Definition
Convective SIGMETs are in-flight weather advisories issued for hazardous convective weather that affects the safety of all aircraft. They are issued for severe thunderstorms with surface winds of 50 knots or greater, hail at the surface of three-quarters of an inch in diameter or greater, tornadoes, embedded thunderstorms, lines of thunderstorms, and thunderstorms producing precipitation of heavy intensity covering 40 percent or more of an area of at least 3,000 square miles. Each convective SIGMET implies severe or greater turbulence, severe icing, and low-level wind shear. They are issued hourly for the eastern, central, and western United States and remain valid for up to two hours.
Plain English
A short weather warning sent out during flight when thunderstorms or related dangers are happening or expected. If you see one for your area, expect rough rides, possible icing, and strong wind shifts near the ground.
Context Anchor
You will see convective SIGMETs during preflight weather briefings, aviation weather checks, and in-flight weather updates when thunderstorms may affect your route.
Derivation
‘Convective’ comes from the Latin convehere, meaning ‘to carry together,’ and refers to the rising and falling motion of air that builds thunderstorms. ‘SIGMET’ is short for Significant Meteorological Information. So a convective SIGMET is a significant weather warning specifically about thunderstorm-type activity.
Why Pilots Care
These advisories identify severe weather capable of producing turbulence, wind shear, or structural stress that can force route changes or flight delays.
Grounding Statement
Picture warm, moist air rising fast, building tall storm clouds that can produce violent wind, hail, lightning, and heavy rain.
Intuition Check
Convective does not mean all clouds or all rain. Here it points to rising-air storm activity, especially thunderstorms; a convective SIGMET is about thunderstorm-level hazards, not routine weather.
Example Sentence 1
Before departure, the pilot reviewed a convective SIGMET covering a line of thunderstorms along the route and decided to delay the flight.
Example Sentence 2
While airborne, the controller relayed an updated convective SIGMET that now covered the arrival airport area.