MEDIUM TERM FORECAST - FOLLOW UP RAINFALL??

Lets take a look at the follow up rainfall potential coming into the weekend. There are signals for decent rainfall to develop in advance of a low pressure system moving through the Bight.


There is not much to add from last nights update (yes keep up to date in the evening's too as I do update from 5am through to 11pm and I do sleep ;)) where we saw this signal of widespread rainfall broaden. This is still continuing today.


Rainfall Outlook for the next 2 weeks.

Rainfall is increasing for the eastern third of the nation with a system today, another over the weekend and another next week with further inland rainfall potential. Models have a lot more than I am painting in at the moment, as I am just being conservative so do expect to see some areas go up and some to come down through QLD and NSW during the next few days. Otherwise numbers picking up over the tropics in response to a trough nearby and moisture. Low pressure troughs and fronts passing through the westerly wind belt to the south of the nation will bring showery weather to the southwest and southeast and also assist in rainfall developing over eastern inland parts of NSW and QLD.

Temperature Outlook for the coming 2 weeks.

No real change over the coming fortnight, though I have drawn an areas of reduced risk of above average temperatures over eastern parts of NSW with the increasing rainfall signal and cloud cover potential in the current data sets. This will refine with time. Otherwise colder weather for the southwest likely with a long wave continues to bring in more onshore winds and showery air. Warm to hot and humid weather over the north of the nation with heat values rising after a nice dry surge mid this week.



THE DATA SETS


18Z GFS Surface Pressure Pattern with Rainfall next 2 weeks.

The weather is expected to be dynamic through the coming days in the east, as we have seen in other posts. But similar ingredients are wafting around later this week and again next week where these could come together once again and bring widespread rainfall to parts of the nation. As mentioned last night, there are signals that a front cuts off into a low from WA into the Bight, which then drags moisture out of the north and northeast, like pulling a lever, may be lifted into areas of rain and thunderstorms through QLD and NSW this weekend. This spread may also involve VIC as well but it is looking more likely further north and east again. Showers and a few storms with hit and miss totals are more likely with the weakening front over parts of southern SA and VIC during the weekend, in a warm airmass. There is another system lurking through next week and that again looks to pull moisture that is racing from east to west over the north of the nation and from the Indian Ocean to increase rainfall chances once again for parts of the nation. Currently there is a bias for central and eastern parts of the nation in the coming 2 weeks.

18Z GFS Precipitable Water Values next 2 weeks.

Significant moisture pushing down from the northwest through the eastern inland is creating the rainfall event today in conjunction with the cold front passing through. The next wave of moisture follows that drier surge coming in on the western flank of the low pressure develops from the north later this week and from the northwest as well, with the next set of fronts set to bring rainfall back to WA mid to late week. That system is expected to slow down and cut off into a low pressure system over the Bight, and you can see the moisture being drawn into this feature through the central and eastern inland with rainfall chances coming up over the weekend. Another pulse of moisture races across northern Australia is expected to be drawn into WA and then absorbed by another system pushing through next week with more rainfall chances for the south and east. There are also increasing signals that the moisture will increase to the point where showers redevelop for the tropics.

18Z GFS Rainfall next 2 weeks.

Rainfall heavy over the coming 48hrs for the southeast and east with a low developing. Then the next rainfall returns to WA with a set of cold fronts Thursday, and some falls over 20mm possible with that system. Then we see that system slow down, cut off into a low pressure system south of SA and a band of rainfall on the eastern flank of this system is possible with some chance of moderate rainfall for areas of inland QLD and NSW once again. This system looks to bring the most widespread rainfall over the east at this time. But patchier rainfall is also possible over the southern states with the low, this will continue to chop and change as we go through this week, and we need this current system off the board to see how this next one redevelops from the west. Beyond that another system is expected to bring more rainfall chances to central, southern and eastern areas of the nation, while the dry bias is still highlighted for the northwest at this time.

LOOKING AT THE ENSEMBLE DATA SETS.


12Z Euro Ensemble Rainfall - Next 2 weeks

The rainfall bias continues to be for the eastern and southern portions of the nation where the most widespread and soaking rainfall is likely. Though numbers are coming up over inland QLD for the weekend and next week as it is for central areas, over the northern tropics too. This is a shift from recent guidance which kept rainfall more likely over southern areas of the nation. That is now shifting.

12Z GFS Ensemble Rainfall - Next 2 weeks

Rainfall numbers are increasing for QLD and NSW beyond this lead system passing through in the coming days, and note the rainfall is increasing in the latest data for parts of northern Australia. This is a good sign that the moisture is being recognised but now being utilised into September.

12Z CMC Ensemble Rainfall - Next 2 weeks

Widespread rainfall is expected in the short term. Note that numbers again are increasing over inland areas of the nation and also over parts of QLD in particular. Showers returning over the northern tropics in response to increasing moisture levels and slightly cooler upper heights. Still reasonable rainfall for the southern parts of the nation with cold fronts moving through irregularly through this time, and there is a chance of seeing more low pressure systems develop out of these as they move through the nations south, and if they cut off from the westerly winds, this is where we will see rainfall chances increase dramatically.

More to come.

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