Temperature probability distribution function, dP/dln T, as a function of the gas temperature at various times during isobaric cooling. The initial distribution (magenta line) is lognormal with a dispersion, σ_T = 0.3, initial mean gas temperature, T_ps = 2.7 × 10⁶ K, and initial pressure, P_ps/k_B = 5.8 × 10⁴ K cm⁻³. We show the distributions of gas temperature at 4 different times relative to t_cool,ps as indicated in the legend. In the last column of the legend, we provide the fraction of the gas that has cooled to 10⁴ K, f_M, at each fraction of the post-shock cooling time. For example, in this illustration, after one post-shock cooling time, even though the peak gas temperature of the PDF has changed very little, ≈85% of the gas has cooled to 10⁴ K. We represent these fractions in the colored bar in which each color corresponds to the PDF of the same color (the fractions, f_M are relative to the ordinate on the right side of the panel). Once the gas starts to cool differentially, it does so very rapidly, in less than t_cool,ps (large blue arrow).