CANBERRA, Feb 29 (Reuters) - Australia could be heading for its third-warmest summer on record, with many places likely to experience a warmer and drier period than normal from March to May, weather authorities said on Thursday.

The weather has a huge impact on crop yields and livestock markets in Australia, a major exporter of agricultural commodities.

It is now growing summer crops, such as sorghum and cotton, with planting of much larger crops of wheat, barley and canola set to begin around April and May.

The Bureau of Meteorology (BOM) said most of Australia has at least an 80% chance of experiencing above average temperatures during the southern hemisphere autumn.

"Australia is on track to have the third-warmest summer on record nationally, after 2018–19 and 2019–20," the bureau said in a statement.

There was a 60% to 75% chance of below median rainfall across large parts of the country, including most of the states of New South Wales, Victoria, Queensland and the Northern Territory.

But the chances of above or below median rainfall were roughly even elsewhere, such as most of South Australia and southern and central Western Australia, it added.

The vast majority of Australia's grain is grown in Western Australia, New South Wales, Victoria and South Australia.

Last year was Australia's eighth-warmest year on record, which the weather bureau attributed to climate change.

Conditions swung from widespread flooding through the hottest winter and driest three months on record to heavy rainfall as the year ended. (Reporting by Peter Hobson; Editing by Clarence Fernandez)