Summer is likely to get off to a stormy and sodden start for much of eastern Australia as an unusual weather combination brings tropics-like deluges on inland regions.

The Bureau of Meteorology has issued a severe weather warning for a swathe of NSW from Cooma in the south-east to Wentworth in the west and towards Cobar in the north.

The region can expect heavy rainfall, reaching in excess of 100 millimetres during Friday and Saturday. Some parts closer to the ranges near Victoria could collect double that rainfall.

Damaging winds averaging 90km/h and peaking at more than 110km/h are possible over alpine areas from late on Friday.