Results of an evaluation of GTG version 2.3 (GTG2.3) are presented in this report. The algorithm was analyzed from 1 November 2005 through 31 January 2006. Additionally, GTG2.3 was compared to several existing operational turbulence forecasts including GTG version 1.0 (GTG). Forecasts were verified with pilot reports of turbulence. The primary findings are: • The two versions of GTG studied here (GTG2.3E and GTG2.3P) had nearly identical performance. The introduction of eddy dissipation rate information into the algorithm did not have any adverse effects on the results. • GTG2.3E performed well in the midand upper levels for forecasts of moderate or greater turbulence. • GTG2.3E showed limited ability to forecast the correct intensity of turbulence. It performs best for the None and Moderate categories. • When compared to Airman's Meteorological Advisories (AIRMETs), GTG2.3E performed well in both midand upper levels. GTG2.3E forecast volumes were much 6 smaller than the volumes associated with the AIRMETs. • GTG2.3E and Significant Meteorological Advisories (SIGMETs) did a poor job forecasting severe turbulence as was indicated by the statistics that were derived from the limited number of severe turbulence reports. GTG2.3E forecast volumes were several orders of magnitude smaller than those produced by SIGMETs. This result may have been due in part to the small numbers of PIREPs reporting severe turbulence.