NATIONAL WEATHER PICTURE - SUNDAY MAY 9TH 2021

Headlines


  • Thunderstorms to return to NE NSW this afternoon.

  • Showers increasing for SE SA, Victoria and Tasmania on Sunday.

  • Warm sunshine for the west and north.

After some patchy rainfall over the inland of NSW overnight, an upper trough is expected to kick of a few thunderstorms about the Mid North and Northern Rivers this afternoon. Thunderstorms can also be seen dancing off the SE NSW coast this morning with some reports of loud thunder from coastal communities, but little rainfall.


Satellite shows the upper trough moving through into eastern NSW this morning where it is running into better moisture profile over the region.


27mm at Narrabri is the top fall with a few 10-20mm rainfall totals this morning near Tamworth as the leading edge of thundery rain moves further to the south and east.

Rain radar as at 8am EST - showing the rain band moving slowly east. Even some falls have snuck into southern QLD which is welcome, where no modelling really had forecast that happening.

The national satellite picture also shows a cold front on the approach to the southeast mainland this afternoon. A sizeable cloud band has developed along the front, but the showery band that is expected to make landfall today will not be as large.


Otherwise the nation is clear through the north and west as well as central areas, thanks to a drier airmass and a high ridging in from the west. This starts a nice stretch of warm sunshine for WA and the NT.

Temperatures to start the day are cool in the southeast where we had some morning fog and a little frost, but otherwise fairly seasonal elsewhere, under cloud over NSW and QLD, it was mild and a cool start out west but temperatures will be moving above average today. Warmer than normal over the north with shallow moisture keep the temperatures up along the northern coastline of Australia with a hot drier day to follow.


Temperatures to start the day over the nation - Valid 830am EST




Thunderstorms are possible about NE NSW today and along the Victorian coastline with a fast moving cold front.


Thunderstorms over NSW will be strong to severe about the Mid North Coast and Northern Rivers with the passage of the upper trough. Storms will have the chance of turning severe with damaging winds and heavy rainfall the main concerns this afternoon. Large hail is a low chance. There is a 60% chance of thunderstorms forming in this zone this afternoon within 25km of a given point.


For Victoria, showers and the chance of thunderstorms developing along a cold front moving through the region this afternoon. Damaging wind gusts are possible but the risk is not especially high. Cold air showers following the front, may bring strong gusty winds to the coastal regions, with the chance of small hail and a rumble of thunder. There is a 50% chance along the coast of thunderstorms forming within 25km of a given point.


A very slight chance of a thunderstorm about the south coast of NSW this morning, with most of the activity offshore the region today as the upper trough moves east though thunderstorms could return to this region on Monday.


Thunderstorm Forecast for Sunday May 9th 2021. Weather Matters

Rainfall for the next few days is still highly variable given the cold air lurking about, with upper lows wafting around and moisture content damming along the east coast with the troughs and weak onshore winds.


A great example is the surprise rainfall over the Northwest Plains overnight with 10-30mm falling through NSW.


Showery periods over coastal SE SA, Victoria and western and southern Tasmania will continue to produce moderate falls through the week. The front that was expected later in the outlook looks now to be washed out and kept south by a ridge.


Inland NSW and QLD, especially in the east of these states, could have showers and thunderstorms return from mid week with a stalled trough, but again confidence is not especially high given the amount of model conjecture at this time. We will probably get more confidence in the evening data tonight on this.


In the west we are looking at dry week with a warm to very warm easterly flow which will dry.


The north, dry season bliss to start the week, though humidity levels will creep up a tad as we go and showers will redevelop for Cape York.


With the low confidence forecast, it is probably easier displaying the raw data for now. My forecast charts will be updated this afternoon.


Euro Rainfall Spread for the next 10 days - LOW CONFIDENCE forecast period. Euro 12z run valid 9th May 2021

For reference - this was the Euro Model from yesterday morning, and it did pick up on the heavier falls over the NW Slopes and Plains in association with that pressure trough. It also was the first to start picking up on heavy rainfall potential for the southeast of NSW and Gippsland in Victoria. We will see how that looks tonight.


Euro Model - 18z run May 8th 2021 - 4 Day rainfall accumulation.


The upper air charts are the best way at looking at not only the flow pattern, but where the weather is being driven at the moment, with pools of cold air being driven north and cut off from the main westerly wave action south of the nation.


That will mean rainfall events will become very tricky to pin down, as they will be associated with the placement, track, intensity and speed as to how these features move through.


That means from run to run in model data you will get great variation of rainfall distribution associated with these systems. As the avid amateur weather watchers know, they can disappear altogether.


Euro 500mb flow pattern for the next 10 days - Valid May 9th 2021. 12z run

You can see from the data this morning, there are multiple attempts at bringing through upper level disturbances which in turn deepen over the east coast bringing periods of heavy rainfall to the NSW South Coast in particular through this period.


Two cold fronts come through southeast Australia now, one today bringing a burst of rain and thunder and then another later in the period.


Showers will be confined to southeast SA and southern and mountain Victoria with moderate falls. Local hail and thunder is possible about coastal areas. Showers may turn to periods of rain over western Tasmania with heavy falls in the usual spots. Lighter falls making it to the east tonight and tomorrow morning.


Behind this first front, the model suggests that a parcel of cold dry air will move north of the front and into NSW on Monday and Tuesday setting the stage for unsettled weather for the eastern third of the state.


The model also suggests this may help to develop an east coast low off the South of Illawarra coast line during late Monday into Tuesday with moderate to heavy falls about. But the GFS model is not so keen on that idea while the ACCESS and CMC models are somewhat on board but with the low pressure in different positions and at different strengths meaning that rainfall is variable.


For now we will stick with the Euro. The first system carries a low confidence but could be quite productive once again for SE NSW and Eastern Victoria in particular with scattered falls back along the GDR to about the QLD border.


There is a secondary shot of colder air that the models indicate comes up later this week into the next weekend with another round of showers and storms for the eastern inland and showers and thunderstorms with moderate falls once again for the coast of NSW. That system carries a VERY LOW confidence as it is out in voodoo land but we will track the merits of that as we go through the week.


Showers will redevelop for the QLD coast north of about Mackay as easterly winds return. There could be some moderate falls from about Cardwell northwards in those trade winds.

One or two showers could creep over the Gulf into the eastern Top End with light falls expected there in onshore southeasters.


The west is mostly dry this week. Perhaps a cold front moving in towards the end of the period but lets just call it dry and warm for the most part and a better handle on that approaching system can be had mid this week.


You can see the above in the video below showing the surface pressure pattern and rainfall forecast every 6hrs for the coming 10 days. BUT I do stress, this will likely change with some of the low pressure systems forecast out east, possibly dropping off the charts at times. Conversely, the models could ramp up the presence of low pressure along the east coast, but for now it is best to go with the straight bat down the middle and keep it as LOW confidence.


Surface pressure pattern and 6hrly rainfall analysis - Euro 12z run May 9th 2021.

The west and north remain dry and complication free with temperatures well and truly moving above the average, but the cooler drier nights are not too far away for the Top End of the NT, especially if there are two shots of colder air that ride north through the eastern inland, bringing up a nice southeasterly surge.


We need a big flush of colder air pushing over the southeast states and the highs to be a little further north and more mobile, to get the dry season in real full swing.


I will leave you with this image which shows the rainfall anomalies for the coming 2 weeks off the GFS, which highlights the high degree of uncertainty, these shoulder seasons produce. Is it going to be a dry end to the month? Or is the Euro right, we see a wet week for the east coming up and rainfall increasing over WA for the end of the month??


GFS Rainfall anomalies - 18z run for the next 2 weeks. Valid May 8th 2021.



Time will tell.


Want more tailored forecasting notes and analysis for your region? email me at karllijnders@weathermatters.org for more details and about how I may be able to assist.

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