1. Low Temperature: The stratosphere is characterized by very low temperatures, typically ranging from -56.7°C (-70°F) at the tropopause to -46.7°C (-52°F) at the stratopause. At these cold temperatures, water vapor is less likely to evaporate and more likely to condense into ice crystals, forming cirrus clouds.

2. Low Convective Activity: Unlike the troposphere, which is characterized by vigorous convective activity that causes vertical mixing of air masses, the stratosphere is relatively stable and experiences minimal convection. This stability prevents water vapor from being transported upward from the troposphere into the stratosphere, where it would likely condense and form clouds.