This article is part of preparing the way for later revelations about instrumentation defects.
Figure 1 (upper), Figure 2 (lower) computed mean insolation for horizontal surface at this exact location and weather parameters, no cloud.
Figure 1 (upper), Experimental work showing nearly daily temperature variation from expected, specifically designed to exclude diurnal but include detail variation at the fastest scale feasible. Time graticule at 10 days, data points at 12 hours. Surprisingly the July 1st hot period has vanished. Plots of other sites show a similar effect. The most frequent warm and cool periods of weather are brief and readily seen.
This computation will produce different values from the mean values computed from thermometer minimum and maximum data because data shape at other times is taken into account, min/max does not. The filter used is also windowed, leakage is negligible.