An unusual winter weather event is threatening heavy rain and potential flooding for large parts of central Australia over the next week, along with near-record cold maximum daily temperatures.
The expansive North-West and Central regions of the Australian continent are renowned for their distinctive landscapes, iconic landmarks, and popular tourist destinations. These areas are also well known for their dry and unforgiving climatic conditions and are amongst some of the harshest found on planet earth.
The North-West and Central regions of Australia are made up of desert and semi-arid lands which are typically exposed to extreme climates, including dry and scorching hot summers and low rainfall all year round. But thankfully for those who call the region home and tourists alike, the oppressive heat of the warmer months gives way to milder daytime temperatures in winter making for easier living and travelling.
It is a vast and normally dry region contained in one of the driest continents on Earth. Despite this however, an unseasonal rain deluge and unusually cold weather event is currently unfolding and will continue to impact the region for the remainder of the week and into the weekend which we will explore further in this article.
WHY IS CENTRAL AUSTRALIA SO DRY?
The remarkably dry climate of central Australia can be attributed to a unique combination of factors. Firstly, a mountain range known as the Great Dividing Range, stretches north-south along the east coast of Australia, and acts as a barrier to the moist Pacific trade winds causing uplift and rainfall on the windward eastern side and lee drying or descending air on the western side.
Secondly, whilst the interior of the continent does contain some small mountain ranges to uplift moisture locally such as the MacDonnell Ranges, the vast majority of this region is flat and low lying with some areas even below sea level such as Lake Eyre, Australia’s largest saltwater lake which has a lowest point of 15.2m below sea level.
As a result, there is a limited scope for air to rise and produce rainfall here and thus instead we see those large flat areas essentially act as an oven to bake the surrounding air and cause a feedback to the atmosphere known as a heat low. These features can bring persistent high temperatures for weeks or even months on end during the warmer months.
Perhaps however, the most influential reason for the dry conditions is the dominance of the subtropical high-pressure belt which is a region of descending air or subsidence caused by the sinking portion of the Hadley cell, which is an atmospheric circulation that causes air to rise at the equator and sink at around 30° latitude north or south.
Furthermore, Australia’s susceptibility to the El Niño-Southern Oscillation (ENSO) plays a significant role in the country’s climate variability. ENSO refers to the heating or cooling of the Pacific Ocean, which can have profound effects on weather patterns. During El Niño events, Australia tends to experience prolonged periods of high temperatures and drought, exacerbating the aridity and amplifying the water scarcity issues.
Collectively, these factors create an arid environment across much of Australia, contributing to its reputation as one of the driest continents on Earth. The intricate interplay between ocean currents, mountain ranges, atmospheric pressure systems, and ENSO events shapes Australia’s climate.
WHAT IS THE TYPICAL WINTER CLIMATE IN THE CENTRAL REGIONS OF AUSTRALIA?
Winter in the central regions of Australia spans from June to August and during this time, the area experiences a noticeable change in temperature and weather conditions from the warmer months.
Daytime temperatures in Central Australia during winter generally range from 15 to 25° Celsius (59 to 77° Fahrenheit), offering a respite from the scorching heat experienced during the summer months.
Central Australia’s winter weather is usually characterized by low humidity and minimal rainfall. As we know, the region is known for its arid and desert conditions, and the winter months are usually no exception. The skies are often clear, providing breathtaking views of the expansive outback and showcasing the vibrant colours of the landscape including just some of the region’s iconic landmarks, such as Uluru, Kata Tjuta, and the MacDonnell Ranges.
Historical rainfall records from the Bureau of Meteorology indicate that Central Australia receives an average annual rainfall of approximately 200-250mm and towns such as Alice Springs receive an average monthly rainfall of 13mm for June and 14.4mm for July.
WHAT IS CAUSING THIS UNUSUAL COLD AND RAINY WEATHER IN CENTRAL AUSTRALIA?
The cold and rainy weather in central Australia can be attributed to moisture originating off the northwest coast of the country, being drawn down and across Australia along a Jetstream.
This moisture is then being uplifted by a large-scale upper-level trough over western parts of the continent, which has led to the formation of a significant North-West cloud band that is bringing widespread moderate to heavy rainfall accompanied by cold weather and below-average daily maximum temperatures, some of which are near record-breaking.
WHAT RAINFALL HAS ALREADY ACCUMULATED DURING THIS WEATHER EVENT?
The rain from this weather event so far has been heavy and widespread over north western and central Australia including:
- Gibb River in the Kimberley received 72mm of rain during the 24 hours to 9am Tuesday. This is more than seven times its June monthly average, more than five times its winter average, and its second wettest winter day in records dating back to 1922.
- Yulara Airport, near Uluru, received 64.6mm of rain in the 48 hours ending 9am Tuesday. This is nearly four times its June monthly average, and its wettest pair of June days since 2004.
- Curtin Springs, NT and Ernabella/Pukatja, SA picked up 55.2mm and 48.6mm, respectively, during the 48 hours ending at 9am on Tuesday. This was the wettest pair of June days since 2001 at both sites.
- Broome’s 30mm in the 24 hours ending at 9am on Tuesday was more than a month’s rain for this time of year and its wettest June day in a decade.
Despite the substantial rain that has already fallen in the past 48 hours, more widespread and heavy rain is still on the way through the remainder of this week.
WHAT RAINFALL TOTALS ARE LIKELY DURING THE REMAINDER OF THIS WEATHER EVENT, AND WHAT EFFECT WILL THIS HAVE ON THE REGIONS IMPACTED?
The Bureau of Meteorology has issued multiple Flood Warnings relating to this weather event accompanied by forecast rainfall totals for the region that could reach 50-100mm, far exceeding the June average of 5-20mm.
Catchments in the flood watch area remain dry ahead of the expected rainfall but this could change rapidly in the days to come. Rises in streams and creeks leading to localised flooding may affect secondary road conditions which is likely to impact travel and movement initially to southwestern parts of the Northern Territory, then spreading into central parts during the week.
WHAT TEMPERATURES ARE BEING RECORDED AS THIS EVENT UNFOLDS AND WHAT TEMPERATURES ARE BEING FORECAST?
As we already discussed, the widespread moderate to heavy rainfall in Central Australia is also accompanied by some very cold weather which has already started to verify in line with forecasts. Below average daily maximum temperatures are being recorded in some areas and continue to be forecast through the week and into the weekend, with a surge of south easterly winds expected to push through and add an extra wind chill factor.
On Tuesday June 27th, Alice Springs recorded a maximum temperature of 16.2° C. On Wednesday June 28th, the temperature sat at just 11.6° C at 3.30pm, which is usually the warmest part of the day. Whilst this is already well below the June average of 19° C, the real impact of this weather event on Alice Springs and surrounding regional areas will be felt in the coming days, with even colder temperatures forecast.
ISN’T AN EL NIÑO WITH BELOW AVERAGE RAINFALL SUPPOSED TO DEVELOP?
In stark contrast to the current unfolding rain event, official agency outlooks in fact predicted a drier than average June for much of the country with an expectation of an El Niño to develop later in this winter, and spring resulting in below average rainfall.
However a valid reason for this not coming to fruition just yet is the lack of ocean to atmospheric coupling of the ENSO where the direct relationship between the Pacific Ocean and the resultant synoptic scale weather systems has not been fully established and is thus still in the developmental stages.
SO, WHAT HAPPENS AS THIS WEATHER SYSTEM MOVES EASTWARD?
As this unseasonal weather event continues to unfold in Central Australia and the system slowly moves eastward, it is becoming apparent that the east coast state of Queensland could be next to experience its fair share of rain and cold weather as well.
Current model guidance suggests that the system will impact central Queensland throughout the weekend and into early next week, all the while continuing to produce significant rainfall totals and lower temperatures.
Additional information was provided by Rowland Beardsell. Other sources and credits:
The Australian Bureau of Meteorology www.bom.gov.au