A preliminary report on a weekend tornado in central Alberta says its winds were so violent they picked up a 10-tonne farm combine and tossed it half the length of a football field.

The report by the Northern Tornadoes Project rated the twister as a four on the Enhanced Fujita scale of wind-damage intensity, just one short of the maximum rating of five.

The storm destroyed three homes and damaged seven more, with the only apparent injury a cut suffered by a first responder.

The storm downed power lines, killed livestock, shredded trees and damaged vehicles.

The report follows up on ground and drone surveys on the tornado that ripped through the rural area between the towns of Carstairs and Didsbury on Saturday afternoon.

The estimated maximum wind speed was 275 km per hour along a 15-km path.