I've been to UAE and Oman, both for xmas/ny, I wouldn't call it moderate. when I had to put up long pants in mid-day to enter the mosque and sadly they happenned to be jeans (you make this mistake only once), I thought I'd die on my way from the parking lot. cold nights are typical for desert in the sense of no civilization open area desert, not cities located on the coastline near a desert. maybe KSA's Riyadh is different because it's located inland, but still cities usually hold temperature pretty well, hence 'summer in the city' tends to be a painful experience during peaks even here in Central Europe.
