It varies.
Ken Kalisch gives a very good description in the book Chameleons Care and Breeding of Jackson's, Panther, Veiled, and Parson's copyright 2007.
Some areas are dry and low, some are high and more humid. The "wadis", are another micro-climate, which are very confusing and not always as humid as people seem to think they are.
Rainfall from 0" in 3 years to 80" a year (depending on the area). Temperature ranges from 32 degrees f. (at night) to summertime highs of 110 degrees f.
This is a brief description by me based on a decent amount of reading.
The book I mention (again) gives a much better description ... it's a pretty good book, by the way, for $12.95