ANOTHER UPDATE ON THAT PESKY MEDIUM TERM MOISTURE MOVEMENT.

A lot of interest in the mid month weather, lets get straight to it as the conversation and analysis continues for the coming 2 weeks of weather.


Moisture Watch Week 1

The models are largely unchanged for the moisture spread this week. We have moisture surging southeast from northwest WA via the Indian Ocean into Bight Waters ahead of a cold front. That will bring patchy rainfall through inland areas of WA through SA and into VIC mid week. Moisture in easterly winds over the tropics will see showers increase over the region mid week and that moisture racing across the Top End later this week but more likely at the end of the weekend, the eastern Top End feeling the moisture most in southeast to easterly winds. The most impactful moisture is sitting offshore the QLD coast and will be drawn around the western face of a high pressure system in northeast winds, and drawn into the inland of NSW. That moisture will then be lifted by a cold front coming through the southeast mid week with a period of moderate rainfall and thunder possible. Interior parts stay dry for now under a ridge but that ridge is moving on to the southeast next week.

Moisture Watch Week 2.

A large part of the nation remains under the influence of increasing moisture values in most global modelling this morning. The Euro is the driest out of the bunch but has active plumes moving through the nation, just not in phase with low pressure. At this stage I am siding with GFS. Moisture in easterly winds continue to impact the east coast, but the fetch of easterly winds will be extending further inland over QLD and into the NT with a northeast flow then turning the moisture southwest into inland SA and NSW before turning southeast ahead of troughs over the inland. There is another plume of moisture expected to moves southeast from the Indian Ocean during this period resulting in another cloud band over WA, I have extended the shaded yellow area further west from yesterday to capture that. The area of moisture is large and will refine as modelling becomes clearer on what system will emerge as the dominant feature to lift the moisture over Australia.

Now while it appears on these charts above that the moisture is extensive, it does not mean it will rain everywhere under the yellow shading. Lets take a look at the model data this morning.


18Z GFS Surface Pressure Pattern for the coming 16 days

GFS continues the trend of wet weather in the medium term. It has been most consistent in bringing moisture through the northwest and north of the nation with a deeper layer of tropical air being drawn south via the upper level winds. GFS also brings moisture southwest and west via easterly winds over the the eastern inland with high pressure sitting west of NZ. Then GFS now introduces a secondary area of moisture coming in via the Indian Ocean, that lifts rainfall chances through WA and over SA into the southeast inland. Again GFS shows you what happens when the moisture is in phase with low pressure and a trough, bringing the higher rainfall amounts of large areas by the 20-22nd of the month. This will continue to evolve as we go this week.

18z GFS Rainfall for the coming 16 days

This model is the wetter out of the main three today but is closely in line with CMC having heavy rainfall a chance with a large scale system coming together with the moisture over SA, VIC, NSW and QLD towards the middle of the month and persisting into the back half of August. For now it is still low confidence, but this model persists with the moisture being utilised. The tropics also getting soupy with showers developing through the outlook period and may extend south with the prevailing wind profile spreading moisture south and southeast through the NT into QLD.

18z GFS Precipitable Water for the coming 16 days

No real change in the forecast period with the weather becoming interesting from the weekend with a stalled boundary over QLD interacting with a decent moisture profile to produce the chance of inland showers and storms and showery weather along the coast. Dry weather training over the south will be eventually be overrun by moisture from the north, west and east. So that trend does continue to feature.

12z Euro Ensemble Precipitable Water Anomalies for the next 15 days

The driest model out of the three is the Euro. While it may offer concern for some people who religiously use yr.no as the holy grail of modelling, well that is not how to forecast weather, I am now using the ensemble data which is harder to interpret. Overall the data sets are wetter but still no where near GFS. Will continue to monitor however I am not aligning myself with this modelling at this time as it is the outlier.

12z Euro Ensemble Rainfall for the coming 15 days

As per the comments above, this is the least likely outcome at this time. It is not impossible but I think it is running too dry.

12z CMC Ensemble Precipitable Water Anomalies for the next 15 days

The CMC modelling is more aligned with GFS this morning and continues the wetter bias for the east of the nation, while it is not as wet over in the west. But this modelling has been bullish in keeping the moisture levels higher as we track through the outlook period. The weather turning unsettled and humid over the tropics with the chance of decent falls for August if this verifies.

12z CMC Ensemble Rainfall for the coming 15 days

As mentioned above the bias of rainfall over eastern inland areas of QLD and NSW is connected to the moisture building up over the region via easterly winds. Widespread moisture is expected to creep south from the tropics and could be drawn into weather systems moving out of the west from WA and SA. So that is something to watch, and this is why I have drawn such a large area in yellow for the second week.

Rainfall is mixed through the outlook so lets look at the medium range deterministic data too


12z ACCESS G Rainfall for the coming 10 days

Rainfall spreads from northwest to southeast across the nation via the Indian Ocean with moderate falls for parts of outback WA and SA. The moisture looks to surge southeast into the eastern inland and may be picked up by a frontal passage and trough over VIC and SA after this period. Moisture continues to pool through the easterly winds, but does not appear to be in phase with low pressure over the eastern inland of QLD and NSW, but this could change easily.

12z KMA Rainfall for the coming 12 days

Rainfall from KMA very much in line with the other models with another surge of moisture coming in from the Indian Ocean and being drawn southeast with upper level winds favouring that to link up with a cold front passing through SA and VIC in the medium term. There is some chance of rainfall spreading throughout the remainder of the east and southeast after this period with moisture lingering.

So while it is relatively dry right now, things will shift in the medium term as forecast in recent weeks. I will have another update on this during Tuesday along with a climate outlook for September.





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