In this paper, we describe the optical design and results from a Raman lidar for day and nighttime measurements of tropospheric water vapor. The system is developed as an eye safe fully automated instrument for meteorological applications in Meteoswiss. A multi-telescope receiver with a “near range” fiber is used having narrow field-of-view and a grating polychromator is used for narrow-band detection.

The role of this new system of observation will in particular be discussed with respect to:

• The validation against other systems located at the same site in MeteoSwiss Payerne, in particular the recent development of the new humidity sensor on the Swiss radiosonde currently in operation at MeteoSwiss, and also the comparison with passive microwave water vapor profiling.

• The new challenge for the numerical weather forecast model for which temperature and wind fields in the 3rd dimension over the Swiss Plateau are already assimilated, while continuous real time water vapor vertical profiling is not so far.

• The importance of this operational lidar as a new tool for upper air continuous observation of the water vapor content: such observations will in particular play a role in our search for a better understanding of the water vapor climate change in the upper air. This system will complement additional state of the art radiosonde techniques (flash sondes, snow white, ..) in the case of the WMO GCOS GRUAN (Global Reference Upper Air Network) program.