Millions of people across southern and eastern Australia should expect a mixed bag of weather today, including 100km/h winds and temperatures nudging 40 degrees.A strong low pressure system in the Southern Ocean is the driving force behind the mish-mash of heat and cold, Weatherzone reports."As polar air surges northwards, warm air from the interior of the continent is being dragged southwards in strong north-westerly winds, as air flows naturally from areas of high pressure to low pressure."READ MORE: Slow-moving Severe