i think but not a 100% certain,its cumo/nimbus

Storm clouds

wet ones

1) Cumulus: "Cumulus clouds are formed when air rises and reaches a level where the moisture in the air condenses. This is usually through convection where a parcel of air is warmer than the surrounding air. As it rises, the air cools at the dry adiabatic lapse rate (approximately 3°C per 1000ft or 1°C per 100m), while the dewpoint of the air falls by 0.5°C per 1000ft. When the temperature of the air reaches the dewpoint, water condenses out of the air to form a cloud. The size of the cloud depends on the temperature profile of the atmosphere and the presence of any inversion. If the top of the cumulus cloud is above the freezing level, then precipitation from the cloud is possible." Source and further information: http://en.wikipedia.org/wiki/Cumulus_cloud 2) Cumulonimbus: "Cumulonimbus (Cb) is a type of cloud that is tall, dense, and involved in thunderstorms and other intense weather. The clouds can form alone, in clusters, or along a cold front in a squall line. Cumulonimbus clouds form from cumulus clouds (namely from cumulus congestus) and can further develop to a supercell, a severe thunderstorm with special features." "Three ingredients are needed for the formation of a perfect cumulonimbus cloud: Plenty of moisture. A mass of warm unstable air. A source of energy to lift the warm, moist air mass rapidly upward. Typically, the clouds form around front lines, near oceans where sea breezes provide storm energy, or over mountains which push the air upwards. When the warm air rises (Often the Earth's surface is heated by terrestrial radiation) above the typically cooler air above it, it starts to cool ( As the heat rises it expands and cools, this is due to pressure at different altitudes) and the water vapor condenses into water droplets. This condensation heats the surrounding air by releasing latent heat, thus continuing the rise of air. As the air mass continues to rise, the water droplets continue to cool and form ice crystals. Gravity causes these droplets and crystals to start to fall, causing a downward movement to compete with the upward lift. Instability between the updrafts and down drafts causes static electrical charges to build up within the cumulonimbus cloud. The discharge of this electricity causes thunder and lightning. Anvil tops of thunderclouds visible over the Pacific Ocean, as seen from the International Space Station" Source and further information: http://en.wikipedia.org/wiki/Cumulonimbus_cloud

Cumulonimbus (thunderheads)

Cumulus clouds are formed and rise very high .A good sign of a storm coming.Also ,jets avoid them .A pilot told me the other day that they can rip the wings off a jet.