In accordance with a theoretical analysis by Kader and Yaglom, interpolation expressions are proposed for the Monin-Obukhov functions for the wind speed and temperature profiles under unstable conditions in the surface layer of the atmospheric boundary layer. The values of the parameters are adjusted to agree with earlier work under weak instability, as reviewed by H¿gstr¿m. The resulting formulations are valid for considerably larger values of their argument than those that were hitherto available. Their advantage is that they yield concise and closed-form stability correction functions which can be readily applied in profile analysis and model calculations. ¿ American Geophysical Union 1992