Bogong moth swarms disrupting weather radars across NSW and Victoria

Consensus Summary

Weather radars across eastern New South Wales and Sydney have been falsely detecting bogong moth swarms as widespread rain for the past month, confusing meteorologists and triggering false alerts. Both the Guardian and ABC report that the moths—migrating in their millions toward the Australian Alps—are reflecting radar signals in a way that mimics light precipitation, particularly near sunrise and sunset. The phenomenon is not new: during the 2000 Olympics, a similar swarm fooled forecasters into predicting rain over the stadium, only for a moth to land on a performer during the closing ceremony. This year’s event, however, is more prolonged, with radar anomalies appearing nightly and expanding from NSW into Victoria, according to the Bureau of Meteorology (BOM).

The bogong moth’s migration is a decades-long ecological phenomenon, with records dating back to the 2000 Olympics and earlier observations spanning 'several decades'. These insects travel hundreds of kilometres annually, drawn to alpine habitats but increasingly disrupted by urban lights and environmental changes. Researchers like Dr Kate Umbers at Western Sydney University have long struggled to track their movements, relying on anecdotal reports and limited tagging methods. The radar data now offers an unprecedented tool to study their routes and population dynamics in real time, potentially answering questions like how many moths equal 'heavy rain' on radar screens. The Guardian notes that while sightings in cities are dramatic, they may not reflect overall population health, as alpine habitats remain threatened by global heating.

Key figures in the story include Dr Kate Umbers, who is leveraging citizen science and radar data to study bogong moths, and Prof Justin Welbergen, whose 'Aerocast' system tracks flying foxes using similar radar techniques. Welbergen suggests the same methods could apply to moths, framing them as 'giant moths' in radar imagery. The BOM confirms that while meteorologists recognize the interference, some weather apps—using unfiltered radar data—may still send false rain warnings. The Guardian highlights Umbers’ delight in the public’s engagement, describing the moths as 'saying: don’t forget about us,' while ABC emphasizes the technical challenges of distinguishing real rain from moth echoes, especially on nights like 'October 2', when both appeared simultaneously.

The two sources diverge on the timeline and scale of the phenomenon. The Guardian frames the return of bogong moths as part of a '26-year' cycle since the 2000 Olympics, suggesting a periodic but worrying decline in populations. ABC, however, focuses on the immediate 'last month' of radar disruptions, with moths appearing nightly after sunset and expanding their range into Victoria. While both agree on the radar interference, ABC provides specific dates ('October 2') and technical details about how radar pulses reflect off insects, whereas the Guardian emphasizes the scientific and conservation implications, including the potential of radar data to reconstruct historical migration patterns over 'several decades'. The Guardian also notes broader ecological concerns, such as habitat loss, while ABC sticks closely to the meteorological and technical aspects.

Despite the confusion, the BOM assures that standard weather forecasts remain reliable, as they incorporate ground observations and satellite data. Researchers like Umbers and Welbergen see the radar anomalies as an opportunity rather than a problem, with Umbers calling the public’s involvement 'the best possible scenario' for understanding the species. The Guardian suggests the moths’ visibility in cities is a chance to raise awareness, though their alpine habitats still face threats. ABC, meanwhile, leaves open the question of how much of the radar interference is truly from moths versus other factors like temperature inversions or 'ducting'—where radar beams bend toward the ground. Both sources agree that the phenomenon is unlikely to resolve soon, with moths expected to continue their annual migration and radar systems to keep detecting them as 'light rain' until further notice.