CLIMATE UPDATE - JULY OUTLOOK UPDATED JUNE 25TH 2021

Headlines


  • No change to the wet signal connected to the Indian Ocean Dipole for the coming month.

  • Wetter than normal weather for July to persist for much of southern and western Australia, could start to creep further inland as we track through July, with rainfall increasing for inland areas.

  • Cooler than normal conditions associated with cloud cover over many parts of Australia. Higher chances of rainfall also leading to cooler days, especially through the outback with potential inland rainfall events.

  • No change for northern Australia with a hot dry season, with more humidity developing. Higher chances of dry season rainfall developing.

CLIMATE DRIVERS


Southern Annular Mode (SAM) - Forecast to dip into the negative territory briefly next week before sharply turning positive in the first week of July. This particular driver is notoriously hard to predict ahead of time, and must be read with caution for long term signals and accuracy.


AAO/SAM forecast for the coming fortnight - Not the sharp shift back to a negative phase next week. It remains to be see if this positive phase is expected to develop at such strength. Therefore it carries a low confidence forecast. Be sure to watch the short term forecasts in the coming days. Valid Friday 25th of June 2021.

Indian Ocean Dipole - (IOD) - Forecast to dip further into a negative phase with a strengthening of that signal during the next few months. A major driver of the rainfall signals during the second half of this year.


BoM model - IOD outlook - Valid Friday 25th of June 2021.

Note the nice spread of models underneath negative values. The mean (black line) is also dropping for a prolonged period, meaning that the above average rainfall signals could persist into the early parts of summer adding more moisture into the atmosphere and contributing to early onset rainfall.

ENSO - Forecast to remain neutral for the second half of this year. There was some chatter of a La Nina developing, but I am not buying that at this time.


CFS 3.4 Nino SSTs Anomalies - showing some signals for potential cooling of the region bound by La Nina and El Nino declaration, at this stage, I am not satisfied with another La Nina developing, however it is certainly not looking like El Nino any time soon. Valid Friday 25th of June 2021.

July Rainfall Outlook - % chance of exceeding the median July Rainfall 2021. Valid Friday 25th of June 2021.

July Temperature Outlook - % chance of exceeding the median July Temperatures 2021. Valid Friday 25th of June 2021.

Analysis and discussion


No point in labouring the point over and over again. The signals have not largely changed through the past few days for the month of June. Most climate models are encouraging if you want above average rainfall and seasonal temperatures. Some areas will be colder than normal for June overall, but that is highly conditional on how much cloud develops in association with the Indian Ocean getting warmer.


Rainfall totals for the coming 4-6 weeks looks solid for southern and western Australia which again is being reflected in most of the climate modelling for the period ahead. This signal has been very strong for a number of weeks now, and we have seen two major storms over the nation during the past two weeks, bringing those higher rainfall totals.


Rainfall percentage of mean - Valid up until June 24th 2021. BoM.

There has been widespread rainfall through QLD which has not been included in these figures, I will update again on Tuesday.

A closer look at the food bowl, and healthy falls generally throughout the basin, some pockets missing out and we have seen a drier picture develop over the east coast which is not uncommon for winter losing the onshore wind profile as the winter westerly winds take over.

Looking ahead to the next 4-6 weeks now and the rainfall does look to follow the same bias as the previous 4 weeks of weather. Wetter than normal weather likely west of the divide through QLD and NSW, more likely through NSW. The rainfall numbers look set to increase for SA with a bit of luck going the way of the areas that have missed out above.


The wet signal continues for WA, with rainfall anomalies of 1-2 inches possible about the west coast of the nation, again subject to whether frontal weather develops at a frequent level and taps into the negative IOD that is currently in place. We have seen that take place 3 times where the fronts have captured the moisture and produced widespread rainfall since May.


Northern Australia should return to dry season conditions, however a taste of what is to come for the rest of the dry has been present this week, showers and thunderstorms about from time to time can be expected, with the dry not as exceptional as last season, with interruptions expected.


QLD, rainfall numbers will pick up during the second half of July at this stage leading into August.


Rainfall for the coming 6 weeks - Euro Model - Valid Friday 25th of June 2021.

Note the rainfall is expected to increase in line with the IOD negative phase. The IOD increases the rainfall chances for parts of QLD through August-October. That coincides with the nation warming up.

Rainfall Anomalies - For the coming 5 weeks - Euro - Valid Friday 25th of June 2021.

Better odds of rainfall increasing over the southwest once again and note the Indian Ocean has anomalies in excess of 4-5 inches over the water mass, which could provide more rainfall opportunities out of the moisture from this being dragged into the jetstream and propelled across the nation.

Taking it out 7 weeks, the signal likely to increase for rainfall anomalies to be above average leading into August, note the spread of the higher values through the south and west, in line with the Indian Ocean being warmer than normal. Still have pockets of below average rainfall expected over QLD and I think that is the right solution based on climatology.

Comparing the rainfall from Euro with GFS, continues to show you the lower skill score that GFS has in this field, and once again is running way to dry for the region and I suspect we can chuck this outlook out. Interesting, it has the complete opposite outlook to Euro, a mirror image.


GFS Rainfall Outlook for the coming 5 weeks - Valid Friday June 25th 2021.

Temperatures throughout the next 4-6 weeks will likely continue to follow the same trend as it has all year with pockets of below average temperatures over the south and west of the nation, this may now extend inland over the central and eastern interior, in line with the IOD strengthening and more cloud bands descending across Australia. That is a fair assessment moving through the coming period.


GFS has been running way to warm for the previous outlooks and continues to do so for much of the nation, based upon a dry bias and it's inability to read the IOD that is phase. It will catch up but I am discounting this solution.


GFS Temperature anomalies - Valid for the next 5 weeks - Valid Friday June 25th 2021.

A warm bias that has continued to be error riddled over the south. Running too cool for the north of the nation in respect to observed temperatures being above average in recent weeks.

Euro Temperature anomalies - Valid for the next 5 weeks - Valid Friday June 25th 2021.

Has been running much better and has indicated the Indian Ocean is now reflected in the temperature outlooks with below average temperatures over the ocean suggesting more cloud and rainfall may be in the area. Conversely above average temperatures are much more defined for the northern parts of the nation in line with more humidity in the region. Colder pockets over the interior in line with inland rainfall events and large cloud bands that are being projected inline with the IOD.

The IOD continues to drive the outlooks for both temperature and rainfall. That becomes more pronounced during the second half of winter and into spring.


I will focus on the ENSO outlook on Tuesday to see how likely another La Nina or El Nino is likely to develop and when, and the next 6-9 months ahead and what influence that will have on the nations weather moving into summer and autumn 2022.


Need more climate information? Email me at karllijnders@weathermatters.org for further details.




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