The generation of a probabilistic view of dynamical weather prediction is traced back to the early 1950s, that point in time when deterministic short-range numerical prediction (NWP) achieved its earliest success. Eric Eady was the first meteorologist to voice concern over strict determinism — i. e., a future determined by the initial sate without account for uncertainties in that state. By the end of the decade, Phillip Thompson and Edward Lorenz explored the predictability limits of deterministic forecasting and set the stage for an alternate view — a stochastic-dynamic view that was enunciated by Edward Epstein. We follow the steps in both operational short-range NWP and extended-range forecasting that justified a coupling between probability and dynamical law. A discussion of the bridge from theory to practice follows and the study ends with a genealogy of ensemble forecasting as an outgrowth of traditions in the history of science.

Outline of the Historical Research Ch. 1. Introduction Ch. 2. Zeitgeist Ch. 3. Extended-range forecasting and predictability limits a. The ferment b. von Neumann’s and Eliassen’s view Ch. 4. Feasibility of the two-week forecast a. Nonperiodic dynamics b. Unresolved scales of motion c. Predictability limits from the GCMs Ch. 5. Dispersion of the glob: A measure of uncertainty Ch. 6. Bridge to operational ensemble prediction Ch. 7. Epilogue Appendix: Genealogy of ensemble prediction