A spell of above-average daytime heat is expected across New South Wales this week, particularly on Wednesday.  

The spell of unseasonable heat can be blamed on a cold front that is expected to sweep across South Australia and Victoria from Wednesday: warm air with strengthening winds from the interior ahead of the system will be forced across the eastern interior as the front makes its way eastward.  

Wednesday is expected to be particularly warm over a large area of NSW, with places like Sydney, Bourke, Cobar and Tibooburra all reaching the mid to high twenties. Tibooburra's expected 28 degrees could be its highest June maximum temperature since records began in 1997, more than nine degrees above the long-term average.

For the most part, temperatures across the central, eastern and northern parts of the state are expected to warm to four-to-seven degrees above the long-term monthly average on Wednesday.

The front should bring widespread falls of 10-20mm over southern South Australia and across Victoria on Wednesday, likely also resulting in a few centimetres of alpine snow later during the evening. Some rainfall is also expected in NSW, mainly in the south and southeast, but generally resulting in less than 5mm to any single location.

While colder air in the wake of the system should bring cooling to NSW, maximum temperatures should remain 1-2 degrees above average, mainly due to the lack of cloud cover associated with the high pressure system that will quickly move in behind the front.