Locals took to social media to report exceptionally loud thunder in all directions before the rain set in, to voice their fears that the ominous rumbles were foreshadowing damaging hail.
BOM meteorologist Helen Kirkup was monitoring the storm and shared her professional opinion with Canberra Weekly.
“In terms of hail, you need a certain level of the atmosphere that’s cold enough that hail can start to grow,” she said.
“Then it stays in that cold layer collecting more and more water before it’s too heavy and it falls.
“In terms of today, the kind of environment we’re in, we’re not predicting we would get hail growing to such large sizes.”
Although lightning and thunder does not necessitate hail, the BOM meteorologists pay attention to where it strikes.
“Firstly, we can see where the lightning is, assess the environment and work out the possibility of whether it can generate large hail,” Ms Kirkup said.
Thunder is the sound of the explosive expansion of air directly around a lightning bolt, which generates an audible shockwave.
Lightning heats air to around 30,000°C – that’s hotter than the surface of the sun.
Thunder can usually be heard up to 15km from the lightning, but under optimum conditions, like on a still night, it may be heard up to 25km away.
Thunderstorms require three things – instability, moisture and a trigger – and all three factors were present in the eastern half of NSW today.
Elsewhere in the region, the South Coast, Illawarra and Central Tablelands are flagged as areas where thunderstorms may have the potential to generate severe characteristics.
Ms Kirkup said the ACT could expect stormy conditions on and off through to the afternoon, after which the system may have moved too far east to impact Canberrans.
Bowral, Jenolan Caves and Taralga have already seen intense rainfall, which may lead to flash flooding.
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