During the 1997 Southern Great Plains Experiment (SGP97), both tethersonde and radiosonde vertical profiles of moisture, temperature, and wind speed and direction were recorded at the ARM/CART Central Facility in Billings, Oklahoma. The tethersonde instrumentation was provided by NOAA NSSL. Although the tethersondes provide much higher vertical resolution (2-5 m) as compared to the ARM/CART radiosondes (10-15 m), the tethersonde was able to fly only under light to moderate wind conditions so that fourteen days of flights were recorded during SGP97. Tethersonde flights began around 7:00 a.m. local time and continued hourly throughout the morning and every 1.5 hours in the afternoon until 5:00 p.m. Radiosondes were released every three hours by ARM/CART at the Central Facility throughout the experiment, and we will use the 9:00 a.m., 12:00 p.m., and 3:00 p.m. launches for comparisons of the tethersonde and ARM/CART radiosonde thermodynamic and wind data. We will also present evapotranspiration estimates through application of the conservation equations for the Atmospheric Boundary Layer (ABL). Using both tethersonde and radiosonde vertical profiles of moisture and temperature, initial estimates of regional evapotranspiration using advection and entrainment parameterizations show good agreement with surface flux data from the Central Facility. Special attention is focused on directly solving for the advection and entrainment terms and the effect of these terms on regional evapotranspiration estimates