Plenty of twists and turns in the weather this week coming up. Today we are dealing with the last of the troughs rotating through the southeast, with the departing low slowly moving east. A cold pool aloft is leading to more widespread cloud and showers about the southern inland.
We have a stalled boundary over the southeast, this trough connected to the low moving away to the east. A cold pool to the north of this boundary is triggering areas of light rainfall, heaviest in the southeast. A few showers and cloud have been floating under the cold pool through southern NSW as well, which has saved some areas from frost.
Rain is staggered along the northern flank of the departing low, the trough is moving north but because it is attached to the low moving southeast, it appears to be stalling and therefore where it is raining now is where it will stay for much of today. Scattered showers could develop under the cold pool over inland areas this afternoon.
Cold west of the divide this morning, areas of frost have been observed in scattered pockets, but where the cloud lingered, those areas were spared the worst of it. The coldest weather this morning is back over the far southwest and northeast.
Dry weather returns to the region from Saturday with a northwest flow developing.
A weakening trough passing through the southeast states on Sunday will bring elevated showers and thunderstorms to the southern and southeastern areas.
The weather then following this system warms up from next week, a new high settles in over the eastern inland of the nation directing a warm northwest flow throughout the a large portion of the nation. That is all ahead of a strong upper trough and cold front which is continuing to evolve on the charts.
Colder shift is possible behind the rainfall next weekend so a heads up that the warm weather at this time of year is followed by wintry air, we are still in the range of wintry westerly bursts.
We saw last night widespread rainfall spreading through from west to east, today we are seeing the block come back in the Tasman Sea, that forces the low south, but the moisture over the eastern inland is still lifted by a trough. Like I said last evening, the rainfall in the medium term comes and go so look at that rainfall on your apps and other contraptions as signals not a forecast of any confidence.
Lets have a look
12Z GFS Surface Pressure Pattern for the coming 16 days
The pressure pattern is largely unchanged this morning with the modelling good surrounding the movement of low-pressure system slowly passing southeast. There will be a trough that rotates around this low that sits over the southeast but hits the ridge and moves out of the region this evening into Saturday. There will be a few showers about the southern parts of VIC and NSW this weekend as a trough passes through from SA. That trough is expected to remain inactive over SA but once it finds the moisture over the east, we see the rainfall increase. Otherwise, the region dries out and warms up next week ahead of a cold front that delivers well above average temperatures. A band of rain will develop from the west during Wednesday afternoon over WA and then passes through SA Thursday or Friday, with the system’s strength and speed determined by the weather occupying the Tasman Sea which we can see playing a part in the rainfall spread. Medium term, there are more weather systems rolling through the southern parts of the nation, moisture building up over the northern and eastern parts of Australia, this lending the forecast trend to turn more spring like and move away from the winter weather associated with the westerly winds.
12z GFS Rainfall for the coming 16 days
Rainfall continues to dominate over the southeast of the nation today, most of the rain over southern NSW and southeast VIC will be connected to the trough. The system coming through on Saturday over VIC will have more isolated showers, before the coverage turns scattered during Sunday as the trough runs into better moisture over the east and into eastern NSW. The chance of thunderstorms over eastern VIC and southeast NSW could bring further moderate falls. Next week it dries out and then we see another stronger system on the approach and how that performs is determined by weather in the Tasman Sea. More rainfall can be seen beyond this, but the pattern is looking spring like and that will lend itself to more productive rainfall events, models won’t see it this far out. Note the presence of more low pressure systems with the modelling starting to pick up the interaction of the warm than average air and the colder than average air, battling it out over the region, which means rainfall will be very tricky to pin down in the longer term, but it is still there and the signals will develop.
12z GFS Precipitable Water Anomalies next 16 days
No real change to the guidance overnight which is nice. The drier air over the nation is starting to be overrun through northeast part of the nation with trade winds and with another impulse over the southwest of the nation. This will start to erode the dominance of the drier air under high pressure and by next week, we will have widespread moisture passing through from the easterly winds and then being pumped into the eastern and central inland of the nation. The trough over eastern inland QLD will bring showers and storms as the moisture is lifted through the region. A signal of the seasonal shift underway and we are seeing that reflected in the temperatures throughout the southern and eastern parts of the nation. A strong cold front and trough then runs into this moisture, you can clearly see this being drawn in from the north and northeast, this is where the rainfall begins to break out over Central and Eastern areas. But where that occurs is still being ironed out and the timing will be crucial to seeing who gets what. Through the medium term we will be watching the north of the nation where moisture increases and whether the Indian Ocean will decide to wake up and play a part in introducing rainfall through the north and west of the nation.
12z Euro Surface Pressure Pattern for the coming 10 days
The Euro in good agreement with the GFS showing the rainfall over the southeast of the nation today with a low pressure system starting to form over the Bight. The trough over the southeast will bring the wettest weather to the nation, with moderate falls possible in the coming few days. Then you can see the impact of the moisture seeping south through QLD, combining with a trough and onshore winds to bring showers and storms through the weekend and into next week. A strong cold front, is expected to move through WA and into the southeast state from later next week, running into moisture and widespread rainfall likely to develop. This morning, the front is being analysed to be forced south however the inland moisture coming in from the east and northeast, means that the rainfall potential still exists, it is just a matter of how widespread and how heavy it will be, this determined by the low pressure system moving east or south over the Bight.
12z Euro Rainfall for the coming 10 days
The rainfall is split with the system next week, the GFS has a rain band coming through SA and into the VIC and NSW no problems, even with the low dividing southeast. The moisture is able to race into Central Australia and then be lifted up by the front passing through. The Euro places the moisture further east hence the lighter falls over SA but good rainfall still for the east and southeast inland. The rainfall will chop and change and this will be the case for the next few days so keep checking back.
12z Euro Precipitable Water Values next 10 days
Very similar to the GFS with the moisture gradually building back up with widespread showers and a few storms developing first in QLD thanks to the trough in the region combining with onshore winds before that weather turns south to spread the rainfall down to about the Wide Bay and Sunshine Coast. A series of troughs out over the west tries to bring in modest moisture through the southern and eastern inland of the nation this weekend but the drier air looks to win out there. It is still next week, once a high has re-established itself over the east, a stronger longer fetch easterly wind will propel the moisture inland to the NT and SA and this is swept up by a strong front which leads to the most interesting system on the board over the coming 10 days, that will likely introduce widespread rainfall for the nation. How far west the moisture comes will determine the spread of rainfall with the first system. There is more moisture left behind for the second week of September.
Rainfall for the next 10 days
Not a whole lot of change to my forecast, with the models still moving that rainfall around next week over the nation, but there will likely be a large scale rainfall event moving eastwards this time next week. But between now and then, rain areas today with light to moderate falls continuing along a stalled boundary over the southeast of the state. A weakening front and or trough passing through Sunday brings the chance of showers back with a few storms. That could drop 5-15mm through southeast inland parts and along the southern ranges. Then dry at warm to hot until more rainfall arrives this time next week into the weekend, where the bulk of what is drawn in here will fall.
I will have another look at the medium term and the Summer 2021/22 outlook later this morning. Updated rainfall charts this evening in the PM Updates so come back then to see the latest full forecasts then.