If you're working or playing outdoors in Melbourne on this very mild Tuesday afternoon, you might be excused for thinking the whole state is experiencing coolish weather atypical of mid-February.

Guess again.

There are some fairly extreme temperature contrasts in Victoria this afternoon, with 40 degrees in the north and temps as low as the high teens at some coastal locations around 4 pm as we write this story.

For example, at 4 pm, it was:

• 39.6°C at Walpeup (a tiny town of 150 people in the Mallee district)
• 18.0°C at Portland Harbour (a large coastal town of about 11,000 residents an hour west of Warrnambool)
• 20.7°C in Melbourne

Those first two towns are about 400 kilometres apart on a north-south axis, and the temperature contrast between them illustrates pretty well the situation in Victoria right now.

A low pressure trough positioned over Victoria today is marking the boundary between two contrasting air masses, with very hot northerly winds affecting northern Victoria and much cooler southerly winds flowing over the state's south.

And while you'd typically (but not always) expect the north of the state to be warmer than the south, the situation is being exacerbated today by those two contrasting airmasses.

Interestingly, on Monday the line between the two airmasses was located further south, with a 10-degree difference between Melbourne's northern and southern suburbs in the afternoon.

Looking ahead, there's more hot weather with temps scraping 40°C for the north of the state on Wednesday, and the southern half will be a little warmer too with Melbourne expecting a top of 27°C.

Things will again cool down significantly in southern Victoria towards the end of the working week with an injection of southerly winds, before a fine and relatively mild weekend in most parts.