Earth extreme temperatures have been recorded from -110 f to plus 140 f, a range of 240 degrees f. Likely Mars is never as warm as 40 degrees f, but I don't think Mars gets as cold as -210 degrees f. If it does occasionally get that cold, it could snow carbon dioxide = dry ice. Carbon dioxide does not have a liquid state at low pressure. The carbon dioxide partial pressure at the surface of Mars (lowest elevation) is 3 to 6 milibars depending on the season. Is one milibar of water vapor partial presure possible at 20 degrees f? The atmosphere of Mars averages 90%? carbon dioxide. Neil