Abstract A dataset collected during a measurement campaign in the middle of the Italian Po Valley is used to investigate the boundary layer structure in stable conditions. Functions derived applying the Monin-Obukhov similarity theory to stable conditions are used as regression curves to fit observed velocity and temperature profiles in the lower half of the boundary layer. Surface fluxes of heat and momentum are best-fitting parameters in this exercise and are compared with those measured by a sonic anemometer. The comparison shows remarkable discrepancies, more evident in cases for which the bulk Richardson number turns out to be quite large. This analysis supports earlier results, that surface turbulent fluxes are not the appropriate scaling parameters for profiles of mean quantities in very stable conditions. One of the practical consequences is that boundary layer height diagnostic formulations which mainly rely on surface fluxes are in disagreement to what obtained by inspecting co-located radiosounding profiles. Moreover the incorrect scaling of similarity profiles in stable conditions leads to the erroneous diagnosis of the 2-m surface temperature used in numerical weather prediction as forecast skill scores.