These are the questions being posed by the models this morning and there are no clear answers, but certainly some great signals, especially f you are living in QLD, the season may be on the shift.

Lets look at the pattern flip.

Before we do, I define a pattern flip as the pattern, literally flipping to complete opposite of what one is currently experiencing at the time of forecast publication.

The pattern flip relates to the westerly wind belt and it diving south from the mainland, you can see where it has been in the first picture, where the ridging over the tropics has been and the weather relating to that, we all know how wintry it has been over the south, and how dry and warm it has been over the north. In between, the weather has been changeable.

The pattern flip will see high pressure replace the westerly wind belt, the upper ridge over the north breaks down allowing for more unstable air to develop with troughs forming. That increases the chance of rainfall for inland areas and more humidity with the heat over the tropics. More settled weather over the south of the nation under the high pressure, with less wind and clear skies.

Lets have a look at the pattern evolving in the medium term.

18Z GFS - Upper air pattern for the coming 2 weeks

This shows the pattern flip above take hold. We need the westerly winds to retreat, the nation to become more settled for a period, with high pressure, this sending the wind regime into the east and bringing moisture back into the eastern inland. The wild card will be whether an upper trough can form over central Australia and move over QLD this time next week into the weekend. This may develop more inland rainfall for QLD But it is a week away this could still change. Next weekend we are keeping an eye on the next long wave trough approaching in from the west. That may start to drag moisture from the Indian Ocean into the front that approaches to produce a separate rainfall event out there. That one probably carries higher confidence based upon climatological expectations. But do not dismiss that moisture over the north as not happening, all models do suggest it sticking around from late next week into the second week of August. That will then see rainfall spread through remaining southern and eastern areas of the nation, and the tropics may start to stir a little from their dry season slumber.

18Z GFS - Precipitable Water Values for the coming 2 weeks

The PW values are very nice over the coming week with the last of the troughs through the south. We have covered that off in short term state based forecasting. Beyond that, into the end of next week, 25-50mm PW values engulf the northern parts of the nation, this starting to increase the humidity at the surface and the dry season feels will be replaced with an early build up regime. Scattered showers about the tropics may be a signal of what is to occur through August and September with the dry season being replaced. That plays well for QLD as the troughs and fronts out west, dragging the moisture from the tropics and through interior parts to lift up rainfall chances for the region from as early as next weekend. Note the moisture offshore WA being drawn into the frontal weather approaching next weekend while the pattern flip keeps dry air over the southeast and southern coastal areas and southeast inland.

12Z Euro - Precipitable Water Anomalies - next 2 weeks.

The Euro also shows the increase in moisture over the north of the nation heralding an early taste of build up while the pattern flip sees the moisture from the south relocate north for a period while the nation resets. The moisture will come south with warmer air during mid month, and that could lift rainfall chances for inland areas of the nation, not just for QLD and WA from next week, but most states into mid month.

18Z CMC M - Rainfall next 2 weeks.

The most aggressive modelling around rainfall curiously is with the CMC model which usually is conservative vs GFS in the medium term, but it is pinging the outcome of moisture being lifted all over the nation in the coming 15 days via fronts from the west and troughs in the east. Now not everywhere will get rainfall, but it is suggesting that rainfall opportunities may increase for many locations. The higher probability for rainfall will be located over QLD and NSW and through WA coming into SA and VIC thereafter. The tropics also quite active.

18Z GFS M - Rainfall next 2 weeks.

The GFS as you can see is much more sedate but still shows the rainfall after the long wave pattern leaves this week, shifting to bringing rainfall chances back to the east and north and returning the rainfall through WA and back into SA and VIC/NSW with a cloud band in around 10 days time at this stage but with so much weather floating around in the outlook it is going to be a little chaotic as the models shows systems, take them away, build a system up and then drop another. So hold on! This is very much a spring time period with heat, cold, moisture and troughs/fronts lurking around.

Rainfall for the coming 2 weeks - Valid Friday 30th of July 2021

Rainfall is very conditional for the northeast around QLD with this the mean of all the modelling available today. The more widespread rainfall likely the closer you are to the coast, but drawing in the inland rainfall as a measure to flag this as an idea and will have an update on that during Sunday. For now the south wet in the coming days, with a break in the rainfall likely mid to late next week. Rainfall returns to the west with a new wave of fronts next weekend. And a few showers and storms possible for the NT and isolated high based showers and storms through the outback if moisture is deep enough also possible.

I will update this again during Sunday afternoon.

0 views0 comments