With the ever increasing heat dissipated by information technology (IT) equipment housed in data centers, it is becoming more important to project the changes that can occur in the data center as the newer higher powered hardware is installed. The computational fluid dynamics (CFD) software that is available has improved over the years. CFD software specific to data center thermal analysis has also been developed. This has improved the time lines of providing some quick analysis of the effects of new hardware into the data center. But it is critically important that this software provide a good report to the user of the effects of adding this new hardware. It is the purpose of this paper to examine a large cluster installation and compare the CFD analysis with environmental measurements obtained from the same site. This paper shows measurements and CFD data for high powered racks as high as 27 kW clustered such that heat fluxes in some regions of the data center exceeded 700 W per square foot. This paper describes the thermal profile of a high performance computing cluster located in an data center and a comparison of that cluster modeled via CFD. The high performance advanced simulation and computing (ASC) cluster had a peak performance of 77.8 TFlop/s, and employed more than 12,000 processors, 50 Tbytes of memory, and 2 Pbytes of globally accessible disk space. The cluster was first tested in the manufacturer’s development laboratory in Poughkeepsie, New York, and then shipped to Lawrence Livermore National Laboratory in Livermore, California, where it was installed to support the national security mission of the U.S. Detailed measurements were taken in both data centers and were previously reported. The Poughkeepsie results will be reported here along with a comparison to CFD modeling results. In some areas of the Poughkeepsie data center, there were regions that did exceed the equipment inlet air temperature specifications by a significant amount. These areas will be highlighted and reasons given on why these areas failed to meet the criteria. The modeling results by region showed trends that compared somewhat favorably but some rack thermal profiles deviated quite significantly from measurements.