This picture is from a server in Colorado which has a different look to it, but is the same water vapor product we get from NOAA. All data is from the GOES satellites. This shows that the top of the water vapor image is at  -40 Centigrade, which corresponds to approximately 27,000 feet.

This is a SKEWT graph which shows dewpoint vs temperature. The point of interest is the closeness of the dewpoint line and the temperature. This indicates  air with a high water content. The bottoms of the clouds during this report were observed at Seatac airport to be "broken at 20,000 feet or overcast at 22,000 feet".

excerpted from 48 hr data, times are PST

08:56PM   02005KT 10  BKN200
07:56PM   36005KT 10  BKN200
06:56PM   00000KT 10  OVC220
05:56PM   30003KT 10  OVC220

On nights with a visible moon it is possible to observe the ice crystals in the upper troposphere directly.