Part II: Case Studies and Statistical Results A New Direction in Clear-Air Turbulence Forecasting Based on Spontaneous Imbalance Part II: Case Studies and Statistical Results Donald McCann McCann Aviation Weather Research, Inc. Overland Park, Kansas don@mccannawr.com John A. Knox Faculty of Engineering, University of Georgia Athens, Georgia Paul D. Williams Department of Meteorology, University of Reading, Reading UK CASE STUDY STATISTICAL RESULTS A major outbreak of upper level turbulence occurred during the morning on 24 October 2007. We counted 317 turbulence pilot reports between 1100 UTC and 1300 UTC. We tested our method with 9542 text pilot reports carefully collected between 1500 UTC and 1700 UTC on each day from 3 November 2005 and 26 March 2006. PIREPs near convection, in mountain waves, or in the planetary boundary layer were not included. The maximum TKE dissipation in the layer with the PIREP FL computed from the corresponding 1-hour RUC2 forecast verifying at 1600 UTC within 50 km of the PIREP location validated the PIREP. 3-hr RUC2 300mb forecast from 0900 UTC. 3-hr RUC2 forecast verifying 1200 UTC 24 Oct 2007 of Lighthill-Ford Radiation (blue) and Richardson number (pink) at FL290. The Lighthill-Ford method’s Relative Operating Characteristic curve is much closer to the upper right corner than Graphical Turbulence Guidance (GTG). The highest score for the differentiation between no turbulence and positive turbulence is for a zero threshold. In other words, when there is positive TKE dissipation forecast, aircraft will likely feel some turbulence. At MODERATE and SEVERE intensities the Heidke Skill Score peaks with higher TKE dissipation; this indicates that the higher the forecast rate, the stronger the expected turbulence. For turbulence at all flight levels our application reaches the U.S. government goal with a PODyes for MODERATE or greater turbulence of .831 and a PODyes of SMOOTH of .851. 3-hr RUC2 forecast of our TKE Dissipation, starting in the lower right clockwise, at FL170, FL230, FL290, and FL350 verifying 1200 UTC 24 Oct 2007. Color fills roughly correspond to LIGHT (blue), MODERATE (yellow), and SEVERE (red) turbulence. Pilot reports within 2000 ft and one hour of verifying altitude and time are plotted in standard notation. Using Lighthill-Ford Radiation as a gravity wave trigger, we are able to skillfully forecast turbulence at all flight levels.