Operational weather forecast models show little skill at predicting regime transitions such as the onset or dissipation of "blocking events" (when large scale weather patterns remain locked in large amplitude waves) even a day or two in advance. Moreover, this deficiency accounts for much of the loss of skill in dynamical forecasts in the 30-day range. Dr. Mak and colleagues will investigate the role and evolution of heat sources (radiation, condensation, and surface heating and cooling) in blocking events as well as how high frequency disturbances (storms) affect vertical circulation patterns in the troposphere on the intraseasonal scale. They hope to clarify the quantitative contributions of these processes, and to delineate their relative importance in regime transitions. The dramatic blocking event of the winter of 1985-86 (which caused a record cold February in Europe) will be the focus of the diagnostic studies. The results obtained in this project should serve as an important contribution to community efforts to improve the skill of extended-range forecasts.
