The rain will extend north and east through the day but ahead of that rain, a warm and breezy day for central and northern parts of the state.

Satellite picture shows all the ingredients slowly coming together, the warmer airmass is well and truly identified throughout the eastern and southeastern parts of the nation. The colder airmass is developing through the southeast later tonight as the front crosses through with a burst of rain and thunderstorms. That arrives in NSW from Monday night into Tuesday.

The warm sector may also give rise to thunderstorms developing through the state, some of these could be gusty with moderate rainfall.

Thunderstorm Forecast - Monday 23rd of August 2021

Storms are a high to very high chance across the southeast and eastern inland of the nation, with gusty winds the main concern. The storms will be discrete ahead of the rain band but become absorbed into a larger rain mass that forms tomorrow evening as the cold air runs over the warm air.

Damaging Winds Risk - Monday 23rd of August 2021

Damaging winds risk is likely to be a higher chance over the south and southeastern coastal areas during the next day or two, inland areas it is conditional on thunderstorms developing and rolling through your region.

There is a risk of low level snow through Tuesday with the rain transitioning to a wintry mix at about 700m and above, snowfalls from 800m and above. So be prepared for some possible winter disruption Tuesday.

Areas of raised dust from SA may impact western parts of NSW during Monday afternoon and evening with reduced air quality and visibility.

Along the boundary there will be more widespread rainfall developing and it will be a day of falling temperatures over southern inland NSW. Rainfall will become moderate to heavy at times over the eastern Riverina and throughout the Southern Highlands and Tablelands and ACT during the evening.

Rain will be most extensive during Tuesday with moderate to heavy falls over the GDR slowly contracting east through the day with a cold southerly to follow with a few showers back over the remainder of the inland. A low is expected to form along the front Tuesday and move offshore, deepening/bombing offshore the coast causing gales and heavy rainfall for parts of the coast.

Some of the models have the low sitting further north of Sydney, others develop the low further south of Sydney. I think sadly we will have to wait until tomorrow morning to refine this forecast, but if you are living between Eden through to Foster on the coast, be aware of the severe weather risks Tuesday.

The low pressure system will likely move off by Wednesday with most of the inland returning to dry, a few showers on and east of the GDR move frequent about the south and central coasts. The gale force winds will ease later.

We have got a frost risk on Thursday designated for a large area, and this will refine as we get closer. So stay tuned for that.

Thursday it should turn dry and milder throughout the east with dry weather statewide by Friday ahead of the next systems out west.

00Z GFS Surface Pressure Pattern for the coming 16 days

The pressure pattern clearly dominated by the dramatic weather event over the southeast and eastern parts of the nation as a cold front passes through. The remainder of the nation is relatively quiet with moisture over the north the only other area of precipitation. Colder air following the front and as a low forms will be felt right across the nation as the southerly winds surge north. The low pressure system offshore NSW is expected to move east, opening the door for frontal weather from WA that brings showers mid week, to spread moisture through the nation. The wettest part of the nation during the second half of the week will be over WA. Then that rainfall will begin to move over SA and then the southeast inland by next weekend. The beginning of the temperature rollercoaster has begun and we will start to see the larger fluctuations in temperature nation wide as we go through this period. Medium term there are hallmarks as I pointed out above, of that rainfall increasing for southern and eastern Australia, the ingredients are there, but can they again come together?

00z GFS Rainfall for the coming 16 days

Rainfall largely confined to this major rainfall event over the southeast of the nation during the coming 3 days and then things will start to ease. The next wave of rainfall then develops for the west with a few cold fronts on approach. The rainfall moderate at times there with a colder shift to southwest winds. That weather will make a pass over SA and then over the southeast during this time next week, some chance there could be more widespread rainfall if the moisture can be drawn in via easterly winds to be lifted into an organised batch of rain.

00z GFS Precipitable Water Anomalies next 16 days

The moisture that is associated with this rain event was derived from the Indian Ocean and got held back over the inland of SA this weekend and now is expected to be drawn south, lifted up and utilised by the lifting mechanism, the cold front, over the east. This is what we need to see in future systems to see widespread rainfall develop. The next chance of this occurring is later in the week over WA and that spreads through the nation and brings more widespread chances of rainfall for the eastern and southeast inland so will be watching that. The moisture over the north should be cleared out from mid this week by a southeast to southerly wind surge. The far north should see the moisture remain in place and this may be drawn south through QLD, another area to watch as we end the month into early September.

00z Euro Surface Pressure Pattern for the coming 10 days

The major rainfall event for the period is clearly the system coming through the east. The rest of the nation is quiet for the coming few days. The pattern then flips when the low pressure system moves off to the east over NZ and this will now see the weather develop over the west of the nation with the next set of cold fronts. Those cold fronts will bring moderate rainfall mid to late week and these could move towards SA and the southeast states from next weekend with further rainfall. The temperature roller coaster ride will continue throughout this period for the south and east, and over the north the weather will turn hotter once again and the humidity values will creep up.

00z Euro Rainfall for the coming 10 days

Rainfall again heaviest and most widespread through the east and south and this will lead to some areas recording 1-2 month's worth of rainfall. The weather drying out over the nation's inland and the south during mid week, the low pressure responsible moving away. The focus of rainfall returns to WA by the middle of the week and will likely stay there during next weekend with a front every 36hrs. Some of those fronts are expected to spread through the southern states and into the southeast during next weekend with further rainfall possible but a better handle on that as we get closer and this rainfall event off the board and the low pressure system further east of the nation towards NZ.

00z Euro Precipitable Water Values next 10 days

The PW values are elevated over the eastern and southeast inland tonight with widespread rainfall likely to develop on and ahead of the front. The rain most widespread through NSW as the moisture runs up over terrain and deepens in response to the system strengthening into a low over eastern NSW. Then a dry surge is expected to send a cold blast of air through the nation, impacting most areas of the country throughout this week. The weather is expected to turn showery over the west with a set of cold fronts developing offshore and moving through with deeper moisture surging in from the Indian Ocean. This will be the focus of the rainfall chances for those wanting more over the southern and eastern parts of the nation.

Rainfall for the next 10 days

Clearly the weather dominated by the strong cold front approaching tonight and bringing a burst of rainfall throughout the southern parts of the nation then spreading throughout the eastern inland Monday and Tuesday with widespread falls, heaviest in the east. The weather is expected to ease from the west during the middle of the week before we turn our attention to the next wave of rainfall on cold fronts passing in from the west next weekend. That could spark more inland rainfall.

Further updates on the rain event unfolding tomorrow, it is going to be a busy day, so to make the most of the service, save your log in details, and save the blog page in your favourites on your devices!!

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