Quality of the inversion fits and number of inversions that satisfy the threshold criterion. Top panels: observed umbral flash profile (black dots), the fit obtained from an inversion whose χ² is near the chosen threshold (solid blue line), and the fit of the inversion with the worst χ² (above the threshold) that was included in the analysis (dashed red line). The left panel corresponds to the Ca II 8542 Å line, and the right panel shows the Ca II H line. The vertical dotted lines in the right panel delimit the line core region we employed in the inversions. Bottom panel: temporal evolution of the number of inversions employed for the analysis of each profile at a selected umbral location. The blue shaded areas indicate the temporal steps when the core of the Ca II 8542 Å is in emission. The vertical dotted line corresponds to the time step illustrated in the top panels.