Top two rows: synthesized instantaneous (solid lines with crosses at the line positions considered) and inverted (dashed lines) Stokes I and V profiles at four time steps (columns) during the development of an UF. Bottom three rows: comparison of the temperature, LOS velocity, and magnetic field strength between the actual atmosphere (solid lines) and the inferred stratifications (dashed lines). The inferred atmospheres are plotted for the inversion with lowest χ² (thick dashed lines), and the uncertainties are indicated by thin dashed lines. Vertical dotted lines serve as references for some of the optical depths discussed in the text.