Science Questions

Sat, 9th Sep 2006

Part of the show Hot Nectar, Warming Weather and Birds Missing the Spring

Question

Doug in Worcestershire asked:

Given that as altitude increases, temperature decreases, does this means that when precipitation falls from clouds it usually falls as snow or sleet or hail at altitude and then melts and warms as it gets nearer the Earth?

Answer

That's very true in a certain number of cases. Water in the clouds can exist in liquid form even below temperatures of zero. This is in the form of super-cooled droplets of water. But in the very thick clouds where the cloud top temperatures can be around minus 40 degrees Celsius, most of it does start off as ice. As it falls down, the cloud base is still below zero and it falls as snow and hail. But as it falls through and begins to warm up it does melt down and we actually see it on the surface as rain.

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