2 WEEK FORECAST FOR THE NATION

A detailed look now at the next 2 weeks across Australia. For the longer 4-6 week outlook that was updated yesterday then head to the Climate Section


There is a split in the modelling over the coming fortnight, making forecasting a little tricky to pin down who gets what. But at this stage for the sake of consistency, I will be favouring the Euro scenario based upon the data sets during the past 5-6 days. But I will show you the other options on the board.


FORECAST


Rainfall Outlook for the coming 2 weeks - Valid Wednesday 14th of July 2021.

Rainfall looks to favour coastal areas with heavy accumulations over those areas exposed to a westerly wind regime. The southwest of WA, through southern SA, into southern VIC and TAS should see the heavy rainfall. Heavy snowfalls possible over the NSW and VIC Alpine areas from Friday onwards with the westerly wind belt strengthening this week and then again from mid next week. The north of the nation under the upper high dry and hot. There is a lot of moisture that could see rainfall numbers pick up over WA with some of the inland areas potentially getting falls in excess of 25mm. And rainfall numbers over the GDR at this stage will fall this week for NSW and into southern QLD. I do think the rainfall retreats back down the divide next week, but again there are mixed signals for next week.

Temperature Outlook for the coming 2 weeks - Valid Wednesday 14th of July 2021.

This is of higher confidence with the warm signal continuing over the north with an upper high persisting. The seasonal conditions persist for southern Australia but I fully expect warmer weather next week, some locations hitting 20C over northern VIC and western and central NSW with a northwest airstream, possibly mid 20s over SA. Then a cooler shift with fast moving fronts developing in the period from this time next week. This reflects the outlook over the coming 4-6 weeks as well. And we may be dealing with an early spring this year, not necessarily hot, but warmer than normal by a degree or two most days.



OVERVIEW


The weather is primarily going to be dominated by the winter westerly pattern this week, easing over the latter part of the weekend, with the cold fronts moving on by during Sunday. Though there are signals for another wave of cold fronts to develop for southern Australia next week. That is where the divergence begins.


The Euro model and most other global agencies push a high through central Australia next week and broaden the upper ridge over northern Australia, establishing a drier picture for a lot of the continent. On the western side of the high a moist northwest flow develops from the Indian Ocean, triggering widespread rainfall over WA from Tuesday next week, with that feature spreading across the southern coast of Australia with lighter falls developing for inland areas of SA, VIC and southern NSW through mid to late next week. There is follow up frontal weather that then brings more rainfall into WA and the southern states into next weekend and the fourth week of July.


The GFS model has shifted away from the moisture plume drifting through the nation, now deciding to reinvigorate the westerly wind belt following an upper trough early next week and this will keep the wet weather going to those areas exposed to the westerly wind regime. If you are not sure what those areas are, keep watching the rainfall observations in the coming days. The westerly wind belt on the 12z and latest 18z runs this morning keep the westerly wind belt active for the remainder of the month, that is good news for those areas of southern Australia who rely on winter rainfall to get them through the warmer season.


The latest CMC and KMA are more inline with Euro where ACCESS is doing what it does best and going off with the fairies and deciding to bring rainfall through the NT and QLD.


This period, the nation will be divided by very warm weather over the northern half under an upper high and seasonal conditions over the southern half, with some pockets of below average temperatures for parts of coastal southwest WA and southeast VIC into southeast NSW.


DATA SETS.


Lets start with the GFS which is again not the modelling I am siding with, however the fact it has continued to hold the same pattern for a second run in a row is interesting and if this persists or if there is a shift in the other global modelling then the forecasts will be adjusted to factor this in.


18Z GFS - Upper Air Pattern next 2 weeks - Valid Wednesday 14th of July 2021.

A fast flow pattern looks to continue right through the period, where the Euro is not as robust in this idea, bringing more moisture and frontal weather during the latter stages of the month. The GFS has a very wet look for the southeast states and further falls for WA but the bias is sitting over the southeast in this scenario. The weather would be drier and warmer over QLD, NT and WA with an upper ridge.

18Z GFS - Upper Air Pattern next 2 weeks - Valid Wednesday 14th of July 2021.

The surface pressure pattern for the remainder of July according to GFS would be wintry with wet weather for large parts of southern Australia with frequent frontal weather, windy conditions and good snowfalls to develop through this period. This is a solution that we will look out for tonight in the 00z run of model data to see how it stacks up against the other data sets.

18Z GFS - Precipitable Water for the next 2 weeks - Valid Wednesday 14th of July 2021.

PW values are elevated this week which we can see playing out in real time with widespread rainfall through eastern and southern Australia, that continues today and through Friday. The GFS like other models clears the elevated PW values out with a cold dry surge this weekend. Next week with the frontal weather returning, note the high PW values cannot move over southeast Australia with the westerly wind profile keeping the moisture back over in WA or offshore as upper level winds stall and become more variable. This brings down rainfall potential for the inland regions.

18Z GFS - Rainfall for the coming 2 weeks - Valid Wednesday 14th of July 2021.

So keeping it with the GFS, the rainfall becomes quite heavy with falls exceeding 350mm for Alpine areas of NSW and VIC and widespread 50-100mm through southern Australia. This again is not the solution I am siding with, but if a solution verified as per below, then yes a wet phase would develop for the southeast. The dry spell would continue for the northern half of the nation.

18Z GFS M - Rainfall for the coming 2 weeks - Valid Wednesday 14th of July 2021.

A closer look at the southeast which would be the wettest part of the nation under this scenario. This is the ensemble and it is very tightly clustered in the rainfall distribution so the winter westerly belt solution is strong within the GFS modelling today. See what the 00z data holds.




But lets take a look at the Euro which is much more settled in it's thoughts for now - showing the same pattern GFS and other models have been showing for days with a low pressure system tapping into large scale moisture over the northwest and spreading it through the nation in conjunction with frontal activity moving in from the west.


12Z Euro - Rainfall for the coming 2 weeks - Valid Wednesday 14th of July 2021.

The rainfall spread we have seen this week, looks likely to continue for the coming 2 weeks, with the southern coastline expecting the most rainfall this period. Inland areas under the upper high remain dry and hot.

12Z Euro - Rainfall for the coming 2 weeks - Valid Wednesday 14th of July 2021.

The rainfall spread is similar to the GFS over the coming 2 weeks ending July 28th. The only difference is that the Euro brings a drier period for the coastline early next week with rainfall returning from around the 21st onwards with the frontal weather taking over shortly there after bringing in the winter rainfall distribution that GFS is expressing.

12Z Euro - Rainfall anomalies for the coming 2 weeks - Valid Wednesday 14th of July 2021.

Rainfall anomalies follow the trend we are seeing through most models with the dry season continuing over northern Australia and the winter westerly belt continuing to provide widespread rainfall for southern coastal areas and the adjacent inland districts.

12Z Euro - Temperature Anomalies for the coming 2 weeks - Valid Wednesday 14th of July 2021.

Well above average temperatures to continue for the coming 10-15 days looks likely for large areas of the nation, with the warm air filtering down next week ahead of frontal weather through southern and eastern Australia. Parts of the west may see below average temperatures if the cloud and rainfall is at the higher end than is forecast. And near seasonal weather over eastern NSW and the ACT is thanks to the winter westerly and rainfall remaining high, off setting the warmer air moving in from the northwest of the nation. There is no extended period of brutally cold weather at this stage for this period. But will monitor the GFS as that may throw up a spanner to that idea and the data expressed by the Euro.


More details this afternoon on the approach of the troughs and fronts, which will bring the risk of hail and thunder through most southern states over the coming days. Also a look at the temperatures over northern Australia as the dry season continues. So details to come with that after 2pm


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