A technique for estimating the ground and near-ground atmospheric temperatures within a Martian local dust storm is presented. It is applied to soundings taken by the Viking orbiter infrared thermal mapper (IRTM) instrument at four times-of-day for one storm. Essentially, a comparison is made between infrared radiances emerging from the storm interior and those from the region surrounding the strom. Particle extinction properties are assumed to be indepenent of position in the storm. Particle extinction properties are assumed to be independent of position in the storm region, and scattering properties must be selected arbitrarily. For the storm studied here, the ground temperature in the interior is at least 6 K cooler, whereas the near-ground atmospheric temperature may be less than or comparable to, those of the surroundings. The thermal structure of the storm interior did not change measureably between 11.5 and 16.6 hours local time. These observations favor theories of dust storm development in which regional winds rather than local, dust-driven convection initiate the mobilization of dust from the surface. It is also concluded that the optical properties of dust particles in this local storm differ from those observed by Mariner 9 during the 1971--1972 global dust storm. ¿ American Geophysical Union 1995