Parts of NSW will face Extreme fire danger ratings on Saturday as temperatures soar across the state.

A mass of hot air sweeping over NSW on Saturday will push temperatures above 40 degrees in many areas, with some places likely to exceed 45 degrees. This heat won't just be confined to the far west, with Bourke and Penrith both forecast to reach around 46-47 degrees.

Image: Forecast surface temperature on Saturday afternoon according to the ECMWF-HRES model.

Saturday's hot weather will help cause Severe to Extreme fire danger ratings over some of the state's fire grounds, including the Greater Hunter and Greater Sydney areas.

On Friday, smoke from close to 100 fires in NSW was being blown across southeastern Australia, reaching all the way down to Melbourne in the middle of the day.

Image: Smoke from NSW fires spreading across central Victoria on Friday.

So far this season, more than 2.7 million hectares of land has been burnt in NSW alone and this figure is rising by the day. These fires have collectively destroyed or damaged more than 1,000 homes across the state. However, close to 13,000 buildings have been saved by the efforts of firefighters.

This season's fires are occurring at the end of an exceptionally dry and warm year in NSW. The state as a whole registered its hottest and third driest January to November period on record. A number of factors have contributed to these conditions, including a strongly positive Indian Ocean Dipole and a persistently negative Southern Annular Mode in late spring and early summer. 

According to the Bureau of Meteorology's latest State of the Climate report, the number of bad fire weather days and the length of the fire weather season has also increased over parts of southeastern Australia in recent decades. The effects of climate change, such as increasing temperatures, are contributing to these changes.