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What is thundersnow and how does it happen?

Friday August 9, 2019 - 18:58 EST
ABC licensed image
In an image from Britain's Met Office, a lightning bolt strikes during a thundersnow storm. - ABC licensed

Snow and thunder storms are forecast for parts of south-east Australia as a deep polar low moves across the region.

When the two weather conditions happen together, it can cause a phenomenon called thundersnow.

It's similar to a regular thunderstorm, except instead of rainfall you see snow.

Here's what you need to know.

How does thundersnow happen?

As with a perfectly formed souffle, the ingredients have to be just right.

According to Bureau of Meteorology extreme weather desk meteorologist Diana Eadie, it's not often that all the conditions align to create thundersnow.

"Essentially what we're seeing is a large cloud band moving across producing snow with some embedded thunderstorms within it, so we observe both lightning and snow at the same time," she said.

"It's similar to a normal thunderstorm — you need the combination of both a , which would normally see rain or snow — with some instability as well.

"So the conditions need to be quite ideal for this sort of occurrence."

Of course, we know thunderstorms are more likely to form in the summer.

They form when warm air rises into colder air in the atmosphere, creating instability, leading to a traditional rainy thunderstorm.

"[Thundersnow is] essentially the same as a regular thunderstorm, except instead of any rainfall coming out of the thunderstorm you see snow instead," Ms Eadie said.

"Because the whole atmosphere and the depth — which the thunderstorm is extending through — is frozen."

According to Science News, to create thundersnow air travels up in a slant pattern rather than the purely vertical pattern of most thunderstorms.

How often do we see it in Australia?

Ms Eadie said instances of thundersnow in Australia were rare "just because we do need the combination of those perfect ingredients".

If there are lightning flashes occurring, they should be easier to see as the snow flakes give it more to reflect off.

But hearing the thunder through the snow can be difficult even if it is happening up there.

According to AccuWeather, snow muffles the thunder crack, meaning you're a good chance of hearing it if you're within about five kilometres of the lightning.

Are there any risks associated with thundersnow?

Ms Eadie said thundersnow was not particularly dangerous, aside from the obvious.

"Of course the risk that we see with any thunderstorm in terms of lightning, but also the risks you see with snow as well — potentially reduced visibility associated with the snow, as well as that lightning," she said.

"And if you get any sort of wind gusts with the storm you could be looking at some localised blizzard activity."


© ABC 2019

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