Use caution though so your chameleon is not getting direct sunlight. Even in indirect sunlight, ( in the shade, with a cover), your chameleon will benefit from the nutritious UV rays, besides getting the benefits of the healthy fresh air.
What to stay away from are windy days, ( if your cham cage is not secure and can blow away), dry temperatures with little humidity, extreme heat (for me it's past 90 degrees) or cold (below 50's- depending if it's in the sun and for a short duration), predators such as birds, raccoons, cats, dogs, etc.
Watch your chameleon to check it's comfort level of distress or pleasure.
I found this pop-up tent at a bargain price if you could use it to protect your chameleon while outdoors from the elements and also for privacy. It can be found here and is a Spring Sale.