In January 2003 GLAS was launched into a near polar orbit aboard the Ice, Cloud and land Elevation Satellite (ICESat). In addition to a high resolution altimetry channel, GLAS contains both 1064 and 532 nm atmospheric backscatter lidar channels. The photon counting 532 channel has been operating since fall of 2003 and has provided incredible views of the vertical structure of atmospheric aerosol, cloud layers and the depth and structure of the planetary boundary layer (PBL). These measurements constitute a unique and valuable data set for the validation of global weather forecast model output. The high vertical and horizontal resolution of the GLAS data provide very accurate measurements of cloud height, tropopause height and PBL height and structure. The ECMWF (European Center for Medium-Range Weather Forecasts) model produces output fields of boundary layer height, cloud height and others that can be directly validated by comparison with the GLAS data. This type of forecast model verification has been used in the past to validate ECMWF model output of boundary layer height and cloud height using data from the Lidar In-space Technology Experiment (LITE). In this paper we demonstrate the utility of GLAS data for the verification of global ECMWF output fields of cloud height and PBL height. We will also examine various other output fields to see how they are related to the atmospheric structure as seen by GLAS. As orbiting lidars such as GLAS and CALIPSO (2005 launch) and those to follow become more commonplace, the value of their data for not only model validation but assimilation will greatly increase.