Latest Aussie MET Excuse for Weather Report Errors: Wrong Kind of Moths

Essay by Eric Worrall

Just in case you thought there couldn’t possibly be any more excuses for bad weather forecasts…

Bogong moths are playing havoc with BOM weather radars

By ABC meteorologist Tom Saunders
Posted Tue at 3:05pmTuesday at 3:05pm, updated Tue at 3:34pm

For the last month, the weather radars across south-eastern Australia have been lighting up with precipitation every night.

The only problem is that on most nights, skies are not cloudy and it certainly has not been raining for a month straight.

“There has been increased ‘echoes’ displaying on radars across eastern New South Wales that aren’t precipitation,” a spokesperson for the Bureau of Meteorology (BOM) said.

But the equipment is not malfunctioning, and this is not a giant UFO.

Instead, the radars are detecting the millions of bogong moths currently migrating south to the Australian Alps for summer, and the swarm appears on radar as widespread rain.

…

Read more: https://www.abc.net.au/news/2026-10-20/nsw-bogong-moths-weather-radars-bom-sydney-canberra/107286624

For once though it might not be the MET’s fault. I asked Claude a bunch of questions, including the following:

…

Is Australia’s inability to determine whether an apparent rain signal due to lack of X-Band radars?

Assessing whether radar coverage explains an unclear rain signal.

Mostly no. Where the BoM struggles to tell real rain from other echoes, the main causes are elsewhere:

1. Many radars lack dual-polarisation. This is the biggest factor. Large parts of the network are older single-polarisation radars, many of them C-band and some not even Doppler. Without ρhv and ZDR, a radar sees only reflectivity, and moths, birds, smoke, dust or sea clutter can look much like light rain. Upgrading these sites to dual-pol would fix far more misidentifications than adding X-band radars. A dual-pol S- or C-band radar separates rain from insects well on its own.
2. The public map shows reflectivity only. The BoM website and app display a simple reflectivity product with clutter filtering. Even where a radar is dual-pol, the public image doesn’t show the hydrometeor classification. The Bureau’s internal products and forecasters have more information than the map does, so some of the apparent inability is a display limitation rather than a sensing one.
3. Coverage gaps and beam geometry. Across much of inland Australia, sites are hundreds of kilometres apart. Far from a radar, the beam is several kilometres up and wide. It can overshoot low rain, catch virga that evaporates before reaching the ground, or pick up elevated non-weather layers. Denser coverage would help here, and in other countries X-band gap-fillers are one way to provide it. But the gain comes from proximity and low beam height, not from the X-band frequency.
4. Propagation effects. Temperature inversions, common on clear nights and along the coast, bend the beam down into the ground or sea. The resulting anomalous propagation echoes look like rain, and dual-pol and Doppler processing are what remove them.

So X-band radars wouldn’t be the fix. In other networks they mainly fill low-level gaps around cities and in complex terrain, and they attenuate badly in exactly the heavy tropical rain Australia cares about. The more useful improvements are dual-pol upgrades to the existing S- and C-band radars, which the current Leonardo replacement programme should progressively deliver, and better use of classification products. Dedicated X-band entomological radars remain the right tool for studying moths in detail, but that’s a research job, not an operational rain-mapping one.

Read more: https://claude.ai/share/512ed4ab-468b-4391-8a6d-abd097ae25f1

Obviously we at WUWT have had our issues over the years with how the Aussie MET and other government meteorological bodies conduct climate science, but on this occasion maybe they are doing the best they can with shockingly outdated equipment.

I mean, its not like an accurate understanding of weather is important in a country like Australia, right? Do I need a /sarc tag?

There is a silver lining to all these moths – apparently they are edible, a major Aboriginal food source back in the day. So if you have ever wanted to try some Aussie bush tucker, Crocodile Dundee style, find yourself a butterfly net and you’re all set.