Thunderstorm
A thunderstorm is a convective storm with thunder and lightning, typically accompanied by heavy rain, strong gusty winds, and sometimes hail. Thunderstorms represent the most violent non-tropical atmospheric phenomenon and contain virtually every hazard known to aviation — simultaneously.
Formation Requirements
- Moisture: Sufficient water vapour in the lower and middle troposphere
- Instability: The atmosphere must be conditionally unstable — warm, moist air at low levels capable of sustained upward motion once a trigger initiates it
- Lift (trigger): A mechanism to force the initial upward motion — frontal lifting, orographic lifting, surface heating, or shortwave trough passage
Aviation Hazards
- Turbulence: Severe to extreme within and around the storm; can destroy aircraft
- Icing: Severe icing in the updraft regions with large supercooled droplets to great altitude
- Hail: Can occur above the storm in seemingly clear air
- Lightning: Can cause instrument errors, static electricity, and structural damage
- Microburst/downburst: Localized violent downdraft
- Windshear: At the leading edge of the outflow (gust front) and within the storm
- Reduced visibility: Heavy precipitation dramatically reduces forward visibility
- Tornadoes: Severe supercell thunderstorms can produce tornadoes
Avoidance Rules
- Do not attempt to fly through a thunderstorm — circumnavigate
- Avoid flying beneath a thunderstorm — hail, turbulence, and microbursts extend below the cloud base
- Maintain 20 NM clearance from any visible cell
- Do not rely on radar gaps — they can close rapidly
- Turbulence extends beyond the visible cloud boundary — give cumulonimbus a wide berth
On the TC Written Exam
Thunderstorms are among the most important exam topics in aviation meteorology. Know: the three conditions for development; all hazards; avoidance strategies; the rule that no thunderstorm may be safely penetrated.
Related Terms
See also: Microburst, Icing, Squall Line, SIGMET, Atmospheric Stability.