Modern weather forecasts rely heavily on data retrieved from numerical weather prediction models. These models continue to improve and have advanced considerably throughout more than half a century. However, forecast reliability depends on the quality and accuracy of initialization data, or a sample of the current global atmosphere when the model run is started. This process of bringing surface observations, radiosonde data, and satellite imagery together to create a picture of the initial atmospheric state is called data assimilation. Satellite upgrades have significantly improved this process, providing more data than ever before. Several recent studies show that passive microwave (PMW) radiance observations from polar orbiting satellites are critical to input into both global and regional weather prediction models.