Melbourne's see-sawing temperatures

Thomas Hough, 10 November 2019

For those who live in Melbourne, see-sawing temperatures are somewhat of a familiar experience, but what causes it?

There have been a couple of instances over the last few weeks where the mercury has climbed 10-14 degrees above average, peaking in the low-to-mid-30's, only to plummet again soon after.

This happened between Tuesday 22nd and Saturday 26th October. In this instance, temperatures climbed from near 20 degrees on the Tuesday, to near 34 degrees on the Thursday. What many might of hoped was a prolonged period of warmth was actually a brief burst of heat, as the mercury dipped to just under 22 degrees on the Friday and 15.5 degrees on the Saturday.

A similar pattern is due to occur over the next couple of days, with temperatures in the city peaking near 18 degrees today (Sunday 10th), and a forecast of 28 and 17 on Monday and Tuesday respectively.

This fluctuation in temperature is due to the passage of low pressure troughs and cold fronts, the boundary between two air masses. Today for example, Melbourne is under a relatively cold airmass and in a cool south-westerly wind regime. These winds will shift north-westerly overnight ahead of an approaching trough and cold front, drawing down a warmer airmass from the north. As the front continues east however these warm northerly winds will move ahead of it, away from Melbourne and western Victoria, with a much cooler airmass behind the front.

Looking further ahead, after a cool day on both Tuesday and Wednesday, warmer conditions will return to Melbourne with much less day-to-day variation in temperatures, as near average conditions see the week out.