A refinement of the use of K-Values in forecasting thunderstorms in Washington and Oregon

Average 1200 GMT K-values and 850-mb temperatures were used to develop an objective aid for making probabiIity forecasts for afternoon and evening Iightning occurrences in two target areas over Oregon and Washington. Thunderstorm and Iightning reports from airway and Forest Service stations were used in this study. The aid was developed on three summer seasons (1970-72 inclusive). Results on dependent data indicate that the objective forecasts can be expected to be better than climatological probabiIities for the two target areas, and should be useful in preparing the short-range forecast of probability of thunderstorm occurrence issued during the early morning. Some qualitative synoptic features are discussed for modifying the objective forecast and to localize the concentration of thunderstorm occurrence in the target areas. Robert F.Y. Lee. Includes bibliographical references (pages 6-7).