CLIMATE - SPRING AND SUMMER UPDATE.

An update to the forecast rainfall and temperature outlooks as promised with the latest data coming through this week.


A FEW THINGS TO NOTE


  • If you are shaded at 60% green in rainfall and 60% blue in temperatures, that still means you are a 40% chance of not recording either of those values.

  • The further you go out in forecasting, the less accurate it gets. If you look at the short term models, they struggle with day to day in Spring, so apply that logic when looking at the forecasts and making the right decisions for you.

  • The forecast for Summer carries a LOW CONFIDENCE. The forecast for Spring carries a MODERATE CONFIDENCE.

  • The weather is never absolute and look at this as a guide and read the analysis not just look at the picture.


Spring Rainfall Outlook

% chance of exceeding median rainfall for the remainder of Spring 2021.

The bias to a wetter than normal spring continues, flying in the face of the drier September for some, but other areas have already recorded above average rainfall for September, through NSW, VIC, pockets of QLD and NT. This will likely continue to play out as the moisture builds, the temperatures rise and the pattern moves away from the westerly wind belt. The retreating westerly wind belt is key to seeing those easterly winds return, and that is in line with Climate expectations. October onwards is when you see the easterly winds return, inland troughs develop, heat troughs form over the west coast and the tropics wake up. It is from these elements that dry starts to Spring are overrun, and the deficits can be made up for quite nicely in one or two events. It is all about timing though....some want rainfall now....some want none at all. These forecasts are based off the guide from the climate drivers which I have covered off this week - which are favouring a wet spell for the nation.

Spring Temperature Outlook

% chance of exceeding median temperatures for the remainder of Spring 2021.

Temperatures are expected to remain seasonal overall, for much of the nation, though as we are seeing this week, a bias to below average temperatures over the eastern and southeastern parts of the nation is quite possible, especially if rainfall frequency increases which modelling supports. The north will have a nasty hot October, with higher than normal humidity values before the temperatures moderate with higher frequency of rainfall. The SSTs support a higher concentration of moisture over the nation, as the prevailing wind pattern shifts from the winter focus (we are seeing this week) to the summer time phase (end of the month - easterly winds). The quicker we see the easterly winds return, take up residence and pump moisture in, will see temperatures moderate over the tropics with increased cloudiness. This will also play out in snuffing out the early season heat we have been observing over the nation in recent weeks too.

DATA

Euro Seasonal Rainfall Outlook (Anomalies) - Spring 2021.

The guide has been all along in guidance here from July and August, wetter through October and November with September being the transition/battle month, which we have seen verify. Rainfall has been a bit lean for parts, not all, of SA and QLD really has seen similar results. The tropics have been active early and above average rainfall has been observed in pockets. The west has been near normal, running near normal over the SWLD for September, but the rainfall likely to ease off during October and November.

Euro Seasonal Temperature Outlook (Anomalies) - Spring 2021.

Temperatures have been near seasonal over much of the nation despite the warmer weather over SA in recent times, colder weather over the next 4-5 days will see the heat values recorded neutralised in the monthly stats. The remainder of Spring will be dominated more by where rainfall events set up rather than cold outbreaks developing from the Southern Ocean.

CANSIPS Seasonal Rainfall Outlook (Anomalies) - Spring 2021.

Probably running a bit too wet for the north, but you never know - but again highlighting the higher moisture content available.

CANSIPS Seasonal Temperature Outlook (Anomalies) - Spring 2021.

Running close to the post like the Euro - mainly seasonal values likely for the period, but the volatile swings in temperature are likely to continue through October.

Summer Rainfall Outlook

% chance of exceeding median rainfall for Summer 2021/22.

Rainfall likely to continue to be above average through northern and eastern Australia. Likely to be influenced by the waning IOD through southeastern areas (hence the smear of higher probabilities over southeast NSW and northeast VIC). Then higher SSTs around much of the nation seeing more moisture available for rainfall to develop. The Coral Sea being warmer than average under the current guidance (maybe linked to the developing La Nina) will elevate rainfall chances for the NT and QLD this wet season. That likely has some influence over the remainder of QLD. I am not factoring in the La Nina event in just yet, I am waiting for one more set of data to come in later this month into October.

Summer Temperature Outlook

% chance of exceeding median temperature for Summer 2021/22.

Temperatures as per Spring, likely to be around normal values for the season, though this does not mean it will be a cold summer, there are still as always, likely to see heatwaves over southern and western parts of the nation, but this could be accompanied by more humidity, making conditions very uncomfortable for large parts of the nation. At this stage, the north of the nation, depending on rainfall, could see a very cool wet season if rainfall anomalies verify. Persistent monsoonal weather in a La Nina is possible this summer, but again, waiting for one more set of data to come through before adjusting/factoring in a La NIna.

DATA

Euro Seasonal Rainfall Outlook (Anomalies) - Summer 2021/22

This is the rainfall outlook - it does not factor in a La Nina yet, and the next update on the climate model data due early October will likely see these charts shift for the Summer time so stay tuned and do not be surprised if rainfall expectations increase over northern and eastern Australia but drop away for southern and western areas.

Euro Seasonal Temperature Outlook (Anomalies) - Summer 2021/22

Closest to the post in terms of all the data sets that are available at summer time.

CANSIPS Seasonal Rainfall Outlook (Anomalies) - Summer 2021/22

As you go further out the resolution on the data becomes a lot less reliable, especially when you see the higher precipitation contours next to the lower precipitation contours. This expresses more uncertainty amongst models but the trend is to see a seasonal outlook for most of the nation with more above average rainfall chances for eastern and northern parts of Australia.

CANSIPS Seasonal Temperature Outlook (Anomalies) - Summer 2021/22

Seasonal Summer would be nice - especially if some areas do miss out on rainfall during the Spring, will offset the any nasty heatwaves.

I will have your state based forecast later today.

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