Thunderstorms Still In The Forecast? Here's When Convective SIGMETs Are Issued. (2024)

Summer isn't over yet! Here's what you need to know about Convective SIGMETs before you fly.

Three Conditions

Convective SIGMETs are issued every hour at 55 minutes past the hour, regardless of weather conditions. The following conditions are included in a routinely issued Convective SIGMET:

• An area of thunderstorms affecting 3,000 square miles or greater, with thunderstorms affecting at least 40% of the area.
• A line of thunderstorms at least 60NM long, with thunderstorms affecting at least 40% of the length.
• Severe or embedded thunderstorms affecting any area that is expected to last 30 minutes or more.

An area qualifying for the issuance of a Convective SIGMET is a lot smaller than you might think. Consider that only 40% of the total area shown below needs to contain thunderstorms:

Even smaller, a Convective SIGMET for a line of thunderstorms 60NM long could look something like this:

"Special" Convective SIGMETs

What happens when dangerous and localized weather pops up that doesn't fit the criteria in the section above? A Convective SIGMET may be issued if any of the following conditions are expected to occur for more than 30 minutes of the valid period:

• Tornado
• Hail 3/4 inch or larger
• Wind gusts 50 knots or greater
• Indications of rapidly changing weather conditions

You obviously don't want to be flying in conditions like these!

Valid Period And Additional Hazards

Convective SIGMETs are valid up to 2 hours, or until superseded by the next hourly issuance. In addition, all Convective SIGMETs imply severe or greater turbulence, severe icing, and low-level wind shear, even though none of them are listed in the report.

All of these conditions are associated with thunderstorms, and it's an assumption that you know a thunderstorm's hazards!

How Do You Read The Details?

There's a lot more to Convective SIGMETs than basic weather information and a valid period. You need to know how to read the affected locations, boundary areas, detailed weather description, and the outlook within a few hours after the initial issuance.

If you're ready to start learning to read Convective SIGMETs like a pro, check out our Aviation Weather Products training course. It breaks down the textual coding into easy-to-understand sections. Check it out for yourself:

How have thunderstorms affected your plans this summer? Tell us in the comments below.

Swayne Martin

Swayne is an editor at Boldmethod, certified flight instructor, and a First Officer on the Boeing 757/767 for a Major US Carrier. He graduated as an aviation major from the University of North Dakota in 2018, holds a PIC Type Rating for Cessna Citation Jets (CE-525), is a former pilot for Mokulele Airlines, and flew Embraer 145s at the beginning of his airline career. Swayne is an author of articles, quizzes and lists on Boldmethod every week. You can reach Swayne at swayne@boldmethod.com, and follow his flying adventures on his YouTube Channel.