Convection makes the earth livable, by transporting excess heat from the surface of the earth into the upper levels of the atmosphere. Without Convection the average temperature on earth could be as high as 125 degrees Fahrenheit. With all of that motion comes moisture. With moisture comes clouds and with clouds comes thunderstorms.

On the surface convection is not innately harmful, in fact necessary for life itself. But when mixed with moisture and the right thermal conditions, it brings lightning and turbulence that can bring havoc to any airspace. Disruptions due to rerouting and the aftermath of a run-in with these storms can have dramatic repercussions.

What makes a thunderstorm so dangerous?

Turbulence costs airlines hundreds of millions of dollars per year in unplanned maintenance, injuries and delays each year. It is responsible for 18% of fatal General Aviation accidents, according to an NTSB study . Within a thunderstorm there are strong conflicting updrafts and downdrafts, which lead to the risk of significant turbulence. Even when a storm is not fully mature, flying over a developing storm can lead to severe flight turbulence, as the strong updrafts exist above the visible cloud top. Turbulence can even exist at high altitude, miles downstream of any convective activity.

Another danger of thunderstorms is hail. The strong updrafts within a thunderstorm can keep large hail suspended in the air while it grows, as well as toss it out miles away from the storm core. Hail most often damages the radome (radar on nose of aircraft) of an aircraft, but is also known to severely damage windshields as well.

Did you feel that? 100 lightning strikes occurred during the last second! Right now there are an estimated 2,000 electrical storms around the globe. Do you know where lightning will strike next? We do!

Lightning is the most unpredictable hazard for the crew, especially for the ground crew when refueling. While most commercial aircraft can handle a direct lightning strike without influencing the flight, strikes can put holes into the aircraft and impact electrical systems, requiring the aircraft to be taken out of service. Unplanned maintenance such as this can be costly for airlines, not only for the repair, but also the lost revenue while the aircraft is not in service.

This is also true when it comes to icing. Most commercial aircraft can handle a little icing without it being a threat to the flight. There is a more severe type of icing, within glaciated convective clouds, called ice crystal icing. This occurs in regions of high ice water content (HIWC) and can build up in the engine, resulting in engine rollback, flameout, and related damage.

Back on the Earth’s surface the above criteria are still a factor, along with IFR ceilings and visibilities. The biggest hazard with thunderstorms at the terminal however is the microburst, an intense downdraft that can affect the speed of aircraft trying to land. This condition has led to several significant aviation accidents in the past, before a low-level wind shear alert system (LLWAS) was installed across the United States to help detect wind shear near the aerodrome.

The graphic below shows an inflight example of what a pilot would see flying near convective weather highlighting the various hazards mentioned above.