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An experimental study of the thermal field established, over a horizontal heated plate (1000×500×12 mm3) in an open top cavity, of aspect ratio Γ = 2 is presented. The working fluid was air at atmospheric pressure and the imposed temperature conditions correspond to a Rayleigh number Ra = 4.1×108, based on the cavity height and the temperature difference across it. Schlieren visualization was used to identify characteristic structures developing over the heated plate. Local temperature measurements along the vertical axis over the plate centre were accomplished using a fine thermocouple (d = 0.025 mm). Distributions of mean and rms temperatures are presented along with the corresponding skewness and flatness distributions. The exponential form of the PDF temperature distributions observed in the present experiments, as in several experiments in hard turbulence, is compatible with the intermittent presence of fluid structures with different origin and past history. Temperature PDFs have been approximated by mixtures of weighed Gaussian distributions to illustrate this concept.