CLIMATE OUTLOOK - JULY

Headlines


  • The wet signal continues for southern and western parts of Australia as the Indian Ocean Dipole continues to strengthening it's negative phase.

  • Drier than normal conditions to persist for eastern and central QLD for another month with rainfall odds swinging back the opposite direction coming into August.

  • The temperatures are expected to broaden the above average values for northern Australia with an increased risk in humidity returning more frequently through the second half of the month.

  • Temperatures are expected to be below average, especially over WA where frequent cloud bands are anticipated to form and extend across the western interior. These will have impacts on temperatures throughout the southern and eastern inland.

Rainfall Outlook - July 2021 - Valid Tuesday 22nd of June 2021

Temperature Outlook - July 2021 - Valid Tuesday 22nd of June 2021

CLIMATIC DRIVERS


Southern Annular Mode (SAM) - Currently positive but expected to surge into negative territory during the coming few days and then remain neutral in line with the climatic waves in this region.

Indian Ocean Dipole (IOD) - Currently negative and expected to remain negative throughout the coming 3-6 months (This forecast product will be updated Friday with fresh notes about the impacts ahead)

ENSO (La Nina/El Nino) - Currently neutral and expected to remain neutral for the coming 3-6 months.


Analysis for July


Rainfall


The big influence on rainfall is the negative IOD and the SAM also moving into negative phases during the month of July, meaning more large cloud bands and widespread rainfall events are allowed to unfold over the nation.


In the short term we can see what happens when the SAM and IOD are in sync and the impacts are above average rainfall for large parts of outback Australia and for areas around southern and western Australia.


Satellite Imagery on Tuesday 22nd of June 2021 - Showing significant cloud extending from the Indian Ocean through SA and into the southeast bringing widespread rainfall. Areas over the Pilbara saw 2-3 months worth of rainfall in a sitting last night, where it is usually dry with no rainfall seen during this time of year. The rainfall will be widespread as it comes southeast through SA today and into the east tonight into Wednesday.

It is fairly conceivable given the precipitable water values being picked up in the short to medium term that the next month will continue down this same path, with more large scale cloud bands developing from the northwest through to the southeast, the trajectory and entry point of these cloud bands will change each time, but the result will be the same, large scale rainfall events with pockets getting moderate to heavy winter rainfall.


Precipitable Water Values - GFS 18z run for the next 2 weeks - Valid Tuesday 22nd of June 2021.

This is showing a large impulse of moisture coming down from Indonesia and over Australia this week (review the satellite) and more moisture draping itself over northern Australia with the potential for widespread rainfall developing over large parts of the nation coming into July. Some areas may start the month with half to one month's worth of rainfall after recording well above average rainfall in June 2021.

Rainfall for the coming 7 week which takes in all of July, showing the movement of rainfall this week and follow up large scale events moving in during the month of July and extending into early August. This will mean what we can see coming through this week, will be replicated over the next few months.


Rainfall totals next 46 days - Raw Data - Euro Ensemble Model - Valid Tuesday 22nd of June 2021. Even rainfall over northern parts of the nation which is unusual.

Seasonally speaking the wet signal does extend well beyond the month of July and into Spring and early Summer as the Indian Ocean Dipole continues to be in negative phase. The event is likely to peak during September or October before waning in the Austral Summer in line with climatological expectations.


Euro Rainfall Anomalies - June through September. Modest signals for above average rainfall over the nation with neutral odds everywhere else. The signal is wetter in the August and September. Valid Tuesday June 22nd 2021.

Euro Rainfall Anomalies - August through October 2021.

Rainfall odds increasing in the above average ranges over the southeast and south of the nation in line with the IOD strengthening. Numbers over WA should also respond to that as well so wouldn't be surprised if the model responds with a wet signal over the northwest. Early season rainfall over the NT and QLD also likely and finally with some luck, rainfall returning to QLD.

Euro Rainfall Anomalies - September through November 2021

The wet signal continues with the early onset rainfall increasing over the north, leading to an increase of rainfall through central and eastern parts of the country, helping to bring some moisture through to the inland via heat troughs that will be deepening over the landmass and frontal weather beginning to retreat south. Again I do think wet weather signals may be higher over WA through this period.

Euro Rainfall Anomalies - October through December 2021

A first look as we head into summer and note the blue on the board north of the nation extending south as we track into December, a heavy monsoon perhaps on the way again? Thanks to the IOD that is possible, but not as highly likely as last year with the La Nina, but something to watch. The IOD at this time is starting to break down however the lag impact of this takes time for the atmosphere to respond so the above average rainfall signals for all states should continue.

The ENSO phase in the pacific will have little impact on the rainfall for Australia with that to remain neutral throughout the next 6 months.


Temperatures


No real shift in the temperature prognosis as the lead in forecasts surrounding the developing IOD have been verified keeping the above average signals over the northern half of Australia in place, and they have too verified in real time.


The colder signal that we have experienced for the first 6 months of the year for southern Australia is expected to break down a little during July, still colder than normal for much of WA with the influence of cloud cover and regular rainfall, this cloud traversing the country with the chance of colder than normal days being quite frequent in response to the cloud cover over inland parts of SA and NSW.


GFS Temperature anomalies for the coming 7 weeks

GFS has been running way too hot in the past number of runs with well above average temperatures covering the nation for June, but that has not verified as per below so I will retreat the temperatures for the northern parts of the nation where there is an increase in humidity keeping overnight and daytime temperatures elevated.

Euro Temperature anomalies for the coming 7 weeks

Running a little closer to the truth at the moment and has performed really well in covering the colder than normal all year and the heat bias over the north and suspect this will continue to be the case. It is moderating the cold bias over the south and that makes sense, with more moisture coming in from the northwest through the southeast. However outback areas could see colder values depending on how persistent cloud bands are over the regions in the coming weeks. Something to watch and assess in the next 4 weeks.


SNOWFALLS

With the colder weather, that doesn't always equate to more snowfalls. The longer term look at snow is not horrendous, but it is not great either.


Snowfalls for the coming few weeks - shows a lot but it will likely be eroded by a lot of rainfall so even though the model is pinging 14 inches of snow, it will likely end up being closer to around 50cm left on the ground on current estimations in association with further rainfall coming along.

GFS Extended for the coming 5 weeks showing reasonable snow signals. Ignore the grey over the northern and central Tablelands as that is merely the chance of a flurry, nothing settling. But watch for rogue systems like we had in early June.


With increased moisture coming through ahead of frontal systems (like we are seeing this week), these fronts will produce a large amount of rainfall before transitioning into snowfalls above 1200m over the east and southeast. That means that there will likely be net loss coverage over time, with more rainfall than snowfalls anticipated.


So you have to look at the outlooks objectively and factor that in. Fingers crossed the signals improve for the region.


Again the rule of thumb that I have drawn graphically still applies for the coming few months, which is more moisture meaning a higher chance of average to above average rainfall over the southern and eastern parts of the nation.


A guide for the climate drivers over the coming months - will this verify? That is the question many have - so lets see how we go.

I will have an update on the Indian Ocean Dipole later this week in line with the latest guidance from the climate models, but on current read, I am expecting little change in the guidance. We just have to see how strong the models predict the event to be and if it is going to be drawn out over a longer period, as that then increases the risk of flooding in the spring over inland QLD, NSW and VIC.


Need more weather information for your part of the world? Tailored forecasts for your region are not only beneficial, but an asset to helping you make the decisions that are right for your circumstance. Being informed means making better decisions. Email me at karllijnders@weathermatters.org



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