CANBERRA, April 12 (Reuters) - Most of Australia's main cropping areas are likely to see median or above-median rainfall during June-August, the country's weather bureau said on Friday, raising the prospect of better yields of winter crops including wheat, barley and canola.

Australia is a major exporter of both grains and the oilseed.

Farmers have been ramping up sowing of winter crops this month, with rainfall in the east fuelling optimism about crops in the region. Dry conditions in the west, however, are threatening production of canola in particular.

The Bureau of Meteorology in its first winter forecast said rain was likely to be below the median in most cropping areas in May, but above-median in June.

The weather bureau also predicted above-average temperatures during the southern hemisphere winter.

Australia's key winter cropping areas are in the southeast and southwest.

(Reporting by Peter Hobson; Editing by Sherry Jacob-Phillips)