I see a definite trend developing between daytime and nightime temp QC readings. Daytime readings tract right on top of QC tracks but right at sunset the actual and QC tracks split to about 4.5 degrees difference (actual above QC). Then before sunrise, QC and actual converge to coincidence. Anyone else seeing anything like this?
I see on your CWOP pages that the closest site is 13 miles away and if that's what they use for QC I personally wouldn't sweat it. I also see some other remote possibilities from your station installation pics. The fat tree limb underneath and/or the huge stones on the ground below could retain heat from the daytime sun.?.? If you really have a problem with it you could try a temporary relocation to another area free of these possible 'heat retainers' to see if the QC temp charts change.
Here is my CWOP temp graphs with one sensor (DW2642) mounted next to the house (north side under an overhang). The DW4009 sensor is out in the open with grass below and nothing nearby that holds the days heat like the house obviously does here. VTCC is the nearby airport.
My 2 bucket tips worth.