From late fall until well into 1989 there will be one weather surprise after another - balmy autumn conditions in the north and heavy snows in the south - and a five-month drought in the southwest, with possible flooding in the Dakotas.

That projection is one of many made in the Rocky Mountain Almanac, a new annual publication.The almanac is published by Gail Pitts, former Denver Post business news reporter, and the editor is Lee Olson, long-time Post editorial page writer.

The almanac's chief feature is its weather forecast, assembled by a team headed by Iben Browning of Albuquerque, N.M. Browning advises businesses about weather, and serves as climatologist for the investment banking house PaineWebber.

The almanac notes, for example, that Buena Vista, Colo., Kalispell, Mont., Los Alamos, N.M. and parts of the Salt Lake Valley have one striking similarity: In winter, they frequently become "banana belts" or unusually warm areas where downslope winds make them much more pleasant places to live than their altitudes would indicate.

That observation is from one of the almanac's contributors, Nolan J. Doesken, assistant state climatologist for Colorado.

His article is part of the almanac's information on the vast Mountain Time Zone, the nearly 800,000-square mile area that stretches from Canada to Mexico and takes in all or nearly all of 13 states.