Upper lows equal weatherman's woes!! Very tricky few days of forecasting coming up with an upper level pattern becoming dominated by parcels of colder air which may destabalise the weather for large parts of the south and east.

Satellite picture on Sunday afternoon showing the cloud band standing up in the southern Great Australian Bight producing thunderstorms near an upper low.

Moisture with this system is rather limited, there is a good supply along the front which will deliver a band of rain through southern SA, southern VIC and Tasmania with 5-20mm likely along that axis during Monday. There is also the risk of thunderstorms with strong wind gusts on the front, but these will be isolated.

Thunderstorm Forecast for Monday 10th May 2021.

60% chance of thunderstorms over northeast NSW within 25km of a given point.

The front will begin to cut off into an upper low over parts of SE Australia during Monday into Tuesday. The system is running into fairly decent moisture that is currently over southeast NSW where showers and thunder have formed in the daytime heating on Sunday.

That moisture may begin to be utilised later on Monday with showers increasing with the chance of a thunderstorm. Areas of rain may develop during Tuesday and Wednesday as the upper low moves through central NSW.

As the system does this, an easterly flow will redevelop over the south and central coasts of NSW and into East Gippsland, allowing rain to become heavy at times. Some localised flash flooding is possible and that forecast may be issued here tomorrow if the trends continue to strengthen.

The rain and showers will ease from Thursday as another front approaches SE Australia from the west, and knocks out the low pressure system away from the coast.

Precipitable water values for the next 4 days, showing the movement of the moist air in line with the upper low and then being bumped out to the east by the next front.

So with that, raw rainfall totals from the models are divergent, but they all have the same idea now, with rain become heavy over southeast NSW. How widespread and inland this rainfall comes, may continue to evolve over the next day as the models are able to handle the upper low better, now we can see it in real time.

GFS Rainfall for the next 4 days - has the most extensive rainfall back over southern inland NSW and the heaviest falls maxing out at 350mm over SE NSW during this period. LOW CONFIDENCE IN THIS SOLUTION.

Euro rainfall for the next 4 days has heavier rainfall for eastern Victoria and far southeast NSW. Better rainfall for northern NSW and southern and southeast QLD. This scenario carries a LOW CONFIDENCE

CMC Rainfall for the next 4 days - showing heavy falls for southeast NSW and Gippsland in Victoria. Scattered falls back into SEQ.

So overall the forecast is tricky to pin down but this is my take on the coming 4 days for the region. The timing of the front and the strength on that front in southeast Australia next week will determine how long the rainfall lingers over SE NSW and Eastern Victoria. It will also how much rainfall comes back to southeast Australia west of the divide through Victoria and southeast SA.

Rainfall next 4 days - Weather Matters Rainfall Forecast.

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