The recent cool wave is as good a reminder as any that we'll be taking our entertainment indoors all too soon. But there's still plenty of outdoor enjoyment to be had before the real autumn sets in.

Friday at 8 at the Jefferson Memorial, the U.S. Air Force Band will stage its annual "Christmas in August" concert -- free and no tickets required. For details call 767-5658.

Wolf Trap is making the most of the last of summer, too. An evening of jazz reeds is offered Friday at 8:30, featuring Pete Fountain, Gerry Mulligan and Les Elgart. Saturday at 8:30, Mickey Gilley, Johnny Lee and the Urban Cowboy Band will perform, and country king Johnny Cash will appear at the outdoor theater Sundat at 8:30.For information on tickets to these events, call 703/928-2900.

At Merriweather Post Pavilion in Columbia, there'll be stars on the ground as well as in the sky. Rock groups Journey and Kansas perform Friday and Saturday, respectively, at 7:30. MacDavis provides some easy summer listening Sunday at 8, and pop singer Bonnie Raitt takes the stage Tuesday at 7:30, followed by Leo Sayer, Wednesday at 7:30. For further information on the Merriweather Post concerts, call 301/982-1800.

If it's outdoor theater you're after, try the Folger Theater Group's production of "Romeo and Juliet," Friday-Saturday and Monday-Thursday at 8 on the Washington Monument grounds. Call 426-6700 for details.

Or enjoy the Rockville Civic Ballet concert, Friday and Saturday at 8:30 at Civic Center Park. Call 424-8000, extension 305, for details