In a laboratory experiment we propagate a continuous-wave, expanded laser beam over a surface with evenly distributed heat and record the received distorted optical signal. Temperature is continuously measured in two fixed points to determine turbulence strength. Through a number of trials covering a wide range of turbulence conditions we demonstrate that the temporal correlation of the received signal fluctuations has a strong dependence on the turbulence strength at the link path. Power spectra of the received signals show a clear increase in both slope and maximum frequency as the temperature gradient increases. Measurements suggest that scintillation also correlates with temporal correlation at weak turbulence conditions and such correlation decays in stronger conditions.