December is a very pleasant time to visit Oman, with milder temperatures, averaging around 25 degrees in Muscat, with night-time temperatures around 17 degrees. Rainfall levels are low.
Be aware the Christmas and New Year are peak season for holidays to Oman and early booking is essential.
In the mountains the temperatures are a little lower and temperatures at night can be feel very cold once the sun has set. The desert also can be very cold at night, so warm clothing is essential.