The weather seems to come up every new thread, and folks are asking the same questions, and then finding weather stations far away at different elevations.
(I think by the way, the missing person discussions could be significantly improved is by creating a new sub-forum for each missing person, thus allowing threads and pinned posts with just the facts at the top, and discussion posts below, for each sub topic. Like a thread dedicated to the weather, another discussion thread about the clothing, the POI, etc. Thus creating greater efficiency in information, less duplication of effort, etc IMO. Perhaps this is not possible without significant additional resources, but I thought I put it out there in case an admin is reading this).
The Sweeney Granite Mountains Desert Research Center is scientifically calibrated yearly (and used by researchers who come to this reserve) and located just 2.6 miles (as the crow flies) from the turnout and hike. The turnout is at 3840 feet, and the hike would have gone up to about 3900 feet. The research center is at 4279 feet above sea level, so only a few hundred feet higher, so you could perhaps add a degree or so to the temperature results from the official UC Natural Reserve weather station.
I've attached the weather graphs specifically for that day that might be of interest.
I live a few hours south in the Lower Sonoran Desert, with summer heat similar to Amboy and Bullhead City. To me, going up to about 4000 feet for camping and hiking is a quite workable and a great alternative to going to the high Sierras or all the way to the coast, especially hiking in the mornings, or late afternoon/early evenings. It is however not common for folks to primitive camp in especially in the lower desert in the summer due to the need for air conditioning. The snow birds are not starting to come back south until about October, and in the lower deserts, they get out of dodge when the temps start creeping into the 90's during the day (April). In the summer, you will find folks camping near water in the deserts in developed campgrounds or RV parks with hookups, but not so much if it doesn't have hookups. My wife and I enjoy it it sometimes, as we have a window AC and mini swamp cooler. The AC can be run off a small generator, and on a day like July 12 at this location (we were camped there the weekend after the disappearance), we would run the small window AC perhaps from about 10 am to 6 or 7 pm). After that and if it is not humid, you can manage with fans.
Weather Analyses | Sweeney Granite Mountains Desert Research Center