Abstract The characteristics of supercooled liquid water (SLW) within icing clouds over eastern China are investigated using in situ aircraft observations and numerical simulations. Supercooled liquid water content increases from 0 to −4°C, but decreases sharply below −4°C. Abundant supercooled large droplets (SLD) were observed, with the effective diameter reaching 175 μm ${upmu }mathrm{m}$ and number concentration (Nt) exceeding 19 cm−3. An aircraft icing rate and intensity forecast algorithm is proposed by incorporating flight conditions and SLW spectral characteristics, together with a new diagnostic relation between cloud droplet shape parameter and Nt implemented into the three‐moment NSSL scheme. Sensitivity simulations indicate that the improved scheme can reproduce well the temperature‐dependent variation of SLW content, and significantly enhance forecasted rate of icing, intensity, and icing cloud layer depth.