Turning the chapter from winter to spring, we brace ourselves for a new season of severe weather and all the familiar elements of hail, wind, and tornadoes. In the weather community, lead forecasters, warning coordination meteorologists, and local spotters all have an annual rite of preparation for the upcoming severe-weather season. It’s a good idea for pilots to follow suit and refresh what they know about this capricious hazard, especially those who have that all-important instrument rating. If I, a seasoned forecaster, can find more to learn about thunderstorms and severe weather every year, perhaps you can, too.
Convection, Updraft
Learning about the storm need not be complicated. We can get tremendous insight into thunderstorms by using the single-cell thunderstorm as a conceptual model. It all starts with an updraft. This can originate from the rising thermal produced by solar heating, or from lift embedded within a nimbostratus cloud. For simplicity’s sake, we normally consider the rising thermal under a hot sun. This grows into a cumulus cloud as the air cools to its dewpoint temperature and saturation occurs. If the lapse rate, or the existing temperature change with height, is sufficiently strong and enough moisture is present, the cumulus cloud will grow vertically into a towering cumulus. It can then evolve further into a cumulonimbus cloud.
