This study presents an extended vertical grid for the regional atmospheric model COSMO, used for numerical weather prediction, reaching up to 33 km. The extended setup has been used to stably simulate eleven months in a domain covering central and northern Europe. Temperature and relative humidity have been validated using radio sonde data in polar and temperate latitudes, focussing on the stratosphere. Temperature values are reproduced very well by the model. Relative humidity could only be met in the mean over the whole time period after excluding data from Russian stations, which showed significantly higher values. A study of orographically induced lee waves over Iceland, well visible in the model but not in the regridded boundary data (ERA-Interim and NCEP reanalysis), showcases the advantage and applicability of the model in the extended vertical grid.