Weather Hazards: Thunderstorms and Icing

Thunderstorms require three ingredients working together: moisture, unstable air, and a lifting force. Once formed, a storm moves through three stages — the cumulus stage of building updrafts, the mature stage where updrafts and downdrafts coexist with heavy rain, lightning, and possible hail, and the dissipating stage of weakening downdrafts. The mature stage is the most hazardous, bringing severe turbulence, wind shear, microbursts, and hail, so the rule is to give any thunderstorm a wide berth rather than fly under or through it. Structural icing is a separate hazard that needs two things at once: visible moisture and a surface temperature at or below freezing. Ice adds weight and spoils the airflow over the wing, cutting lift and adding drag. Clear ice from large supercooled droplets is dense and stubborn, while rime ice from small droplets is rough and brittle. An airplane without ice protection has no business in known icing.