An evaluation of TAMDAR soundings in severe storm forecasting

Input from many sources is used in the short-term prediction of severe thunderstorms, but one of the more critical observations continues to be a vertical sounding of temperature, humidity and wind. Indeed, NWS forecasters often call for special RAOB launches at 1800 UTC on a potential severe storm day because they want to observe recent changes in the vertical structure of the atmosphere, including the depth of the surface-based moist layer, cap strength, and the vertical wind shear. Automated soundings made by aircraft on ascent and descent via ACARS, the Aircraft Communication Addressing and Reporting System, provide vertical information for temperature and wind at selected (generally major) airports, but no information on moisture, a very critical parameter. In fact, the distribution of moisture in the vertical has been difficult to measure with sufficient accuracy and vertical detail except via the standard RAOB.

Over the last couple of years NOAA/ESRL/GSD, along with other groups, has been evaluating a new airborne sensor deployed on commercial aircraft, known as TAMDAR, for Troposheric AMDAR (Aircraft Meteorological Data Relay). TAMDAR adds the critical measurement of moisture to wind and temperature observations in the vertical. In addition, the instrument, developed and deployed by AirDat, LLC, a private firm located in Raleigh, North Carolina, in part through funding from NASA, has been deployed experimentally on smaller aircraft that fly lower than the larger commercial jets and service many more airports than the ACARS fleet. This has provided more en route mid-tropospheric reports and sites for ascent/descent soundings than had previously been available, which makes TAMDAR potentially valuable for forecasting the severe storm environment. In this paper we will show examples from the last two years of the potential value of TAMDAR soundings in an area that stretches from the eastern Dakotas to the Ohio Valley and south to portions of the Gulf states. Comparisons will be made with standard and, when available, special RAOB launches.