CLIMATE UPDATE - JULY OUTLOOK UPDATED TUESDAY JUNE 29TH 2021

Headlines


  • Large parts of the nation sitting slightly more bias towards a wetter July, especially with rainfall numbers increasing as we go through the month.

  • Indian Ocean the main influence for rainfall chances over the nation.

  • Large parts of the nation sitting slightly more bias towards a cooler July which is conditional upon rainfall spread through the month and cloud cover.

  • The signal unchanged for northern Australia with warmer than normal dry season weather, due to the Indian Ocean influence.

Rainfall Outlook July 2021 - Valid Tuesday 29th of June 2021.

Lost the drier bias over the nation, but wide areas sit at a 50/50 chance of being either wetter or drier than normal for July, that is normal for this time of year and is dependent on cloud bands rolling through the nation bringing inland rainfall. It doesn't take much for the areas in white to go into above average rainfall with low rainfall totals during this time of year. The east coast now likely to see above average rainfall chances increase with a bumper start due to rainfall kicking off July. Slight bias to above average rainfall for most of the coastal areas of Australia. The Indian Ocean influence will become more entrenched as go through the month but really starting to cause significant rainfall and possible flooding from August into the spring.

Temperature Outlook July 2021 - Valid Tuesday 29th of June 2021.

Not much shift in the temperature outlook for the month of July. Signals for above average temperatures over northern Australia connected to more humid conditions and warmer nights and day times, but no record breaking heat likely, just persistent 1C anomalies with that humidity sticking around. Cooler bias over the south is conditional connected to more clouds and rainfall coming in with each cold front thanks to moisture being drawn in from the Indian Ocean, but I am not overly convinced of the record cold values expressed by models for April and May being repeated for July into August.

Climate Drivers Update


Southern Annular Mode (SAM) - Neutral trending Positive - Valid Tuesday 29th of June 2021.

The SAM is rising through neutral values today and through to positive values by the weekend, meaning this suppresses the westerly wind influence over southern Australia during positive phases. The short term modelling does bring in high pressure through the southern ocean. Short term modelling supports rainfall over eastern inland areas, which is in line with a positive SAM phase. The SAM phase is erratic and hard to predict ahead of time, it is forecast to dive back to neutral early next week and medium term modelling has responded with more frontal weather over southern Australia.

Surface Pressure Pattern with Rainfall - GFS 18z run - Valid Tuesday 29th of June 2021.

Note the westerly wind belt returns as the SAM surges back to neutral values early next week and possibly negative territory for the second week of July. That could bring much more active cold front activity. Certainly something to consider while the east cops a soaking this week, the west and south of the nation may see rainfall return at regular intervals next week and colder weather as well.

Indian Ocean Dipole (IOD) - Negative - Valid Tuesday 29th of June 2021.

This driver has been the clear influence over the recent 2 months over the western and southern parts of the nation. Cloud bands have featured over many weeks, this week it has taken a breather. But these little breaks will become less frequent, and cloud bands become more frequent as we go through the months ahead. When the IOD is negative, more moisture is available through the atmosphere, which is transported southeast via the jet stream bringing up rainfall chances ahead of fronts and or low pressure systems through wide areas of Australia. The chances for rainfall improve over inland NSW and QLD with regards to the IOD during the spring time.


Indian Ocean Dipole - BOM Model - Spaghetti plot for the months ahead.

Most of the models under El Nino thresholds and most under neutral values. That means a strong IOD event is likely to develop from mid July and persist to about December. Some models have a significant event, some of the strongest you can see, but will wait and see the next update in a week to see if the depth of the event continues to strengthen. The stronger the event, the more intensive the rainfall spread. A 2016 flood event cannot be ruled out on current values.

Lets take a look at how the event unfolds month to month and look at the models individually and compare them to the BoM model.


There has been a shift towards a strong event in recent data updates which is encouraging and peaking at the correct time for significant rainfall.


IOD July - Valid Tuesday June 22nd 2021.

BoM model declares the IOD this month and deepens next month, other models a little slower and I am in line with the UKmet and Euro approach, with the values trending more negative as we go through the month of July, meaning rainfall will pick up as we go through the month. If the BoM model was correct, the current outlook would be wetter and we would be seeing more rainfall over WA later in the weekend and next week with the next wave of weather moving in.

IOD August - Valid Tuesday June 22nd 2021.

BoM model strengthening the IOD, where the global models now push over the threshold, likely declaring the IOD negative from this point. Rainfall from this event should be more evident over much of the nation from northwest through southeast. The SAM critical to the distribution of rainfall through southern and western Australia. For eastern and northeastern Australia, a positive SAM could bode better for these regions with onshore winds from the east combining with a moisture laden jet stream, all you need is a trough in the region and rainfall would be productive under such circumstances.

IOD September - Valid Tuesday June 22nd 2021.

The IOD peaking through this period, with all models bringing a strong event to the region, with high levels of rainfall likely to unfold as the nation continues to warm up and that airmass clashing with colder air over the south. Widespread rainfall could be heavy at times, and we will be looking at the flood potential as we go throughout the later part of winter and spring time for this period. More details on the flood risk coming in a few weeks time with more data to look at between now and then.

IOD October - Valid Tuesday June 22nd 2021.

The IOD slowly starting to mix out as the nation continues to warm and the seasonal shift continues of Australia. These values however will keep an elevated rainfall signal over much of Australia with the flood risk continuing for the eastern inland and possibly the southeast. Rainfall accumulations between now and then will determine the scope of flooding but after a very wet start to the year for large parts of the east and southeast, catchments are wet. But the wet signal overall continues in October.

IOD November - Valid Tuesday June 22nd 2021.

Models starting to weaken the IOD further with some by the end of the month resolving the event, with neutral conditions developing, but if the IOD peaks at a stronger negative level, then the resolution of the IOD may continue into December, again lifting rainfall through the entire spring as well as early summer. That would keep the flood risk elevated. Also early onset rainfall may be underway due to the IOD still at negative levels. This would see a much more and earlier build up from October and November.


ENSO - Pacific Ocean - Neutral

Pacific Ocean continues to signal a neutral phase for the remainder of the year but interestingly the BoM model and now some of the more credible climate modelling is pinging a weak La Nina developing during summer time, which if that were to eventuate with the negative IOD still in place, a very wet signal would persist into Summer and Autumn of 2022. Now at this stage I am still siding with the conservative and higher skill score modelling which suggests neutral values into the Summer and Autumn. The influence under my current forecast from the Pacific Ocean is small at this time.


BoM Model Spaghetti plot - ENSO 3.4 Region for the next 6 months. Valid June 5th 2021.

Shows the neutral signal earlier in the month which I am still siding with, this would have little impact on rainfall potential for the summer time over eastern and northern Australia. I do feel like that is the right outcome, but I have one eyebrow raised at the update below this.

BoM Model Spaghetti plot - ENSO 3.4 Region for the next 6 months. Valid June 19th 2021.

Not quite calling a La Nina watch but it is quite possible one may be called if the negative values continue to strengthen in the coming 4-6 weeks. This is important information to consider if you are on the land over the east and south of the nation.

The climate expert models also suggesting a neutral season ahead however the overall trend is looking cooler in the Pacific Basin which is going to bring us no impact. But if it continues to trend negative over the coming few weeks or month or so, then global model climate agencies may start to ping a La Nina watch come August.


IRC ENSO Probabilisitc Outlook - ENSO Forecast - Valid 19th of June 2021.

Neutral values, weak signal for La Nina, very unlikely to see El Nino for the next 9 months.

IRI/CPC Model Spaghetti plot - ENSO 3.4 Region for the next 9 months. Valid June 19th 2021.

Most global climate models are cooling the basin over the coming months, a few push us into La Nina but the majority keep it cool neutral again siding with this solution.

The rainfall data for the coming month of July.


Rainfall totals looking seasonal for much of the nation over the coming 30-45 days from most of the global ensembles, pockets of no rainfall over the interior is based upon the dry bias that the models pick up for outback areas. And with not much data returning from those areas anyway, it is generally considered low accuracy forecasting. This period is a low to moderate accuracy forecast period anyway, the accuracy improves through later winter and then again in the summer months.


CFS Control (single data run)- Rainfall for the coming 6 weeks - Valid Tuesday 29th of June 2021.

CFS Ensemble (multidata sets)- Rainfall for the coming 6 weeks - Valid Tuesday 29th of June 2021.

Euro Ensemble (multidata sets)- Rainfall for the coming 6 weeks - Valid Tuesday 29th of June 2021.

GFS Ensemble (multidata sets)- Rainfall for the coming 5 weeks - Valid Tuesday 29th of June 2021.


The rainfall anomalies through this period are quite mixed, but I think the dry bias which some modelling has been touting, along with a warm year, have not verified and I am siding with the Euro through this period, which has picked the year well. But it is good to see all angles through the period.


GFS Control (single dataset)- Rainfall anomalies for the coming 6 weeks - Valid Tuesday 29th of June 2021. A low chance of occurring.

GFS Ensemble(multi dataset)- Rainfall anomalies for the coming 6 weeks - Valid Tuesday 29th of June 2021. A low chance of occurring probably has a bit too much rainfall for QLD and too dry over the southwest and west.

CMC Ensemble (multi dataset)- Rainfall anomalies for the coming 6 weeks - Valid Tuesday 29th of June 2021. Probably closer to the truth with the upcoming Indian Ocean Dipole, closer to the Euro Outcome.

Euro Control (single dataset)- Rainfall anomalies for the coming 6 weeks - Valid Tuesday 29th of June 2021. A little dry over the central and southern interior, probably a little too wet for QLD, but this is the single run of Euro.

Euro Ensemble (multi dataset)- Rainfall anomalies for the coming 6 weeks - Valid Tuesday 29th of June 2021. Probably the more accurate outcome from the suite of models with a 50/50 chance for most of the nation deviating from seasonal rainfall for the period.


Temperatures


The data is largely unchanged for the period and for July the signal has been rock solid for the past 4 updates. Warmer than normal for the north and cooler than normal for pockets of the south. The bias is not so strong for the colder signal over the south as it were earlier in the year, but the persistence of average to below average temperatures continues for another month. As shown yesterday in the Indian Ocean Update, the signal for cooler than normal weather may increase through the spring.


CFS Ensemble (multi dataset)-Temperature anomalies for the coming 6 weeks - Valid Tuesday 29th of June 2021. Running closer to the truth than some other models, probably a little too cold for coastal areas but it will be warmer over northern Australia, that is based off recent observations.

GFS Ensemble (multi dataset)-Temperature anomalies for the coming 6 weeks - Valid Tuesday 29th of June 2021. Running a little too warm for the country and has all year. I think cooler than normal for many areas of southern and western Australia is a higher chance than warmer than normal.

CMC Ensemble (multi dataset)-Temperature anomalies for the coming 6 weeks - Valid Tuesday 29th of June 2021. Likely running a little too cold for the nation, really banking on a wet month coming up, but I think the truth is in between the GFS and CMC solution.

Euro Ensemble (multi dataset)-Temperature anomalies for the coming 6 weeks - Valid Tuesday 29th of June 2021. This is most likely the right outcome for the month, with a good part of the nation at 50/50 chance of deviating from normal values. A seasonal month for many, though warm bias over the north and a cold bias for pockets of the south.


I will have more on this come Friday with another climate update when the next lot of data comes in. I don't expect much change then, but always good to keep adjusting the forecast as we go and Climate Forecasts should be updated 2-3 times a week.


Need more weather information for your part of the world? Do you need more specific climate discussion? Email me at karllijnders@weathermatters.org for more details.










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