Clouds Formation Before The Storm

+ Nimbostratus is not subdivided into species.
Towering vertical (Family D2)
These clouds can have strong vertical currents and rise far above bases which form anywhere in the low to lower-middle altitude range from near surface to about 10,000 ft (3,000 m) and consequently elude classification into the three conventional height ranges. Like smaller cumuliform clouds in family D1, these towering giants usually initially form in the low altitude range but the bases can rise into the middle range when the moisture content of the air is very low. Unlike families A through D1 that each include a cumuliform and stratiform-category genus, family D2 instead has one cumuliform-category genus and one cumulus species, but no stratiform-category genus or species except for the occasional inclusion of very thick nimbostratus.