Cloud murus cloud and is the result of air feeding into the storm. Supplementary cloud formations detached from the main cloud are known as accessory clouds. The heavier precipitating clouds, nimbostratus, towering cumulus (cumulus congestus), and cumulonimbus typically see the formation in precipitation of the "pannus" feature, low ragged clouds of the genera and species cumulus fractus or stratus fractus. A group of accessory clouds comprise formations that are associated mainly with upward-growing cumuliform and cumulonimbiform clouds of free convection. "Pileus" is a cap cloud that can form over a cumulonimbus or large cumulus cloud, whereas a "velum" feature is a
Tornado outbreak of May 15–17, 2013 severe thunderstorms early that morning over northwestern Texas, for a threat of large hail and damaging winds. A low-pressure area associated with the trough moved over Oklahoma that day, producing light to moderate rainfall and non-severe thunderstorms across that state into parts of North Texas. Later forecasts expanded the slight risk further into northern and central Texas, and later into far southern Oklahoma, and indicated an enhanced risk of a few isolated tornadoes in north Texas. The atmosphere began to destabilize due to a decrease in cloud cover over western and central Texas; the sunshine and heating, combined with sufficient