Here's a rule of thumb: You lose about 4 degrees for every 1000 feet of elevation gain.
Vegas is around 2,000; Peaks in Red Rock are 6,000+ feet. 4 X 4 = 16 degrees cooler.
Here's a trick I use. If you see snow on Bridge Mountain from Vegas, there's still snow on the north facing routes. From Vegas you are looking at Bridge Mountain's East Face, where snow melts much faster.
Mt. Charleston has a snow base of 63 inches and the forecast is calling for more snow early next week.
Lake Mead: Liberty Bell Arch Hike update: Considerable construction on the highway in that area. The gravel parking pull-off on the east side of the road where people usually park for the trail had heavy equipment on it and it looks like the "trail head" is being dug under and eliminated. We still hiked the trail by parking at the Arizona Hot Springs parking area and hiking over to the Liberty Arch trail using the old jeep trail that you can find about 10 minutes down the AZ Hot Springs trail.
I will update this trail when construction is finished.