A LOOK INTO THE MEDIUM TERM - LETS TALK RAINFALL.

Focusing on the weather coming up Sunday and Monday is causing the most interest.


SYNOPSIS


A cold front is expected to move through the region from Sunday afternoon into Monday, running not only into warmer than normal weather over the eastern inland but modest moisture that hangs back over inland SA through NSW during the weekend. The ingredients are there for all this to combine to produce widespread rainfall.


The modelling is fairly strong on the idea of rainfall increasing over eastern VIC and into southeast NSW Monday and that extending over Central NSW through later Monday.


The timing of the change is still to be locked down, GFS a bit faster than the Euro.


I will also mention, that the latest GFS has pulled back on rainfall numbers, but is the only model to show this.


Rainfall next 5 days

The main rainfall event that is on the board in the medium term is coming through later Sunday through Tuesday. A much closer look can be found in your state based AM updates this morning. Now some of the latest modelling have falls higher than what I am drawing in for the southeast of NSW and eastern VIC, but I am keeping it middle ground and adjustments will be made through the coming days.

MODEL DATA - RAINFALL NEXT 5 DAYS

Significant rainfall expected to develop from Sunday afternoon into Monday thanks to the warm air clashing with the colder air moving in from the south in combination with moisture that is being drawn in through the northerly flow aloft and the moisture that hangs back over SA also being propelled into southeast and eastern inland.

Now to the rest of the outlook


SYNOPSIS


And the modelling is fairly mixed now, and showing more rainfall potential next week. The Euro model is out on it's own in keeping a pool of cold air in the middle levels over the eastern inland, that provides the chance of showers and storms for the eastern inland of NSW mid to late next week, however most other models do not have that, so even though you can see falls on your apps this morning for mid to late week, I would not be surprised if that is gone this evening.


There is the chance of a rainfall event to kick off nearby the QLD coast with moisture surging south through the Coral Sea and into the Tasman in response to the slow moving low. If that low can sit closer to the south coast of NSW, then there could be rainfall increasing for the coastal areas of central QLD - a low risk.


The low pressure system is being forecast to not be as stationary off the NSW and VIC coast next week however, with the models now moving it off to NZ a little more efficiently. That will support frontal weather over WA bringing the next batch of rainfall to the west of the nation, linking into moisture from the Indian Ocean possibly bringing a band of rainfall through western and southern Australia from later next week.


The weather over the southeast could return to showery ahead of that with a weak upper trough passing through before the frontal weather arrives.


The north of the nation will see moisture rolling through in waves from east to west during this period. The first wave on the trade winds will bring a few showers over Cape York through the NT and into northern WA. That moisture will rotate around the nation and could be drawn south and southeast ahead of frontal weather - models are not putting that together but it is an element to watch in the medium term.


The modelling is starting to pick up rainfall once again in the medium term for southern and eastern Australia and indeed the longer term modelling has heavier falls through September.


RAINFALL MODELLING

12z CMC - Rainfall for the next 10 days

Not as robust in the short term with the system coming across Sunday and Monday, however this along with the latest GFS are the outliers for rainfall totals over the southeast of the nation. Tropics becoming more alive early in the period with the wave of moisture passing through from east to west during the weekend into next week. Some of that moisture may be drawn southeast through QLD with isolated showers and storms ahead of a colder surge. The showery weather over the south of the nation is connected to cold fronts which are expected to be modest under this guidance. That is in part due to the low pressure system that this model holds up over the Tasman, blocking the passage of fronts from the west.

12z ACCESS - Rainfall for the next 10 days

ACCESS has still got healthy rainfall for the southeast and eastern inland of NSW and VIC, but has softened the intensity from last night, but the message is the same. It also has better rainfall for western NSW and parts of eastern SA too. More widespread moisture creep into the west through QLD also would bode well for the rainfall chances to elevate for the end of the month. A new front over in WA is likely to bring rainfall in about a week from now. The model moves the low pressure system off to the southeast quicker during the week allowing frontal weather to come through the southeast at the end of the period.

12z KMA - Rainfall for the next 12 days

Not a huge amount of change from last night, widespread rainfall for the southeast with the biggest falls reserved for on and west of the GDR in NSW and northeast VIC but still some wrap around coming into southeast coastal NSW and Gippsland. The change from last night is the rainfall building up over eastern inland QLD which will have to watch in the coming day or two to see if the moisture can be lifted next week. That is conditional on the low pressure being slow moving off the NSW coast. A new front for WA expected this time next week, the model also introducing the moisture from the Indian Ocean.

LOOKING AT MEDIUM TERM RAINFALL FROM THE LARGER DATA SETS.

12Z GFS Rainfall for the next 16 days

The numbers have dropped off on the GFS runs since yesterday, and now is the driest model for much of the nation, but rainfall is still forecast for most areas.

12Z Euro Rainfall for the next 15 days

Numbers are increasing through the southeast in line with the lead system bringing widespread rainfall. The moisture increasing over inland QLD is with a return to easterly winds throughout the outlook and could provide some rainfall opportunities in the coming 2 weeks, will have to keep watch. Numbers also coming up over WA in relation to the frontal weather anticipated to pass through mid to late next week with moderate to heavy falls possible. Still far too dry over inland areas for the negative IOD phase which concerns me a little about the rainfall forecasts/guide from the climate models which we have been following for months.

12Z CMC Rainfall for the next 15 days

Widespread rainfall for the southeast with the frontal weather and a low over the southeast. This model has more rainfall for the east coast of NSW and QLD then running across the northern parts of the nation with the easterly winds. The wet weather returns to the southwest of the nation during the middle to latter part of next week. Beyond that there is more frontal weather and easterly winds to keep the rainfall going in the same areas as the week coming and the inland of the nation largely dry.

Rainfall for the coming 16 days

Rainfall totals are anticipated to move around a bit in line with the low confidence forecasting, but the most robust rainfall event may be in the short term coming through Sunday to Tuesday. This has developed rapidly on modelling in the past 24hrs and this may be the case again through this period, where systems start to appear in the short term modelling. Areas where this could happen is over southwest WA and over the eastern inland of NSW and QLD as well with moisture about and the potential troughs deepening on the northern flank of high pressure as those centres pass into the Tasman Sea. Will have to also monitor the moisture rotating around the northern parts of the nation and then being drawn into the west of the nation and held there in advance of frontal weather passing through. Can the cold fronts pick up the moisture to produce rain bands?

Climate Update due later this morning for Spring 2021.




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