The potential of data assimilation for operational numerical weather forecasting has been appreciated for many years. For space weather it is a new path that we are just beginning to explore. With the emergence of satellite constellations and the networks of ground based observations, sufficient data sources are now available to make the application of data assimilation techniques a viable option. The first ionospheric space weather product to be launched by SEC utilizing data assimilation techniques will be available in the fall of this year. The product, US-TEC, characterizes the ionospheric total electron content. Extensive validation has quantified the differential and absolute accuracy of the product, which shows great promise for application to GPS users. This is the first step along a path that will likely lead to major improvement in space weather forecasting, paralleling the advances achieved in meteorological weather forecasting.