It is a high impact scenario playing out over the east with a deep trough and high levels of moisture expected to lead to widespread rain and thunderstorm activity over the course of a 3-4 day period. The slow movement of a developing low will determine where the heavy rainfall ends up, but most models are suggesting 1-3 months rainfall once again for inland parts of QLD, NSW and now into portions of VIC and eastern SA.
Flood watches likely to be reissued and renewed flood risks are likely to develop for many locations and river systems. Please stay up to date with the BoM warning lists.
I will provide you the guide to where the heavy rainfall odds are likely to be and there are two parts to this feature again. One severe element is the deep low that forms along the trough and tracks southeast from SA through the NSW/VIC border. The other severe element is the east of NSW and QLD where a trough will stall and rounds of showers and thunderstorms will develop.
Riverine Flood Risk NSW and VIC.
The below data sets support the risk of flooding from minor upwards with ongoing floods having renewed peaks as well.
Riverine Flood Risk QLD
The below data sets support the risk of flooding from minor upwards in all zones, the risk is highest the further south and east you are in the state.
Lets take a look at the latest model data.
The short term is dominated by the major rainfall event expected to unfold from eastern SA through VIC, NSW, ACT and QLD. This will lead to flooding for many river catchments in these states, but a lower risk for SA. The west is drier with a downstream easterly flow which is pulling in drier air. The tropics wet and seasonal with high humidity values. The weather slowly clears from later this weekend from the east and southeast inland but the humidity may persist over the east coast of NSW and QLD.
UKMET - Rainfall Next 7 Days - MODERATE RISK
I would like to reiterate from last night that this is a conservative model. I don't think I have seen the rainfall as heavy and broad in many years. This model had half the amount of rainfall earlier in the month and we know how that ended. I am rather concerned about the rainfall projections for the east over saturated ground.
The medium term offers another area of low pressure passing over the south and southeast of the nation. Now whether this moves through northeast rather than east, will determine how much rainfall will break out. At this stage the weather is looking low confidence next week for the south and east. The weather over in the west remaining hot and dry until a trough deepens over the inland with scattered showers and thunderstorms developing. The tropics seeing another uptick in thunderstorm coverage and areas of rainfall as the instability and moisture increases further.
ICON - Rainfall Next 8 Days - LOW CHANCE FOR THE EAST, HIGH CHANCE WEST.
A bit too dry for the east but it is coming on board after being drier last night. Has the west correct. Dry weather for the next week.
CMC - Rainfall Next 10 Days - LOW CHANCE.
Rainfall unchanged for the east on this model but it is drier than the other modelling suggests.
EURO - Rainfall Next 10 Days - HIGH CHANCE
This model has 3 rainfall events and has heavy falls over eastern SA now through northern VIC and most of NSW and QLD. Rainfall numbers will jump around from location to location but the rainfall potential is very high over the course of 5 days before it eases, but more rainfall may redevelop again next week. The west likely dry and the tropics more unsettled.
ACCESS - Rainfall Next 10 Days - MODERATE CHANCE.
Heavy falls also on ACCESS, some of those brown spots are 100-150mm in some areas, but stacked against locations that have lighter rainfall, so the rainfall will be uneven. The rainfall is a little further north over parts of VIC, note the torrential rainfall over QLD, some areas inland would see 300mm (purple dots). Dry for the west and more unsettled up north.
KMA - Rainfall Next 12 Days - MODERATE CHANCE.
Very similar spread to the ACCESS and Euro once again with soaking rainfall for much of QLD and NSW through VIC and pockets of SA. Under the low, the rainfall could be heavy and torrential if this is correct. The west is dry is correct.
GFS - Rainfall Next 16 Days - LOW CHANCE
Probably drier than some of the other modelling above but significant falls for QLD and VIC and curiously lighter falls for NSW. The north is quite unsettled. The west is dry.
The ensembles have turned sharply wet in the past few days with a deep moisture supply being recognised and now picking up the deep low passing over the southeast and the sharp trough over the eastern states. The drier trend over in the west is also looking more likely. It does appear the third system next week is one to watch.
GFS - Rainfall Next 16 Days (median of 35 members) - MODERATE CHANCE.
The ensemble data is much more realistic based upon the current climate data in the short term. This has heavier falls for QLD, NSW and much of VIC extending back into SA. The tropics turning more active. Look at the deterministic data above to see the difference over 16 days.
CMC - Rainfall Next 15 Days (median of 30 members) - MODERATE CHANCE
The rainfall similar to the GFS, the ensemble data has heavier falls than the single deterministic data. The weather over the east coast of QLD and up over the NT above average. The west is drier and light falls if anything develops.
EURO - Rainfall Next 15 Days (median of 51 members) - HIGH CHANCE
We are dealing with significant rainfall signals on the Euro and this is probably closest to the post across the board if you compare with the below and deterministic data. Drier further west with hot weather.
I thought I would add the control member and this is of concern for many areas - grey shading is falls over 150mm and maroon shading is falls up to 150mm.
No change in this guide. It has been running very wet consistently over the east for the past 3 months!
CFS - Rainfall Next 6 Weeks
This rainfall projection is NOT MUCKING AROUND. I know that this is not what many don't want but the reality is, flooding is going to be with many through Christmas and into early 2022. I hope I am wrong, but prepare for this! NOW IS THE TIME TO PREPARE IN THE EAST!!
I will have more on the short term coming up after 7am EDT.