Plenty asking when the next rainfall is expected across the nation. Lets take a look at the latest data.
We know that this week is rather quiet with weather dominated by high pressure over the south, which will dam the moisture over the north of WA, NT and QLD. This is the pattern flip I banged on about for about 3 weeks, we now have removed the westerly wind belt, the moisture is now unable to be drawn southeast with the fronts which would pull the moisture southeast not present or sitting north enough, that means the moisture stays up north this week.
Rainfall for the next 2 weeks.
This was the forecast from yesterday showing the forecast rainfall (some of that fell overnight), as you can see the numbers are not that heavy for the coming fortnight for the nation, but this will likely chop and change in the coming week as we get better guidance on the systems coming through for the end of the month.
18Z GFS Surface Pressure Pattern for the coming 14 days
Quiet this week is still fair. The weather starts to shift next weekend with a trough moving into the moisture that builds up in the easterly wind regime. Showers and storms may break out over NSW and QLD with scattered showers or patchy rainfall coming into SA and VIC. Then there are more substantial signals for widespread rainfall forming to round out the month and to kick off September, so perhaps that is the message to remember, wet end to August and start to September.
18Z GFS Precipitable Water Anomalies for the coming 14 days
The anomalies paint the quiet picture this week with the dry air damming through the southern parts of the nation under high pressure. That moisture over southern QLD and northern NSW may trigger showers, so keep watch if you live in that region. Otherwise the reset of the moisture coming around the high and to be placed in a position to be picked up by the frontal weather or troughs from the west will take about a week and then we should se rainfall numbers increase towards next weekend.
18Z GFS Rainfall for the coming 14 days
GFS still picking the rainfall bias for southeast and eastern Australia with the moisture increasing in easterly wins, then that moisture being lifted by a trough passing through from the west next weekend. So we will have to keep an eye on those trends. East coast looks wetter for the end of the month too, but this is deterministic data from the GFS and is much more volatile.
Lets look at the Euro Ensemble Data Sets regarding rainfall - because clearly many want to know when the next lot is coming and this graphic shows it well.
Time line along the bottom and follow the green line which is the mean of all the members. This model is drier than GFS so there is a chance that these values could be too dry, which I think could be the case.
STATE BY STATE.
Rainfall no existent for the coming week with high pressure over the region, but numbers do come up later next week into the weekend with moisture and frontal weather combining to bring back areas of rainfall through the region. About 20-40mm is fair for the period but most of that to fall during later next week onwards.
Wheatbelt of WA
It is similar for the Goldfields and Wheatbelt with lighter rainfall coming into the inland during the next 10 days, so that suggests that the rainfall next week may be strictly coastal and heavier through areas exposed to the westerly wind regime. A few members do show falls over 40mm suggesting a low chance of a cloud band for now.
A relatively dry spell coming up, with maybe 1-2mm of rainfall through the region in the coming 7 days, though you can see from next weekend the rainfall opportunities return with a front passing through with potential for moisture to get involved. Follow the green line as that is the average of the data sets and you can see 15-25mm likely during the following weekend. Some members bring as much as 50mm but as little as 5mm through this period, so that expresses uncertainty.
Similar rainfall timing coming through southern VIC as per the north, but the rainfall not as heavy as the northern parts of the state which suggests that there could be a cloud band spreading through inland areas from next weekend into the following week. Not much rainfall expected during the coming week.
A fairly dry and settled period of weather over the coming week with rainfall numbers picking up from next weekend, so the next week dry for now. The modelling for the rainfall next weekend into the following week is highly uncertain, with some members saying up to 50mm but also suggesting 2-5mm possible with that feature, follow the green line for the most likely outcome.
Drier trend through Central NSW with a dry 7-8 days. The rainfall is expected to turn from next weekend but favours areas further south with 5mm most likely to fall from that feature, but some members suggest 25mm is possible if a cloud band gets involved.
A dry week coming up for northern NSW, with rainfall numbers picking up later next weekend into the following week and the spread in the members expresses the uncertainty connected to that event, and being 10 days out, that is to be expected. But you can see the shift in the drier spell later in the period.
East Coast of NSW
Light showers for the NSW coast this weekend with more rainfall developing through next week into the weekend, with a slow accumulation likely. Some models suggesting falls of up to 60mm but at this time, it is looking lean and stick with the green line for the average rainfall for coastal areas of NSW. The rule of thumb will be the wetter the further north you go.
A relatively dry week for the EP with a front possibly bringing a light fall or two on the weekend but then dry until next weekend when another band of light rainfall moves through, some members have a heavier rainfall event, but at this time, follow the green line which says 10-20mm possible from late next week.
Adelaide and Surrounds
Similar spread for the YP and into Adelaide suggesting rainfall opportunities to pick up from later next week with only a few passing showers expected today and again on Monday. At this stage the weather will be largely dry for the coming week. Rainfall looks to be more widespread from next Friday through the region. Lighter falls for the Riverlands, Murraylands and Mallee at this time. Falls of 2-10mm for the region later next week is fair. Similar falls for the Flinders and Mid North is also fair.
Rainfall likely to be coastal through this period of stagnant high pressure with onshore easterly winds being suppressed by ridging close by, so a gradual increase in rainfall over the next 10 days. Note the members start to split through the longer term expressing uncertainty with rainfall possibly getting heavier, but follow the green line for your guide. 10-20mm most likely.
The wettest part of the nation is likely to be the FNQ coast with onshore trade winds bringing frequent showers. These models don't pick up on the topographic rainfall influences so 50-100mm is fair for some locations over the comin 10-15 days. The onshore flow looks to be with us for a good chunk of this period.
Southern and Central QLD
Inland QLD remains dry on the northern flank of the ridge even though moisture continues to increase over the northern inland of the nation. 1-5mm likely through this period but most areas remain dry through the final stages of the pattern flip.
I will have another update tomorrow with a look at the Climate Drivers again and the remainder of August 2021.