photo #4987166

A huge Cumulonimbus cloud becomes known as a supercell storm when it develops a mesocyclone, which is a broad, rotating central column where the cloud is drawing in air to form a massive updraft. This is the least-common type of thunderstorm, and it is by far the most severe. A supercell can persist for several hours, tormenting large areas as it sweeps across the terrain below. The one spotted here by Mike Olbinski (Member 45) over Sudan, Texas, US developed a feature known as a murus, or wall cloud. This is where the base of its mesocyclone is distinctly lower in one region. This feature develops where the inflow of air has picked up moisture brought down in the storm’s precipitation region, visible here on the horizon to the right. This extra moisture, marked by the murus, adds energy to the up-rushing air in this part of the mesocyclone, increasing its spin. This is why the wall cloud feature is where the finger of spinning cloud known as a tuba can form and develop into a tornado like the one shown here. As Mike knows well, spotting supercells, murus, tuba, and tornados is best done from a safe distance.