I did a 15-day ride out of Khatgal last year. Temperatures were mild, day and night, throughout. Rain was always light and/or brief. I recommend bringing leggings to protect the inside of your shins so that you can wear shorts on warm days. I did not have them, so I invented the "slock." Cut the toes off a pair of socks, then pull them up over your knees.
We had 2 bad days of biting flies, no insect problems the rest of the time.
If you are going to visit the Reindeer People/Dukha/Tsaatan be prepared for bitter cold. They will be above timberline and you might get a July blizzard like we got.
Guide Tuya (my guide) out of the Garage (I forget the #, 24?) guesthouse does not drink alcohol and knows a bit of English.
Guide Bolt and his client both threatened to kill each other in Renchinklume.
Be sure to take things to reciprocate hospitality with.
--Will