Since the frequency response is dependent on both frequency and time, it may be visualized as a three-dimensional plot. The following two slides depict the power density obtained by squaring the absolute value of the frequency response $H(t, f)$. The results are normalized such that $\mathrm{E}\left[|H(t,f)|^2\right] = 1$.
The first slide is fully three-dimensional and may be rotated to get a better view. Observe how the notches propagate through frequency and time.
The second slide visualizes $|H(t, f)|^2$ as a heat map. Observe how the different types of fading over time (slow, fast) and over frequency (flat, selective) impact the behavior. The way the notches propagate is distinct for the four different combinations of fading.