Weather News

Have you ever seen a fogbow?

Ben Domensino, Friday June 25, 2021 - 10:38 EST

Western Australia has been in the grip of a wintry air mass this week, causing Perth's coldest run of mornings in years, frequent fog, and even a fogbow.

Cold air with widespread rain was dragged over Western Australia earlier this week when a strong low pressure system developed to the south of the state on Monday and Tuesday.

Since then, the low has moved further east and a large high pressure system has drifted across Western Australia in its wake.

This weather setup created a combination of lingering cold air, clear skies and light winds, which were the perfect ingredients for a string of chilly mornings.

Image: Modelled 850 hPa temperature, wind and heigh on Wednesday night, showing a low pressure system centred near South Australia driving cold air over Western Australia.

Perth's minimum temperature in June averages around 9-10ºC. But this week's minimums have been well below that mark:

  • Tuesday 1.9ºC
  • Wednesday 2.8ºC
  • Thursday 3.4ºC
  • Friday 2.7ºC

This has already been Perth's coldest run of mornings since 2014 and it's not over yet. Saturday's forecast low of 3ºC would make this Perth coldest string of five mornings at or below 3.4ºC since 2010.

The cold air has also been felt right up to the Pilbara and Kimberley this week. On Thursday, Marble Bar dropped to 6.0ºC, which was its coldest morning in 21 years.

But while the shivers have been widespread, there have also been some beauty in this week's cold snap.

Low temperatures after the widespread rain have allowed fog to be a frequent feature across southwestern Australia over the last few mornings. On Wednesday, the fog interacted with light from the rising sun to create an impressive fogbow that could be seen in a few places along the state's Lower West coast.

Image: A fogbow at Seascapes Beach, WA on Wednesday, June 23. Source: @kati_cooper_coastalbliss / Instagram

Fogbows form in the same way as rainbows, with light being refracted and reflected by small drops of water suspended in the air. But because fog droplets are much smaller than rain, they cause most of the colour to be filtered out by refraction, which gives fogbows a characteristic white glow.

Perth's run of cold mornings will come to an end after Saturday, with the temperature only forecast to reach 7ºC on Sunday morning and getting back up to 11ºC on Monday morning.

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