Sensible, (H), and latent, (LE), heat fluxes and turbulence statistics in St. Louis, Missouri and the surrounding region are presented. The urban-scale analyses were derived from a series of aircraft transects at 150 m above ground across the metropolitan area during the afternoon convective period. The results revealed that H varied by a factor of two to four in the region; the largest values were associated with the urban heat island. LE varied by a factor of four, but low values of LE overlayed the urban heat island. Consequently, the Bowen Ratio, (H/LE), varied from 1.5 over the city to values less than 0.2 in nonurban areas. The areas along the Mississippi River and adjacent lowlying marshland northeast of the downtown area displayed smallest values of H and Bowen Ratio. The derived surface heat storage term (G) for this area as well as for the urban area exceeded either H or LE. The boundary layer over the river area is thus in a state of nonequilibrium.