 This also explains why moisture in the mid-levels of the troposphere, roughly at the 500 hPa level, is normally a requirement for development.However, when dry air is found at the same height, temperatures at 500 hPa need to be even colder as dry atmospheres require a greater lapse rate for instability than moist atmospheres.At heights near the tropopause, the 30-year average temperature (as measured in the period encompassing 1961 through 1990) was −77 °C (−105 °F).