more organised line of showers and thunderstorms may form this afternoon along the dry line, pushing into coastal areas by afternoon and evening, with a high chance of hail and strong winds.


As such no change to the thunderstorm forecast for today in both states.


Thunderstorm Forecast - Wednesday 12th May 2021

Thunderstorm Forecast - Wednesday May 12th 2021.

The currently satellite clearly shows the trough invigorating the showers and thunderstorms over the region, with some of them potentially gusty. Further thunderstorms are expected to form inland near the trough during the day time heating process as the upper low starts to approach with the trough.


Thunderstorm analysis as at 9am EST.


Current thunderstorms that are active - yellow

Convective region where further storms will fire - red

Upper low - blue.


Overnight there was some reasonable rainfall with falls of 20-40mm with scattered falls in excess of 50mm. Kingaroy received 60mm. That is their heaviest rainfall in quite a number of months. A similar spread of rainfall is expected on Wednesday before conditions settle down with a drier airmass on Thursday.


Rainfall observed overnight through inland QLD - 24hrs to 9am on 12th of May 2021.

The remainder of inland QLD remains dry and calm with high pressure ridging into the region. This will see the dry spell continue right into next week.


In the southeast of NSW, we still have heavy rainfall this morning, with scattered thunderstorms rotating around an upper low that is starting to lift north and east today. Flash flooding has been reported around Bega and Merimbula overnight with heavy falls of rainfall. 100-200mm has fallen in scattered pockets in the southeast with 30-50mm widespread elsewhere surrounding this.


A further 30-50mm of rainfall is likely today, possibly more than that, with local thunderstorms still rotating around the upper low as it moves north and east.


Observed Rainfall for SE NSW - 24hrs to 9am 12th May 2021.

Rainfall in east Gippsland also was locally heavy with 100-150mm of rainfall recorded in some locations with heavy rainfall persisting this morning. A further 30-50mm of rainfall is possible in the far east with locally higher falls bordering with NSW where thunderstorms move in from the Tasman Sea.


Observed rainfall for East Gippsland - 24hrs 12th of May 2021



Minor flooding has developed along some river systems overnight. Ensure you stay up to date with official warnings from the Bureau of Meteorology throughout the day.


Conditions dry out over the east tomorrow, but the rain as mentioned returns to the southern and southeast parts of Australia with the next cold front.


Want more information for your local town or holding an event you need weather advice for? email me at karl@weathermatters.org for further details on what I can provide for you.

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