Cumulonimbus is a dense, towering vertical cloud, typically forming from water vapor condensing in the lower troposphere that builds upward carried by powerful buoyant air currents. Above the lower portions of the cumulonimbus the water vapor becomes ice crystals, such as snow and graupel, the interaction of which can lead to hail and to lightning formation, respectively. When occurring as a thunderstorm these clouds may be referred to as thunderheads. Cumulonimbus can form alone, in clusters, or along squall lines. These clouds are capable of producing lightning and other dangerous severe weather, such as tornadoes, hazardous winds, and large hailstones. Cumulonimbus progress from overdeveloped cumulus congestus clouds and may further develop as part of a supercell. Cumulonimbus is abbreviated Cb.

कपासी वर्षी बादल लम्बवत रचना वाले बादल होते हैं अर्थात इनका विस्तार ऊंचाई में अधिक होता है। इस वज़ह से ये पर्वत सदृश या लम्ब्वत स्तम्भ के रूप में द्रष्टिगत होते हैं। इसके साथ वर्षा ओला तथा तड़ित झंझा की अधिक सम्भावना रहती है। यह मुसलाधार वर्षा कराते है।इस प्रकार बादल भूमध्य रेखा ,पर पाया जाते हैं