Forecasting Supercell and Non Supercell Thunderstorm Anvils for NASA Space Shuttle Operations.
Van Speybroeck, Kurt M., Bunkers, Matthew , Zeitler, Jon

The National Weather Service (NWS) Spaceflight Meteorology Group (SMG) provides weather forecasts for all NASA Space Shuttle landings. The Space Shuttle weather-related Flight Rules describe the weather conditions that are acceptable for planned and emergency landing situations. According to current Flight Rules, the Space Shuttle must avoid thunderstorms, lightning, attached or detached (< 3 hours old) non-transparent anvils, and precipitation at all landing sites by specified distances.

Flight Rule weather definitions for landing sites state that cumulonimbus clouds (-20 degrees C or colder in any part of the convective cloud) are to be treated as thunderstorms for Flight Rule purposes. The maximum reflectivity representing the anvil cloud edge according to the Flight Rules weather definitions is 0dBZ.

Forecasting the motion of non-transparent anvils represents one of the more difficult forecast elements at SMG. Predictive techniques to forecast anvil motion have been developed at the NASA Applied Meteorology Group (AMU), using model data and upper level wind observations. An additional predictive system is proposed by exploring the relationship between storm motion and anvil location/motion. If the storm motion can be accurately determined in the short term, the anvil location and motion may also be more accurately determined. This study examines thunderstorm anvils generated by thunderstorm classification: supercell and non-supercell storms. By using a combination of the Bunkers supercell motion algorithm and the local steering winds, an anvil storm motion relationship is developed. Non-supercell thunderstorms and anvil motion are explored using mesoscale forcing and local steering winds. These relationships are tested against archived weather data during several Space Shuttle missions where thunderstorm flight rules were considered critical for launch or landing. Results and the operational application of the forecast system are discussed. Finally, operational limitations and conclusion will be presented.