Mesoscale Convective Systems or MCS, formed particularly in the mid latitudes, are responsible for a great deal of damage especially in the summer time. These systems are hard to predict and forecast since many of the instruments used to collect data inside of them are not always reliable and are limited in use. A new satellite-based atmospheric limb sounding technique, called GPS radio occultation, has all-weather capability and may be able to provide vertical profiles of atmospheric parameters inside MCSs to help better understand these destructive storms. This study examines 9 GPS radio occultation observations from the Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) that occur inside MCSs. We found that the COSMIC profiles consistently penetrate close to the surface and agree well with near-by radiosonde data in terms of refractivity, the fundamental atmospheric parameter provided by RO. However, the temperature and moisture retrievals that are estimated by a 1D variational assimilation procedure (i.e. a combination of RO refractivity and a first guess model) exhibit a dry bias that is currently under investigation.