Explore data assimilation experiments for operational weather forecasting in this comprehensive lecture from the Workshop on Data Assimilation in Weather and Climate Models. Delve into the mathematical approach used by leading operational weather forecast centers worldwide to estimate accurate atmospheric states and uncertainties. Learn how data assimilation integrates observations and short-range forecasts, and discover its applications beyond weather prediction, including climate monitoring and reanalysis. Gain insights into the methods employed at the National Atmospheric Research Laboratory (NARL) for operational weather forecasting. Understand the importance of data assimilation in investigating processes within Land, Atmosphere, and Oceans, and its role in addressing the scarcity of well-trained scientists in this field.