The Weather Never Sleeps

Understanding Unstable Air

The thunderstorm outlook on a recent summer evening told pilots to watch out if they went flying in the Southeast the next afternoon.

"Destabilization associated with surface heating and cold air aloft accompanying an upper low (forecast to move across the Southeast) will continue to support the threat for hail and isolated wind gusts with the stronger storms, mainly during the afternoon and early evening," the outlook said.

The words hail, wind gusts, and stronger storms made clear what sorts of hazards awaited someone who went flying. The word destabilization got right to the point about why parts of the Southeast were in for a wild afternoon.

A weather briefing that outlines the danger of thunderstorms should be enough to keep an alert and cautious pilot out of trouble, whether or not he or she knows anything about air stability and why destabilization of the air could lead to atmospheric violence.

On the other hand, a pilot who does understand the implications of unstable air - air that's been destabilized - would have taken off the following afternoon knowing that simply avoiding the day's thunderstorms wouldn't have guaranteed a smooth ride. It would not have been a good day to take a friend for a first flight because the air could have been uncomfortably bumpy even far from any storms.

Expecting thunderstorms and turbulence on a day when meteorologists say the air is unstable isn't too much of a stretch. We can think of an unstable atmosphere being like an unstable person; little is needed to trigger violence.

Thunderstorms, of course, can produce the ultimate in atmospheric violence: lightning, strong updrafts and downdrafts that help to create severe turbulence, heavy icing, microbursts, hailstones that can break an airplane's windshield, and even tornadoes.

A little basic knowledge of how the atmosphere works will help pilots to understand air stability and learn what to expect when the forecast is for either stable or unstable air.