Final answer:
In a CB, the heaviest ice accretion is expected to occur at the freezing level of the atmosphere, where temperatures are 0 degrees Celsius or below. This is because water droplets or ice crystals can stick to the aircraft surface and build up as ice. The presence of CBs with strong updrafts and moisture content increases the likelihood of heavy ice accretion.
Step-by-step explanation:
In a convective boundary (CB), the heaviest ice accretion is expected to occur at the freezing level of the atmosphere, where the temperature is 0 degrees Celsius (32 degrees Fahrenheit) or below.
This is because at this temperature, supercooled liquid water droplets or ice crystals can stick to the aircraft surface and build up as ice. Higher up in the atmosphere, where temperatures are colder, the water droplets may be in the form of ice already and won't stick to the aircraft as easily.
Furthermore, the heaviest ice accretion is more likely to occur in the presence of cumulonimbus clouds (CBs) due to their strong updrafts and abundant moisture content.