A severe thunderstorm fired up quickly over Georgetown, Sun City and Serenada late Wednesday night, dropping the largest hail of the spring season thus far.

Hail reports in these populated areas ranged from golf ball size (1.75″ diameter) to baseball size (2.75″ diameter). This was the largest hail that fell anywhere in the country yesterday.

Hail forms inside of a thunderstorm as super-cooled water droplets are lifted higher into the storm by the updraft until they freeze. The updraft, a wind blowing vertically upward inside of the thunderstorm, keeps the hail stone suspended, violently colliding into other droplets inside of the clouds and growing by collision and coalescence.

The hailstone will remain suspended in the upper levels of the cloud until its weight and gravity overcome the strength of the updraft, and the hailstone falls to the Earth. The stronger the updraft is, the longer the stone will stay suspended, and the larger it is able to grow.

National Weather Service chart showing hail size vs. updraft speed

Last night’s baseball size hail was produced by an 81 mph updraft wind, and fell into roofs and cars at estimated speeds of 50-60 miles per hour. To produce updraft winds inside of a thunderstorm that strong, you need tremendous instability in the atmosphere, and strong wind shear to keep the updraft and the downdraft in the thunderstorm separate and self-sustaining.