Can we develop a physics-based model of magnetic field evolution that could predict solar flares and coronal mass ejections?
¥Since these phenomena are almost certainly magnetically driven, they must incorporate magnetic field observations (line-of-sight and vector magnetogram data)
¥Governing evolutionary equations believed to be (pretty) well described by 3-d magnetohydrodynamics (MHD)
¥How does one incorporate the observations (the A-word)  into an MHD model?  Solving this problem is absolutely critical if we ever want to have a predictive (forecasting) model of space weather.