Today was a great laboratory for hatching thunderstorm activity. It was severe clear in the morning and mostly calm. The muggy feel and heat tend to make everyone suspect thunderstorms but what is the real indicator or “trigger” for convective activity?
One essential ingredient is a steep temperature drop with altitude. If the air cools more rapidly than usual in the climb get suspicious. Meteorologists call this CAPE or convective potential. Compare adiabatic cooling (heat loss due to expansion) to ambient temperature drop. The more quickly the air cools as you climb, the more unstable the air and more probably airmass thunderstorms. Think of a balloon full of hot air rising…if the air inside cools quicker than the outside air it stops going up…If is cooler outside it keeps going up (or accelerates!) Today at 4500 was quite pleasantly chilly though hot and muggy on the surface…watch out!
The presence of moisture is also a necessary indicator. “Muggy” is a little too imprecise. Watch for a dewpoint above 20 degrees Celsius…this is a sure indicator of TSM…there is plenty of moisture for free convection.
The last ingredient besides unstable air and moisture is a lifting force. Today a cold front came “shoveling” from the west. Remember colder air is denser and runs along the surface lifting the moist warm air ahead of it. Perfect recipe for thunderstorms; boom, a whole line of severe storms rolled through after lunch…as predicted! This seems like August weather and it is not even official summer yet!