Originally Posted by Gary Evans
It doesn't have to be hot air to initially rise or continue to rising but only to be warmer than the surrounding air. Thermals can originate from a water surface triggered by the temperature difference caused by cloud shadows.
definition of thermal-from the dictionary:
1. Of, relating to, using, producing, or caused by heat.
so we need to get into details: when i said'hot air' i meant 'air at higher temperature' (of course, than the air around it). i know that may be thermals even at temperatures below freezing. it's the temperature differential what makes air rise.