What Is the Criteria for Issuing a Convective SIGMET?

Active thunderstorms must meet specific conditions before a WST is released.

Wednesday, March 06, 2024 at 01:43 PM ET

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When convective weather is plentiful, expect delays when departing or arriving high-impact airports. [Courtesy: Scott Dennstaedt]

Key Takeaways:

Convective SIGMETs are "NOWcasts" issued by the Aviation Weather Center to warn pilots of organized, dangerous convection that poses a significant en route hazard, as opposed to scattered, easily avoidable thunderstorms.
Routine convective SIGMETs are issued when specific minimum criteria are met, including a line of thunderstorms at least 60 miles long with at least 40 percent affected length, or an area of active thunderstorms affecting at least 3,000 square miles with 40 percent coverage and exhibiting strong radar reflectivity or significant satellite/lightning signatures.
A convective SIGMET will also be issued for embedded or severe thunderstorms expected to occur for more than 30 minutes, regardless of the area size. Special convective SIGMETs may be issued immediately for reported tornadoes, hail ≥ 3/4 inch, or wind gusts ≥ 50 knots.

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Question: What is the criteria used by forecasters for issuing a convective SIGMET?

Answer: During the warm season, convective weather has a huge impact on the National Airspace System (NAS). As the amount of usable airspace diminishes on any given day, this ultimately engenders delays in the system. A departure within busy airspace usually means a delay. In the worst-case scenario, ground stops may be levied depending on route of flight and destination airport. Nevertheless, forecasters at the Aviation Weather Center (AWC) are busy at work issuing advisories to warn pilots of these dangerous convective areas.