take the lowest humidity figure in regards to minus 55 Celsius which is
70%. Compare with my table ( yellow being the frost point ) here...the frost point at minus 55C is 58.2RH.|
The minimum RH needed to start cirrus clouds at minus 55C is 75%RH
150% supersaturation with regards to ice translates in 101% saturation with regards to water.
Under natural conditions. You add human made nuclei delievered via aircraft and the game changes. See pdf document RH_WMO ....
RH-WMO = RH with regards to water
RH-Standard = RH with regards to ice
Above 100% is "supersaturated"