In March of 2003, the Army Research Laboratory conducted a 1-week Urban Experiment to validate the current understanding of the surface layer stability transition and airflow around a two-story rectangular building. This Experiment was, in part, an extension of the ongoing Surface Layer Stability Transition Forecasting effort. The Experiment design was based on published wind tunnel measurements simulating airflow around a variety of building sizes. Using wind tunnel results as a forecast of airflow features, the wind tunnel parameters were enlarged for the given building and the orientation was proportionately skewed for prevailing winds. Finally, four 10m meteorological towers were installed in specific locations along the building's North, Northeast, South, and Southwest sides. These ground layer towers reported standard meteorological parameters at the 2m and 10m levels. An additional 5m tower sampled the atmosphere above the roof.

Preliminary results confirmed, visually and quantitatively, the presence of the forecasted cavity flow, a bi-level accelerated flow between buildings, and the anticipated prevailing wind direction. The stability transitions were greatly influenced by the inhabited building. Unlike the forecasted stability transitions for an open desert, these urban environment transitions were not always evident. In fact, there were times when the daytime unstable surface layer persisted well into the traditional stable nighttime periods. Lessons learned and recommendations for improving future urban measurements/forecasting methods conclude this paper.